essential oil of rose, is readily associated with its characteristic aroma.
Note the structures of these two molecules, geranial and geraniol.3 SOS
Geranial GeraniolThey are identical except that geranial has a carbon double-bonded
to oxygen at one end (called an aldehyde in organic chemistry), and
geraniol has a carbon bonded to a hydroxy group at the end (called an
alcohol in organic chemistry). Thus, the difference between geranial
and geraniol is the presence or absence of a mere two hydrogen atoms
and a stronger bond (and more rigid structure) at one end of the mol-
ecule. This seemingly subtle difference in molecular shape produces
a profound difference in the associated aroma (lemon versus rose).
Small changes in molecular shape, to the extent that they affect the
binding of these molecules to the various olfactory GPCRs, may have
substantial effects on the patterns of neural signals generated in the
olfactory pathway, resulting in substantial effects on the quality of the
perceived aromas.
Now consider these three molecules—2-butene-1-thiol, 3-methyl-1-
butanethiol, and 2-quinolinemethanethiol—with their long chemical
names and structures somewhat different from other molecules we
have discussed thus far in this chapter.
SH S
yf ro v7 SH2-butene-I-thiol 3-methyl-1-butanethiol 2-quinolinemethanethiol