Question

For the ionic reaction of hydrochloric acid with the following alkenes, predict the correct sequence of reactivity as measured by reaction rates:
$\left(I\right)ClCH=C{H}_2$
$\left(II\right)(C{H}_3{)}_{2}C=C{H}_2$
$\left(III\right)OHCCH=C{H}_2$
$\left(IV\right)(NC{)}_{2}C=C(CN{)}_2$

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

Answer 1

The correct option is D II > I > III > IV

For the ionic reaction of hydrochloric acid with alkenes, the correct sequence of reactivity as measured by reaction rates is $\left(II\right)(CH3{)}_{2}C=C{H}_2>(I)ClCH=C{H}_2>(III)OHCCH=C{H}_2>(IV\left)\right(NC{)}_{2}C=C(CN{)}_2$.

In this reaction, pi electrons are donated to a proton. Methyl group is electron donating group and increases the electron donating ability of C=C bond. Hence alkene II is most reactive. Other groups (cyano chloro and carbonyl) are electron withdrawing groups. They decrease the electron donating ability of C=C bond. This decreases the reactivity.