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(" ".^2CH_2overset1CH_3)underset(|)overset3(CH)-overset4CH_2overset5CH_2overset6CH_3`
The longest chain here contains six carbon atoms and not five . Therefore, the correct name is 2-methylhexane.
(ii)`overset7CH_3-overset6CH_2-undersetunderset(CH_3)|overset5CH-overset4CH_2-undersetunderset(" "CH-CH_3)|overset3(CH)-overset2CH_2-overset1CH_3`
Since 'e' comes before 'm' in alphabetical order , therefore , numbering must be done from right to left. Therefore, the correct name is 3-ethyl-5-methylheptane.