Directions: This section contains 3 paragraphs. Based upon the paragraph, 3 multiple choice questions have to be answered. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. Passage I Amines have the formula \(\mathrm{RNH}_{2}\) and can be prepared by different methods. Some of them are (i) reduction of nitriles (ii) reduction of amides (iii) reduction of azides and (iv) Gabriel phthalimide synthesis. The most important property of amines is their basicity due to the presence of lone pair of electrons on nitrogen. Answer the following questions. The conversion of \(\mathrm{RCH}_{2} \mathrm{CH}_{2} \mathrm{Br}\) to \(\mathrm{RCH}_{2} \mathrm{CH}_{2} \mathrm{~N}_{3}\) by \(\mathrm{NaN}_{3}\) is an example of (a) \(\mathrm{S}_{\mathrm{N}} 1\) reaction (b) \(\mathrm{S}_{\mathrm{N}} 2\) reaction (c) nucleophilic addition reaction (d) electrophilic addition reaction

Amines, organic compounds containing nitrogen, possess unique properties which make them vital in both biological systems and industrial applications. The synthesis of amines is a fundamental concept in organic chemistry, as these compounds populate a variety of chemicals including pharmaceuticals, dyes, and polymers.

The general formula for a primary amine is \(\mathrm{RNH}_{2}\), where R represents an organic substituent. Synthesizing amines can be approached via several key methods including the reduction of nitriles, amides, azides, and through the Gabriel phthalimide synthesis.

Reduction of Nitriles and Amides

When nitriles \(\mathrm{R-C\equiv N}\) undergo reduction, typically through the use of hydrogen in the presence of a metal catalyst, the result is a primary amine. A similar reduction process can be applied to amides \(\mathrm{RCONH}_{2}\), converting them to amines with the introduction of hydrogen.

Reduction of Azides

Azides \(\mathrm{R-N}_{3}\) are also substrates for amine synthesis. When reduced, azides lead to primary amines, offering a pathway for synthesizing amines from functional groups containing nitrogen.

Gabriel Phthalimide Synthesis

The Gabriel phthalimide synthesis is a specialized method for producing primary amines. It involves the use of phthalimide, potassium salt, and subsequent hydrazinolysis to generate a phthalhydrazide, which is then reacted with an alkyl halide to yield the desired amine.

In summary, the synthesis of amines is a versatile area of organic chemistry with multiple methods tailored to the desired amine and conditions of the reaction.

Amines can be prepared through nucleophilic substitution reactions, where a nucleophile replaces a leaving group in a molecule. This type of reaction is fundamental in organic chemistry for modifying the structure of a molecule to introduce new functional groups. Specifically, nucleophilic substitution is prominent in the creation of amines from alkyl halides and related precursors.

Nucleophilic substitution can occur primarily through two mechanisms: S\(_{N}\)1 and S\(_{N}\)2. S\(_{N}\)1 reactions involve a two-step process where the leaving group first departs, forming a carbocation which is then attacked by the nucleophile. This type of reaction is typical with tertiary substrates due to their ability to stabilize the carbocation through alkyl groups.

On the other hand, S\(_{N}\)2 reactions are single-step mechanisms where the nucleophile attacks the electrophilic carbon at the same time as the leaving group departs. S\(_{N}\)2 mechanisms tend to occur with primary and secondary substrates due to the less hindered access to the electrophilic carbon atom.

For example, the conversion of \(\mathrm{RCH}_{2}\mathrm{CH}_{2} \mathrm{Br}\) to \(\mathrm{RCH}_{2}\mathrm{CH}_{2}\mathrm{~N}_{3}\) using \(\mathrm{NaN}_{3}\) is an exemplary S\(_{N}\)2 reaction. The nucleophilic azide ion attacks the carbon bonded to bromine and simultaneously displaces the bromine atom. Due to the bimolecular nature of this mechanism, it is characterized by a concerted reaction with no intermediate.

One of the most significant properties of amines is their basicity, which refers to the ability of a compound to accept protons. Amines exhibit basicity due to the presence of a lone pair of electrons on the nitrogen atom, which can readily form a bond with a proton (\(\mathrm{H}^+\)).

The basicity of amines varies depending on their structure, the electronic effects of substituents, and the solvent in which they are present. In general, alkyl amines tend to be stronger bases compared to ammonia due to the electron-releasing effect of the alkyl group, which increases the electron density around the nitrogen atom.

Factors Affecting Amine Basicity

Several factors influence the basicity of amines:

• Substituent Effect: Electron-releasing groups enhance basicity by increasing electron density, while electron-withdrawing groups decrease basicity by reducing electron availability.
• Steric Hindrance: Bulky groups around the nitrogen atom can hinder the approach of protons, decreasing basicity.
• Solvent Effects: Solvents can influence basicity by either stabilizing or destabilizing the amine or its corresponding conjugate acid.

A solid grasp of these concepts ensures a thorough understanding of the behavior of amines in various chemical contexts and their pivotal role in numerous chemical synthesis and reactions.