Comprehensive Organic Chemistry: Hydrocarbons, Functional Groups, Reaction Mechanisms, and Nomenclature

Fundamentals of Hydrocarbons and Nomenclature Systems

• Definition of Hydrocarbons:

  • Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen atoms.
  • They form the foundational framework of organic chemistry, dividing into aliphatics, aromatics, and hydrocarbon derivatives.

• Broad Classification:

  • Aliphatics: Hydrocarbons containing open chains (straight or branched) or non-aromatic carbon rings. Divided into:
  • Alkanes: Saturated chains containing only single carbon-carbon bonds.
  • Alkenes: Unsaturated chains containing one or more carbon-carbon double bonds.
  • Alkynes: Unsaturated chains containing one or more carbon-carbon triple bonds.
  • Aromatics: Benzene-based ring systems characterized by delocalized conjugated $\pi$-electron systems.
  • Derivatives: Hydrocarbons bearing oxygen-, nitrogen-, sulfur-, or halogen-containing functional groups (e.g., alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amides, amines, and haloalkanes).

• Saturated vs. Unsaturated Carbon Skeletons:
  • Saturated Hydrocarbons: Compounds in which all carbon-carbon bonds are single bonds ($\sigma$-bonds). Each carbon atom is bonded to the maximum stoichiometric quantity of other atoms.
  • Unsaturated Hydrocarbons: Compounds possessing one or more multiple bonds (double or triple bonds), leaving carbons bonded to fewer than the maximum number of atoms possible.

• IUPAC Nomenclature Framework:
  • Established by the International Union of Pure and Applied Chemistry to provide unambiguous, systematic identification.
  • The construction sequence follows a strict order:
  • Locant - Multiplier - Substituent PREFIXES - ROOT - Locant - Functional Group SUFFIX

• Component Definitions of the Systematic Name:

  • Locants: Numerical markers defining the precise carbon positions of substituents, unsaturations, and principal functional groups. Every substituent and functional group requires an individual locant.
  • Multipliers: Numerical prefixes (e.g., di-, tri-, tetra-, penta-) denoting repeated identical groups. Multipliers are disregarded when alphabetizing substituents.
  • Substituent Prefixes: Secondary groups attached to the parent carbon chain, placed at the front of the name in alphabetical order.
  • Root: Designates the number of carbon atoms comprising the longest continuous carbon chain that contains the principal functional group.
  • Functional Group Suffix: Terminal modifier indicating the highest-priority functional group present.

• Alkyl Chain Root and Substituent Stems:

  • An alkyl group is an alkane lacking one terminal hydrogen atom; its suffix changes from -ane to -yl (e.g., $CH_4$ = methane, $-CH_3$ = methyl).
  • Standard stems for carbon lengths $1$ through $10$:
  • $1$ carbon: meth- (substituent: methyl-)
  • $2$ carbons: eth- (substituent: ethyl-)
  • $3$ carbons: prop- (substituent: propyl-)
  • $4$ carbons: but- (substituent: butyl-)
  • $5$ carbons: pent- (substituent: pentyl-)
  • $6$ carbons: hex- (substituent: hexyl-)
  • $7$ carbons: hept- (substituent: heptyl-)
  • $8$ carbons: oct- (substituent: octyl-)
  • $9$ carbons: non- (substituent: nonyl-)
  • $10$ carbons: dec- (substituent: decyl-)

• Common Branched Alkyl Groups:

  • Isopropyl: $-\text{CH}(\text{CH}_3)_2$
  • Isobutyl: $-\text{CH}_2\text{CH}(\text{CH}_3)_2$
  • Isopentyl: $-\text{CH}_2\text{CH}_2\text{CH}(\text{CH}_3)_2$
  • sec-Butyl: $-\text{CH}(\text{CH}_3)\text{CH}_2\text{CH}_3$
  • tert-Butyl: $-\text{C}(\text{CH}_3)_3$

• The First Point of Difference Rule:

  • The principal functional group receives the lowest possible locant.
  • If multiple functional groups exist, the highest-priority group determines numbering direction.
  • Substituents are assigned locants based on the numbering direction that yields the lowest number at the first point of difference when comparing locant sets term by term.
  • Example: 2-methylpentane is correct; 4-methylpentane is incorrect.
  • Example: 2,2,4-trimethylpentane is correct; 2,4,4-trimethylpentane is incorrect (first difference occurs at the second locant: $2 < 4$).
  • Example: 2,4,4-trimethylhexane is correct; 3,3,5-trimethylhexane is incorrect ($2 < 3$).
  • Functional group priority example: pentan-2-ol is correct; pentan-4-ol is incorrect.
  • Combined example: 4-methylpentan-2-ol is correct; 2-methylpentan-4-ol is incorrect (hydroxyl takes precedence for lowest locant).

• Alphabetization Conventions:

  • Substituents appear alphabetically regardless of their associated locants (e.g., ethyl precedes methyl).
  • Simple multiplier prefixes (di-, tri-, tetra-) are ignored in alphabetization (e.g., ethyl precedes dimethyl).
  • The structural prefix iso- is treated as part of the alkyl name and is alphabetized; hyphenated prefixes (sec-, tert-) are ignored in alphabetization (e.g., alphabetical sequence: sec-butyl $\rightarrow$ ethyl $\rightarrow$ isobutyl $\rightarrow$ dimethyl $\rightarrow$ propyl).
  • Alphabetical ordering resolves locant assignment only when numbering from either direction yields an identical numerical set.

Alkanes: Structure, Physical Trends, and Reactions

• Molecular Characteristics of Alkanes:

  • General formula: $C_nH_{2n+2}$
  • Carbon hybridization: $sp^3$
  • Molecular geometry: Tetrahedral around each carbon atom with bond angles of $109.5^\bot$
  • Alkanes represent a homologous series where each consecutive member differs by a methylene unit ($-CH_2-$).

• Electronegativity and Bond Polarity:

  • Carbon Pauling electronegativity: $2.55$
  • Hydrogen Pauling electronegativity: $2.20$
  • Electronegativity difference ($\Delta EN$) for $C-H$: $2.55 - 2.20 = 0.35$
  • Electronegativity difference ($\Delta EN$) for $C-C$: $2.55 - 2.55 = 0.00$
  • Both values fall below the $0.4$ to $0.5$ non-polar boundary, rendering alkanes completely non-polar.

