Question

The decreasing order of reactivity towards electrophilic addition of the following is:
I. $CH\equiv CH$
II. $C{H}_2=C{H}_2$
III. $H_{2}C=CH-Cl$
IV. $\underset{\stackrel{|}{Cl}}{HC}=\underset{\stackrel{|}{Cl}}{CH}$

• A. I > II > III > IV
• B. II > I > III > IV
• C. IV > III > I > II
• D. IV > III > II > I

Answer 1

Answer: (B)

II > I > III > IV

The order of electrophilic addition (EA) is alkene > alkyne. But, if alkene has EWG (electron-withdrawing group) reactivity of alkene is less than that of alkyne.

Due to EWG electron density at ($C=C$) or nucleophilicity decreases, so addition of electrophile to ($C=C$) is slow.

So, the decreasing order of EA is:

(II) - (alkene) > I - (alkyne) > III - (alkene with one EWG) > (IV) - (alkene with two EWGs).