question_answer

Propene \[\xrightarrow{HBr}\,\,A\xrightarrow[\left( ii \right)\text{ }{{H}_{2}}O/boil]{\left( i \right)Mg/ether}B\]In the above sequence of reactions B is

A)  propane                             

B)  butane

C)  propene                            

D)  ethane

Correct Answer: A

Solution :

                 \[\underset{propene}{\mathop{C{{H}_{3}}CH=C{{H}_{2}}}}\,\xrightarrow[\begin{smallmatrix}  add\text{ }according\text{ }to \\  Markownikoffs  \\  rule \end{smallmatrix}]{HBr}\]\[4C{{H}_{3}}-\underset{\begin{align}   & | \\  & Br \\  & 2-bromopropane \\  & (A) \\ \end{align}}{\mathop{C}}\,H-C{{H}_{3}}\] \[\xrightarrow{\left( I \right)\text{ }Mg/ether}C{{H}_{3}}-\underset{\begin{align}   & | \\  & MgBr \\  & isopropyi\text{ }magnesium \\  & bromide \\  & \left( Grignards\text{ }reagent \right) \\ \end{align}}{\mathop{C}}\,H-C{{H}_{3}}\]                 Note - Grignards reagent on reaction with any compound captaining active H-atom decompose to give alkane (when H-atom is attached to O, N or S or acidic in nature is known as active H-atom).