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Organic Compounds Containing Nitrogen - Amines: Classification and nomenclature

Grade 12ICSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Amines are organic derivatives of ammonia (NH3NH_3) formed by replacing one or more hydrogen atoms with alkyl (RR) or aryl (ArAr) groups.

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Classification: Amines are classified as Primary (1∘1^\circ), Secondary (2∘2^\circ), and Tertiary (3∘3^\circ) based on the number of carbon atoms directly attached to the nitrogen atom.

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Primary amines have the functional group −NH2-NH_2 (amino group); Secondary amines have −NH−-NH- (imino group); Tertiary amines have the −N<-N< (tertiary nitrogen) group.

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IUPAC Nomenclature: Aliphatic amines are named as alkanamines (alkane + amine). For example, CH3NH2CH_3NH_2 is Methanamine.

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In 2∘2^\circ and 3∘3^\circ amines, the prefix 'N−N-' is used to identify the smaller alkyl groups attached to the nitrogen atom, while the largest group is treated as the parent alkanamine.

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Aromatic Amines: The simplest aromatic amine is Aniline (C6H5NH2C_6H_5NH_2). In IUPAC, it is named Benzenamine.

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Structure: The nitrogen atom in amines is sp3sp^3 hybridized. It possesses a lone pair of electrons, resulting in a trigonal pyramidal geometry with bond angles slightly less than 109.5∘109.5^\circ (e.g., 108∘108^\circ in (CH3)3N(CH_3)_3N).

📐Formulae

CnH2n+1NH2 (General formula for primary aliphatic amines)C_nH_{2n+1}NH_2 \text{ (General formula for primary aliphatic amines)}

R−NH2(1∘ Amine)R-NH_2 \quad (1^\circ \text{ Amine})

R−NH−R′(2∘ Amine)R-NH-R' \quad (2^\circ \text{ Amine})

R−N(R′)−R′′(3∘ Amine)R-N(R')-R'' \quad (3^\circ \text{ Amine})

[R4N]+X−(Quaternary ammonium salt)[R_4N]^+ X^- \quad (\text{Quaternary ammonium salt})

💡Examples

Problem 1:

Give the IUPAC name for CH3−CH2−CH(NH2)−CH3CH_3-CH_2-CH(NH_2)-CH_3.

Solution:

Butan-2-amine

Explanation:

The parent carbon chain consists of 4 carbon atoms (butane). The amino group (−NH2-NH_2) is located on the second carbon atom to give the lowest possible locant.

Problem 2:

Write the structure and IUPAC name of N,NN,N-Dimethylethanamine.

Solution:

CH3−CH2−N(CH3)2CH_3-CH_2-N(CH_3)_2

Explanation:

The parent chain is 'ethanamine' (2 carbons). Two methyl groups are attached to the nitrogen atom, indicated by the 'N,NN,N-Dimethyl' prefix.

Problem 3:

Classify (CH3)3C−NH2(CH_3)_3C-NH_2 as primary, secondary, or tertiary amine.

Solution:

Primary (1∘1^\circ) amine.

Explanation:

The nitrogen atom is attached to only one carbon atom (a tertiary butyl group). Classification is based on the nitrogen atom's connectivity, not the carbon's.

Problem 4:

What is the IUPAC name for C6H5−NH−CH3C_6H_5-NH-CH_3?

Solution:

NN-Methylbenzenamine (or NN-Methylaniline)

Explanation:

The compound is a secondary amine where a methyl group is substituted on the nitrogen of aniline (benzenamine).

Amines: Classification and nomenclature Revision - Class 12 Chemistry ICSE