Question

Which of the following pairs are position isomers?

I.	\[\begin{array}{cc} \phantom{.......................}\ce{O}\\ \phantom{.......................}||\\ \ce{CH3 - CH2 - CH2 - CH2 - C - H} \end{array}\]
II.	\[\begin{array}{cc} \phantom{.................}\ce{O}\\ \phantom{.................}||\\ \ce{CH3 - CH2 - CH2 - C - H} \end{array}\]
III.	\[\begin{array}{cc} \ce{CH3 - CH2 - C - CH2 - CH3}\\ \phantom{}||\\ \phantom{}\ce{O} \end{array}\]
IV.	\[\begin{array}{cc} \ce{CH3 - CH - CH2 - C - H}\\ \phantom{...}|\phantom{............}||\phantom{}\\ \phantom{...}\ce{CH3}\phantom{.........}\ce{O}\phantom{} \end{array}\]

(i) I and II

(ii) II and III

(iii) II and IV

(iv) III and IV

Answer 1

(ii) II and III

Explanation:

In position isomerism, two or more compounds differ in the position of substituent, functional group or multiple bonds but molecular formula is same. In pentanone-2 and pentanone-3, position of ketonic group is different.

CH₃ – CH₂ – CH₂ – CO – CH₃ and CH₃ – CH₂ – CO – CH₂ – CH₃