Comprehensive Study Notes: Organic Chemistry Fundamentals, Hydrocarbons, Monofunctional Derivatives, and Biological Macromolecules

Bibliographic Foundation & Curriculum Framework

• Source Reference Manual: Manual de Chimie Clasa a-X-a.
  • Manual Authors: Luminiȕa Vlădescu, Corneliu Tărăbășan, Mihăilă-Luminiȕa, Irinel Doicin.
  • Publishing House: Editura Grup Editorial Art.
  • Evaluation Authors (Grid Test Formulators):
    • Prof. Univ. Dr. Sanda Andrei (Alkanes, Alkenes, Carboxylic Acids).
    • Prof. Univ. Dr. Constantin Bele (Alkadienes, Arenes, Alcohols).
    • Prof. Univ. Dr. Adela Pintea (Introduction to Organic Chemistry, Alkynes, Biologically Active Organic Compounds: Saccharides, Proteins).
• Curricular Scope:
  • Chapter 1: Introduction to the Study of Organic Chemistry (Comprehensive study of bonds, valency, classification of carbons, formulas, and isomerism).
  • Chapter 2: Hydrocarbons (Excluding Section 2.6: Petroleum, Coal, Fossil Fuels, and Raw Material Sources):
    • 2.1. Alkanes.
    • 2.2. Alkenes.
    • 2.3. Alkynes.
    • 2.4. Alkadienes.
    • 2.5. Arenes.
  • Chapter 3: Monofunctional Organic Compounds:
    • 3.1. Alcohols.
    • 3.2. Carboxylic Acids.
  • Chapter 4: Organic Compounds of Practical Importance (Excluding Sections 4.2: Essences and Flavors; 4.3: Medicines, Drugs, Vitamins; 4.4: Natural, Artificial, and Synthetic Fibers; 4.5: Natural and Synthetic Dyes, Paints):
    • 4.1. Organic Compounds with Biological Activity (Saccharides and Proteins).

Introduction to the Study of Organic Chemistry

• Historical Foundations of Organic Chemistry:

  • The concept and formal term organic chemistry was introduced into the scientific lexicon by Swedish chemist J.J. Berzelius.
  • The first organic substance synthesized exclusively in a laboratory setting from an inorganic precursor was urea, prepared by Friedrich Wöhler in 1828 via the thermal isomerization of ammonium cyanate:         $NH_4OCN \xrightarrow{\Delta} (NH_2)_2C=O$

• Organogenic Elements & Chemical Bonding:

  • Organogenic elements are strictly defined as all chemical elements that enter into the molecular architecture of organic compounds. While predominantly nonmetals, they fundamentally include carbon ($C$), hydrogen ($H$), oxygen ($O$), nitrogen ($N$), halogens ($F, Cl, Br, I$), sulfur ($S$), and phosphorus ($P$).
  • Carbon Valence & Catenation:
    • Carbon forms its stable octet not by gaining or losing 4 electrons (which would require prohibitive ionization energies), but by sharing 4 valence electrons via four covalent bonds (tetravalency).
    • Every organic compound fundamentally contains at least one carbon atom.
    • Carbon possesses the unique chemical capacity for catenation—the ability to bind directly to other carbon atoms to form open (linear or branched) or cyclic chains of varying saturation.
  • Covalent Bond Geometry & Overlap:
    • A single covalent sigma ($\sigma$) bond forms via the total coaxial (end-on) interpenetration of two atomic orbitals, each belonging to a separate bonding atom.
    • In an $sp^3$-hybridized carbon atom, four single $\sigma$ bonds are spatially directed toward the vertices of a regular tetrahedron, forming bond angles of $109^\circ 28'$
    • A double bond consists of one strong $\sigma$ bond and one lateral-overlap pi ($\pi$) bond ($1\sigma + 1\pi$).
    • A triple bond consists of one coaxial $\sigma$ bond and two perpendicular lateral $\pi$ bonds ($1\sigma + 2\pi$).
    • Nitrogen Bonding: A trivalent nitrogen atom can form three single $\sigma$ bonds, one single bond and one double bond ($\sigma + \pi$), or one triple bond ($\sigma + 2\pi$).
    • Oxygen Bonding: Divalent oxygen forms either two single $\sigma$ bonds (as in water, alcohols, and ethers) or one double bond ($\sigma + \pi$, as in carbonyl derivatives).
    • Bond Length and Polarity: The single $C-C$ covalent bond is purely nonpolar (identical electronegativities) and has a bond length of $1.54\,\text{\AA}$, which is distinctly longer than a double bond ($C=C$, $1.33\,\text{\AA}$) or a triple bond ($C\equiv C$, $1.20\,\text{\AA}$).
  • Structural Validity Assessment:
    • Valid formulas adhere strictly to atomic valencies: $H_3C-COOCH_3$ (methyl acetate) and $H_3C-CH_2-OH$ (ethanol).
    • Formulas violating valency include: $H_3C-CH_2=O$ (pentavalent carbon), $H_2C=CH-N-CH_3$ (divalent, neutral nitrogen lacking hydrogen/bonding partner), $H_3C-CH_2-NH_3$ (pentavalent nitrogen forming 5 single bonds without ionic charge), and $H_3C-CH_2=O-CH_2-CH_3$ (trivalent neutral oxygen with a double and single bond).

• Classification of Carbon Atoms:

  • Carbon atoms within organic catenas are classified strictly according to the number of direct covalent bonds they share with adjacent carbon atoms:
    • Primary ($1^\circ$) Carbon: Directly bonded to only one other carbon atom (or zero, as in methane).
    • Secondary ($2^\circ$) Carbon: Directly bonded to two other carbon atoms.
    • Tertiary ($3^\circ$) Carbon: Directly bonded to three other carbon atoms.
    • Quaternary ($4^\circ$) Carbon: Involved in four covalent bonds shared exclusively with other carbon atoms (e.g., central carbon of neopentane or carbons engaged in a double bond to another carbon and two single carbon bonds).
  • Structural Dissections:
    • In the branched alkene 2,3,5-trimethyl-2-hexene:             $H_3C-C(CH_3)=C(CH_3)-CH_2-CH(CH_3)-CH_3$             Contains: 5 primary carbons, 1 secondary carbon, 1 tertiary carbon, and 2 quaternary carbons (the two central $sp^2$ carbons each share bonds with two adjacent methyl carbons and the double bond to each other).
    • In 2,2-dimethylpentane, $H_3C-C(CH_3)_2-CH_2-CH_2-CH_3$:             Contains 4 primary carbons (three from the tert-butyl end, one from the terminal ethyl end), 2 secondary carbons ($C3$ and $C4$), 0 tertiary carbons, and 1 quaternary carbon ($C2$).
    • In 4-methylcyclohexene:

            It is an unsaturated, cyclic hydrocarbon (cycloalkene). It contains 3 tertiary carbon atoms ($C1$ and $C2$ of the double bond, each bonded to two ring carbons and one $H$, and $C4$, bonded to two ring carbons and the methyl branch) and 3 secondary carbons ($C3, C5, C6$), plus 1 primary carbon (methyl group).

