Functional Groups, Hydrocarbons & Alkane Nomenclature – Comprehensive Study Notes

Functional Groups – General Principles

Definition: A functional group is a specific grouping of atoms within a molecule that exhibits a characteristic pattern of chemical reactivity.
- Governs the chemistry of every organic compound, independent of molecular size or complexity.
- Compounds are categorized into families according to the functional groups present; identical groups behave similarly in every molecule.

C–C Multiple-Bond Functional Groups

Alkene
- Structural feature: $C=C$ (double bond)
- Name ending: -ene
- Example: $\text{H}2C=CH2$ , ethene.
Alkyne
- Structural feature: $C\equiv C$ (triple bond)
- Name ending: -yne
- Example: $HC\equiv CH$ , ethyne.
Arene (aromatic ring)
- No special suffix; core structure is a benzene ring.
- Example: benzene itself.

Carbon Singly Bonded to an Electronegative Atom

Halide (R–X; X = F, Cl, Br, I)
- No suffix in substitutive nomenclature (named as fluoro-, chloro-, etc.)
- Example: $\text{CH}_3Cl$ , chloromethane.
Alcohol (R–OH)
- Suffix: -ol
- Example: $\text{CH}_3OH$ , methanol.
Ether (R–O–R')
- Suffix (common): ether; IUPAC: alkoxy-alkane.
- Example: $\text{CH}3OCH3$ , dimethyl ether.
Phosphate Species
- Monophosphate: $\text{R–OPO}_3^{2-}$ , e.g., methyl phosphate.
- Diphosphate: $\text{R–OP}2\text{O}6^{3-}$ , e.g., methyl diphosphate.
Amine (R–NH2, R2NH, R_3N) – suffix -amine; example: methylamine.
Imine (Schiff base, R_2C=N–R'); example: acetone imine.
Nitrile (R–C≡N) – suffix -nitrile; example: ethanenitrile.
Thiol (R–SH) – suffix -thiol; example: methanethiol.
Sulfide (R–S–R'), Disulfide (R–S–S–R'), Sulfoxide (R–S(=O)–R') with corresponding names sulfide, disulfide, sulfoxide; examples: dimethyl sulfide, dimethyl disulfide, dimethyl sulfoxide.

Carbonyl-Containing Functional Groups (C=O)

Aldehyde (R–CHO)
- Suffix: -al
- Example: $\text{CH}_3CHO$ , ethanal.
Ketone (R–CO–R')
- Suffix: -one
- Example: $\text{CH}3COCH3$ , propanone (acetone).
Carboxylic Acid (R–COOH)
- Suffix: -oic acid
- Example: $\text{CH}_3COOH$ , ethanoic acid.
Ester (R–COOR')
- Suffix: -oate
- Example: $\text{CH}3COOCH3$ , methyl ethanoate.
Thioester (R–COSR') – suffix -thioate; example: methyl ethanethioate.
Amide (R–CONH_2) – suffix -amide; example: ethanamide.
Acid Chloride (R–COCl) – suffix -oyl chloride; example: ethanoyl chloride.

Master Table – Representative Functional Groups & Chapters (selected)

Alkyl halide (R–X) – Ch. 7
Alcohol (R–OH) – Ch. 9
Ether (R–O–R) – Ch. 13
Thiol (R–SH) & Sulfide (R–S–R) – Ch. 13
Alkene, Alkyne – Ch. 7–8
Aromatic compounds – Ch. 10
Carbonyl derivatives (ketone, aldehyde, carboxylic acid, acyl halide, anhydride, ester, amide) – Ch. 19–20
Amine – Ch. 22

Hydrocarbons – Classification

Comprised solely of C and H.
Saturated hydrocarbons
- Only single bonds; achieve the maximum number of H atoms.
- Example family: alkanes.
Unsaturated hydrocarbons
- Contain multiple bonds (alkenes, alkynes, arenes).
- Possess fewer than the maximal H; can add $H_2$ under suitable conditions.

Alkanes – Fundamentals

Simplest hydrocarbon family; all C–C bonds are sigma bonds formed by sp³–sp³ overlap.
General formula: $CnH{2n+2}$ .
Also called aliphatic (from Greek "aleiphas" = fat).

Natural Sources

Fossil fuels account for most native alkanes.
- Natural gas (C₁–C₄): methane, ethane, propane, butane (LPG).
- Petroleum separated by fractional distillation:
- C₅–C₁₁: straight-run gasoline (bp $30–200\,^\circ\text{C}$ ).
- C₁₁–C₁₄: kerosene.
- C₁₄–C₂₅: gas oil.
- Heavier residue ➜ lubricating oils, waxes, asphalt, petroleum jelly.

Straight vs. Branched Examples

Straight-chain: methane (CH₄), ethane, propane, butane, pentane.
Branched: isobutane (2-methylpropane), 2-methylbutane, 2,2-dimethylpropane.

