Structure and Nomenclature of Substituted Alkanes
In the Alkanes notes, you learned about two systems of naming molecules. Here we expand
those systems to allow us to name molecules with heteroatom (non-CH) substituents. We’ll also
encounter a third nomenclature method. It is the oldest of the ways to name compounds and not
a system at all. It dates from the days before the existence of atoms and elements was postulated.
Thus, each compound was given a unique name, frequently based on some physical
characteristic (e.g. appearance, odor, or source). While most of these names have fallen out of
use (e.g. sulfuric acid is no longer called oil of vitriol or zinc oxide = flowers of zinc), some
survive (e.g. plaster of Paris = calcium sulfate), and a few have even been incorporated into
systematic naming (e.g. benzene, which appears in a later handout).
Alcohols
The term “alcohol” has an interesting origin. Like many words in science beginning with
“al-,” this term has an Arabic origin. “Al-” means “the.” (Thus, alchemy is “the chemistry.”)
The last two syllables come from the word for an early eye shadow made of antimony powder.
The word for the process by which this powder was made is very similar to the word for the
powder itself. The process is essentially distillation. Medieval Europeans learned of distillation
through the operation of making liquor. Of course, the active ingredient of liquors is ethanol, but
at the time the name of the process by which ethanol was concentrated was given to the chemical
itself. Hence the original name of ethanol was alcohol.
Molecules containing one or more –OH groups are so common in nature that many have
common names. For example:
CH3OH CH3CH2OH CH3
CH CH3
OH
CH2
CH
CH2
OH
OH
HO
CH2CH2
OHHO
wood alcohol grain alcohol rubbing alcohol glycerin
methyl alcohol ethyl alcohol isopropyl alcohol ethylene glycol glycerol
methanol ethanol 2-propanol 1,2-ethanediol 1,2,3-propanetriol