• Intermolecular Forces (London Dispersion Forces):

  • Non-polar alkanes interact solely via London Dispersion Forces (LDFs).
  • LDFs arise from instantaneous asymmetries in the electron cloud surrounding atomic nuclei, creating temporary, induced dipoles.
  • The magnitude of LDFs depends directly on:
  • The total number of electrons (which correlates with molecular weight).
  • The contact surface area of the molecule.

• Physical Properties and Chain Length Fractions:

  • $1$ to $5$ Carbon Atoms ($BP < 30^\bot\text{C}$): Gaseous at standard ambient temperature and pressure; used as combustible heating and cooking fuels (methane, ethane, propane, butane).
  • $5$ to $16$ Carbon Atoms ($BP = 30^\bot\text{C} \text{ to } 275^\bot\text{C}$): Liquids; primary components of motor fuels (gasoline spans $C_5 \text{ to } C_{10}$; kerosene spans $C_{10} \text{ to } C_{16}$).
  • $16$ to $22$ Carbon Atoms ($BP > 250^\bot\text{C}$): Heavy, viscous liquids; used in oil furnaces and as lubricating oils.
  • $18+$ Carbon Atoms ($BP > 400^\bot\text{C}$): Semi-solids; utilized in lubricating greases, petroleum jelly, cosmetics, and paraffin waxes for candles and wax paper.
  • $26+$ Carbon Atoms ($BP > 500^\bot\text{C}$): High-molecular-weight solid residues; used in asphalts and road tars.

• Boiling Point and Melting Point Data for Linear Alkanes ($C_1 \text{ to } C_{14}$):

  • Methane ($CH_4$): $BP = -164^\bot\text{C}$, $MP = -183^\bot\text{C}$
  • Ethane ($C_2H_6$): $BP = -89^\bot\text{C}$, $MP = -183^\bot\text{C}$
  • Propane ($C_3H_8$): $BP = -42^\bot\text{C}$ (worksheet observed: $-49^\bot\text{C}$), $MP = -190^\bot\text{C}$
  • Butane ($C_4H_{10}$): $BP = -0.5^\bot\text{C}$, $MP = -138^\bot\text{C}$
  • Pentane ($C_5H_{12}$): $BP = 36^\bot\text{C}$, $MP = -130^\bot\text{C}$
  • Hexane ($C_6H_{14}$): $BP = 69^\bot\text{C}$, $MP = -95^\bot\text{C}$
  • Heptane ($C_7H_{16}$): $BP = 98^\bot\text{C} \text{ to } 100^\bot\text{C}$, $MP = -91^\bot\text{C}$
  • Octane ($C_8H_{18}$): $BP = 125^\bot\text{C}$, $MP = -57^\bot\text{C}$
  • Nonane ($C_9H_{20}$): $BP = 151^\bot\text{C}$, $MP = -51^\bot\text{C}$
  • Decane ($C_{10}H_{22}$): $BP = 174^\bot\text{C}$, $MP = -30^\bot\text{C}$
  • Undecane ($C_{11}H_{24}$): $BP = 196^\bot\text{C}$
  • Dodecane ($C_{12}H_{26}$): $BP = 216^\bot\text{C}$
  • Tridecane ($C_{13}H_{28}$): $BP = 234^\bot\text{C}$

• Boiling Point Trends and Branching Effects:

  • Boiling point increases by approximately $20^\bot\text{C} \text{ to } 30^\bot\text{C}$ (with an empirical experimental average of $38^\bot\text{C}$) per methylene ($-CH_2-$) group added to the chain.
  • Straight-chain alkanes possess higher boiling points than branched isomers of equal molecular mass due to larger accessible surface area, enabling closer packing and more extensive dispersion contacts.
  • Example: n-butane ($CH_3-CH_2-CH_2-CH_3$) boils at $0^\bot\text{C}$, whereas branched isobutane / 2-methylpropane ($CH_3-CH(CH_3)-CH_3$) boils at $-12^\bot\text{C}$.

• Melting Point Packing Anomalies:

  • While melting points generally rise with molecular mass, the curve displays an alternating pattern between odd and even carbon numbers.
  • Even-numbered alkanes pack efficiently into organized crystalline lattices, requiring substantial thermal energy to disrupt (average increase: $38.25^\bot\text{C}$ per even carbon added).
  • Odd-numbered alkanes pack less symmetrically and more loosely, requiring comparatively less thermal energy to transition into liquid (average increase: $33^\bot\text{C}$ per odd carbon added).
  • Highly symmetrical branched isomers, such as 2-methyl isomers (iso-alkanes), often display higher melting points than their linear analogs due to compact crystalline packing.

• Solubility and Density:

  • Insoluble in polar solvents (e.g., water) due to lack of net dipole moments and inability to form hydrogen bonds.
  • Soluble in non-polar organic solvents (benzene, chloroform, ether).
  • Alkanes have densities below $1.0\,\text{g}\,\text{cm}^{-3}$; when mixed with water, liquid alkanes float as the upper layer.

• Combustion Reactions:

  • Complete Combustion: Occurs with stoichiometric or excess oxygen, producing carbon dioxide, water vapor, and heat:     $C_3H_{8(g)} + 5\,O_{2(g)} \rightarrow 3\,CO_{2(g)} + 4\,H_2O_{(l)}$
  • Incomplete Combustion: Occurs when oxygen is limited, producing solid carbon particulate (soot), toxic carbon monoxide gas, carbon dioxide, and water:     $C_8H_{18(l)} + 9\,O_{2(g)} \rightarrow C_{(s)} + 5\,CO_{(g)} + 2\,CO_{2(g)} + 9\,H_2O_{(l)}$
  • Higher alkanes are progressively harder to ignite because their lower volatility and stronger LDFs impede rapid vaporization.

