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

Introduction to Alcohols

Definition: Alcohol is a term applied to all organic compounds whose molecules contain hydroxyl groups ( $-OH$ ) attached to a saturated carbon atom.
General Formula: For aliphatic alcohols without rings, the general molecular formula is $C_nH_{2n+1}OH$ .
Structural Basis: In these compounds, the hydroxyl group ( $-OH$ ) replaces a hydrogen atom ( $H$ ) in a basic hydrocarbon skeleton.

Classification of Alcohols

Alcohols are categorized into different classes based on the nature of the carbon skeleton and the position/environment of the hydroxyl group.

Aliphatic Alcohols: - Characterized by the formula $C_nH_{2n+1}OH$ . - Require the absence of rings for this specific formula to hold true.
Aromatic Alcohols (Phenols): - In phenols, the hydroxyl group ( $-OH$ ) is attached directly to the aromatic ring. - Example: Phenol is the simplest aromatic alcohol where the $-OH$ is on a benzene ring.
Side-Chain Aromatic Alcohols: - If an $-OH$ group is on a side chain of a ring (not directly on the aromatic ring itself), it behaves as a typical aliphatic alcohol.
Significance of Classification: - Structural differences and the environment of the $-OH$ group determine chemical behavior. - Oxidation reactions, for example, are highly dependent on the structural type (primary, secondary, or tertiary).

Types of Alcohols Based on Hydroxyl Group Count

Alcohols can be classified according to the number of hydroxyl groups present in a single molecule:

Monohydric Alcohols: Contain one $-OH$ group.
Dihydric Alcohols: Contain two $-OH$ groups (e.g., diols).
Trihydric Alcohols: Contain three $-OH$ groups (e.g., triols).
Polyhydric Alcohols: Alcohols containing four or more hydroxyl groups.

Detailed Classification of Monohydric Alcohols

Monohydric alcohols are further subdivided based on the number of carbon atoms attached to the carbon holding the hydroxyl group:

Primary Alcohols ( $1^{\circ}$ ): The carbon bearing the $-OH$ group is bonded to only one other carbon atom. - Ethanol: $H_3C-CH_2-OH$ - Propan-1-ol: $H_3C-CH_2-CH_2-OH$ - 2-methylpropan-1-ol
Secondary Alcohols ( $2^{\circ}$ ): The carbon bearing the $-OH$ group is bonded to two other carbon atoms. - Propan-2-ol: $H_3C-CH(OH)-CH_3$ - Butan-2-ol: $CH_3-CH_2-CH(OH)-CH_3$ - 3,3-dimethylcyclohexan-1-ol
Tertiary Alcohols ( $3^{\circ}$ ): The carbon bearing the $-OH$ group is bonded to three other carbon atoms.
Aromatic (Phenol): Specifically defines structures where the $-OH$ is bonded directly to a benzene ring.

Examples of Multi-hydric Alcohols

Propan-1,3-diol: A dihydric alcohol with $-OH$ groups on the first and third carbons.
Propan-1,2,3-triol: Known commonly as glycerol, a trihydric alcohol.
Hexan-1,2,3,4,5,6-hexaol: A polyhydric alcohol (specifically a hexol).

Nomenclature of Alcohols

IUPAC Rules

Select the longest carbon chain containing the carbon with the $-OH$ group.
Drop the final "-e" from the alkane name and replace it with the suffix "-ol."
Number the carbon chain starting from the end closest to the $-OH$ group.
Locate, number, and name all substituents present on the parent chain.

Common Names

Alcohols can be named as "alkyl alcohol."
This method is typically useful only for small alkyl groups.
Examples: Isobutyl alcohol and sec-butyl alcohol.

Specific Classifications for Diols

Vicinal Diols: Two $-OH$ groups located on adjacent carbon atoms. These are also known as Glycols. - 1,2-ethanediol is commonly called ethylene glycol. - 1,2-propanediol is commonly called propylene glycol.
Germinal Diols: Two $-OH$ groups located on the same carbon atom.
Numbering: Two numbers are always required to locate the specific positions of the two $-OH$ groups (e.g., 1,6-hexanediol or hexan-1,6-diol).

