Write structures for each of the following compounds. Why are the given names incorrect? Write correct IUPAC names.
(i) 2-Ethylpentane
(ii) 5-Ethyl – 3-methylheptane

Explanation

(i)`CH_3-underset(C_2H_5)underset|CH-CH_2-CH_2-CH_3`
Longest chain is of six carbon atoms and not that of five. Hence, correct name is 3-Methylhexane.
(ii)`overset7CH_3-overset6CH_2-overset5underset(CH_3)underset|CH-overset4CH_2-underset(C_2H_5)underset|overset3CH-overset2CH_2-overset1CH_2`
Numbering is to be started from the end which gives lower number to ethyl group. Hence, correct name is 3-ethyl-5- methylheptane.