Bicyclic Terpenes
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.ch004
Fundamental Bicyclic Groups and Structural Relationships to the Menthane-Type (Type A) Monocyclics The bicyclic terpene hydrocarbons differ in fundamental structure from the monocyclic terpene hydrocarbons as any bicyclic compound differs from any monocyclic compound. The fundamental chemical structures and reactions of these bicyclics and their hydrogenated and other derivatives are currently classified in the terpene literature as belonging to one of four groups — the thujane (or sabinane) group, the carane group, the pinane group, and thecamphanegroup. The names "thujane group" and "bornane group" are recommended to designate, respectively, the first and fourth type of bicyclic structures. Reasons for the choice of thujane over sabinane, and for the replacement of the historical name camphane by the newly coined name "bornane" will be discussed in the specific sections of this report dealing with the nomenclature of these two groups of bicyclic terpene hydrocarbons. A l l of the fundamental bicyclic types contain bridges; in two types the bridge is a "valence bridge" — that i s , contains no carbon atom; in the other two types the bridge is an "atomic bridge" — that i s , contains one carbon. The bridge carbon may have only hydrogens attached or may have methyl groups attached. Some bi-cyclics are completely saturated compounds; these all contain a gem-dimethyl con-figuration and an additional isolated methyl group. Others are unsaturated. Those which contain one double bond may have this bond inside or outside the ring structure. Practically all of those which contain two double bonds have only one double bond within the ring, the other being outside. The bicyclic terpene structures are related much more closely to the menthanetype (Type A) monocyclics than to the dimethylcyclohexane-type (Type B) monocyclics. These structural relationships are shown in Chart 7. In this chart the recommended established fixed numbering of p-menthane and the familiar conventional terpene formulas are used. It is immediately evident that all of the structures contain a gem-dimethyl configuration; furthermore, from the viewpoint of chemical structure of the bicyclics, the ring carbon No. 4 and the isopropyl tertiary carbon No. 8 in the p-menthane are the two significant carbons. Each of the four types of bicyclics contains carbon No. 4 as the carbon at one end of the bridge. In the thujane type, the other end of the bridge can be carbon No. 2 (as shown in Chart 7) or carbon No. 6; the isopropyl group containing carbon No. 8 is intact as a ring substituent. For the other three bicyclic types, the tertiary carbon No. 8 is involved either as a carbon in the second ring (as in carane) or as a carbon in the bridge (as in pinane and bornane); hence, these three types do not contain an isopropyl group. The other end of the bridge in the carane, pinane, and bornane type, as shown in Chart 7, can be respectively carbon No. 5, No. 6, and No. 1. For carane and pinane, these bridge ends could also be, respectively, carbon No. 3 and No. 2. Therefore, on the basis of their carbon skeletons, the bicyclic terpenes belong to the following condensed ring structures: thujane type to bicyclo[3.1.0I]hexane; carane type to bicyclo Q4.1.0^heptane; pinane type to bicyclo Q3.1.1I)heptane; and 26
In SYSTEM OF NOMENCLATURE FOR TERPENE HYDROCARBONS; Advances in Chemistry; American Chemical Society: Washington, DC, 1955.
NOMENCLATURE
Chart 7:
FOR T E R P E N E
HYDROCARBONS
27
Structural Relation of B i c y c l i c to Menthane-Type (Type A) Monocyclic Terpene Hydrocarbons
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1955 | doi: 10.1021/ba-1955-0014.ch004
The Recommended Fixed Numbering of p-Menthane is Shown. Corresponding Carbons in the Bicyclic Structures Carry Identical Numbers Merely to Demonstrate Relationships. In No Case Does the Bicyclic Numbering Coincide with the Recommended Fixed Numberings, Which Are Shown in Chart 8. The Name "Bornane" for Type IV Is the New Name Recommended in This Report to Replace the Historical Name "Camphane".
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II
Thujane C3.1.0] Bicyclohexane
III
IV
Carane
Pinane
Bornane
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