• Elemental Analysis & Chemical Formulas:

  • Qualitative Elemental Analysis: Determines the nature and identities of the organogenic elements present. Carbon and hydrogen are qualitatively verified by combustion in the presence of copper(II) oxide ($CuO$), oxidizing carbon to $CO_2$ (precipitating $CaCO_3$ in lime water) and hydrogen to $H_2O$ (turning anhydrous copper sulfate blue).
  • Quantitative Elemental Analysis: Quantifies the percentage concentration by mass of each constituent element. Oxygen is traditionally calculated by difference:         $\%O = 100\% - (\%C + \%H + \%N + \%\text{halogens} + \dots)$
  • Empirical Formula (Formula Brută): Expresses the simplest whole-number ratio of the atoms of constituent elements in the compound.
  • Molecular Formula: Specifies the exact type and real numerical total of atoms present in a single molecule of the compound. It is related to the empirical formula by an integer multiple $n$:         $\text{Molecular Formula} = (\text{Empirical Formula})_n$         where $n = \frac{\text{Molar Mass}}{\text{Empirical Mass}}$. When $n = 1$, the molecular formula is identical to the empirical formula.
  • Worked Formula Derivations:
    • Compound A: Molar mass $M = 84\,\text{g/mol}$. Elemental analysis: $C = 57.14\%$, $H = 4.76\%$. Oxygen by difference: $100\% - (57.14\% + 4.76\%) = 38.10\%$.
      • Atomic ratios: $n_C = \frac{57.14}{12} = 4.761$, $n_H = \frac{4.76}{1} = 4.760$, $n_O = \frac{38.10}{16} = 2.381$.
      • Dividing by the smallest value ($2.381$): $C = 2$, $H = 2$, $O = 1$. Empirical formula: $(C_2H_2O)_n$.
      • Molar mass of empirical unit: $2(12) + 2(1) + 16 = 42\,\text{g/mol}$.
      • Multiple: $n = \frac{84}{42} = 2$.
      • Molecular formula: $C_4H_4O_2$.
    • Compound B: Molar mass $M = 88\,\text{g/mol}$. Mass ratio $C:H:O = 6:1:4$.
      • Sum of mass parts: $6 + 1 + 4 = 11$
      • Mass fractions: $m_C = \frac{6}{11} \times 88 = 48\,\text{g}$, $m_H = \frac{1}{11} \times 88 = 8\,\text{g}$, $m_O = \frac{4}{11} \times 88 = 32\,\text{g}$.
      • Number of moles of atoms: $n_C = \frac{48}{12} = 4$, $n_H = \frac{8}{1} = 8$, $n_O = \frac{32}{16} = 2$.
      • Molecular formula: $C_4H_8O_2$.

• Isomerism Classifications:

  • Constitutional (Structural) Isomerism: Compounds possessing identical molecular formulas but distinct atomic connectivity and sequence.
    • Chain (Skeleton) Isomers: Differ in the branching pattern of the carbon skeleton (e.g., n-pentane, isopentane, neopentane).
    • Position Isomers: Differ in the location of a functional group, unsaturation, or substituent along an identical carbon framework (e.g., 1-pentene vs. 2-pentene).
    • Functional Group Isomers: Differ in the functional group class (e.g., butanoic acid, $H_3C-CH_2-CH_2-COOH$, and methyl propanoate, $H_3C-CH_2-COOCH_3$, both possessing the molecular formula $C_4H_8O_2$; or an alkene and a cycloalkane of formula $C_5H_{10}$: pentene vs. cyclopentane).
  • Stereoisomerism (Spatial Isomerism): Identical atomic connectivity, but differing in the spatial three-dimensional orientation of atoms.
    • Enantiomers (Optical Isomers): Non-superimposable mirror images containing one or more asymmetric (chiral) carbon atoms:

            The pair above depicts lactic acid (2-hydroxypropanoic acid) enantiomers around the chiral carbon bonded to $-H$, $-OH$, $-CH_3$, and $-COOH$. * Geometric (cis-trans or diastereomeric) Isomers: Arise due to restricted rotation about a double bond ($C=C$) or ring, requiring each unsaturated carbon to bear two non-identical substituents:

            The left image shows cis-1-chloropropene (similar priority groups on the same side of the double bond plane), and the right shows trans-1-chloropropene (groups across the double bond plane).

Hydrocarbons: Alkanes (Paraffins)

• General Characteristics & Homology:
  • General formula: $C_nH_{2n+2}$.
  • Saturated acyclic hydrocarbons; all carbon atoms are in the $sp^3$ hybridization state forming $\sigma$ bonds.
  • In a homologous series, each member differs from adjacent members by a methylene unit ($-CH_2-$). Structural characteristics and general chemical properties are conserved throughout the series, while the carbon-to-hydrogen mass ratio ($\frac{12n}{2n+2}$) continuously increases toward an asymptotic limit of $6:1$.
• Nomenclature & Alkyl Radicals:
  • Monovalent Radicals: Formed by removing one hydrogen atom from an alkane: methyl ($-CH_3$), ethyl ($-CH_2-CH_3$), propyl ($-CH_2-CH_2-CH_3$), isopropyl ($-CH(CH_3)_2$).
  • Divalent Radicals:
    • Removing two hydrogen atoms from the same carbon (geminal radical): methylene or methylidene ($=CH_2$), ethylidene ($CH_3-CH=$), isopropylidene ($(CH_3)_2C=$).
    • The geminal divalent radical derived from propane at the secondary carbon is specifically termed isopropylidene ($(CH_3)_2C=$).
    • Removing two hydrogens from adjacent carbons (vicinal radical): ethylene ($-CH_2-CH_2-$), propylene ($-CH(CH_3)-CH_2-$).
  • IUPAC Systematic Naming: The longest continuous carbon chain establishes the parent alkane name; numbering begins from the end that gives the lowest set of locants to substituents at the first point of difference.
    • Incorrect vs. Correct Naming Examples: "4-ethyl-3,3-dimethylpentane" is incorrect because the longest continuous chain has 6 carbons, making it a hexane derivative (specifically, 3-ethyl-2,2-dimethylhexane).
• Structural Isomerism in Alkanes:
  • Alkanes exhibit solely chain isomerism (izomerie de catenă).
  • Butane ($C_4H_{10}$): 2 isomers (n-butane, isobutane / 2-methylpropane).
  • Pentane ($C_5H_{12}$): 3 isomers (n-pentane, isopentane / 2-methylbutane, neopentane / 2,2-dimethylpropane). Of these, exactly 1 isomer (isopentane) contains a tertiary carbon atom.
  • Hexane ($C_6H_{14}$): 5 isomers (n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane). Of these, exactly 1 isomer (2,2-dimethylbutane) contains a quaternary carbon atom.
• Physical Properties:
  • States of Aggregation (Normal Conditions: $25^\circ\text{C}$, $1\,\text{atm}$):
    • $C_1 - C_4$ (methane to butane): gases.
    • $C_5 - C_{16}$ (pentane to hexadecane): liquids.
    • $C_{17}+$ (heptadecane and above): solids.
  • Density: All alkanes have densities significantly less than $1\,\text{g/cm}^3$ ($0.6 - 0.8\,\text{g/cm}^3$), meaning they float on water.
  • Solubility: Alkanes are strictly nonpolar; completely insoluble in polar solvents like water, but readily soluble in nonpolar organic solvents (benzene, diethyl ether, carbon tetrachloride). Liquid alkanes themselves serve as excellent nonpolar solvents.
  • Odor: Completely odorless (mercaptans must be added to commercial natural gas/methane for leak detection).
  • Boiling Points: Increase regularly with increasing molar mass (longer chains create stronger London dispersion forces). For constitutional isomers with identical molecular formulas, branching increases molecular compactness, lowers accessible surface area, decreases intermolecular dispersion forces, and progressively lowers boiling points (e.g., among $C_6H_{14}$ isomers, linear n-hexane has the highest boiling point, while highly branched 2,3-dimethylbutane and 2,2-dimethylbutane boil at lower temperatures).
• Chemical Properties & Reactivity:
  • Termed paraffins (from Latin parum affinis = low affinity) due to their general chemical inertness toward acids, bases, and typical redox reagents at standard temperatures.
  • Halogenation (Photochemical Substitution):
    • Alkanes react with halogens ($Cl_2, Br_2$) via homolytic free-radical substitution triggered by UV light ($h\nu$) or elevated temperatures ($300 - 400^\circ\text{C}$).
  • Monochlorination Products of Butane Isomers: n-Butane yields 2 monochloro derivatives (1-chlorobutane, 2-chlorobutane); isobutane yields 2 monochloro derivatives (1-chloro-2-methylpropane, 2-chloro-2-methylpropane). Total monochloro isomers from $C_4H_{10}$ isomers: 4 derivatives.
  • Symmetry Effects in Pentane Monochlorination: Neopentane (2,2-dimethylpropane), possessing 12 completely chemically equivalent primary hydrogens across 4 identical methyl groups, generates strictly 1 monochloro derivative (1-chloro-2,2-dimethylpropane).
  • Monochlorination of Hexane Isomers: 2,3-Dimethylbutane generates strictly 2 monochloro derivatives: 1-chloro-2,3-dimethylbutane (substitution at one of the 12 primary hydrogens) and 2-chloro-2,3-dimethylbutane (substitution at one of the 2 tertiary hydrogens).
• Thermal Decomposition (Cracking and Dehydrogenation):
  • At temperatures exceeding $500 - 650^\circ\text{C}$, alkanes undergo carbon-carbon ($C-C$) bond homolysis (cracking) and carbon-hydrogen ($C-H$) bond cleavage (dehydrogenation):         $\text{Alkane} \xrightarrow{\Delta} \text{Smaller Alkane} + \text{Alkene} \quad (\text{Cracking})$$\text{Alkane} \xrightarrow{\Delta} \text{Alkene} + H_2 \quad (\text{Dehydrogenation})$
  • Thermal Pyrolysis of Pentane ($600^\circ\text{C}$): Dehydrogenation yields 1-pentene and 2-pentene; cracking of the $C1-C2$ bond yields methane and 1-butene / 2-butene; cracking of the $C2-C3$ bond yields ethane and propene, alongside propane and ethene. Together with residual uncracked pentane and hydrogen, a total of 8 distinct hydrocarbons are produced.
  • Formation of Butene via Cracking: To produce butene ($C_4H_8$) via an alkane cracking step ($C_nH_{2n+2} \rightarrow C_4H_8 + C_{n-4}H_{2(n-4)+2}$), the reacting alkane must contain a minimum of 5 carbon atoms (pentane yielding butene and methane).
• Oxidation Reactions:
  • Complete combustion: Highly exothermic, producing $CO_2$ and $H_2O$.
  • Controlled catalytic oxidation of methane at $400 - 600^\circ\text{C}$ over metal/oxide catalysts yields formaldehyde (metanal, methanal):         $CH_4 + O_2 \xrightarrow{400 - 600^\circ\text{C},\,\text{catalyst}} HCHO + H_2O$
  • Incomplete combustion/partial pyrolysis at high temperatures produces carbon black (negru de fum) used in the manufacture of rubber tires and printing inks:         $CH_4 + O_2 \rightarrow C + 2\,H_2O$
• Reactions in Which Alkanes Cannot Participate: Under normal chemical conditions, alkanes cannot undergo addition reactions (owing to the complete absence of $\pi$ bonds) or polymerization reactions.

