Question

Assertion :The acidic strength sequence $BM{e}_3<B(MeO{)}_3$ Reason: The acidic strength can also be explained by considering the existing back bonding.

• A. Assertion is true, Reason is true and Reason is correct explanation for Assertion.
• B. Assertion is true, Reason is true and Reason is not the correct explanation for Assertion
• C. Assertion is true, Reason is false.
• D. Assertion is false, Reason is true.

Answer 1

The correct option is D

Assertion is false, Reason is true.

In both the compounds, Boron forms $3$ covalent bonds with the three methyl groups in trimethylborane and trimethoxyborane.

Boron has $3$ valence electrons of its own and gains $3$ more electrons in the covalent bond. Hence, it has a total of $6$ electrons.

The octet is not complete and boron is electron deficient. It thus, acts as lewis acid.

Trimethyl borane is more acidic than trimethoxy borane due to involvement of back-bonding of boron with oxygen which somehow, suppresses the electron deficiency of boron. Thus, assertion is false and reason is true.