AROMA CHEMICALS : - IFEAT

Gamma-C9 lactone appears in four notes, tonka-coumarin/coconut/peach/floral, but with the
coconut note dominating. A sugar-tobacco note exists in gamma-C5 and -C6, in delta-C8 and -C9
lactones, and it is particularly strong in gamma-C5 lactones.
The bottom row of Table 3 provides our proposal on the odour character contributed by individual
lactones.
NOTES
Table 3. Odour characteristics of lactones
γ-lactones
δ-lactones
C5 C6 C7 C8 C9 C10 C11 C12 C8 C9 C10 C11 C12
Sugar-Tobacco ● ● ● ●
Tonka-Coumarin ● ● ● ● ● ● ●
Coconut ● ● ● ● ● ●
Peach ● ● ● ● ● ● ●
Floral ● ● ● ● ● ●
Milk-Butter ● ● ● ●
proposal
Jasmin Hay Hay Tuberose Jasmin Milk Rum Osmanthus Plum
Musk Nut Tuberose Cream Whisky Nectarine
Hay Osmanthus Tropical Fruits
Chiral lactones
A single peak is observed when lactones are analyzed by normal gas chromatography,. However,
this peak can represent a 50:50 racemic mixture of two ‘chiral’ enantiomers (spatial mirror
images). Separation of enantiomers is difficult since almost all their physical properties are the
same. It has taken approximately ten years to develop a new technology of chiral gas
chromatography for separating racemates into two peaks by as shown in Figure 1.
Enantiomers are distinguished, according to their spatial structure as an (R)-isomer or an (S)-
isomer. The identity as an (R) or (S)-isomer is determined as shown in Figure 2 by the following
steps :
• First of all, the four groups attached to the stereogenic carbon are identified and given
priorities according to the Cahn-Ingold-Prelog sequence rule (1 = high, 4 = low).
• Once priority numbers have been established, we imagine looking-down the bond from the
stereogenic atom (usually carbon) toward the atom of lowest priority (4, often H). The
other three substituents (1, 2, 3) will be facing you.
• Next connect these three atoms with an arrow running from highest to lowest priority
number (1->2->3).
• If this arrow runs clockwise, the enantiomer is called (R) (Latin: rectus, ‘right’) but if it
runs counterclockwise, it is called (S) (Latin: sinister, ‘left’)
It should be noted that not all lactones in nature are racemic, chiral, optically active or optically
enriched, and this means that they are not racemates.
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