Hydrocarbons: Alkenes (Olefins)

• General Characteristics & Bonding:
  • General formula: $C_nH_{2n}$.
  • Acyclic unsaturated hydrocarbons containing exactly one carbon-carbon double bond ($C=C$).
  • The two unsaturated carbon atoms are in the $sp^2$ hybridization state, exhibiting trigonal planar geometry with bond angles of $120^\circ$. The remaining saturated carbons in higher alkenes maintain $sp^3$ tetrahedral geometry ($109^\circ 28'$).
• Isomerism in Alkenes:
  • Alkenes exhibit chain isomerism, position isomerism (location of the double bond), functional group isomerism with cycloalkanes ($C_nH_{2n}$), and geometric (cis-trans / diastereomeric) isomerism.
  • Alkene Isomer Totals:
    • For $C_4H_8$: 3 acyclic alkene constitutional isomers (1-butene, 2-butene, 2-methylpropene/isobutene). With geometric isomers accounted for (cis-2-butene and trans-2-butene), there are 4 alkene isomers. Including cyclic constitutional isomers (cyclobutane, methylcyclopropane), there are 6 total structural isomers.
    • For $C_5H_{10}$: 5 constitutional alkene isomers (1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene). With cis/trans geometric forms of 2-pentene, there are 6 distinct stereoisomers.
  • Geometric Isomerism Requirements: A compound of the type $R_1R_2C=CR_3R_4$ exhibits cis-trans isomerism if and only if $R_1 \neq R_2$ and $R_3 \neq R_4$. Therefore, 1-alkenes ($H_2C=CH-R$) never exhibit geometric isomerism because the terminal carbon bears two identical hydrogen atoms. 2-Hexene ($CH_3-CH=CH-CH_2-CH_2-CH_3$) and 3-hexene ($CH_3-CH_2-CH=CH-CH_2-CH_3$) both possess distinct groups at each unsaturated carbon, exhibiting clear cis and trans isomers.
• Synthesis Methods:
  • Dehydrohalogenation of Alkyl Halides: Occurs by heating haloalkanes in the presence of strong base in alcoholic medium (potassium hydroxide in ethanol, $KOH/\text{alcohol}$):         $R-CH_2-CH_2-X + KOH \xrightarrow{\text{alcohol},\,\Delta} R-CH=CH_2 + KX + H_2O$(Note: Aqueous $KOH$ leads instead to nucleophilic substitution yielding alcohols).
  • Dehydration of Alcohols: Concentrated strong mineral acid ($H_2SO_4$ or $H_3PO_4$) at temperatures around $170 - 200^\circ\text{C}$:         $R-CH_2-CH_2-OH \xrightarrow{H_2SO_4,\,200^\circ\text{C}} R-CH=CH_2 + H_2O$
• Physical Properties:
  • Aggregation States: $C_2 - C_4$ (ethene, propene, butenes) are gases; $C_5 - C_{17}$ are liquids; $C_{18}+$ are solids.
  • Solubility & Density: Insoluble in water, highly soluble in organic solvents (benzene, chloroform, ether); densities are below $1\,\text{g/cm}^3$.
• Chemical Reactivity & Transformations:
  • Addition Reactions (Cleavage of the $\pi$ Bond):
    • Catalytic Hydrogenation: Addition of $H_2$ over transition metal catalysts ($Ni, Pt, Pd$) yields alkanes:             $R-CH=CH_2 + H_2 \xrightarrow{Ni} R-CH_2-CH_3$
    • Halogenation: Addition of bromine ($Br_2$) dissolved in carbon tetrachloride ($CCl_4$) rapidly yields vicinal dibromoalkanes. Rapid decolorization of the reddish-brown bromine solution is the diagnostic qualitative test for unsaturation ($\pi$ bonds):             $CH_3-CH_2-CH=CH_2 + Br_2 \rightarrow CH_3-CH_2-CHBr-CH_2Br \quad (1,2\text{-dibromobutane})$
    • Hydrohalogenation ($HX$): Follows Markovnikov's rule: the electrophilic proton ($H^+$) attaches to the unsaturated carbon bearing the greater number of hydrogen atoms, while the halide ($X^-$) adds to the more substituted carbon.
    • Hydration: Addition of water in the presence of strong acid ($H_2SO_4$) catalyst yields alcohols (following Markovnikov's rule):             $CH_2=CH_2 + H_2O \xrightarrow{H_2SO_4} CH_3-CH_2-OH$
  • Allylic Substitution (High-Temperature Halogenation):
    • When propene reacts with chlorine at high temperatures ($500^\circ\text{C}$), substitution occurs selectively at the allylic $sp^3$ carbon rather than addition across the double bond, yielding allyl chloride (3-chloropropene):             $H_2C=CH-CH_3 + Cl_2 \xrightarrow{500^\circ\text{C}} H_2C=CH-CH_2Cl + HCl$
  • Oxidation Reactions:
    • Mild Oxidation (Baeyer's Reaction): Reaction with cold, neutral or weakly alkaline potassium permanganate ($KMnO_4$) solution. The purple solution decolorizes and forms a dark-brown precipitate of manganese dioxide ($MnO_2$), converting the alkene into a vicinal diol (glycol):             $3\,R-CH=CH_2 + 2\,KMnO_4 + 4\,H_2O \rightarrow 3\,R-CH(OH)-CH_2OH + 2\,MnO_2\downarrow + 2\,KOH$
    • Energetic/Destructive Oxidation ($KMnO_4$ or $K_2Cr_2O_7$ in $H_2SO_4$):
      • Cleaves both the $\sigma$ and $\pi$ components of the double bond completely.
      • Terminal $=CH_2$ groups oxidize completely to $CO_2 + H_2O$.
      • Monosubstituted carbons ($=CH-R$) oxidize to carboxylic acids ($R-COOH$).
      • Disubstituted carbons ($=C(R_1)R_2$) oxidize to ketones ($R_1-CO-R_2$).
      • Targeted Oxidative Cleavages:
        • Formation of Isobutyric Acid exclusively: The alkene must be symmetrical and cleave into two isobutyric acid fragments. The precursor is 2,5-dimethyl-3-hexene:                     $(CH_3)_2CH-CH=CH-CH(CH_3)_2 + 4\,[O] \rightarrow 2\,(CH_3)_2CH-COOH$
        • Formation of Butanone exclusively: Requires a symmetrical alkene whose fragments each feature an ethyl and a methyl substituent at the double bond: 3,4-dimethyl-3-hexene:                     $CH_3-CH_2-C(CH_3)=C(CH_3)-CH_2-CH_3 + 2\,[O] \rightarrow 2\,CH_3-CH_2-CO-CH_3$
        • Formation of Methyl-butanone and Acetic Acid: Cleavage of 3,4-dimethyl-2-pentene:                     $(CH_3)_2CH-C(CH_3)=CH-CH_3 + 3\,[O] \rightarrow (CH_3)_2CH-CO-CH_3 + CH_3-COOH$

