Alcohols are often referred to by their common names, rather than their IUPAC names. In this
version of naming, the name of the alkyl group is followed by the word alcohol. Examples include
ethyl alcohol (rather than ethanol) and isopropyl alcohol (rather than 2-propanol.)
MCAT EXPERTISE
The MCAT may use the common names for some alcohols, as well as some of the molecules
we will see later. For alcohols, these include ethyl alcohol and isopropyl alcohol—know what
these common names refer to!Alcohols with two hydroxyl groups are called diols or glycols and are indicated with the suffix –diol.
The entire hydrocarbon name is preserved, and –diol is added. When naming diols, one must
number each hydroxyl group. For example, ethane-1,2-diol is an ethane molecule that has a
hydroxyl group on each carbon. This molecule is also known by its common name, ethylene glycol.
Diols with hydroxyl groups on the same carbon are called geminal diols; diols with hydroxyl groups
on adjacent carbons are called vicinal diols. Geminal diols, or hydrates, are not commonly seen
because they spontaneously dehydrate (lose a water molecule) to produce carbonyl compounds
with the functional group C=O.
MNEMONIC
Vicinal diols are in the vicinity of each other, on nearby carbons. Geminal diols—like the
Gemini twins—are paired, or in this case, on the same carbon.MCAT Concept Check 1.2:
Before you move on, assess your understanding of the material with these questions.Fill in the correct names for the alkanes listed below. If more than one compound can be
described with a given molecular formula, name the straight-chain alkane to which the