Isomerism

Isomers share a molecular formula but differ in structure.
Constitutional (structural) isomers subdivide into:
1. Skeletal – different C skeletons.
2. Functional – different functional groups.
3. Positional – same group, different location.
Exercise example: $C2H7N$ has two isomers: C–C–N and C–N–C connectivities.

Alkane Nomenclature – Common Names

Base names indicate chain length (meth-, eth-, prop-, etc.) plus suffix -ane.
Prefixes that modify:
- n-: straight chain (e.g., n-butane).
- iso-: methyl branch at the penultimate carbon (e.g., isobutane).
- neo-: two methyl branches on the penultimate carbon (e.g., neopentane).

IUPAC Nomenclature Rules for Alkanes (Substitutive System)

Choose Parent Chain
- Longest continuous carbon chain; must include double/triple bond if present.
- If equal length possibilities, select the one with more branch points.
Number the Chain
- Start from the end nearer the first substituent.
- If equidistant, start at the end nearer the second point of difference.
Identify & Number Substituents
- Assign each substituent a locant (number).
- Same carbon with two groups: repeat number.
Assemble the Name
- Write as one word, numbers separated by commas, numbers–letters by hyphens.
- Alphabetize different substituents.
- Use multiplicative prefixes (di-, tri-, tetra-) for identical groups; these prefixes are NOT considered in alphabetization.

Worked Examples

3-ethyl-2-methylhexane.
3-ethyl-4,7-dimethylnonane.
Exercise outcome: CH₃CH₂CH(CH₃)CH₂CH₂CH(CH₃)₂ ➜ 4-ethyl-3-methyloctane.
Structural drawing from name: 3-isopropyl-2-methylhexane.

Alkyl Groups

Formed by removing one H from an alkane; suffix -yl.
Straight-chain groups: methyl (Me), ethyl (Et), propyl (Pr), butyl (Bu), pentyl (amyl), etc.
Branched alkyl groups carry historical names (isopropyl, sec-butyl, tert-butyl, neopentyl).
Degree of substitution
- Primary (1°): carbon attached to one other carbon.
- Secondary (2°), Tertiary (3°), Quaternary (4°) likewise.
- Hydrogen atoms are classified similarly (primary, secondary, tertiary).

Complex Substituents

When a substituent itself is branched, number it from the point of attachment to the main chain.
Parentheses enclose the full substituent name; alphabetize by the first letter (numerical prefixes ARE alphabetized for complex substituents but NOT for simple multiplicative prefixes).
Examples:
- 4-(1-methylethyl)heptane = 4-isopropylheptane.
- 4-(1,1-dimethylethyl)octane = 4-tert-butyloctane.

Physical & Chemical Properties of Alkanes

Low chemical reactivity ➜ nickname paraffins (Latin parum affinis = little affinity).
Form a homologous series; successive members differ by $\text{–CH}_2$ units.
Melting & Boiling Points
- Increase with molecular weight.
- Greater branching lowers b.p. (reduced surface area → weaker London forces).
Density
- Least dense class of organic compounds; < 1.00\,\text{g·mL}^{-1} (float on water).
Solubility
- Insoluble in water; soluble in non-polar solvents ("like dissolves like").
Combustion
- Reaction with $O2$ to produce $CO2$ , $H_2O$ , and heat; basis for fuel use.
Halogenation (e.g., chlorination)
- Requires UV light $h\nu$ ; sequential substitution yields $\text{CH}3Cl \rightarrow \text{CH}2Cl2 \rightarrow \text{CHCl}3 \rightarrow \text{CCl}_4$ .

Pheromones – Hydrocarbons in Chemical Communication

Many insects (and some vertebrates) employ pheromones for aggregation, warning, or mating.
Examples:
- Cockroach aggregation pheromone: undecane.
- Female tiger moth sex attractant: 2-methylheptadecane.
- Housefly sex attractant (muscalure): cis-9-tricosene (23-carbon alkene; C=C between C9–C10).
Human relevance: menstrual synchrony, olfactory response to musks (androsterone, civetone, pentalide, etc.).
Synthetic pheromones used as environmentally friendly pest-control agents.

Haloalkanes (Alkyl Halides)

IUPAC treats halogens as substituents: fluoro-, chloro-, bromo-, iodo-.
Naming protocol mirrors alkane rules:
1. Choose longest chain (must include multiple bond if present).
2. Number to give first substituent (halo or alkyl) the lowest possible locant.
3. If different halogens occur, list them alphabetically with locants (e.g., 2-bromo-1-chloro-3-methylbutane).

Alcohols

Functional group: hydroxyl, $\text{–OH}$ ; suffix -ol (e.g., ethanol).
Chain numbering always begins at the carbon bearing the OH.
Steps for naming:
1. Select longest chain containing OH.
2. Number to give the OH the lowest locant.
3. Assemble name with locant for OH and substituents (if any).
Examples:
- 1-propanol.
- 2-butanol.
- 4-methylpentan-1-ol (preferred over 2-methyl-5-pentanol).
- 3-chloropropan-1-ol.
- 4,4-dimethylpentan-2-ol.
Common/functional class names accepted by IUPAC for small alcohols: propyl alcohol, sec-butyl alcohol, tert-butyl alcohol, etc.
Glycols (Diols): two OH groups; named as diols.
- Ethane-1,2-diol (ethylene glycol).
- Propane-1,2-diol (propylene glycol).
- Propane-1,3-diol (trimethylene glycol).

