Ques. 1NEET 2013
Which of the following is electron-deficient ?
- (BH3)2
- PH3
- (CH3)2
- (SiH3)2
Answer
(1) (BH3)2
Solution
(BH3)2 is diborane, B2H6.
Valence electrons = 2 3 + 6 1 = 12, but 8 two-centre bonds would need 16 electrons.
As per NCERT, diborane has four terminal 2c–2e B–H bonds and two 3c–2e B–H–B (banana) bonds ⇒ it is electron-deficient.
PH3, (CH3)2 (ethane) and (SiH3)2 (disilane) have enough electrons for all normal covalent bonds.
Answer: (1)