Hydrocarbons: Alkynes (Acetylenes)

• Electronic Structure & Geometry:
  • General formula: $C_nH_{2n-2}$.
  • Characterized by a carbon-carbon triple bond ($-C\equiv C-$), composed of one coaxial $\sigma$ bond and two mutually perpendicular $\pi$ bonds.
  • The two unsaturated alkyne carbons are in the $sp$ hybridization state, generating a linear geometry with a bond angle of $180^\circ$.
  • Because of linear geometry and cylindrical $\pi$ symmetry, alkynes never exhibit cis-trans geometric isomerism.
• Physical Properties:
  • Aggregation States: $C_2 - C_4$ (ethyne, propyne, 1-butyne, 2-butyne) are gases at ambient conditions; higher terms are liquids and solids.
  • Acetylene (Ethyne, $C_2H_2$): Colorless, odorless gas (traces of phosphine and hydrogen sulfide provide technical acetylene with a garlic-like odor); partially soluble in water ($1:1$ by volume at standard temperature and pressure) due to weak polarity of the $sp-s$ $C-H$ bond, but highly soluble in acetone under pressure.
  • Thermodynamic Instability: Liquefied or compressed acetylene is thermodynamically unstable and prone to explosive spontaneous decomposition into its elements ($C_2H_2 \rightarrow 2\,C + H_2$). It must be stored dissolved in acetone adsorbed onto a porous material (kieselguhr).
• Acidity of Terminal Alkynes & Formation of Acetylides:
  • Acidity Hierarchy: Ethyne and 1-alkynes possess weakly acidic protons attached directly to the $sp$-hybridized carbon ($\equiv C-H$), resulting from the high $s$-character ($50\%$) of the $sp$ orbital holding electron density close to the carbon nucleus. Acidity order:         $\text{Alkanes} < \text{Alkenes} < \text{Alkynes} \quad (CH_3-CH_3 < CH_2=CH_2 < CH\equiv CH)$
  • Active Metal Substitution (Alkali Acetylides):
    • Terminal alkynes react with active metals ($Na, K$) at temperatures exceeding $150^\circ\text{C}$ (or in liquid ammonia at $-33^\circ\text{C}$) via hydrogen substitution, forming ionic acetylides:             $HC\equiv CH + Na \xrightarrow{150^\circ\text{C}} HC\equiv C^-Na^+ + \frac{1}{2}\,H_2$$HC\equiv C^-Na^+ + Na \xrightarrow{>150^\circ\text{C}} Na^+-C\equiv C^-Na^+ + \frac{1}{2}\,H_2$
    • Internal alkynes (such as 2-pentyne or 2-hexyne) lack terminal acidic acetylenic hydrogens and are completely incapable of forming acetylides.
    • Hydrolysis of sodium and calcium acetylides regenerates acetylene quantitatively:             $CaC_2 + 2\,H_2O \rightarrow HC\equiv CH + Ca(OH)_2$
  • Heavy Metal Acetylides (Precipitation Reactions):
    • Tollens' Reagent (Ammoniacal Silver Nitrate / Diamminesilver(I) Hydroxide, $[Ag(NH_3)_2]OH$): Reacts with terminal alkynes via substitution, precipitating grey-white di-silver acetylide:             $HC\equiv CH + 2\,[Ag(NH_3)_2]OH \rightarrow Ag-C\equiv C-Ag\downarrow + 4\,NH_3 + 2\,H_2O$
    • Fehling's / Ilosvay's Reagent (Ammoniacal Copper(I) Chloride, $[Cu(NH_3)_2]Cl$): Yields a brick-red precipitate of copper(I) acetylide ($Cu_2C_2$):             $HC\equiv CH + 2\,[Cu(NH_3)_2]Cl \rightarrow Cu-C\equiv C-Cu\downarrow + 2\,NH_4Cl + 2\,NH_3$
    • Unlike alkali metal acetylides, dry heavy metal acetylides ($Ag_2C_2, Cu_2C_2$) are covalent, water-stable, and detonate violently upon mechanical shock, impact, or heating.
• Addition Reactions:
  • Hydrogenation:
    • Complete hydrogenation over active nickel ($Ni$) catalysts yields alkanes:             $HC\equiv CH + 2\,H_2 \xrightarrow{Ni} CH_3-CH_3$
    • Partial/stereoselective catalytic hydrogenation over Lindlar catalyst (palladium poisoned with lead salts/quinoline, $Pd/Pb^{2+}$) arrests the reaction at the alkene stage, yielding cis-alkenes:             $R-C\equiv C-R' + H_2 \xrightarrow{Pd/Pb^{2+}} \text{cis-}R-CH=CH-R'$
  • Halogenation: Decolorizes bromine water sequentially to form 1,2-dibromoethene and 1,1,2,2-tetrabromoethane. In the gas phase, reaction with chlorine is fiercely violent and explosive, producing elemental soot (carbon) and hydrogen chloride:         $C_2H_2 + Cl_2 \rightarrow 2\,C + 2\,HCl$
  • Hydrohalogenation: Addition of $HCl$ in the presence of mercury(II) chloride ($HgCl_2$) at $170^\circ\text{C}$ yields vinyl chloride (chloroethene), the monomer for polyvinyl chloride (PVC):         $HC\equiv CH + HCl \xrightarrow{HgCl_2,\,170^\circ\text{C}} H_2C=CH-Cl$
  • Hydration (Kucherov Reaction):
    • Carried out in the presence of mercury(II) sulfate ($HgSO_4$) and sulfuric acid ($H_2SO_4$).
    • Addition of water produces an unstable enol intermediate that spontaneously tautomerizes to a carbonyl compound:             $HC\equiv CH + H_2O \xrightarrow{HgSO_4,\,H_2SO_4} [H_2C=CH-OH] \rightarrow CH_3-CHO \quad (\text{Acetaldehyde / Ethanal})$
    • Hydration of propyne or any higher terminal/internal alkyne yields ketones exclusively (e.g., propyne yields propanone/acetone):             $CH_3-C\equiv CH + H_2O \xrightarrow{HgSO_4,\,H_2SO_4} [CH_3-C(OH)=CH_2] \rightarrow CH_3-CO-CH_3$

