Question

The IUPAC Name of

$C{H}_3-\underset{C{H}_3}{\underset{|}{CH}}-\underset{C{H}_3}{\underset{|}{CH}}-\underset{CHO}{\underset{|}{CH}}-C{H}_2-C{H}_2-C{H}_3$ 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 substituents 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
(b) 3, 4-Dimethyl -2- propylpentanal