Turpenes

THE SMELL OF CHRISTMAS One of many Christmas pleasures is the aroma of a freshly cut tree. Both spruce and pine have it. So do cranberry fields in the morning, orange peelings, and some paint thinners. The substances known as essential oils are responsible for these odors. They are now called terpenes, compounds produced by plants from isoprene, a hydrocarbon that has its five carbon atoms arranged in a branched chain. Isoprenes combine to give many terpenes. Camphor and pinene are among the simple two-isoprene terpenes that help form the odor of pine. Larger terpenes can be found in rosin, steroids, and chlorophyll. Thousands of terpenes are known and new ones are regularly found.

Most terpenes found in conifers are volatile and evaporate during warm days. When it is cool the needles accumulate large amounts, some of which escape if the needles are damaged. Simply brushing against a green bough on a ski slope is enough to bring forth the rich smell of pine.