Hydrocarbons: Alkadienes (Dienes)

• Classification by Double Bond Arrangement:
  • General formula: $C_nH_{2n-2}$; functional isomers with alkynes and cycloalkenes.
  • Cumulated Dienes (Allenes): Adjacent double bonds sharing a common central carbon ($=C=$). The central carbon is $sp$-hybridized, and the terminal carbons are $sp^2$-hybridized (e.g., allene / 1,2-propadiene, $H_2C=C=CH_2$).
  • Conjugated Dienes: Double bonds separated by exactly one single $C-C$ $\sigma$ bond ($-C=C-C=C-$), allowing continuous overlap and delocalization of $\pi$ orbitals across all 4 carbon centers:

        (Representative example: 2-methyl-1,3-butadiene / isoprene). * Isolated (Disjunct) Dienes: Double bonds separated by one or more $sp^3$-hybridized carbon atoms ($-C=C-(CH_2)_n-C=C-$), behaving as independent, uncoupled alkene centers (e.g., 1,4-pentadiene).

• Addition Reactions of 1,3-Butadiene:
  • Due to $\pi$-electron delocalization, conjugated dienes undergo both 1,2-addition and 1,4-addition:
  • Bromination of 1,3-Butadiene:
    • 1,2-addition yields 3,4-dibromo-1-butene ($H_2C=CH-CHBr-CH_2Br$).
    • 1,4-addition yields 1,4-dibromo-2-butene ($BrCH_2-CH=CH-CH_2Br$), which represents the major thermodynamic product at ambient conditions.
    • Exhaustive addition of two equivalents of $Br_2$ yields 1,2,3,4-tetrabromobutane.
  • Chlorination: Yields predominantly 1,4-dichloro-2-butene alongside 3,4-dichloro-1-butene.
• Natural and Synthetic Elastomers:
  • Natural Rubber: High-molecular-weight macromolecular polymer of isoprene (2-methyl-1,3-butadiene). Naturally occurring polymer has the specific all-cis configuration: cis-1,4-polyisoprene:         $[C_5H_8]_n$
    • Harvested from the latex of the rubber tree (Hevea brasiliensis).
    • Properties of Raw Natural Rubber: Insoluble in water; soluble in organic solvents (benzene, gasoline, carbon disulfide); tacky and sticky above $30^\circ\text{C}$; hard, brittle, and crystalline below $0^\circ\text{C}$. Elastic only within the narrow thermal window of $0 - 30^\circ\text{C}$.
  • Gutta-Percha: The natural all-trans stereoisomer of 1,4-polyisoprene, extracted from the leaves of Palaquium gutta. Unlike natural rubber, it is non-elastic, rigid, tough, and serves as an electrical insulator.
  • Vulcanization of Rubber: Process invented by Charles Goodyear involving heating raw rubber with small percentages of elemental sulfur ($1 - 5\%$) at $130 - 140^\circ\text{C}$.
    • Sulfur atoms insert across the residual double bonds to build covalent polysulfide and disulfide cross-links ($-C-S-S-C-$) bridging adjacent polyisoprene chains.
    • Vulcanization extends the thermal elasticity range drastically to between $-70^\circ\text{C}$ and $+140^\circ\text{C}$, while eliminating stickiness and organic solvent solubility.
    • Ebonite: When raw rubber is vulcanized with very high proportions of sulfur ($25 - 40\%$), all unsaturations become fully cross-linked into a rigid, non-elastic, hard material used as an electrical and chemical insulator.
  • Synthetic Rubbers:
    • Buna N (SKN): Synthetic elastomer formed by the copolymerization of 1,3-butadiene with acrylonitrile ($CH_2=CH-CN$). Highly resistant to oils, organic solvents, and fuels.
    • Buna S (SBR): Formed by the copolymerization of 1,3-butadiene with styrene (vinylbenzene, $C_6H_5-CH=CH_2$). Extensively used for vehicular tires.
    • Polybutadiene (Buna): Formed by homopolymerization of 1,3-butadiene.

Hydrocarbons: Arenes (Aromatic Hydrocarbons)

• Structure and Aromaticity of Benzene:
  • Molecular formula: $C_6H_6$. Atomic ratio: $C:H = 1:1$.
  • Kekulé Representation vs. Modern Delocalization: Kekulé proposed a six-membered carbon ring with alternating single and double bonds. Modern chemical structure establishes benzene as a completely flat, regular, symmetric hexagon.
  • All 6 carbon atoms are identical, planar, and in the $sp^2$ hybridization state, possessing bond angles of exactly $120^\circ$.
  • The carbon-carbon bond lengths are completely equivalent throughout the ring at $1.39 - 1.40\,\text{\AA}$, intermediate between standard single bonds ($1.54\,\text{\AA}$) and standard double bonds ($1.33\,\text{\AA}$).
  • Due to complete $\pi$-electron delocalization across the aromatic sextet, replacement of any single hydrogen atom on benzene yields strictly one monosubstituted derivative. Disubstitution generates exactly three constitutional isomers: ortho (1,2), meta (1,3), and para (1,4).
• Classification of Arenes:
  • Mononuclear Arenes:
    • Benzene ($C_6H_6$).
    • Toluene / Methylbenzene ($C_6H_5-CH_3$).
    • Ethylbenzene ($C_6H_5-CH_2-CH_3$).
    • Cumene / Isopropylbenzene ($C_6H_5-CH(CH_3)_2$):

    *   Styrene / Vinylbenzene / Ethenylbenzene ($C_6H_5-CH=CH_2$):

    *   Dimethylbenzenes (Xylenes, $C_6H_4(CH_3)_2$): ortho-xylene (1,2-dimethylbenzene), meta-xylene (1,3-dimethylbenzene), para-xylene (1,4-dimethylbenzene):

    *   1,4-Diethylbenzene ($C_2H_5-C_6H_4-C_2H_5$) and 1-ethyl-3-methylbenzene.
*   *Polynuclear Arenes with Condensed Rings:*
    *   *Naphthalene ($C_{10}H_8$):* Two condensed benzene rings. Positions 1, 4, 5, 8 are chemically equivalent and designated as $\alpha$; positions 2, 3, 6, 7 are equivalent and designated as $\beta$.
    *   *Anthracene ($C_{14}H_{10}$):* Three linearly condensed benzene rings:

    *   *Phenanthrene ($C_{14}H_{10}$):* Three angularly condensed benzene rings:

*   *Aromatic Stability Ranking:* Benzene possesses the highest aromatic character and resonance stabilization energy per ring. In condensed systems, as the number of rings increases, individual ring resonance energy diminishes, rendering anthracene and phenanthrene more reactive toward additions and oxidations than benzene or naphthalene.