• Free Radical Halogen Substitution Mechanism:

  • Halogen reactivity: Fluorine reacts explosively in the dark; chlorine and bromine undergo photochemical substitution requiring ultraviolet ($\text{UV}$) light; iodine fails to react.
  • Overall reaction for chlorination of methane:     $CH_{4(g)} + Cl_{2(g)} \xrightarrow{\text{UV}} CH_3Cl_{(g)} + HCl_{(g)}$
  • Mechanism stages:
  • Initiation: Homolytic fission of the halogen molecule by UV photons, producing two neutral free radicals:       $Cl_2 \xrightarrow{\text{UV}} 2\,Cl\cdot$
  • Propagation: Chain reaction steps regenerating reactive radical intermediates:       $CH_4 + Cl\cdot \rightarrow CH_3\cdot + HCl$$CH_3\cdot + Cl_2 \rightarrow CH_3Cl + Cl\cdot$
  • Termination: Radical recombination steps that reduce radical concentrations and end the chain:       $Cl\cdot + Cl\cdot \rightarrow Cl_2$$CH_3\cdot + Cl\cdot \rightarrow CH_3Cl$$CH_3\cdot + CH_3\cdot \rightarrow CH_3CH_3$
  • Polysubstitution Mixtures: Excess halogen causes successive substitution, yielding a mixture of $CH_3Cl$, $CH_2Cl_2$, $CHCl_3$, and $CCl_4$.
  • Bond Fission Types:
  • Homolytic Fission: The covalent bond breaks symmetrically; each fragment retains one electron, forming free radicals:       $X-Y \rightarrow X\cdot + Y\cdot$
  • Heterolytic Fission: The covalent bond breaks asymmetrically; one atom takes both bonding electrons, forming ions:       $X-Y \rightarrow X^+ + Y^- \quad \text{or} \quad X-Y \rightarrow X^- + Y^+$

Alkenes: Unsaturation, Geometric Isomerism, and Reactivity

• Molecular Characteristics of Alkenes:

  • Functional group: Carbon-carbon double bond ($C=C$), consisting of one $\sigma$-bond and one $\pi$-bond.
  • General formula: $C_nH_{2n}$
  • Carbon hybridization: $sp^2$
  • Geometry: Trigonal planar around double-bonded carbons with bond angles of $120^\bot$
  • Suffix: -ene

• Nomenclature Rules for Alkenes:

  • The root must represent the longest continuous carbon chain containing the double bond, even if a longer saturated chain exists.
  • The chain is numbered from the end that gives the double-bonded carbons the lowest possible locants.
  • If multiple double bonds are present, stems employ multipliers: -diene, -triene.

• Cis-Trans (Geometric) Isomerism:

  • Caused by restricted rotation around the rigid carbon-carbon double bond ($\pi$-bond).
  • Cis Isomer: Identical or priority substituent groups lie on the same side of the double bond axis.
  • Trans Isomer: Identical or priority substituent groups lie on opposite sides of the double bond axis.
  • Condition for Isomerism: Each carbon atom of the double bond must be attached to two distinct chemical groups. If either alkene carbon is bonded to two identical groups (e.g., $=CH_2$ or $=C(CH_3)_2$), geometric isomerism cannot exist.

• Physical Properties of Alkenes:

  • Non-polar, water-insoluble, and soluble in organic solvents.
  • Boiling points are slightly lower than those of corresponding alkanes with identical carbon counts, as the planar unsaturation alters molecular packing efficiency and diminishes cohesive dispersion contacts.

• Addition Reactions Across the Double Bond:

  • Halogenation: Electrophilic addition of diatomic halogens in an inert solvent ($CCl_4$), converting alkenes into vicinal dihaloalkanes:     $CH_2=CH_2 + Cl_2 \xrightarrow{CCl_4} CH_2Cl-CH_2Cl$
  • Hydrogenation: Catalytic addition of molecular hydrogen using a platinum ($Pt$), palladium ($Pd$), or nickel ($Ni$) catalyst to form alkanes:     $CH_2=CH_2 + H_2 \xrightarrow{Pt} CH_3-CH_3$
  • Hydrohalogenation: Addition of hydrogen halides ($HCl$, $HBr$, $HI$) under thermal activation (represented by $\Delta$), yielding monohaloalkanes:     $CH_2=CH-CH_3 + HCl \xrightarrow{\Delta} CH_3-CHCl-CH_3$
  • Hydration: Addition of water across the double bond catalyzed by concentrated sulfuric acid ($H_2SO_4$) at $100^\bot\text{C}$, yielding an alcohol:     $CH_2=CH-CH_3 + H_2O \xrightarrow[H_2SO_4]{100^\bot\text{C}} CH_3-CH(OH)-CH_3$

• Markovnikov's Rule:

  • Governing principle: "The rich get richer."
  • In the addition of an asymmetrical reagent ($HX$, $H_2O$) to an asymmetrical alkene, the hydrogen atom attaches to the double-bonded carbon that already carries the greater number of hydrogen atoms.
  • The electrophilic halide or hydroxyl group attaches to the more substituted carbon, yielding the major product.

• Polymerization and Alkene Preparation:
  • Addition Polymerization: Alkene monomers join under high pressure and temperature to yield long-chain synthetic polymers:     $n\,CH_2=CH_2 \rightarrow -[CH_2-CH_2]_n-$
  • Alkene Preparation via Dehydration of Alcohols: Acid-catalyzed elimination using alumina ($Al_2O_3$) and heat ($\Delta$):     $CH_3-CH(OH)-CH_3 \xrightarrow[Al_2O_3]{\Delta,\,H^+} CH_2=CH-CH_3 + H_2O$

Alkynes: Structure, Physical Properties, and Addition Reactions

• Molecular Characteristics of Alkynes:

  • Functional group: Carbon-carbon triple bond ($C \equiv C$), consisting of one $\sigma$-bond and two orthogonal $\pi$-bonds.
  • General formula: $C_nH_{2n-2}$
  • Carbon hybridization: $sp$
  • Geometry: Linear geometry around the triple bond with bond angles of $180^\bot$
  • Suffix: -yne

• Nomenclature Rules for Alkynes:

  • Numbering begins from the end of the parent chain nearest the triple bond.
  • Chains with multiple triple bonds use suffixes -diyne, -triyne.
  • When selecting the parent chain, the continuous carbon sequence containing the triple bond must be prioritized over longer saturated side pathways.

