# How many carbons are there in (CH_3)_2CHOH?

The molecular formula of isopropanol is ${C}_{3} {H}_{7} O H$. Of butanol, it is ${C}_{4} {H}_{9} O H$; of pentanol, ${C}_{5} {H}_{11} O H$. I am simply adding a methylene group, $C {H}_{2}$, to extend the carbon chain.