• Electrophilic Aromatic Substitution ($S_EAr$):
  • Halogenation: Catalyzed by Lewis acids ($FeCl_3, FeBr_3, AlCl_3$):         $C_6H_6 + Cl_2 \xrightarrow{FeCl_3} C_6H_5Cl + HCl \quad (\text{Chlorobenzene})$$C_6H_6 + Br_2 \xrightarrow{FeBr_3} C_6H_5Br + HBr \quad (\text{Bromobenzene})$
    • Iodination: Reversible due to reducing action of $HI$; requires an oxidizing catalyst ($HNO_3$) to destroy $HI$ as it forms:             $C_6H_6 + I_2 \xrightarrow{HNO_3} C_6H_5I + HI$
    • Naphthalene Halogenation: Yields strictly 1-chloronaphthalene ($\alpha$-chloronaphthalene) because electrophilic attack at the $\alpha$ position proceeds through a carbocation intermediate with greater resonance stabilization than attack at the $\beta$ position.
  • Nitration: Carried out using a sulfonitric mixture ($HNO_3 + H_2SO_4$), where concentrated sulfuric acid acts as a dehydrating agent and generates the active electrophile, the nitronium ion ($NO_2^+$):         $C_6H_6 + HNO_3 \xrightarrow{H_2SO_4} C_6H_5-NO_2 + H_2O \quad (\text{Nitrobenzene})$
    • Polynitration of Benzene: Because $-NO_2$ is strongly deactivating, further nitration requires high temperatures and excess acid, selectively yielding meta-dinitrobenzene and eventually 1,3,5-trinitrobenzene.
    • Nitration of Toluene: Methyl group directs to ortho and para positions; exhaustive nitration yields 2,4,6-trinitrotoluene (TNT):             $C_6H_5-CH_3 + 3\,HNO_3 \xrightarrow{H_2SO_4} \text{TNT} + 3\,H_2O$
    • Nitration of Naphthalene: Yields selectively 1-nitronaphthalene ($\alpha$-nitronaphthalene).
  • Sulfonation: Introduction of the sulfonic group ($-SO_3H$) using concentrated sulfuric acid or oleum ($H_2SO_4 + SO_3$):         $C_6H_6 + H_2SO_4 \rightleftharpoons C_6H_5-SO_3H + H_2O \quad (\text{Benzenesulfonic Acid})$
    • Sulfonation is a reversible reaction (hydrolysis at elevated temperatures regenerates the original arene and sulfuric acid).
    • Temperature Control in Naphthalene Sulfonation:
      • At low temperature ($80^\circ\text{C}$), the kinetically controlled product dominates: $\alpha$-naphthalenesulfonic acid (acidul $\alpha$-naftalinsulfonic).
      • At high temperature ($160^\circ\text{C}$), thermodynamic control dominates, isomerizing the product to $\beta$-naphthalenesulfonic acid (acidul $\beta$-naftalinsulfonic):

*   *Friedel-Crafts Alkylation & Acylation:*
    *   *Alkylation:* Benzene reacts with alkyl halides, alkenes, or alcohols in the presence of anhydrous $AlCl_3$ (wet $AlCl_3$ hydrolyzes into inactive $Al(OH)_3$):

            $C_6H_6 + CH_3-Cl \xrightarrow{\text{anhydrous } AlCl_3} C_6H_5-CH_3 + HCl \quad (\text{Toluene})$$C_6H_6 + CH_2=CH_2 \xrightarrow{AlCl_3,\,H_2O} C_6H_5-CH_2-CH_3 \quad (\text{Ethylbenzene})$$C_6H_6 + CH_2=CH-CH_3 \xrightarrow{AlCl_3,\,H_2O} C_6H_5-CH(CH_3)_2 \quad (\text{Cumene})$ * Acylation: Benzene reacts with acid chlorides ($R-COCl$) or acid anhydrides in the presence of anhydrous $AlCl_3$ to form aromatic ketones:             $C_6H_6 + CH_3-COCl \xrightarrow{AlCl_3} C_6H_5-CO-CH_3 + HCl \quad (\text{Acetophenone / Phenyl methyl ketone})$$C_6H_6 + CH_3-CH_2-COCl \xrightarrow{AlCl_3} C_6H_5-CO-CH_2-CH_3 + HCl \quad (\text{Propiophenone / Phenyl ethyl ketone})$

• Directing Effects on the Benzene Ring:
  • Substituents of the First Order (Ortho/Para-directing, Activating): Donate electron density to the aromatic ring via positive mesomeric ($+M$) or inductive ($+I$) effects. They activate the ring toward electrophilic attack and direct new incoming substituents to the ortho and para positions:         $-OH, -OR, -NH_2, -NHR, -NR_2, -CH_3, -CH_2CH_3, -R$Exception: Halogens ($-F, -Cl, -Br, -I$) are net deactivating due to strong negative inductive effects ($-I$), but direct ortho and para due to unshared electron pair resonance donation ($+M$).
  • Substituents of the Second Order (Meta-directing, Deactivating): Strongly withdraw electron density from the aromatic ring via negative inductive ($-I$) and negative mesomeric ($-M$) effects. They deactivate all ring positions, but deactivate the meta position least, directing incoming electrophiles strictly to the meta position:         $-NO_2, -COOH, -SO_3H, -CHO, -CO-R, -CN, -CCl_3$
• Addition and Oxidation Reactions:
  • Hydrogenation:
    • Benzene adds 3 molecules of $H_2$ under vigorous conditions ($Ni$, $200^\circ\text{C}$, high pressure) to produce cyclohexane:

    *   Naphthalene hydrogenates stepwise: first ring hydrogenates smoothly to tetralin (1,2,3,4-tetrahydronaphthalene), and exhaustive hydrogenation yields decalin (decahydronaphthalene).
*   *Photochemical Halogenation (Addition):* Benzene reacts with chlorine under intense ultraviolet ($UV$) radiation via radical addition across all 3 formal double bonds, producing 1,2,3,4,5,6-hexachlorocyclohexane (HCH / lindane, an agricultural insecticide):

        $C_6H_6 + 3\,Cl_2 \xrightarrow{h\nu} C_6H_6Cl_6$

• Side-Chain Halogenation of Alkylarenes: In the presence of light ($h\nu$) and high heat, chlorine substitutes into the aliphatic alkyl side-chain rather than the aromatic nucleus. Toluene sequentially yields benzyl chloride ($C_6H_5-CH_2Cl$), benzylidene chloride ($C_6H_5-CHCl_2$), and benzotrichloride ($C_6H_5-CCl_3$).
• Oxidations:
  • Benzene Ring Oxidation: Benzene resists standard oxidants ($KMnO_4, K_2Cr_2O_7$). Over vanadium pentoxide ($V_2O_5$) catalyst at $500^\circ\text{C}$, it undergoes catalytic air oxidation to maleic acid, which rapidly eliminates water to form maleic anhydride (the trans isomer of maleic acid is fumaric acid):         $C_6H_6 + \frac{9}{2}\,O_2 \xrightarrow{V_2O_5,\,500^\circ\text{C}} \text{Maleic Acid} + 2\,CO_2 + H_2O$
  • Naphthalene Oxidation: Oxidation over $V_2O_5$ at $350^\circ\text{C}$ oxidizes one ring destructively, generating phthalic anhydride:

*   *Anthracene Oxidation:* Treated with potassium dichromate ($K_2Cr_2O_7$) in glacial acetic acid ($CH_3COOH$), oxidation targets the reactive 9,10 positions to yield 9,10-anthraquinone:

*   *Alkyl Side-Chain Oxidation:* Alkyl side-chains on arenes containing at least one benzylic hydrogen atom oxidize quantitatively to benzoic acid ($C_6H_5-COOH$) under the action of hot acidic $KMnO_4 / H_2SO_4$ (toluene, ethylbenzene, and cumene all yield benzoic acid; o-xylene yields phthalic acid).