• Physical Properties of Alkynes:

  • Non-polar molecules; insoluble in water, soluble in organic solvents.
  • Boiling points are slightly higher than those of corresponding alkanes and alkenes.
  • The linear geometry of the triple bond minimizes steric bulk, facilitating close intermolecular alignment and producing stronger cohesive London dispersion forces.

• Addition Reactions of Alkynes:

  • Halogenation: Requires two molar equivalents of halogen to achieve complete saturation:     $HC \equiv CH + 2\,Br_2 \xrightarrow{\Delta} CHBr_2-CHBr_2 \quad (1,1,2,2\text{-tetrabromoethane})$
  • Hydrogenation: Complete reduction requires two molar equivalents of hydrogen in the presence of a platinum catalyst:     $HC \equiv CH + 2\,H_2 \xrightarrow[\Delta]{Pt} CH_3-CH_3$
  • Hydrohalogenation: Follows Markovnikov's rule across both addition steps, generating geminal dihaloalkanes:     $HC \equiv C-CH_3 + HCl \xrightarrow{\Delta} H_2C=CCl-CH_3 \xrightarrow{HCl} H_3C-CCl_2-CH_3$
  • Hydration: Catalyzed by acid and mercury(II) ions ($H^+, Hg^{2+}$), producing an unstable enol intermediate that rapidly tautomerizes into a ketone:     $HC \equiv C-CH_3 + H_2O \xrightarrow{H^+,\,Hg^{2+}} [H_2C=C(OH)-CH_3] \rightleftharpoons H_3C-C(=O)-CH_3$

Cyclic Hydrocarbons: Ring Strain, Nomenclature, and Properties

• Characteristics of Alicyclic Rings:

  • Closed carbon ring structures containing three or more carbon atoms.
  • Generic prefix: cyclo-
  • Suffixes: -ane, -ene, -yne, depending on unsaturation.

• Ring Strain and Stability Variations:

  • Cyclopropane: Nominal internal bond angle is $60^\bot$. Drastic compression from the tetrahedral angle ($109.5^\bot$) produces extreme ring strain, rendering the molecule unstable and chemically reactive. Due to high surface polarization, it is an exception among cycloalkanes in showing minor water solubility.
  • Cyclobutane: Planar ring angle of $88^\bot$ to $90^\bot$ creates significant angle strain and torsional strain, making it unstable.
  • Cyclopentane: Internal bond angle of $108^\bot$ approaches the ideal tetrahedral angle of $109.5^\bot$, resulting in high thermodynamic stability.
  • Cyclohexane: Internal planar angle is $120^\bot$; however, it puckers into non-planar chair conformations that achieve strain-free tetrahedral angles of $109.5^\bot$, making it exceptionally stable.

• Nomenclature Rules for Cyclic Systems:

  • The ring serves as the root if its carbon count equals or exceeds that of any attached alkyl substituent.
  • If an attached acyclic alkyl chain contains more carbons than the ring, the ring becomes a cycloalkyl prefix (e.g., cyclobutyl-).
  • Rings with multiple substituents are numbered to assign the lowest locant set. Ties are broken by alphabetical precedence.
  • In cyclic alkenes and alkynes, the multiple bond is assigned positions $1$ and $2$ by definition; numbering proceeds through the multiple bond to give substituents the lowest locants.

• Physical Properties of Cycloalkanes:

  • Non-polar; insoluble in water (except cyclopropane).
  • Boiling and melting points are consistently higher than those of corresponding straight-chain alkanes with the same carbon count, because ring rigidity provides larger effective contact surface area, enhancing dispersion forces.

Aromatic Compounds: Resonance, Derivatives, and Substitution Chemistry

• Structure and Resonance of Benzene:

  • Molecular formula: $C_6H_6$
  • Geometry: Planar hexagonal ring; all six carbons are $sp^2$ hybridized with bond angles of $120^\bot$.
  • Resonance: Six delocalized $\pi$-electrons circulate continuously across the ring, giving all carbon-carbon bonds an intermediate length and strength between single and double bonds. This resonance stabilization accounts for benzene's chemical stability and resistance to addition reactions.

• Common Monosubstituted Benzene Derivatives:

  • Toluene: Methylbenzene ($C_6H_5-CH_3$
  • Phenol: Hydroxybenzene ($C_6H_5-OH$
  • Aniline: Aminobenzene ($C_6H_5-NH_2$
  • Anisole: Methoxybenzene ($C_6H_5-OCH_3$
  • Styrene: Vinylbenzene / Ethenylbenzene ($C_6H_5-CH=CH_2$
  • Benzaldehyde: Formylbenzene ($C_6H_5-CHO$
  • Benzoic Acid: Benzenecarboxylic acid ($C_6H_5-COOH$
  • Acetophenone: Methyl phenyl ketone ($C_6H_5-COCH_3$
  • Benzonitrile: Cyanobenzene ($C_6H_5-CN$
  • Cumene: Isopropylbenzene ($C_6H_5-CH(CH_3)_2$

• Benzene as an Attached Substituent:

  • Phenyl Group: A benzene ring directly attached to an aliphatic chain of seven or more carbon atoms (or a chain with higher priority functional groups). Notation: $-C_6H_5$.
  • Benzyl Group: A phenyl ring bonded via a methylene bridge. Notation: $-CH_2-C_6H_5$.

• Disubstituted Benzene Isomerism (The OMP System):

  • Ortho (o-): Substituents occupy positions $1$ and $2$.
  • Meta (m-): Substituents occupy positions $1$ and $3$.
  • Para (p-): Substituents occupy positions $1$ and $4$.

• Polycyclic Aromatic Hydrocarbons (PAHs):

  • Molecules composed of two or more fused benzene rings that share adjacent ring carbons:
  • Naphthalene: Two fused benzene rings ($C_{10}H_8$
  • Anthracene: Three linearly fused rings ($C_{14}H_{10}$
  • Phenanthrene: Three angularly fused rings ($C_{14}H_{10}$
  • Pyrene: Four fused rings ($C_{16}H_{10}$
  • Benzo[a]pyrene: Five fused rings; a known carcinogen

• Physical Properties of Aromatic Compounds:

  • Highly symmetrical planar rings enable efficient crystalline packing, producing higher melting points than comparable aliphatic hydrocarbons.
  • Completely non-polar; insoluble in water.
  • Distinctive aromas: found in vanillin (vanilla), benzaldehyde (cherries/almonds), naphthalene (mothballs), methyl salicylate (wintergreen), and cinnamaldehyde (cinnamon).

