Question

In $BF_3$, the $B??F$ bond length is $1.30\, ??, when$BF_3$is allowed to be treated with$Me_3N$, it forms an adduct,$Me_3N \to BF_3$, the bond length of$B ??F$ in the adduct is

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

Answer 1

Answer: (A)

greater than $1.30, ??

Answer 2

In $BF^3$, there is back bonding in between fluorine and boron due to presence of p-orbital in boron. back bonding imparts double bond characteristics. As $BF^3$ forms adduct the back bonding is no longer present and thus double bond characteristic disappears. bond becomes a bit longer than earlier (1.30 $??).