structural formula what sort of odor the compound would
have or whether it would have any, yet we can divide odoriferous
substances into classes according to their constitution. What are
commonly known as "fruity" odors belong mostly to what the chemist calls
the fatty or aliphatic series. For instance, we may have in a ripe fruit
an alcohol (say ethyl or common alcohol) and an acid (say acetic or
vinegar) and a combination of these, the ester or organic salt (in this
case ethyl acetate), which is more odorous than either of its
components. These esters of the fatty acids give the characteristic
savor to many of our favorite fruits, candies and beverages. The pear
flavor, amyl acetate, is made from acetic acid and amyl alcohol--though
amyl alcohol (fusel oil) has a detestable smell. Pineapple is ethyl
butyrate--but the acid part of it (butyric acid) is what gives Limburger
cheese its aroma. These essential oils are easily made in the
laboratory, but cannot be extracted from the fruit for separate use.

If the carbon chain contains one or more double linkages we get the
"flowery" perfumes. For instance, here is the symbol of geraniol, the
chief ingredient of otto of roses:

(CH_{3})_{2}C = CHCH_{2}CH_{2}C(CH_{3})_{2} = CHCH_{2}OH

The rose would smell as sweet under another name, but it may be
questioned whether it would stand being called by the name of
dimethyl-2-6-octadiene-2-6-ol-8. Geraniol by oxidation goes into the
aldehyde, citral, which occurs in lemons, oranges and verbena flowers.
Another compound of this group, linalool, is found in lavender, bergamot
and many flowers.

Geraniol, as you would see if you drew up its structural formula in the
way I described in the last chapter, contains a chain of six carbon
atoms, that is, the same number as make a benzene ring. Now if we shake
up geraniol and other compounds of this group (the diolefines) with
diluted sulfuric acid the carbon chain hooks up to form a benzene ring,
but with the other carbon atoms stretched across it; rather too
complicated to depict here. These "bridged rings" of the formula
C_{5}H_{8}, or some multiple of that, constitute the important group of
the terpenes which occur in turpentine and such wild and woodsy things
as sage, lavender, caraway, pine needles and eucalyptus. Going further
in this direction we are led into the realm of the heavy oriental odors,
patchouli, sandalwood, cedar, cubebs, ginger and camphor. Camphor can
now be made