Summary of Key Numerical / Formulaic Data

Alkane general formula: $CnH{2n+2}$ .
Boiling-point trend: $\text{b.p.} \uparrow$ with $M_w$ ; branching $\downarrow \text{b.p.}$ .
Halogenation of methane (overall): $\text{CH}4 + 4\,\text{Cl}2 \xrightarrow{h\nu} \text{CCl}_4 + 4\,\text{HCl}$ (stepwise substitution).

Ethical & Practical Implications

Use of synthetic pheromones offers targeted pest control, reducing reliance on broad-spectrum insecticides.
Hydrocarbon fuels form the backbone of current energy infrastructure but are associated with environmental impact; understanding structure–property relationships (volatility, combustion) informs cleaner utilization.
Functional-group reactivity underpins drug design, material science, and biochemical processes; mastery of nomenclature ensures clear communication across scientific disciplines.

Functional Groups – General Principles

A functional group is a specific atomic grouping within a molecule that determines its chemical reactivity and categorizes organic compounds. Compounds with identical functional groups behave similarly.

Major Functional Group Types

C–C Multiple-Bond Functional Groups: Include Alkenes ( $C=C$ , -ene suffix), Alkynes ( $C ext{\equiv}C$ , -yne suffix), and Arenes (aromatic rings, e.g., benzene).
Carbon Singly Bonded to an Electronegative Atom: Examples include Halides (R–X; X = F, Cl, Br, I), Alcohols (R–OH, -ol suffix), Ethers (R–O–R'), Phosphate Species, Amines (R–N, -amine suffix), Imines ( $C=N-$ ), Nitriles (R–C $\equiv$ N, -nitrile suffix), and Thiols (R–SH, -thiol suffix).
Carbonyl-Containing Functional Groups (C=O): Include Aldehydes (R–CHO, -al suffix), Ketones (R–CO–R', -one suffix), Carboxylic Acids (R–COOH, -oic acid suffix), Esters (R–COOR', -oate suffix), Thioesters (R–COSR'), Amides (R–CONH $_2$ ), and Acid Chlorides (R–COCl).

Hydrocarbons

Comprised solely of C and H.
Saturated hydrocarbons: Contain only single bonds (e.g., alkanes); general formula $CnH{2n+2}$ .
Unsaturated hydrocarbons: Contain multiple bonds (alkenes, alkynes, arenes); have fewer H atoms and can add $H_2$ .
Natural sources include fossil fuels (natural gas, petroleum).

Alkane Characteristics & Nomenclature

Alkanes: Simplest hydrocarbon family, all C–C bonds are sigma bonds, low chemical reactivity (paraffins).
Isomerism: Isomers share molecular formula but differ in structure.
- Constitutional (structural) isomers: Differ in carbon skeleton (skeletal), functional groups (functional), or group location (positional).
Nomenclature:
- Common Names: Use prefixes like n- (straight), iso- (methyl branch at penultimate carbon), neo- (two methyl branches at penultimate carbon).
- IUPAC Rules:
  1. Choose longest continuous carbon chain (including multiple bonds if present).
  2. Number the chain from the end nearer the first substituent.
  3. Identify and number substituents (locants).
  4. Assemble name: one word, numbers by commas, numbers-letters by hyphens, alphabetize different substituents (multiplicative prefixes di-, tri- not considered in alphabetization for simple groups).
Alkyl Groups: Formed by removing one H from an alkane; suffix -yl. Can be primary (1°), secondary (2°), tertiary (3°), or quaternary (4°) based on carbon substitution. Complex substituents are enclosed in parentheses and alphabetized by their first letter.

Physical & Chemical Properties of Alkanes

Melting & Boiling Points: Increase with molecular weight, but greater branching lowers boiling point.
Density: Less dense than water (< 1.00\,\text{g·mL}^{-1}).
Solubility: Insoluble in water, soluble in non-polar solvents.
Reactions: Undergo combustion with $O_2$ to produce $CO_2$ , $H_2O$ , and heat. Also undergo halogenation (e.g., with $Cl_2$ under UV light) leading to sequential substitution.

Haloalkanes & Alcohols

Haloalkanes (Alkyl Halides): Halogens are treated as substituents (fluoro-, chloro-, bromo-, iodo-); named using alkane rules, prioritizing lowest locant for first substituent.
Alcohols: Contain a hydroxyl group (–OH); suffix -ol. Chain numbering starts at the carbon bearing the OH. Glycols are diols (two OH groups).

Applications & Implications

Hydrocarbons are fundamental to energy (fossil fuels). Functional group reactivity is crucial for drug design and materials science.
Pheromones (often hydrocarbons) are used by insects for communication and are synthesized for environmentally friendly pest control.