Question

Addition of hydrogen bromide to but-2-ene and but-1-ene forms ______.

Options

• 1 - bromobutane and 2- bromobutane respectively

• 1 - bromobutane only·

• 2 - bromobutane only

• 2 - bromobutane and 1 -bromobutane respectively

Answer 1

Addition of hydrogen bromide to but-2-ene and but-1-ene forms 2 - bromobutane only.

Explanation:

\[\begin{array}{cc}
\ce{H3C\underset{2 - Butene}{- CH = CH} - CH3 + HBr -> H3C - CH2 - CH - CH3}\\
\phantom{.........................................}|\\
\phantom{..........................................}\ce{\underset{2 - Bromobutane}{Br}}\end{array}\]

\[\begin{array}{cc}
\ce{H3C\underset{2 - Butene}{- CH2 - CH} = CH2 + HBr -> H3C - CH2 - CH - CH3}\\
\phantom{.........................................}|\\
\phantom{..........................................}\ce{\underset{2 - bromobutane}{Br}}\end{array}\]

Addition takes place via Markowni koff's rule and both give 2-bromobutane as products.