Alcohols are then classified into primary, secondary (sec-, s-), and tertiary (tert-, t-), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. (The respective numeric shorthands 1°, 2°, and 3° are sometimes used in informal settings.) The primary alcohols have general formulas . The simplest primary alcohol is methanol (), for which R=H, and the next is ethanol, for which , the methyl group. Secondary alcohols are those of the form RRCHOH, the simplest of which is 2-propanol (). For the tertiary alcohols, the general form is RRR"COH. The simplest example is tert-butanol (2-methylpropan-2-ol), for which each of R, R, and R" is . In these shorthands, R, R, and R" represent substituents, alkyl or other attached, generally organic groups.