alcohol

An alcohol is any organic molecule that carries an -OH (hydroxyl) group bonded to a saturated, sp3 carbon. The drinking alcohol in beer and wine, ethanol (CH3-CH2-OH), is the most famous member, but the same -OH group sits in rubbing alcohol, sugar, cholesterol, and countless medicines. The defining feature is simply that oxygen-hydrogen group hanging off a carbon skeleton.

Structurally, picture water (H-O-H) and then replace one of its hydrogens with a carbon chain: you get R-O-H, an alcohol. The oxygen keeps its two lone pairs and its bent shape, so an alcohol behaves a lot like a souped-up water molecule attached to a greasy organic tail. The C-O and O-H bonds are both polar because oxygen is strongly electronegative, which gives alcohols their characteristic mix of properties — they dissolve in water when small, hydrogen-bond strongly, and have a reactive O-H.

Alcohols matter because they are a central hub of organic chemistry. They are easy to make (from alkenes, from carbonyls, from Grignard reagents, from substitution) and easy to convert onward (into alkenes by dehydration, into aldehydes/ketones/acids by oxidation, into ethers, esters, and alkyl halides). Learning what -OH can do is learning how to navigate between many other functional groups.