Question

Which of the following order is correct regarding acidic character of hydrocarbons given below?
I. $CH \equiv CH > CH _{2}= CH _{2}> CH _{3}- CH _{3}$
II. $HC \equiv CH > CH _{3} C \equiv CH > CH _{3} C \equiv CCH _{3}$

• A. Only I
• B. Only II
• C. Both I and II
• D. None of these

Answer 1

Answer: (C)

Both the orders regarding acidity of hydrocarbon are correct.
I. Acidic strength $\propto$ per cent $s$-character and $s$-character is $50 \%$ in alkynes, $33 \%$ in alkanes and $25 \%$ in alkanes.
II. Inductive effect defines acidic strength and polarity of $C - H$ bond of alkyne. Groups having $+I$-effect increases electron density around $C - H$ bond, hence polarity decreases and acidic strength of alkyne decreases.