est-known example;
(_b_) the terpenes proper, C_{10}H_{16}, which constitute the major
proportion of the whole group; and (_c_) the polyterpenes
(C_{5}H_{8})_{_n_}, of which _colophene_ and _caoutchouc_ are the most
common examples.

Eleven different terpenes having the formula C_{10}H_{16} have been
isolated from various plant juices, and their molecular arrangement
carefully worked out. The following three examples will serve as typical of
the general structural arrangement of these hydrocarbons:

Limonene Camphene Pinene

H
|
C
/|\
/ | \
/ | \
/ | \
/ | \
CH_{3} H / | \
| | / | \
C C /CH_{3} | CH_{3}\
/ \\ CH_{3} / | \ H_{3}C \|/ CH_{2}
/ \\ \ / | \ | C |
H_{2}C CH C | CH_{2} | / |
| | /| | | | / |
| | CH_{3} | HCH | | / |
| | | | | | / |
H_{2}C CH_{2} CH_{2}=C | CH_{2} | / |
\ / \ | / | / |
\ / \ | / | / |
CH C |/ |
| | HC CH
C H \ //
// \ \ //
H_{2}C CH_{3} \ //
\ //
\ //
\ //