Question

Which o f the following has the minimum heat of dissociation of N $\rightarrow$ B bond ?

• A. [(CH3)3N $\rightarrow$ BF3]
• B. [(CH3)3N $\rightarrow$B(CH3)F2]
• C. [(CH3)3N $\rightarrow$B(CH3)2F]
• D. [(CH3)3N $\rightarrow$ B(CH3)3]

Answer 1

Answer: (D)

(CH3)3N $\rightarrow$ B(CH3)3

Answer 2

Boron trimethyl is a weaker Lewis acid than the boron trihalides or monoborane. The electron donating effect of the methyl groups hinders the complex formation with trimethyl amine. Hence the bond N $\rightarrow$B is weakest in

[(CH3)3 N $\rightarrow$B(CH3)3]. Me3N as donor (capacity). BBr3 > BCl3 > BF3 ~ BH3 > BMe3.