Question

Which of the following represents the correct order of acidic strength ?
(i) $HC \equiv CH > H _2 C = CH _2> CH _3- CH _3$
(ii) $HC \equiv CH > CH _3- CH _3> H _2 C = CH _2$
(iii) $CH _3 C \equiv CH > HC \equiv CH > CH _3- C \equiv C - CH _3$
(iv) $HC \equiv CH > CH _3- C \equiv CH > CH _3- C \equiv C - CH _3$

• A. (i) and (iii)
• B. (ii) and (iv)
• C. (i) and (iv)
• D. (iii) and (iv)

Answer 1

Answer: (C)

Due to the maximum percentage of $s$ character $(50 \%)$, the $s p$ hybridised orbitals of carbon atoms in ethyne molecules have highest electronegativity, hence, these attract the shared electron pair of the $C - H$ bond of ethyne to a greater extent than that of the $s p^2$ hybridised orbitals of carbon in ethene and the $s p^3$ hybridised orbital of carbon in ethane. Thus in ethyne, hydrogen atoms can be liberated as protons more easily as compared to ethene and ethane.