carbon atoms long) lead to light, fresh smells; medium
chains (six to seven or eight to 10 carbons) to green notes
and to citrus, respectively; and longer chains ( 11 to 13
carbons) to fatty notes. Radicals seem to continue to display similar odor effects common to esters with the same
radical (i.e. geraniol, geranyl acetate and geranyl butyrate
all have rosy metallic characters; see F- 2, F- 3).
One should note that the isomer terms are not normally used when indexing chemicals alphabetically, so
cis-3-hexenol is usually indexed under H for hexenol.
Below are some examples to illustrate how this system can
be used practically.
Making Sense of Material Names
Assuming one has never smelled the chemical phenyl
ethyl isobutyrate, what is the prediction of its odor?
These are the active groups such as alcohols (R-OH),
aldehydes (R-CHO) and esters (R-COOH) and have
by far the biggest effect on the odor of a molecule. The
functional groups are like the arms and legs on the molecule’s body and therefore tend to interact more with the
environment and noses. There is some indication that the
vibrational qualities of these groups may be responsible
for the odor. The active groups on molecules—alcohols,
aldehydes, acetates, butyrates, etc.—show specific odor
characteristics that can be detected irrespective of the
radical of the molecule they are on (e.g. amyl acetate,
benzyl acetate, geranyl acetate—all have a sour-fruitiness
when compared with their alcohols). For functional
groups, see F- 5.
•;Factor;1. MW: Phenyl ethyl (105) isobutyrate (87)
MW = 192 ; this is a medium-sized molecule.
•;Factor;2. Solubility: Without testing one can guess—
no hydroxyl groups, so probably insoluble in water.
•;Factor;3.;Body: Phenyl = medicinal; ethyl = fresh.
•;Factor;4. Specific;structures: Phenyl ethyl = rose
•;Factor;5. Functional;groups: Butyrate = fruity,
VOL. 35 JUNE 2010
As readers may know, isomers are chemicals with mol-
ecules made up from the same elements and numbers
of atoms in a different arrangement and with the same
molecular weight. The functional groups and the carbon
chains are positioned differently, thus forming different
structures. Where these are markedly different, they are
listed under radicals and special structures. If the differ-
ences are small, e.g. n- or iso- isomers, they may not have
a drastic effect on the odor, perhaps making it more or
less fresh or fruity for example, but generally the effect is
little more than a basic structural change. One may need
to concern oneself with these when getting closer to a
target smell, but for the purpose of keeping this system
manageable, it can be disregarded for the time being. The
point is not that isomers have the same smells as each
other, but that they do share clear similarities despite
the oft-quoted example of leavo-carvone (spearmint) and
dextro-darvone (dill). A reminder of common terms used:
One must remember that the functional group tends
to have a bigger effect on the smell compared to the
body. So, phenyl ethyl isobutyrate, it can be reasoned,
should have a fruity, buttery, sour, floral, rose note. Stef-
fen Arctander describes the material’s odor as “refreshing
fruity-rosy odor, more fruity than rosy … moderate to
poor tenacity.” 2 He also notes that it finds use in flavors
•;Factor;1. phenyl ethyl (105), alcohol ( 17) MW = 122;
a smaller molecule more volatile higher impact
•;Factor;2. Solubility = the alcohol group imparts water
solubility; therefore, the impact will be low.
•;Factor;3. Phenyl = medicinal; ethyl = fresh (same as
•;Factor;4. Phenyl ethyl = rose floral (same as the iso
•;Factor;5. Alcohol = mild floral.
•;cis- same side
•;1, 2, 3, 4, 5, 6, etc.: indicate the position of functional
groups (the arms of a molecule)
•;a-, b-, g-, d- : indicate position relative to a functional
Phenyl ethyl alcohol should be a mild floral rose, prob-
ably quite weak compared to the butyrate. Arctander notes
that this material is mild and warm, with a rose-honeylike
odor of moderate to poor tenacity. 2 Poorer grades, he adds,
impart earthy, green grassy notes due to impurities.