Additional IUPAC Examples

Benzyl alcohol: An aromatic alcohol where the $-OH$ is on a methylene group attached to a benzene ring.
Prop-2-en-1-ol: Contains a double bond and a hydroxyl group.
Pent-1,3-diene-3-ol: A dienol structure.
Hex-3-yn-2,5-diol: A diol containing a triple bond.

Isomerism in Alcohols

Positional Isomerism: Arises when the $-OH$ group is located at different positions on the same carbon skeleton. - Example: Pentan-2-ol and Pentan-3-ol.
Functional Group Isomerism: Alcohols are functional group isomers of ethers. - Example: Pentan-2-ol ( $C_5H_{12}O$ ) and ethylpropylether ( $C_5H_{12}O$ ).

Ethers

Definition: Ethers are a class of organic compounds containing an oxygen atom linked to two alkyl groups by single bonds.
General Formula: $R-O-R'$
Metamerism: Ethers exhibit metamerism, where different alkyl groups are attached to the same functional group. - Example: Diethyl ether and methyl propyl ether.

Nomenclature of Ethers

IUPAC systematic name: Names them as alkoxyalkanes. - 1-methoxypropane ( $H_3C-O-CH_2CH_2CH_3$ ) - 1-methoxyethane ( $H_3C-O-CH_2CH_3$ )
Common Names: Names the two alkyl groups followed by the word "ether." - Methylpropyl ether - Ethyl methyl ether

Amines

Definition: An amine is a functional group containing a nitrogen atom with a lone pair.
Structural Relationship: Amines resemble ammonia ( $NH_3$ ) structurally, where the nitrogen can bond with up to three organic groups or hydrogen atoms.

Nomenclature of Amines

Primary Amines ( $1^{\circ}$ ): Named in systematic (IUPAC) nomenclature by replacing the "-e" of the parent alkane with "-amine."
Simple Secondary ( $2^{\circ}$ ) and Tertiary ( $3^{\circ}$ ) Amines: Often named using common nomenclature by designating the organic groups separately in front of the word "amine."

Aryl Amines

Aniline (Phenylamine): $-NH_2$ directly on a benzene ring.
N-methylaniline (N-methylphenylamine): A secondary amine where one hydrogen of aniline is replaced by a methyl group.
Benzylamine: $-NH_2$ group attached to a benzyl group ( $C_6H_5CH_2-$ ).
p-toluidine (p-methylaniline): An aniline derivative with a methyl group in the para position.

Carbonyl Compounds

Definition: Compounds containing the Carbonyl functional group ( $C=O$ ).
Types: Primarily include Aldehydes and Ketones.
Double Bond Equivalence (DBE): The formula provided is $DBE = (- 2) + 1$ .
Isomerism: Aldehydes and ketones are functional group isomers of each other.

Aldehydes

General Structure: $RCHO$ .
Naming: Carbonyl carbon is always at the end of the chain and assigned position #1.
Examples: - Methanal: $H-CHO$ - Ethanal: $H_3C-CHO$ - Propanal: $H_3CH_2C-CHO$ - Prop-2-enal - But-2-enal - Prop-2-ynal - But-2-ynal - Benzaldehyde: $-CHO$ on a benzene ring.

Ketones

General Structure: $RCOR'$
Examples: - Propan-2-one (Propanone): Common name is acetone. - Butan-2-one (Butanone) - Pentan-3-one: Also called diethyl ketone. - But-3-en-2-one - Hex-4-yn-3-one - Benzophenone: Di-phenyl ketone. - Acetophenone: Methyl phenyl ketone.

Amides

Amides are derivatives of carboxylic acids where the $-OH$ is replaced by an amine group.

Primary Amides: - Named by taking the parent acid name, dropping the "-oic acid" or "-ic acid" ending, and adding "-amide." - The carbonyl carbon is always given the #1 location number.
Secondary Amides: - Named using an upper-case "N" to indicate that an alkyl substituent is attached to the nitrogen atom. - Alkyl groups on the nitrogen are treated as substituents (e.g., N-methylethanamide).
Tertiary Amides: - Named similarly to secondary amides but using two "N" indicators for the two substituents on the nitrogen. - N,N-dimethylethanamide - N-methyl-N-phenylethanamide