Chemistry MCQs for NEET — Practice Questions with Answers

While the NCERT example shows specific cleavage at the less hindered side for $S_N2$, for tertiary alkyl groups, the reaction with HI often proceeds via an $S_N1$ mechanism. The tertiary carbocation formed is highly stable, leading to the formation of the tertiary alkyl iodide. The context implies the general principle of bond cleavage with HI.

The text states: 'Phenols do not react further to give halides because the $sp^2$ hybridised carbon of phenol cannot undergo nucleophilic substitution reaction needed for conversion to the halide.' This directly explains why iodobenzene is not formed from the phenyl group.

The NCERT text explicitly states: 'Para isomer is obtained in 90% yield' for the bromination of anisole.

The text states, 'The alkoxy group (-OR) ... activates the aromatic ring towards electrophilic substitution in the same way as in phenol.'

When symmetrical ethers react with HI, the C-O bond breaks, forming an alcohol and an alkyl iodide. If excess HI is present and heated, the alcohol can further react to form alkyl iodide. However, with limited HI, ethanol and iodoethane are the primary products. The provided example 7.7 (i) shows $CH_3CH_2 – O – CH_2CH_3$ reacting with HI to give $CH_3CH_2OH$ and $CH_3CH_2I$.

According to the NCERT text, 'The diazonium salts have the general formula $ ext{R} ext{N}_2^+ ext{X}^-$ where R stands for an aryl group and $ ext{X}^-$ ion may be $ ext{Cl}^-$, $ ext{Br}^-$, $ ext{HSO}_4^-$, $ ext{BF}_4^-$, etc.'

The NCERT text states that the $ ext{X}^-$ ion in diazonium salts 'may be $ ext{Cl}^-$, $ ext{Br}^-$, $ ext{HSO}_4^-$, $ ext{BF}_4^-$, etc.' $ ext{OH}^-$ is not listed as a common anion in the general formula, although it can replace the diazo group in a reaction.

The NCERT text explicitly states, 'For example, $ ext{C}_6 ext{H}_5 ext{N}_2^+ ext{Cl}^-$ is named as benzenediazonium chloride'.

The NCERT text mentions, 'Primary aliphatic amines form highly unstable alkyldiazonium salts'.

The NCERT text states, 'Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273-278 K)'.