Hydrogen bonding in labdane diterpenoids, labda-7,12(E),14-triene-17-oic acid and labda-12(Z),14,17-triene-18-oic acid

Two labdane diterpenoids, labda-7,12(E),14-triene-17-oic acid (1) and labda-12(Z),14,17-triene-18-oic acid (2), C20H30O2, have been isolated from Croton oblongifolius. Both 1 and 2 crystallized in the monoclinic system, space group C2, with cell dimensions of a = 21.912(1) A, b = 7.4002(4) A, c = 11.5079(7) A, β = 101.999(1)o and a = 21.308(2) A, b = 11.9067(9) A, c = 7.5606(6) A, β = 100.763(1)o, respectively. Compound 1, a rare example of carboxylic group bound to a cyclohexene ring, forms an infinite intermolecular hydrogen-bonded polymer [O1 ⋅ ⋅ ⋅ O2(−x + 1/2, y + 1/2, −z + 2) 2.697(2) A], whereas molecules of compound 2 are linked to form an asymmetric hydrogen-bonded dimer [O1 ⋅ ⋅ ⋅ O2(−x, y, −z) 2.657(3) A].