Table 2.

Relative steric energies (kcal/mol) of the four conformers (see Fig. 4) of germacrene A and related germacrene-type sesquiterpenes calculated by the Allinger MM2 force field method in the present work. Populations (%) at 25 °C are given in parenthesis for germacrene A.^a

Sesquiterpene	UU	UD	DD	DU
Germacrene Aa, b	0.00 (84)	1.37 (8.3)	1.49 (6.7)	2.65(1)
Germacrene Bc	0.00	1.78	0.04	1.23
Costunolidec	0.00	3.75	4.76	4.50
Hedycaryolc	0.45	0.00	0.22	1.41
Dehydrogermacrene Ac	0.04	0.47	0.00	2.00

^aCalculated assuming entropy differences between conformers are negligible.

^bMM3 calculations gave similar relative energies: UU (0.00), UD(1.99), DD (1.82), DU (3.56).

^cThe relative steric energies agree with literature data. See references 34b, 50, 51, 52, and 53