Crystal structure analysis of -carotene

The crystals of fl-carotene (C40H56) are monoclinic (P21/c), with the unit-cell dimensions a =7-55, b =9.51, c =24.8 A, and fl = 105.3 °, and with two molecules in the unit cell. The main chain of the molecule tends to be planar, but the chain is curved in its course. The fl-ionone ring is s-cis about the C(7)-C(6) bond, thus interrupting the all-trans structure of the chain. ~Tith photographically registered intensities, refinement of parameters by a least-squares method yielded a discrepancy index, R, of 0.19.