IUPAC name of CH3−CH(C2H5)−CH2−CH(OH)−CH3 is 4-methyl -2- hexanol. The parent compound contains a 6 C atom chain and a hydroxyl group. Hence, it is a derivative of hexanol. The hydroxyl group is present on the second C atom and methyl substituent is present on the fourth C atom.
Note: The longest chain of C atoms containing the −OH group is selected as the parent alkane and numbered from the end closer to −OH group.