Question

The IUPAC name of

$C{H}_3-\underset{C{H}_3}{\underset{|}{CH}}-\underset{C{H}_3}{\underset{|}{C}}-\underset{CHO}{\underset{|}{CH}}-C{H}_2-C{H}_2-C{H}_3$ is?

• A. 2 - (1, 2 - Dimethy (propyl) pentanal
• B. 3, 4 - Dimethyl - 2 -propylpentanal
• C. 4 - Formyl - 2, 3 - dimethylheptane
• D. None of the above

Answer 1

The correct option is B

3, 4 - Dimethyl - 2 -propylpentanal

Although the longest chain from either end is 7-carbons long, the correct way to start numbering is from the aldehyde -CHO carbon.
This leaves us with two options.


When there are two or more longest chains, we choose to number in such a way that then are maximum number of substituents.

Option I is more appropriate as it has 3 substituents compared to option II, which has only one substituent at $C_2$.

Word root = pent
Primary suffix = ane
Secondary suffix = al
Secondary prefix = 3,4-dimethyl-1,2-propyl

Alphabetically 3,4 - dimethyl precedes 2-propyl hence the answer is 3,4-Dimethyl-2-propylpentanal