• Electrophilic Aromatic Substitution Reactions:

  • Because of resonance stabilization, benzene resists addition and undergoes substitution instead, preserving ring aromaticity.
  • Halogenation: Requires a Lewis acid catalyst ($FeBr_3$ or $AlCl_3$):     $C_6H_6 + Br_2 \xrightarrow{FeBr_3} C_6H_5Br + HBr$
  • Friedel-Crafts Alkylation: Reaction with alkyl halides catalyzed by anhydrous aluminum chloride ($AlCl_3$):     $C_6H_6 + CH_3CH_2Cl \xrightarrow{AlCl_3} C_6H_5-CH_2CH_3 + HCl$
  • Nitration: Reaction with concentrated nitric acid in the presence of sulfuric acid catalyst at elevated temperatures:     $C_6H_6 + HNO_3 \xrightarrow{H_2SO_4} C_6H_5-NO_2 + H_2O$

Haloalkanes (Alkyl Halides): Properties, Synthesis, and Elimination

• Structural Classifications of Haloalkanes:

  • Hydrocarbons containing one or more halogen atoms ($F$, $Cl$, $Br$, $I$), denoted by the general formula $R-X$.
  • Prefixes: fluoro-, chloro-, bromo-, iodo-.
  • Functional suffix remains -ane when no higher-priority group is present.

• Physical Properties of Haloalkanes:

