Question

In which of the following compounds B – F bond length is shortest ?

• A. $BF_{4}^{-}$
• B. BF3$\rightarrow$ NH3
• C. BF3
• D. BF3$\leftarrow$N(CH3)3

Answer 1

Answer: (C)

BF3

Answer 2

Partial double bond character is developed in B–F bond of BF3 (due to formation of dative p bond)

In other case B is sp3 hybridised (tetrahedral molecule or ion) and the possibility for $\pi$ bonding no longer exists.