Question

Which of the following has correct numbering according IUPAC :

• A. $CH_3 - CH_2 - \overset{6}{CH_2} - \overset{5}{CH} - \overset{4}{CH_2} - \overset{3}{CH} - \overset{2}{CH_2} - \overset{1}{CH_3}$ $\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad |$ $\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad C_2H_5$ $\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad |$ $\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad CH_3$
• B. $\overset{1}{CH_2} = \overset{2}{CH} - \overset{3}{CH_2} - \overset{4}{CH_2} - \overset{5}{C} \equiv N$
• C. $\overset{1}{CH_3} - \overset{2}{CH} - \overset{3}{CH_2} - \overset{4}{CH_2} - \overset{5}{CH_3}$ $\qquad \qquad |$ $\qquad \qquad CHO$
• D. $CH_3 - CH_2 - \overset{2}{CH} - \overset{3}{C} - CH_2 - CH_3$ $\qquad \qquad \qquad \qquad | \qquad ||$ $\qquad \qquad \qquad \qquad C \equiv N \quad CH_2$ $\qquad \qquad \qquad \qquad \overset{1}{\qquad} \qquad \overset{4}{\qquad}$

Answer 1

Answer: (D)

4

Answer 2

The IUPAC naming conventions prioritize functional groups. Nitrile ($C \equiv N$) has higher priority than a double bond ($C=C$) and an aldehyde ($CHO$).

1. Option (1): The longest continuous carbon chain must be selected. The given numbering uses an 8-carbon chain, but a 9-carbon chain exists (by including the ethyl group in the main chain). Thus, incorrect.
2. Option (2): Nitrile carbon must be C1. The given numbering starts from the double bond, which is incorrect as nitrile has higher priority.
3. Option (3): Aldehyde carbon must be C1. The given numbering treats it as a substituent on C2 of a pentane chain, which is incorrect.
4. Option (4): The numbering correctly assigns C1 to the nitrile carbon and provides the lowest possible locants for the double bond (starting at C3). The parent chain correctly includes both the nitrile group and the double bond. This follows IUPAC rules.