  • Boiling Points: Markedly higher than corresponding alkanes due to carbon-halogen bond dipoles (C^{\delta+} - X^{\delta-}$), which introduce permanent dipole-dipole attractions in addition to enhanced London dispersion forces.\n - Boiling points rise with halogen size: R-F < R-Cl < R-Br < R-I, following the increase in polarizability and electron count.\n - **Physical State at Room Temperature:** Chloromethane (CH_3Cl$), fluoromethane ($CH_3F$), bromomethane ($CH_3Br$), and chloroethane ($CH_3CH_2Cl$) are gases; iodomethane ($CH_3I) is a dense liquid.\n - **Water Solubility:** Only small haloalkanes (CH_3F$,$CH_3Cl$,$CH_3Br$,$CH_3I) show slight water solubility; solubility decreases sharply with longer alkyl chains.\n\n\n\n- **Synthesis of Haloalkanes:**\n - **Alkene Halogenation:** Electrophilic addition of halogens in CCl_4.\n - **Alkene Hydrohalogenation:** Addition of HX across an unsaturation following Markovnikov's rule:\n    CH_2=CH-CH_3 + HCl \xrightarrow{\Delta} CH_3-CHCl-CH_3\n - **Alcohol Substitution:** Replacement of a hydroxyl group by a halogen using strong hydrohalic acid:\n    CH_3CH_2OH + HCl \xrightarrow{H^+} CH_3CH_2Cl + H_2O\n\n- **Reactions of Haloalkanes:**\n - **Nucleophilic Substitution:** Hydrolysis in dilute aqueous base to regenerate primary or secondary alcohols:\n    CH_3CH_2Cl + H_2O \xrightarrow{\text{conc. } NaOH_{(aq)}} CH_3CH_2OH + HCl\n - **Base-Induced Elimination (Dehydrohalogenation):** Heating with alcoholic sodium hydroxide (NaOH in ethanol) strips a hydrogen halide molecule, forming an alkene, a halide salt, and water:\n    CH_3CH_2Cl + NaOH\text{ (alcoholic)} \xrightarrow{\Delta} CH_2=CH_2 + NaCl + H_2O\n\n# Alcohols, Ethers, and Thiols: Functional Dynamics and Transformations\n\n- **Alcohols — Structure and Classification:**\n - Functional group: Hydroxyl group (-OH), suffix *-ol*.\n - Primary (1^ot$) Alcohol: The hydroxyl-bearing carbon is bonded to one alkyl group and two hydrogen atoms ($R-CH_2OH).\n - Secondary (2^ot$) Alcohol: The hydroxyl-bearing carbon is bonded to two alkyl groups and one hydrogen atom ($R_2CHOH).\n - Tertiary (3^ot$) Alcohol: The hydroxyl-bearing carbon is bonded to three alkyl groups and zero hydrogen atoms ($R_3COH).\n\n- **Physical Properties of Alcohols:**\n - High boiling points due to strong intermolecular hydrogen bonding formed between hydroxyl groups.\n - Small alcohols (C_1 \text{ to } C_4) are completely miscible with water. Solubility decreases with chain length as the hydrophobic non-polar alkyl tail dominates over the hydrophilic hydroxyl head.\n - Boiling points rise consistently with increasing chain length:\n - Methanol: 65^ot\text{C}\n - Ethanol: 79^ot\text{C}\n - 1-Propanol: 97^ot\text{C}\n - 1-Butanol: 117^ot\text{C}\n - 1-Pentanol: 138^ot\text{C}\n - 1-Hexanol: 156^ot\text{C}\n\n- **Oxidation Pathways of Alcohols:**\n - Oxidizing agent: Acidified potassium dichromate(VI) (K_2Cr_2O_7$in$H_2SO_4$, denoted as$H^+ / Cr_2O_7^{2-}).\n - **Primary Alcohol Oxidation:** Oxidizes first to an aldehyde, then to a carboxylic acid:\n    R-CH_2OH \xrightarrow{H^+ / Cr_2O_7^{2-}} R-CHO + H_2O \xrightarrow{H^+ / Cr_2O_7^{2-}} R-COOH\n - Distillation isolation: Removing the volatile aldehyde as it forms prevents over-oxidation to the carboxylic acid.\n - Reflux isolation: Condensing vapors back into the reaction vessel ensures complete oxidation to the carboxylic acid.\n - **Secondary Alcohol Oxidation:** Oxidizes cleanly to a ketone:\n    CH_3-CH(OH)-CH_3 \xrightarrow{H^+ / Cr_2O_7^{2-}} CH_3-CO-CH_3 + H_2O\n - **Tertiary Alcohol Oxidation:** Resists oxidation under these conditions due to the lack of an oxidizable \alpha-hydrogen on the carbinol carbon.\n\n- **Dehydration and Ether Condensation:**\n - Intramolecular dehydration of an alcohol over alumina (Al_2O_3) with acid and heat forms an alkene.\n - Intermolecular condensation of two primary alcohol molecules under acid catalysis (H^+ / \Delta) yields a symmetrical ether and water:\n    2\,CH_3CH_2OH \xrightarrow{H^+ / \Delta} CH_3CH_2-O-CH_2CH_3 + H_2O\n\n- **Ethers (R-O-R'):**\n - Structure: An oxygen atom bridging two alkyl or aryl groups. The oxygen cannot occupy a terminal position.\n - Nomenclature: The shorter alkyl segment combines with oxygen to form an *alkoxy-* substituent (e.g., *methoxy-*), while the longer chain forms the alkane root.\n - Physical properties: The bent C-O-C$geometry creates a small dipole moment, but the lack of an$-OH group prevents self-hydrogen-bonding. Boiling points are substantially lower than isomeric alcohols and close to those of alkanes of comparable mass.\n - Ethers with 2 \text{ to } 3 carbons are gases; larger homologs are volatile liquids.\n - Cleavage by hydrohalic acids: Cleaved by concentrated HI$or$HBr to yield an alkyl halide and an alcohol:\n    R-O-R' + HX \rightarrow R-X + R'-OH\n\n- **Thiols (R-SH):**\n - Functional group: Sulfhydryl group (-SH), suffix *-thiol*.\n - Physical properties: Because sulfur is less electronegative than oxygen, thiols do not form strong intermolecular hydrogen bonds. They have lower boiling points and poorer water solubility than corresponding alcohols, along with strong, skunk-like odors.\n - Oxidation: Mild oxidation couples two thiol molecules into a disulfide bridge:\n    2\,R-SH \xrightarrow{[O]} R-S-S-R + H_2O\n\n# Carbonyl Compounds: Aldehydes and Ketones\n\n- **The Carbonyl Moiety:**\n - Functional structure: Carbon-oxygen double bond (C=O).\n - Electronic geometry: Carbon is sp^2$hybridized with a planar trigonal configuration ($120^ot bond angles).\n - The electronegativity difference between carbon (2.55$) and oxygen ($3.44$) creates a permanent bond dipole ($C^{\delta+} = O^{\delta-}).\n\n- **Aldehydes (R-CHO):**\n - Carbonyl carbon occupies a terminal chain position, forming a *formyl group* (-CHO).\n - Suffix: *-al* (the formyl carbon is automatically designated carbon 1).\n - Physical properties: Molecules exhibit permanent dipole-dipole interactions. They cannot donate hydrogen bonds to each other, but the carbonyl oxygen accepts hydrogen bonds from water, making small aldehydes (C_1 \text{ to } C_4) water-soluble.\n - Short-chain aldehydes have sharp, pungent odors; longer-chain homologs have pleasant floral or fruity scents.