Monofunctional Derivatives: Alcohols

• Molecular Structure & Hydrogen Bonding:

  • Alcohols contain a hydroxyl functional group ($-OH$) bonded directly to an $sp^3$-hybridized, saturated carbon atom.
  • The carbon-oxygen-hydrogen bond angle ($C-O-H$) is approximately $109^\circ$ (close to the tetrahedral angle).
  • Polarity and Dipole: Because oxygen is strongly electronegative ($\approx 3.44$), it draws shared electron pairs away from carbon and hydrogen, developing a partial negative charge ($\delta^-$) on the oxygen atom and corresponding partial positive charges ($\delta^+$) on the carbon and hydroxyl hydrogen atoms.
  • Intermolecular Hydrogen Bonding: Polar $-OH$ groups establish extensive networks of hydrogen bonds between alcohol molecules. Consequences of these associations:
    • Abnormally high boiling points and melting points compared to alkanes or ethers of similar molecular weight.
    • Significantly elevated viscosity (flows slowly, e.g., glycerol).
    • High surface tension.
    • Boiling points increase with the number of hydroxyl groups per molecule ($\text{Monools} < \text{Diols} < \text{Triols}$).

• Classification of Alcohols:

  • By Hydrocarbon Framework: Saturated (e.g., ethanol), unsaturated (e.g., allyl alcohol), aromatic (e.g., benzyl alcohol, where $-OH$ is on a side-chain, distinct from phenols where $-OH$ is directly attached to the aromatic nucleus).
  • By Number of Hydroxyl Groups: Monohydroxy (monools, e.g., methanol, ethanol), dihydroxy (diols/glycols, e.g., 1,2-ethanediol), trihydroxy (triols, e.g., 1,2,3-propanetriol / glycerol):

*   *By the Nature of the Carbinol Carbon ($C-OH$):*
    *   *Primary ($1^\circ$) Alcohol:* $-OH$ attached to a carbon bonded to only one other carbon (e.g., ethanol, 1-propanol, isobutyl alcohol).
    *   *Secondary ($2^\circ$) Alcohol:* $-OH$ attached to a carbon bonded to two other carbons (e.g., 2-propanol, 2-butanol).
    *   *Tertiary ($3^\circ$) Alcohol:* $-OH$ attached to a carbon bonded to three other carbons (e.g., 2-methyl-2-propanol / tert-butanol, 2-methyl-2-butanol).

• Individual Alcohols:
  • Methanol ($CH_3OH$, Methyl Alcohol / Wood Alcohol):
    • Colorless, highly volatile, mobile liquid with a characteristic faint odor; completely miscible with water, ethanol, and organic solvents.
    • Burns with an almost invisible, pale blue flame, releasing high caloric energy to form carbon dioxide and water:             $2\,CH_3OH + 3\,O_2 \rightarrow 2\,CO_2 + 4\,H_2O$
    • Biological Toxicity: Highly lethal poison. Ingested or absorbed through the skin, it is oxidized in the liver by the enzyme alcohol dehydrogenase into highly toxic metabolites: formaldehyde (formic aldehyde, $HCHO$) and formic acid ($HCOOH$). These induce severe metabolic acidosis, optic nerve damage leading to permanent blindness, and central nervous system collapse (fatal dose is as low as $30\,\text{mL}$).
  • Ethanol ($CH_3-CH_2-OH$, Ethyl Alcohol):
    • Biochemical Production: Produced via enzymatic alcoholic fermentation of hexose sugars (glucose, fructose) derived from grains, fruits, or sugar beets, mediated by yeast (Saccharomyces cerevisiae) enzymes (zymase):             $C_6H_{12}O_6 \xrightarrow{\text{zymase}} 2\,C_2H_5OH + 2\,CO_2$             The resulting natural aqueous solution reaches a maximum ethanol concentration of $12 - 18\%$ (beyond which yeast enzymes denature and cease metabolic activity).
    • Industrial Production: Hydration of ethene under high pressure ($70\,\text{atm}$) and temperature ($300^\circ\text{C}$) using phosphoric or sulfuric acid catalyst:             $CH_2=CH_2 + H_2O \xrightarrow{H_3PO_4,\,\Delta} CH_3-CH_2-OH$
    • Physiological and Biological Action: Central nervous system depressant; suppresses the secretion of antidiuretic hormone (ADH / vasopressin), stimulating diuresis (water loss); causes peripheral vasodilation (dilates surface blood vessels, producing a subjective sensation of warmth but accelerating internal heat loss); metabolized in the liver to acetaldehyde ($CH_3CHO$) and subsequently to acetic acid ($CH_3COOH$).
    • Breathalyzer Test: Detection of ethanol in the human body utilizes the oxidation of ethanol by acidic potassium dichromate ($K_2Cr_2O_7 + H_2SO_4$). Orange hexavalent chromium ($Cr^{6+}$) is reduced to dark green trivalent chromium ($Cr^{3+}$):             $3\,CH_3CH_2OH + 2\,K_2Cr_2O_7 + 8\,H_2SO_4 \rightarrow 3\,CH_3COOH + 2\,Cr_2(SO_4)_3 + 2\,K_2SO_4 + 11\,H_2O$
    • Practical Uses: Universal solvent in paints, lacquers, perfumery; disinfectant ($70\%$ aqueous concentration provides optimal bacterial membrane penetration); thermometric fluid for low temperatures (freezing point of $-114^\circ\text{C}$, usable for temperatures well below $0^\circ\text{C}$).
  • Glycerol (1,2,3-Propanetriol):
    • Trihydric alcohol; sweet-tasting, colorless, odorless, viscous, hygroscopic liquid.
    • Forms three hydrogen bonds per molecule, endowing it with greater viscosity and surface tension than ethanol or water.
    • Natural constituent of quality wines, imparting body and smoothness; used in cosmetics, skin lotions, and pharmaceutical topical formulations; incorporated into plastics as a plasticizer to retain flexibility.
    • Nitration (Glyceryl Trinitrate / Nitroglycerin): Esterification of glycerol with concentrated nitric acid in the presence of concentrated sulfuric acid yields glyceryl trinitrate (dynamite base):             $C_3H_5(OH)_3 + 3\,HNO_3 \xrightarrow{H_2SO_4} C_3H_5(ONO_2)_3 + 3\,H_2O$
    • Glyceryl trinitrate is an unstable, heavy, colorless oily liquid that violently detonates upon physical shock or heating. It undergoes spontaneous intramolecular redox auto-oxidation, converting instantly and entirely into hot gaseous products:             $4\,C_3H_5(ONO_2)_3 \rightarrow 12\,CO_2 + 10\,H_2O + 6\,N_2 + O_2$

Monofunctional Derivatives: Carboxylic Acids & Derivatives

• Nomenclature, Structure & Physical Properties:

  • General formula of saturated acyclic monocarboxylic acids: $C_nH_{2n}O_2$ or $C_{n-1}H_{2n-1}COOH$
  • Characterized by the carboxyl functional group ($-COOH$), composed of a carbonyl group ($C=O$) and a hydroxyl group ($-OH$) bound to the same carbon atom.
  • Hydrogen-Bonded Dimers: Strong hydrogen bonding causes carboxylic acids to exist as stable cyclic dimers in both liquid and nonpolar solution states:         $R-C(=O\cdots H-O)-(O-H\cdots O=)C-R$
  • Physical States at Ambient Conditions ($25^\circ\text{C}$):
    • Lower aliphatic monocarboxylic acids ($C_1 - C_3$: formic, acetic, propionic) are liquids, completely miscible with water.
    • Medium aliphatic acids ($C_4 - C_9$) are oily liquids with pungent, unpleasant rancid odors, exhibiting limited water solubility.
    • Higher saturated fatty acids ($C_{10}+$: palmitic, stearic) are waxy solids, completely insoluble in water.
    • All dicarboxylic acids (oxalic, malonic, succinic, maleic, fumaric) and aromatic carboxylic acids (benzoic, phthalic) are crystalline solids at room temperature.

