Question

In $B{F}_3$, the B - F bond length is 1.30 A. When $B{F}_3$ is allowed to react with $M{e}_{3}N$, it forms an adduct, $M{e}_{3}N$$\to$$B{F}_3$. The bond length of B - F in the adduct is:

• A. greater than $1.30$A
• B. smaller than $1.30$A
• C. equal to $1.30$A
• D. none of these

Answer 1

The correct option is A greater than $1.30$A

In $B{F}_3$, there is back bonding in between fluorinc and boron due to presence of p-orbital in boron. back bonding imparts double bond characteristics. As $B{F}_3$ forms adjuct the back bonding is no longer present and thus double bond characteristic disappears. Hence, bond becomes a bit longer than earlier ( 1.30 $A^0$).