Organic Chemistry: Amines and Amino Acids - SS3 Chemistry Past Questions and Answers - page 1

A primary amine has one carbon atom directly bonded to the nitrogen atom. In option (a), CH3CH2NH2, there is one carbon atom (CH3CH2) directly bonded to the nitrogen atom (NH2), making it a primary amine.

The systematic IUPAC name for CH3NHCH2CH3 is ethylamine. It is named based on the longest carbon chain containing the nitrogen atom, which is ethane (CH3CH2) in this case.

An aromatic amine is an amine in which the nitrogen atom is attached to an aromatic ring. In option (b), C6H5NH2, the nitrogen is attached to the phenyl group, which is an aromatic ring, making it an aromatic amine

The IUPAC name for (CH3)2CHNH2 isopropylamine. It is named based on the longest carbon chain containing the nitrogen atom, which is propane (CH3CH2CH) in this case, and the substituents on the carbon chain (isopropyl group).

A secondary amine has two carbon atoms directly bonded to the nitrogen atom. In option (d), CH3CH2NHCH3, there are two carbon atoms (CH3CH2) directly bonded to the nitrogen atom, making it a secondary amine.

Classification and Nomenclature of Amines:

Amines are organic compounds that contain the amino functional group (NH2) attached to a carbon atom. They can be classified based on the number of alkyl or aryl groups attached to the nitrogen atom, which determines their primary, secondary, or tertiary nature.

1.    Primary Amines: Primary amines have one alkyl or aryl group and two hydrogen atoms attached to the nitrogen atom. The general formula is R-NH2, where R represents an alkyl or aryl group.

Example: Ethylamine (Common Name) or Ethanamine (IUPAC Name)

CH3CH2-NH2

2.    Secondary Amines: Secondary amines have two alkyl or aryl groups and one hydrogen atom attached to the nitrogen atom. The general formula is R2-NH, where R represents an alkyl or aryl group.

Example: Dimethylamine (Common Name) or N-Methylethanamine (IUPAC Name)

CH3-NH-CH3

3.    Tertiary Amines: Tertiary amines have three alkyl or aryl groups and no hydrogen atoms attached to the nitrogen atom. The general formula is R3-N, where R represents an alkyl or aryl group.

Example: Trimethylamine (Common Name) or N, N-Dimethylethanamine (IUPAC Name) CH3-N(CH3)2

Nomenclature of Amines:

The nomenclature of amines follows the IUPAC system, where the longest carbon chain containing the nitrogen atom is identified. The -e of the corresponding alkane is replaced with -amine.

If there are multiple substituents attached to the nitrogen, their names are listed alphabetically, and the prefix N- is used to indicate the substitution.

Examples:

1.    CH3CH2-NH2: Common Name - Ethylamine; IUPAC Name - Ethanamine

2.    CH3-NH-CH3: Common Name - Dimethylamine; IUPAC Name - N-Methylethanamine

3.    CH3-N(CH3)2: Common Name - Trimethylamine; IUPAC Name - N,N-Dimethylethanamine

Significance of Classification:

The classification of amines based on the number of alkyl or aryl groups attached to the nitrogen atom is essential in organic chemistry. It determines the reactivity and properties of amines. For example:

●     Primary amines can undergo further reactions to form secondary and tertiary amines.

●     Tertiary amines are more basic than secondary amines due to the absence of a hydrogen atom attached to the nitrogen.

Understanding the classification and nomenclature of amines allows chemists to communicate effectively and accurately describe the structure and properties of these important organic compounds. It also aids in predicting their behaviour in various chemical reactions and applications in pharmaceuticals, dyes, and other industries.

Amines are generally hydrophobic due to the presence of nonpolar alkyl or aryl groups. This hydrophobic character makes amines less soluble in water and more soluble in organic solvents.

Amines can undergo esterification reactions with carboxylic acids and alcohols to form amides and esters, respectively. This is a chemical property of amines, as it involves the formation of new chemical bonds.

A secondary amine has two alkyl or aryl groups and one hydrogen atom attached to the nitrogen atom. Dimethylamine fits this description, while methylamine (a) and ethylamine (d) are primary amines, and trimethylamine (c) is a tertiary amine.

Primary amines can be oxidised to carboxylic acids using appropriate oxidising agents. The amino group (-NH2) is converted to a carboxyl group (-COOH) during the oxidation process.