Write IUPAC names for the following structures :
(i) `CH_(3) -underset(OH)underset(|)(CH) - underset(O)underset(||)C - CH_(2)-CH_(3)`
(ii) `CH_(3)-underset(NH_(2))underset(|)CH-CH_(2)-COOH`
(iii) `CH_(3)- underset(OH)underset(|)CH-CH_(2)-OH`
(iv) `CH_(2) = CH - CH=CH_(2)`

Explanation

(i) `CH_(3)- underset(OH)underset(|)(CH) - underset(O)underset(||)C - CH_(2) - CH_(3)`
Here the principal functional group, ketone is located at the C-3 on the five carbon chain. The -OH group, the hydroxyl substituent is at C-2. Therefore the IUPAC name is 2-hydroxypentan-3-one.
(ii) `CH_(3) - underset(NH_(3))underset(|)CH-CH_(2)-COOH`
Here the principal functional group is carboxylic acid. The amino substituent is located at C-3 on four carbon chain. Therefore the IUPAC name 3-aminobutanoic acid.