\n - Reactions:\n - Catalytic Hydrogenation (Reduction): Hydrogenation over platinum under heat and pressure reduces aldehydes to primary alcohols:\n      R-CHO + H_2 \xrightarrow{Pt,\,\Delta} R-CH_2OH\n - Oxidation: Rapidly oxidized by acidified dichromate to carboxylic acids:\n      R-CHO \xrightarrow{H^+ / Cr_2O_7^{2-}} R-COOH\n\n- **Ketones (R-CO-R'):**\n - Carbonyl group is positioned at an internal carbon along the chain.\n - Suffix: *-one*\n - Smallest ketone: Propanone (acetone, CH_3-CO-CH_3).\n - Boiling points: Higher than non-polar alkanes due to dipole-dipole attractions, but lower than alcohols of comparable mass because they lack self-hydrogen-bonding.\n - Comparative boiling points:\n - Propanal: 49^ot\text{C}$; Propanone:$56^ot\text{C}$; 1-Propanol:$97^ot\text{C}\n - Butanal: 75^ot\text{C}$; Butanone:$80^ot\text{C}$; 1-Butanol:$118^ot\text{C}\n - Synthesis: Produced by oxidizing secondary alcohols using acidified dichromate.\n\n- **Qualitative Discrimination via Fehling's Test:**\n - Employs Fehling's solution containing deep-blue copper(II) ions (Cu^{2+}).\n - **Aldehydes:** Reduce alkaline Cu^{2+}$to copper(I) oxide ($Cu_2O$) or metallic copper ($Cu_{(s)}), forming a characteristic red-orange precipitate as the aldehyde oxidizes to a carboxylic acid.\n - **Ketones:** Resist mild oxidation, yielding no reaction; the solution remains clear blue.\n\n# Carboxylic Acids: Acid-Base Behavior, Dimers, and Reactions\n\n- **Structure of the Carboxyl Group:**\n - Terminal functional group combining a carbonyl and a hydroxyl on the same carbon atom (-COOH).\n - Hybridization: Carboxyl carbon is sp^2$hybridized with trigonal planar geometry ($120^ot bond angles).\n - Suffix: *-oic acid*\n\n- **Hydrogen-Bonded Dimerization and Physical Properties:**\n - Carboxylic acids possess both a hydrogen bond donor (-OH$) and a strong hydrogen bond acceptor ($C=O).\n - In pure liquid and solid states, pairs of molecules associate through reciprocal hydrogen bonds to form stable cyclic dimers.\n - Dimerization doubles effective molecular size and significantly raises boiling points:\n - Butane: -0.5^ot\text{C}\n - Butanal: 74.8^ot\text{C}\n - Butan-2-one: 79.6^ot\text{C}\n - Butan-1-ol: 117.2^ot\text{C}\n - Butanoic acid: 165.5^ot\text{C}\n\n\n\n- **Solubility Profile:**\n - C_1 \text{ to } C_4 chains: Completely miscible with water.\n - C_5 \text{ to } C_9 chains: Moderately soluble.\n - C_{10}+ chains: Insoluble, as the non-polar hydrocarbon tail dominates over the polar carboxyl head.\n\n- **Weak Acid Ionization:**\n - Carboxylic acids behave as weak acids, ionizing partially in water to establish dynamic equilibria:\n    R-COOH + H_2O \rightleftharpoons R-COO^- + H_3O^+\n\n- **Synthesis of Carboxylic Acids:**\n - **Exhaustive Oxidation of Primary Alcohols or Aldehydes:** Carried out under reflux with acidified potassium dichromate (H^+ / Cr_2O_7^{2-}).\n - **Arene Oxidation:** Heating alkylbenzenes (such as toluene) with alkaline potassium permanganate (KMnO_4) oxidizes the side chain down to a benzoic acid ring:\n    C_6H_5-CH_3 \xrightarrow[\Delta]{KMnO_4} C_6H_5-COOH\n\n- **Reactions with Metals, Bases, and Carbonates:**\n - **Redox Reaction with Active Alkali Metals:** Produces a carboxylate salt and hydrogen gas:\n    2\,R-COOH + 2\,Na \rightarrow 2\,R-COO^-Na^+ + H_{2(g)}\n - **Neutralization with Hydroxide Bases:** Produces a carboxylate salt and water:\n    R-COOH + NaOH \rightarrow R-COO^-Na^+ + H_2O\n - **Reaction with Carbonate Salts:** Produces a carboxylate salt, water, and carbon dioxide gas:\n    2\,R-COOH + Na_2CO_3 \rightarrow 2\,R-COO^-Na^+ + CO_2 + H_2O\n\n# Esters and Saponification: Synthesis, Odors, and Soap Action\n\n- **Structure and Nomenclature of Esters:**\n - Functional group: Carbonyl carbon bonded directly to an alkoxy bridge (R-COO-R').\n - Hybridization: Carbonyl carbon is sp^2$hybridized with trigonal planar geometry ($120^ot bond angles).\n - Nomenclature rules:\n - The alkyl group attached to the bridging oxygen is named first as a substituent.\n - The acyl group (containing the carbonyl carbon) forms the root with the suffix *-oate*.\n - A space separates the two words (e.g., *ethyl propanoate*).\n\n- **Physical Properties of Esters:**\n - Dipolar carbonyl group renders esters polar, but the absence of an -OH group prevents self-hydrogen-bonding.\n - Boiling points are substantially lower than those of isomeric carboxylic acids and alcohols, and are comparable to aldehydes and ketones of similar mass.\n - Esters with four or fewer carbons are volatile liquids with slight water solubility; higher esters are waxy, water-insoluble solids.\n - Characterized by distinct, pleasant fruit fragrances:\n - Ethyl acetate / ethyl ethanoate: Solvent / fruity aroma\n - Isopentyl acetate: Banana fragrance\n - Octyl acetate: Orange scent\n\n- **Ester Reactions:**\n - **Fischer Esterification:** Reversible acid-catalyzed condensation of a carboxylic acid and an alcohol under reflux:\n    CH_3COOH + CH_3CH_2OH \xrightleftharpoons[\Delta]{H^+} CH_3COOCH_2CH_3 + H_2O\n - **Acid Hydrolysis:** The reverse of esterification, driven by excess water under acid catalysis:\n    R-COOR' + H_2O \xrightleftharpoons[\Delta]{H^+} R-COOH + R'-OH\n - **Ammonolysis / Reaction with Amines:** Reaction with ammonia, primary amines, or secondary amines replaces the alkoxy group, forming amides and releasing alcohols:\n    CH_3COOCH_3 + CH_3NH_2 \rightarrow CH_3CONHCH_3 + CH_3OH\n\n- **Saponification (Base-Induced Hydrolysis):**\n - Irreversible cleavage of an ester by strong aqueous base, yielding an alcohol and a carboxylate salt:\n    CH_3COOCH_3 + NaOH \rightarrow CH_3COO^-Na^+ + CH_3OH\n - Industrial Saponification of Triglycerides: Natural fats (triesters of glycerol with long-chain fatty acids) are boiled with sodium or potassium hydroxide, yielding glycerol (\text{propane-1,2,3-triol}) and fatty acid carboxylate salts (*soaps*).\n\n- **Cleaning Action of Soap:**\n - Soap molecules consist of a long, non-polar hydrophobic hydrocarbon tail and a highly polar, charged hydrophilic head (-COO^-Na^+).\n - In water, soap molecules assemble into spherical aggregates called *micelles*:\n - Hydrophobic tails turn inward to dissolve non-polar grease and oil.