• Acidity & Chemical Reactions:

  • Aqueous Dissociation: Carboxylic acids dissociate reversibly in water, yielding carboxylate anions stabilized by resonance delocalization across both oxygen atoms:         $R-COOH + H_2O \rightleftharpoons R-COO^- + H_3O^+$
  • Relative Acid Strength Hierarchy:$\text{Mineral Acids } (HCl, H_2SO_4, HBr) > \text{Formic Acid } (HCOOH) > \text{Acetic / Alkyl Carboxylic Acids } (R-COOH) > \text{Carbonic Acid } (H_2CO_3) > \text{Hydrogen Sulfide } (H_2S) > \text{Hydrocyanic Acid } (HCN) > \text{Phenols } (C_6H_5OH) > \text{Water } (H_2O) > \text{Alcohols } (R-OH)$
  • Displacement Reactions (Salt Exchange):
    • A stronger acid always displaces a weaker acid from its respective salt:
      • Acetic acid decomposes sodium carbonate and hydrogen carbonate, liberating carbon dioxide gas:                 $2\,CH_3COOH + Na_2CO_3 \rightarrow 2\,CH_3COONa + CO_2\uparrow + H_2O$
      • Acetic acid displaces hydrocyanic acid from sodium cyanide ($NaCN$):                 $CH_3COOH + NaCN \rightarrow CH_3COONa + HCN$
      • Acetic acid displaces phenol from sodium phenoxide:                 $CH_3COOH + C_6H_5ONa \rightarrow CH_3COONa + C_6H_5OH$
      • Mineral acids ($HCl, H_2SO_4$) displace acetic and formic acids from their sodium salts:                 $CH_3COONa + HCl \rightarrow CH_3COOH + NaCl$
  • Thermal Decomposition of Formic Acid: Dehydrated by heating in the presence of concentrated sulfuric acid to release carbon monoxide gas:         $HCOOH \xrightarrow{H_2SO_4,\,\Delta} CO\uparrow + H_2O$(Note: In the absence of strong acid catalysts, energetic thermal pyrolysis yields $CO_2 + H_2$).
  • Synthesis via Functional Group Hydrolysis:
    • Hydrolysis of geminal trihalogenated derivatives (e.g., benzotrichloride / trichlorophenylmethane):             $C_6H_5-CCl_3 + 2\,H_2O \xrightarrow{OH^-} C_6H_5-COOH + 3\,HCl$
    • Hydrolysis of nitriles ($R-CN$):             $R-CN + 2\,H_2O \xrightarrow{H^+\text{ or }OH^-} R-COOH + NH_3$
    • Hydrolysis of amides ($R-CONH_2$):             $R-CONH_2 + H_2O \rightarrow R-COOH + NH_3$
    • Hydrolysis of esters ($R-COOR'$):             $R-COOR' + H_2O \rightleftharpoons R-COOH + R'-OH$
    • Hydrolysis of acid anhydrides: Acetic anhydride reacts with phenol to generate phenyl acetate and acetic acid:             $(CH_3CO)_2O + C_6H_5OH \rightarrow C_6H_5OOC-CH_3 + CH_3COOH$
  • Fischer Esterification Equilibrium: Reversible reaction between a carboxylic acid and an alcohol catalyzed by strong mineral acid ($H_2SO_4$):         $R-COOH + R'-OH \xrightleftharpoons{H_2SO_4} R-COOR' + H_2O$         According to Le Chatelier's principle, the equilibrium conversion is shifted toward ester formation by operating with an excess of one reactant (excess alcohol) or by continuous removal of water/ester from the system via distillation.

• Fatty Acids, Triglycerides (Fats), Soaps, and Detergents:

  • Fatty Acids: Monocarboxylic acids with an unbranched (linear) aliphatic carbon chain containing an even number of carbon atoms ($\ge C_4$, typically $C_4 - C_{24}$).
    • Saturated Fatty Acids: Butyric ($C_4H_8O_2$ / $C_3H_7COOH$), Palmitic ($C_{16}H_{32}O_2$ / $C_{15}H_{31}COOH$), Stearic ($C_{18}H_{36}O_2$ / $C_{17}H_{35}COOH$).
    • Unsaturated Fatty Acids: Oleic acid ($C_{18}H_{34}O_2$ / $C_{17}H_{33}COOH$, one cis double bond at position 9), Linoleic acid ($C_{18}H_{32}O_2$, two double bonds), Linolenic acid ($C_{18}H_{30}O_2$, three double bonds).
  • Triglycerides (Triacylglycerols / Natural Fats): Triesters of glycerol with fatty acids:
    • Mixed Triglycerides: Contain two or three different fatty acid acyl groups in the same glycerol molecule (e.g., dipalmitostearin, distearoolein, oleopalmitostearin).
    • Isomer Totals for Tri-substituted Mixed Fats: A triglyceride yielding glycerol, palmitic acid, stearic acid, and oleic acid upon hydrolysis can exist in exactly 3 distinct constitutional positional isomers depending on which acyl chain occupies the central ($\beta$ or position 2) hydroxyl site of glycerol.
    • Physical Consistency of Fats: Saturated fatty acid triglycerides pack closely and are solids or semisolids at room temperature (animal fats: tallow, lard). Triglycerides rich in cis-unsaturated fatty acids have bent hydrocarbon chains preventing tight packing and are liquids at room temperature (vegetable oils).
  • Chemical Reactions of Fats:
    • Catalytic Hydrogenation: Industrial hardening of liquid vegetable oils into solid fats (margarine manufacture). Unsaturated fatty acid side-chains add hydrogen over nickel catalysts at $150 - 200^\circ\text{C}$, converting double bonds to single bonds.
    • Halogen Addition: Unsaturated fats add bromine or iodine across double bonds; used analytically to determine the degree of unsaturation (iodine value).
    • Drying (Siccativity) of Oils: Vegetable oils rich in polyunsaturated fatty acids (such as linseed oil) undergo auto-oxidation and cross-linking polymerization upon prolonged exposure to atmospheric oxygen, curing into hard, transparent, impervious, highly adherent films (used as binders in oil paints and protective varnishes).
    • Saponification: Alkaline hydrolysis of fats with aqueous sodium or potassium hydroxide ($NaOH, KOH$), producing free glycerol and metal salts of fatty acids (soaps):             $\text{Triglyceride} + 3\,NaOH \rightarrow \text{Glycerol} + 3\,R-COO^-Na^+ \quad (\text{Hard Soap})$$\text{Triglyceride} + 3\,KOH \rightarrow \text{Glycerol} + 3\,R-COO^-K^+ \quad (\text{Soft Soap})$
  • Soaps and Synthetic Detergents:
    • Soaps: Ionic surfactants composed of a long nonpolar hydrophobic hydrocarbon "tail" ($C_{11}-C_{17}$) and an ionic hydrophilic carboxylate "head" ($-COO^-Na^+$). In hard water containing $Ca^{2+}$ and $Mg^{2+}$ ions, soaps precipitate as insoluble calcium and magnesium carboxylates, destroying lathering power.
    • Synthetic Detergents: Engineered surface-active agents (tensioactive substances) that lower the surface tension of water, stabilize emulsions, and retain cleansing power in hard water. Classified into:
      • Anionic Detergents: Sodium alkyl sulfates ($R-O-SO_3^-Na^+$) and sodium alkylarylsulfonates ($R-C_6H_4-SO_3^-Na^+$).
      • Cationic Detergents: Quaternary ammonium salts ($[R-N(CH_3)_3]^+Cl^-$), possessing potent bactericidal properties.
      • Nonionic Detergents: Polyethoxylated alcohols ($R-O-(CH_2-CH_2-O)_n-H$); do not ionize in aqueous solution.
      • Biodegradability: Natural soaps and synthetic detergents with unbranched, linear alkyl chains are readily degraded by environmental microorganisms; detergents with branched hydrocarbon chains resist microbial breakdown, causing environmental foaming and aquatic pollution.