Question

Arrange the following in decreasing order of basic strength
(I) $CH _{3} CH _{2} MgBr$
(II) $H - C \equiv CMgBr$
(III) $CH _{3} CH _{2} OMgBr$

• A. I, III and II
• B. II, I and III
• C. III, II and I
• D. I, II and III

Answer 1

Answer: (D)

The best way to compare their basic strength is to compare the acidic strength of their conjugate acid and then reverse the order because there is inverse relation in the strength of conjugate pair. The order of acidic strength of conjugate acid is

$CH _{3} CH _{2} OH < H - C \equiv C - H > CH _{3} CH _{3}$

$\therefore \,\,$ Decreasing order of basic strength is

$CH _{3} CH _{2}^{-}> H - C \equiv C ^{-}> CH _{3} CH _{2} O ^{-}$