Question

Back bonding in $B{F}_3$ does not affect:

• A. Planarity
• B. Lewis acidity
• C. Bond length
• D. All of the above

Answer 1

The correct option is A Planarity

In Lewis acids, one of the atom has an available empty orbital that could accept an electron pair from another compound i.e the Lewis base. Backbonding to the empty orbital reduces Lewis acid behaviour. The stronger the effect of back bonding, the weaker the eagerness to accept an electron pair. In boron trifluoride, $B{F}_3$, backbonding is possible as a lone pair of electrons from $F$ atom flow into the vacant p orbital of the electron-deficient $B$ atom.

In $B{F}_3$ back bonding occurs and it doesn't change its planarity, bond angle and geometry. But, as back bond is a partial double bond so bond length decreases and back bonding also affects the lewis acidic character.