\n - Hydrophilic heads face outward toward the aqueous solvent.\n - This arrangement suspends oil droplets in water, forming an emulsion that washes away during rinsing.\n\n\n\n# Nitrogen-Containing Functional Groups: Amines and Amides\n\n- **Amines — Structure and Classification:**\n - Organic derivatives of ammonia (NH_3$) wherein one, two, or three hydrogen atoms are replaced by alkyl or aryl groups ($R-NR'_2).\n - Nitrogen hybridization: sp^3$with a trigonal pyramidal shape derived from tetrahedral electron-pair geometry ($109.5^ot bond angles).\n - **Primary (1^ot$) Amine:** Nitrogen is bonded to one alkyl group and two hydrogen atoms ($R-NH_2).\n - **Secondary (2^ot$) Amine:** Nitrogen is bonded to two alkyl groups and one hydrogen atom ($R_2NH).\n - **Tertiary (3^ot$) Amine:** Nitrogen is bonded to three alkyl groups and zero hydrogen atoms ($R_3N).\n\n- **Nomenclature Rules for Amines:**\n - The longest continuous carbon chain attached to nitrogen serves as the parent alkane; the terminal *-e* is replaced with *-amine*.\n - The position of the amine group is specified by a numerical locant.\n - Additional alkyl groups attached to nitrogen are designated using the prefix *N-* (e.g., *N-ethyl-N-methylpropan-1-amine*).\n\n- **Physical Properties of Amines:**\n - Highly polar N-H bonds allow primary and secondary amines to form intermolecular hydrogen bonds, giving them higher boiling points than non-polar alkanes or ethers of similar molecular weight.\n - Because nitrogen is less electronegative than oxygen (\Delta EN$of$N-H < O-H), amine hydrogen bonds are weaker than those in alcohols, resulting in lower boiling points for amines compared to equivalent alcohols.\n - Tertiary amines lack N-H bonds and cannot donate hydrogen bonds to each other, resulting in substantially lower boiling points.\n - Amines have sharp, fishy odors.\n - Amines with fewer than six carbons are water-soluble because the nitrogen lone pair accepts hydrogen bonds from water molecules.\n\n- **Synthesis of Amines via Alkylation:**\n - Nucleophilic substitution of alkyl halides by ammonia or existing amines:\n - **Primary Amine Synthesis:**\n      CH_3CH_2I + NH_3 \rightarrow CH_3CH_2NH_2 + HI\n - **Secondary Amine Synthesis:**\n      CH_3CH_2I + CH_3CH_2NH_2 \rightarrow (CH_3CH_2)_2NH + HI\n - **Tertiary Amine Synthesis:**\n      CH_3CH_2I + (CH_3CH_2)_2NH \rightarrow (CH_3CH_2)_3N + HI\n\n- **Amides — Structure and Classification:**\n - Structure: A carbonyl group bonded directly to a nitrogen atom (R-CO-NR'_2).\n - Hybridization: Carbonyl carbon is sp^2$hybridized (trigonal planar,$120^ot$); nitrogen is$sp^3$hybridized (tetrahedral geometry,$109.5^ot).\n - Classification:\n - **Primary (1^ot$) Amide:** Nitrogen is bonded to two hydrogen atoms ($R-CONH_2).\n - **Secondary (2^ot$) Amide:** Nitrogen is bonded to one alkyl group and one hydrogen atom ($R-CONHR').\n - **Tertiary (3^ot$) Amide:** Nitrogen is bonded to two alkyl groups and zero hydrogen atoms ($R-CONR'_2).\n\n- **Physical Properties of Amides:**\n - Primary and secondary amides possess both polar carbonyl groups and N-H bonds, enabling extensive intermolecular hydrogen-bonding networks.\n - As a result, primary and secondary amides exhibit exceptionally high melting and boiling points, with many existing as crystalline solids at room temperature.\n\n- **Synthesis of Amides:**\n - Condensation of a carboxylic acid with ammonia or an amine at elevated temperatures (100^ot\text{C}) in the presence of a catalyst:\n - Carboxylic Acid + Ammonia \rightarrow$Primary ($1^ot) Amide + Water\n - Carboxylic Acid + Primary (1^ot$) Amine$\rightarrow$Secondary ($2^ot) Amide + Water\n - Carboxylic Acid + Secondary (2^ot$) Amine$\rightarrow$Tertiary ($3^ot) Amide + Water\n\n- **Hydrolysis of Amides:**\n - **Basic Hydrolysis (Amide Saponification):** Cleavage by aqueous sodium hydroxide under heat produces a carboxylate salt and a free amine (or ammonia):\n    R-CONH-R' + NaOH \xrightarrow{\text{heat}} R-COO^-Na^+ + R'-NH_2\n - **Acidic Hydrolysis:** Cleavage by aqueous hydrochloric acid under heat produces a free carboxylic acid and an ammonium salt:\n    R-CONH-R' + HCl + H_2O \xrightarrow{\text{heat}} R-COOH + R'-NH_3^+Cl^-\n\n# Comprehensive IUPAC Functional Group Priority and Nomenclature Architecture\n\n- **The Master Priority Hierarchy:**\n - When a molecule contains multiple functional groups, the highest-ranking group in the priority table determines the principal functional group suffix and dictates numbering direction to receive the lowest locant.\n - All lower-ranking groups are treated as substituents and named with prefixes.\n\n\n\n- **Priority Table from Highest to Lowest:**\n - **1. Carboxylic Acid:**\n - Prefix: *carboxy-*\n - Suffix: *-carboxylic acid* / *-oic acid*\n - Example: Ethanoic acid\n - **2. Ester:**\n - Prefix: *(R)-oxycarbonyl-*\n - Suffix: *-oate*\n - Example: Methyl ethanoate\n - **3. Acid Chloride:**\n - Prefix: *halocarbonyl-*\n - Suffix: *-oyl halide*\n - Example: Ethanoyl chloride\n - **4. Amide:**\n - Prefix: *carbamoyl-*\n - Suffix: *-carboxamide* / *-amide*\n - Example: Ethanamide\n - **5. Nitrile:**\n - Prefix: *cyano-*\n - Suffix: *-nitrile*\n - Example: Ethanenitrile\n - **6. Aldehyde:**\n - Prefix: *formyl-*\n - Suffix: *-al* / *-carbaldehyde*\n - Example: Ethanal\n - **7. Ketone:**\n - Prefix: *oxo-*\n - Suffix: *-one*\n - Example: 2-Propanone\n - **8. Alcohol:**\n - Prefix: *hydroxy-*\n - Suffix: *-ol*\n - Example: Methanol\n - **9. Thiol:**\n - Prefix: *mercapto-*\n - Suffix: *-thiol*\n - Example: Methanethiol\n - **10. Amine:**\n - Prefix: *amino-*\n - Suffix: *-amine*\n - Example: Methylamine\n - **11. Alkene:**\n - Prefix: *alkenyl*\n - Suffix: *-ene*\n - Example: Propene\n - **12.$$ Alkyne:**
  • Prefix: alkynyl
  • Suffix: -yne
  • Example: Butyne

• Subordinate Functional Groups (Always Prefixes):

  • All groups below alkynes do not take suffix endings; they are treated as substituents on an alkane parent (-ane):
  • Alkane: Prefix alkyl-; suffix -ane; example: Butane
  • Ether: Prefix alkoxy-; suffix -ane; example: Methoxy methane
  • Alkyl Halide: Prefix halo- (fluoro-, chloro-, bromo-, iodo-); suffix -ane; example: Bromomethane
  • Nitro: Prefix nitro-; suffix -ane; example: Nitromethane