Question

Boron and nitrogen form bonds analogous to carbon-carbon bonds. For example, compound ammonia borane, $N{H}_3-B{H}_3$, contains $B-N$ bond analogous to the $C-C$ bond in ethane. Borazine $\left(B_3{N}_3{H}_6\right)$ is analogous to benzene and is prepared by reacting $N{H}_{4}Cl$ with $BC{l}_4$ followed by reduction using $LiB{H}_4$. The correct statement(s) is/are:

• A. boron nitride $\left(BN\right)$ has a structure similar to graphite and is a good conductor of electricity
• B. the $B-$center in borazine is susceptible to nucleophilic attack
• C. ethane is a gas at room temperature, while ammonia borane is not so
• D. the reaction of $HCl$ with borazine gives hexachloro derivative of borazine

Answer 1

Answer: (B), (C)

the $B-$center in borazine is susceptible to nucleophilic attack
ethane is a gas at room temperature, while ammonia borane is not so

Boron nitride is inorganic graphite and it is not a conductor of electricity, unlike graphite. Its band/energy gap is very high $\approx 5eV$, equivalent to that of the diamond. $B$ and $N$ have similar electronegativity (3 and 5 valence electrons respectively) thus, they form a very strong covalent bond.

Being covalent in nature and with high band gap its electrons movement is only inside its own molecules so it does not conduct electricity since conduction of electricity means movement of charge by the electrons from one molecule to another.

Since $B$ is an electron deficient centre, therefore is susceptible to nucleophilic attack while nitrogen is susceptible to electrophilic attack.

Ammonia borane also called borazane, have dipolar interaction between to electron rich $N$ and electron deficient $B$. It is highly polar molecule. The $H$ atoms attached to boron are basic and those attached to nitrogen are somewhat acidic. This tends to form a dihydrogen bond between borazane molecules similar to hydrogen bonding. Thereby strong intermolecular interactions are responsible for its solid state.

With hydrogen chloride, borazine forms an adduct.

Therefore option $B$ and $C$ are correct.