CHM 102: Alcohols, Ethers, Amines, and Carbonyl Compounds

Introductory Organic Chemistry II: Alcohols, Ethers, Amines, and Carbonyl Compounds

This course material is presented by Dr. Azeez L. A., a Professor of Analytical, Environmental, and Nano Chemistry (CHM 102).

Alcohols: Definition and General Structure

Alcohols are organic compounds characterized by the presence of one or more hydroxyl groups ($-OH$) attached to a saturated carbon atom.

Classification of Alcohols

Alcohols are classified based on the nature of the hydrocarbon skeleton and the environment of the hydroxyl group.

Based on the Hydrocarbon Skeleton

1. Aliphatic Alcohols: These follow the general formula $C_nH_{2n+1}OH$, provided there are no rings in the structure. In these molecules, the $-OH$ group replaces a hydrogen atom in a basic hydrocarbon skeleton.

2. Aromatic Alcohols (Phenols): In these compounds, the $-OH$ group is attached directly to an aromatic ring (benzene ring).

3. Side-chain Aromatic Alcohols: If a hydroxyl group is attached to a side chain of an aromatic ring (rather than the ring itself), it behaves as a typical aliphatic alcohol (e.g., benzyl alcohol).

Based on the Environment of the Hydroxyl Group

The chemical behavior of alcohols, such as their susceptibility to oxidation, depends heavily on their structural type:

• Primary ($1^\circ$) Alcohols: The carbon atom bonded to the $-OH$ group is attached to only one other carbon atom.     * Examples:         * Ethanol: $H_3C - CH_2 - OH$         * Propan-1-ol: $CH_3 - CH_2 - CH_2 - OH$         * 2-methylpropan-1-ol

• Secondary ($2^\circ$) Alcohols: The carbon atom bonded to the $-OH$ group is attached to two other carbon atoms.     * Examples:         * Propan-2-ol: $CH_3 - CH(OH) - CH_3$         * Butan-2-ol: $CH_3 - CH(OH) - CH_2 - CH_3$         * 3,3-dimethylcyclohexan-1-ol

• Tertiary ($3^\circ$) Alcohols: The carbon atom bonded to the $-OH$ group is attached to three other carbon atoms.

Based on the Number of Hydroxyl Groups

Alcohols are categorized by the quantity of $-OH$ groups within the molecule:

• Monohydric Alcohols: Contain one $-OH$ group.

• Dihydric Alcohols: Contain two $-OH$ groups (e.g., Propan-1,3-diol).

• Trihydric Alcohols: Contain three $-OH$ groups (e.g., Propan-1,2,3-triol).

• Polyhydric Alcohols: Contain four or more $-OH$ groups (e.g., Hexan-1,2,3,4,5,6-hexaol).

Nomenclature of Alcohols

IUPAC Rules

1. Identify the longest carbon chain that contains the carbon atom bearing the $-OH$ group.

2. Drop the suffix -e from the parent alkane name and add the suffix -ol.

3. Number the carbon chain starting from the end closest to the $-OH$ group.

4. Identify, number, and name all substituents attached to the chain.

Additional Nomenclature Examples

• Benzyl alcohol: An aromatic ring with a $-CH_2OH$ side chain.

• Prop-2-en-1-ol: An unsaturated alcohol containing a double bond.

• Pent-1,3-diene-3-ol: A dienol.

• Hex-3-yn-2,5-diol: An alkyne-diol.

Common Names

Alcohols can be named as alkyl alcohols (e.g., isobutyl alcohol, sec-butyl alcohol). This system is generally useful only for small alkyl groups.

Diols and Glycols

• Diols: Require two numbers to locate the two $-OH$ groups. The suffix -diol is added to the full alkane name (e.g., hexan-1,6-diol).

• Vicinal Diols (Glycols): 1,2-diols where hydroxyl groups are on adjacent carbons. Their common names often derive from the alkene from which they were produced:     * 1,2-ethanediol is known as ethylene glycol.     * 1,2-propanediol is known as propylene glycol.

• Geminal Diols: Alcohols where two hydroxyl groups are attached to the same carbon atom (noted as 'germinal' in the source).

