Chapter 3: Functional Groups - Structure and Nomenclature (Part 1: Non carbonyl functional groups)

Alkyl Halides, Vinyl Halides, and Aryl Halides

  • Alkyl halide: a halogen atom attached to a sp3-hybridized carbon of an alkyl group.

  • Vinyl halide: a halogen bonded to a sp2-hybridized carbon of an alkene.

  • Aryl halide: a halogen bonded to a sp2-hybridized carbon in an aromatic ring.

Examples of Halides

  • Alkyl halides:

    • CHCl3 (chloroform)

    • CHClF2 (Freon-22R) [1,1,1-trichloroethane is C–Cl3 on ethane; Freon-22 is CHClF2]

    • CH3–CCl3 (1,1,1-trichloroethane) – refrigerant

    • haloethane (general term for halogenated ethanes)

    • noninflammable anesthetic (general halide anesthetic)

  • Vinyl halides:

    • CH2=CHCl (vinyl chloride; monomer for poly(vinyl chloride))

    • CF2=CF2 (tetrafluoroethylene; monomer for Teflon R)

  • Aryl halides:

    • para-dichlorobenzene (mothballs)

Nomenclature of Alkyl Halides

  • Examples:

    • fluoroethane → fluoroeethane (ethyl fluoride)

    • 1-chlorobutane → n-butyl chloride

    • iodocyclohexane → cyclohexyl iodide

    • trans-1-chloro-3-methylcyclopentane

    • 3-(iodomethyl)pentane

    • 4-(2-fluoroethyl)heptane

  • Common naming vs IUPAC: halogen position and identity determine the name; prefixes such as di-, tri- used when multiple halogens appear.

Classification of Alkyl Halides

  • General formula: CH3–X (methyl halides) or R–X

  • Primary (1°) halide: halogen attached to a primary carbon (R–CH2–X)

  • Secondary (2°) halide: halogen attached to a secondary carbon (R2–CH–X)

  • Tertiary (3°) halide: halogen attached to a tertiary carbon (R3C–X)

  • Others:

    • geminal dihalide: two halogens on the same carbon (e.g., R–CX2)

    • vicinal dihalide: halogens on adjacent carbons (R–CHX–CHX'–R')

Alcohols and Phenols

  • Alcohols: organic compounds containing hydroxyl (-OH) groups; highly useful in nature, industry, and households.

Structure of Water and Methanol

  • Oxygen is sp3 hybridized and tetrahedral.

  • Bond angles:

    • 9 O02H angle in water: \,\angle H-O-H = 104.5^{\circ}

    • C-O-H angle in methanol: \angle C-O-H = 108.9^{\circ}

  • Carbinol carbon: the carbon atom bonded to the hydroxyl group.

Classification of Alcohols

  • Primary (1°): the carbon bearing the —OH is bonded to one other carbon.

  • Secondary (2°): the carbon bearing the —OH is bonded to two other carbons.

  • Tertiary (3°): the carbon bearing the —OH is bonded to three other carbons.

  • Aromatic (phenols): the —OH is bonded to a benzene ring.

Examples of Classifications

  • Primary alcohol: CH3–CH2–OH (ethanol) or similar structures

  • Secondary alcohol: CH3–CH(OH)–CH2CH3 (butan-2-ol)

  • Tertiary alcohol: (CH3)3C–OH (2-methylpropan-2-ol, tert-butanol)

  • Phenols: phenol, methylphenols, etc.

IUPAC Nomenclature for Alcohols

  • Steps:

    • Find the longest carbon chain containing the carbon bearing the —OH.

    • Drop the -e from the alkane name; add -ol.

    • Number the chain to give the —OH group the lowest possible number.

    • List substituents with their numbers in alphabetical order.

