Question

The number of alkenes (including stereoisomers) which can produce 2-butanol by the successive treatment of (i) $B_{2}H_{6}$ in tetrahydrofuran solvent and (ii) alkaline $H_{2}O_{2}$ solution is/are

Answer 1

Structure of butan-2-ol is
$CH_{3}-\underset{O H}{\underset{\left|\right.}{C} H}-CH_{2}-CH_{3}$
Now, the simple format of HBO (hydroboration oxidant) reaction is
$R - CH = CH _2+ B _2 H _6 \xrightarrow{ THF }\left( R - CH _2 CH _2\right)_3 B \xrightarrow{ H _2 O _2 / \overline{ O } H } RCH _2 \underset{\overset{|}{OH}}{CH _2}$
So, $CH_{3}-CH=CH-CH_{3}$ definitely an option as the mechanistic approach for the $BH_{3}$ addition is as

$\left( CH _3 CH _2- CHCH _3\right)_3 B \xrightarrow{ H _2 O _2 / \overline{ O } H } CH _3 CH _2- \underset{\overset{|}{OH}}{CH }CH _3$
Now, $CH_{3}-CH=CH-CH_{3}$ can have both cis and trans-forms.