Isomerism in Alcohols

1. Positional Isomerism: Molecules with the same molecular formula but different positions of the $-OH$ group (e.g., pentan-2-ol and pentan-3-ol).

2. Functional Group Isomerism: Alcohols are functional group isomers of ethers. For example, pentan-2-ol (an alcohol) and ethylpropylether (an ether) share the same molecular formula.

Ethers

Ethers are a class of compounds containing an oxygen atom linked by single bonds to two alkyl or aryl groups ($R - O - R'$).

Nomenclature

• IUPAC: Named as alkoxyalkanes (e.g., 1-methoxypropane, 1-methoxyethane).

• Common Name: Named as alkyl alkyl ethers (e.g., methylpropyl ether, ethyl methyl ether).

Metamerism

Ethers exhibit metamerism, where the distribution of carbon atoms on either side of the functional group differs (e.g., diethyl ether vs. methyl propyl ether).

Amines

Amines are functional groups featuring a nitrogen atom with a lone pair. They are structurally related to ammonia ($NH_3$), where one or more hydrogen atoms are replaced by organic groups.

Nomenclature of Amines

• Primary ($1^\circ$) Amines: In IUPAC nomenclature, the suffix -e of the parent alkane is replaced with -amine.

• Secondary ($2^\circ$) and Tertiary ($3^\circ$) Amines: In common nomenclature, organic groups attached to the nitrogen are named separately in front of the word "amine."

Aryl Amines

Aryl amines feature the nitrogen group attached to an aromatic ring:

• Aniline (Phenylamine): Base aromatic amine ($C_6H_5NH_2$).

• N-methylaniline (N-methylphenylamine): Secondary aromatic amine.

• Benzylamine: Nitrogen attached to a benzyl group ($C_6H_5CH_2NH_2$).

• p-toluidine (p-methylaniline): Aniline with a methyl group at the para position.

Carbonyl Compounds: Aldehydes and Ketones

Carbonyl compounds contain the $C=O$ functional group. This group includes aldehydes and ketones, which are functional group isomers of one another.

Double Bond Equivalence (DBE): The formula is provided as: $DBE = (- 2) + 1$

Aldehydes ($RCHO$)

In aldehydes, the carbonyl group is at the end of the carbon chain.

• Methanal: $H - CHO$

• Ethanal: $CH_3 - CHO$

• Propanal: $CH_3 - CH_2 - CHO$

• Prop-2-enal: Unsaturated aldehyde.

• But-2-enal: Unsaturated aldehyde.

• Prop-2-ynal: Aldehyde with a triple bond.

• But-2-ynal: Aldehyde with a triple bond.

• Benzaldehyde: Aromatic aldehyde.

Ketones ($RCOR'$)

In ketones, the carbonyl group is located between two carbon atoms.

• Propan-2-one (Propanone/Acetone): $CH_3 - CO - CH_3$

• Butan-2-one (Butanone): $CH_3 - CO - CH_2 - CH_3$

• Pentan-3-one (Diethyl ketone): $CH_3 - CH_2 - CO - CH_2 - CH_3$

• But-3-en-2-one: Unsaturated ketone.

• Hex-4-yn-3-one: Ketone with a triple bond.

• Benzophenone: Diaryl ketone.

• Acetophenone: Methyl phenyl ketone.

Amides

Amides are derivatives of carboxylic acids where the hydroxyl group is replaced by a nitrogen group.

Nomenclature of Amides

• Primary Amides: Named by dropping the -oic acid or -ic acid suffix from the parent acid and adding -amide. The carbonyl carbon is always designated as position #1.

• Secondary Amides: Named by using an upper-case N to indicate that an alkyl group is attached to the nitrogen atom; these alkyl groups are treated as substituents.

• Tertiary Amides: Named similarly to secondary amides, but using two N designations (e.g., N,N-).

Examples of Amides

• N-methyl-N-phenylethanamide: A tertiary amide with a methyl and a phenyl group on the nitrogen.

• N,N-dimethylethanamide: A tertiary amide with two methyl groups on the nitrogen.