Question

Which of the following alkenes on ozonolysis give a mixture of ketones only?

(i)	CH3 – CH = CH – CH3
(ii)	\[\begin{array}{cc} \ce{CH3 - C - CH = CH2}\\ |\phantom{.......}\\ \ce{CH3}\phantom{....} \end{array}\]
(iii)
(iv)	\[\begin{array}{cc} \phantom{...................}\ce{CH3}\\ \phantom{..............}/\\ \ce{(CH3)2 C = C}\\ \phantom{..............}\backslash\\ \phantom{...................}\ce{CH3} \end{array}\]

Answer 1

(iii)
(iv)	\[\begin{array}{cc} \phantom{...................}\ce{CH3}\\ \phantom{..............}/\\ \ce{(CH3)2 C = C}\\ \phantom{..............}\backslash\\ \phantom{...................}\ce{CH3} \end{array}\]

Explanation:

Alkenes which have two substituents on each carbon atom of the double bond give a mixture of ketones on ozonolysis. Thus, options (iii) and (iv) give mixture of ketones.

(iii) 

(iv)

\[\begin{array}{cc}
\phantom{....................}\ce{CH3}\phantom{..................................}\ce{CH3}\phantom{}\\
\phantom{...............}/\phantom{.....................................}/\phantom{}\\
\ce{(CH3)2 C = C ->[(i) O3/CCl4, 196 K][(ii) Zn/H2O] (CH3)2 C = O + O = C}\\
\phantom{...............}\backslash\phantom{.....................................}\backslash\\
\phantom{....................}\ce{CH3}\phantom{..................................}\ce{CH3}\phantom{}
\end{array}\]

On the other hand, alkenes (i) and (ii) give a mixture of two aldehydes.

(i) \[\ce{CH3CH = CH - CH3 ->[O3/CCl4, 196 K][Zn/H2O] CH3CH = O + O = CHCH3}\]

 

(ii) \[\begin{array}{cc}
\ce{CH3 - CH - CH = CH2 ->[O3/CCl4, 196 K][Zn/H2O] CH3 - CH - CH = O + O = CH2}\\
\phantom{...}|\phantom{.....................................}|\phantom{....................}\\
\phantom{...}\ce{CH3}\phantom{.................................}\ce{CH3}\phantom{.................}
\end{array}\]