Examples of Nomenclature

  • Primary alcohols:

    • CH3CH2OH → ethanol

    • CH3CH2–CH2OH → 1-propanol (propan-1-ol)

    • C6H5CH2OH (benzyl alcohol) → benzyl alcohol

    • 2-methylpropane-1-ol → 2-methylpropan-1-ol

  • Secondary alcohols:

    • butan-2-ol (CH3–CH(OH)–CH2–CH3)

    • cyclohexanol

    • cholesterol (polyfunctional example)

  • Tertiary alcohols:

    • 2-methylpropane-2-ol → 2-methylpropan-2-ol

    • triphenylmethanol

    • 1-methylcyclopentanol

Alkenols (Enols)

  • The hydroxyl group takes precedence; assign the carbon with the —OH the lowest number.

  • End the name with -ol, but indicate the double bond by using the ending -ene before -ol.

  • Example: CH2=CH–CH2–CH–OH → pent-4-ene-2-ol (old: 4-penten-2-ol)

Hydrogen Bonding in Alcohols

  • OH group enables hydrogen bonding between molecules, affecting boiling points, melting points, and solubility.

  • Example trends (bp in °C) and solubility:

    • Methanol: bp 65; completely soluble in water

    • Ethanol: bp 78.5; completely soluble in water

    • Propanol: bp 97; completely soluble in water

    • Butanol: bp 117.7; solubility 7.9 g/100 g H2O

    • Pentanol: bp 137.9; solubility 2.7 g/100 g H2O

    • Hexanol: bp 155.8; solubility 0.59 g/100 g H2O

Acidity of Alcohols and Phenols

  • Alcohols are weak acids (similar to water).

  • Phenols are more acidic because the conjugate base (phenoxide) is resonance-stabilized.

  • Approximate pKa: pK_a \approx 16-18 for typical alcohols/phenols.

Naming Priority

  • Priority of functional groups in naming organic compounds (highest to lowest):

    1. acids (highest) 2. esters 3. aldehydes 4. ketones 5. alcohols 6. amines 7. alkenes, alkynes 8. alkanes 9. ethers 10. halides (lowest)

Hydroxy Substituent

  • If —OH is part of a higher-priority class, it is named as a hydroxy substituent.

  • Example: 4-hydroxybutanoic acid (gamma-hydroxybutyric acid, GHB)

    • Structure: HO–CH2–CH2–CH2–COOH with OH on C4

Common Names for Alcohols

  • Alcohols can be named as alkyl alcohols (useful for small alkyl groups):

    • CH3–CH(OH)–CH3 → isobutyl alcohol (common), IUPAC: 2-methylpropan-1-ol

    • CH3–CH2–CH(OH)–CH3 → sec-butyl alcohol, IUPAC: butan-2-ol

Glycols

  • 1,2-Diols (vicinal diols) are called glycols.

  • Common names often reflect the derived alkene: ethane-1,2-diol (ethylene glycol); propane-1,2-diol (propylene glycol)

Phenol Nomenclature

  • The —OH group is assumed to be on carbon 1 of the ring.

  • For disubstituted phenols, use ortho- (1,2-), meta- (1,3-), para- (1,4-).

  • Methyl phenols are cresols (e.g., m-, o-, p-cresol).

Ethers

  • Ethers have the functional group R1–O–R2, where R1 and R2 are carbon groups (sp3 or sp2); can be same or different.

  • Symmetrical ethers: R1 = R2 (e.g., diethyl ether, IUPAC: ethoxyethane).

  • Unsymmetrical ethers: R1 ≠ R2 (e.g., benzyl ethyl ether, IUPAC: ethoxymethylbenzene).

Examples of Ethers

  • Diethyl ether: CH3CH2–O–CH2CH3 (symmetrical)

  • Methyl phenyl ether: CH3–O–Ph (unsymmetrical)

  • Tetrahydrofuran (THF): a cyclic ether (ephemeral example of a symmetrical cyclic ether)

Common Names of Ethers

  • Name the two alkyl groups attached to oxygen and add the word ether.

  • Alphabetical order of the alkyl groups.

  • Examples:

    • CH3CH2–O–CH2CH3 → diethyl ether or ethyl ether

    • tert-butyl methyl ether → methyl tert-butyl ether (MtBE)

IUPAC Names: Alkoxy Alkane

  • The more complex alkyl group becomes the parent alkane; the smaller group becomes an alkoxy substituent.

