NEET Practice Questions (MCQs) with Answers & Solutions

The summary states: 'Out of staggered and the eclipsed conformations of ethane, staggered conformation is more stable as hydrogen atoms are farthest apart.' This minimizes torsional strain or repulsive interactions between electron clouds of C-H bonds. (Chapter: Hydrocarbons, Page 326)

The NCERT text on Newman projections states: 'The rear carbon atom (the carbon atom away from the eye) is represented by a circle...' (Chapter: Hydrocarbons, Page 305)

The NCERT states: 'This rotation results into infinite number of spatial arrangements of hydrogen atoms attached to one carbon atom with respect to the hydrogen atoms attached to the other carbon atom. These are called conformational isomers (conformers). Thus there are infinite number of conformations of ethane.' (Chapter: Hydrocarbons, Page 305)

According to the NCERT text, 'Aromatic primary amines cannot be prepared by this method [Gabriel phthalimide synthesis] because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.' Ammonolysis of aryl halides, conceptually similar to Gabriel phthalimide synthesis in its reliance on nucleophilic substitution, also faces limitations due to the low reactivity of aryl halides towards nucleophilic substitution. Reduction of nitro compounds, reduction of amides, and Hoffmann bromamide degradation are all viable methods for preparing aromatic primary amines.

The NCERT states, 'Hoffmann developed a method for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.' This perfectly describes the Hoffmann bromamide degradation reaction.

The NCERT text mentions, 'Alkylamines are found to be stronger bases than ammonia. In alkylamines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines.' It also specifically states, 'Aliphatic amines are stronger bases than ammonia due to +I effect of alkyl groups leading to high electron density on the nitrogen atom.'

The NCERT text explicitly states, 'This process of cleavage of the C–X bond by ammonia molecule is known as ammonolysis. ... The primary amine thus obtained behaves as a nucleophile and can further react with alkyl halide to form secondary and tertiary amines, and finally quaternary ammonium salt.'

The NCERT states, 'Ammonolysis has the disadvantage of yielding a mixture of primary, secondary and tertiary amines and also a quaternary ammonium salt. However, primary amine is obtained as a major product by taking large excess of ammonia.'

The NCERT states, 'Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum and also by reduction with metals in acidic medium. Reduction with iron scrap and hydrochloric acid is preferred because FeClâ‚‚ formed gets hydrolysed to release hydrochloric acid during the reaction. Thus, only a small amount of hydrochloric acid is required to initiate the reaction.'

The NCERT text mentions, 'Nitriles on reduction with lithium aluminium hydride (LiAlHâ‚„) or catalytic hydrogenation produce primary amines. This reaction is used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine.'