  • Examples:

    • CH3–O–C(CH3)3 → 2-Methoxy-2-methylpropane

    • CH3–O–cyclohexane → methoxycyclohexane

Naming ethers: Common vs IUPAC

  • Common naming steps:
    1) Name the substituents attached to oxygen.
    2) Put substituent names in alphabetical order.
    3) Add ether at the end.

  • IUPAC naming steps:
    1) Identify the more complex R group as the parent (mother chain).
    2) The simpler R group becomes the alkoxy substituent.
    3) Combine to form the name.

  • Examples:

    • Substituents: methyl and tert-butyl → tert-butyl methyl ether (common); IUPAC: methoxy-2-methylpropane (if parent is 2-methylpropane)

Epoxides

  • Epoxides (oxiranes) are three-membered cyclic ethers (two carbons + one oxygen).

  • They have significant ring strain and are highly reactive.

  • Nomenclature overview:

    • Nomenclature as starting alkene plus oxide (epoxide as substituent: epoxy- group)

    • Classic names: add oxide to the end after naming as if an alkene

  • Ring strain and reactivity make epoxides useful in organic synthesis.

Epoxides (continued): Notable examples

  • Disparlure (Gypsy moth pheromone) contains an epoxide motif

  • Various bioactive epoxides and inhibitors exist (illustrative examples shown in slides)

Nomenclature: IUPAC vs Classic for Epoxides

  • IUPAC approach when epoxide is the parent:

    • Number the chain with the oxygen as atom 1 (oxirane as core) → oxirane naming.

    • If named as substituent, use the term epoxy as the substituent on the parent chain.

  • Examples (schematics):

    • If an epoxide is on a longer chain, name substituents and indicate the epoxy group accordingly with stereochemistry if needed.

Epoxides: Exercise

  • Exercise: Give the names of epoxides below as substituents or as parent epoxides depending on the naming approach.

Amines

  • Biologically Active Amines:

    • Alkaloids are an important group of biologically active amines (often plants-derived); many drugs of addiction are alkaloids.

    • Examples of biologically relevant amines shown include neurotransmitters and related molecules:

    • Dopamine (a neurotransmitter)

    • Epinephrine (adrenal hormone)

    • Serotonin (a neurotransmitter)

    • Histamine (dilates blood vessels)

    • Piperazine, etc.

  • Common biologically active amines include those involved in signaling and metabolism.

Classes of Amines

  • Primary (1°) amines: one alkyl group bonded to nitrogen (RNH2).

  • Secondary (2°) amines: two alkyl groups bonded to nitrogen (R2NH).

  • Tertiary (3°) amines: three alkyl groups bonded to nitrogen (R3N).

  • Quaternary (4°) ammonium salts: four alkyl groups bonded to nitrogen with a positive charge (R4N+).

Classification of Amines (Illustrative Examples)

  • Primary: CH3–CH2–NH2 (ethylamine)

  • Secondary: N-ethylaniline (aniline with an ethyl substituent on N)

  • Tertiary: N,N-diethylaniline

  • Quaternary: quinuclidine (a tertiary amine in a cyclic structure that can bear a positive charge in salts)

Common Names of Amines

  • Common names are formed from the names of the alkyl groups attached to the nitrogen, followed by the suffix -amine.

    • Examples: methylamine, dimethylamine, diethylamine, etc.

Amine as Substituent

  • When a molecule contains a higher-priority functional group, the amine is named as a substituent (e.g., amino- groups).

IUPAC Names for Amines

  • Based on the longest carbon chain containing the amine functionality; the -e of the parent alkane is replaced with -amine.

  • Examples (old vs new IUPAC naming):

    • CH3CH2CHCH3 with an NH2 group → 2-butanamine (IUPAC: butan-2-amine)

    • CH3CHCH2CH2NHCH3 → N-methylbutan-2-amine (new IUPAC)

    • CH3CH2CHCH3 with N substituents → 3-methyl-1-butanamine, N-methyl-2-butanamine, etc.

    • A complex example: N,N-tetramethylhexan-3-amine (new IUPAC) and the corresponding older forms such as 2,4,N,N-tetramethyl-hexan-3-amine.