The crystal structures of p-chloro-trans-cinnamic acid (I) and p-(p-chloropheny1)propionic acid (11) have been determined from X-ray diffractometer data. Both molecules are approximately planar and the crystal packing is similar when viewed down the b axis. Crystals of both compounds are monoclinic, space group P2,la. with Z = 4 in a unit cell of dimensions; for (I) : a = 32.813(9), b = 3.890(1), c = 6.538 (1) 8, p = 95.94(2)"; and for (11) : a = 30.024(6), b = 5.071 (1). c = 5,728(1) 8, p = 98-70(1)". The structures were refined by full-matrix least-squares to R 0.059 [(I), 11 60 observed reflections] and 0.052 [(11), 1372 observed reflections].The cinnamic acid crystallizes in the p-form with head-to-head packing so that the ethylenic bonds lie near each other, thus explaining why a photo-dimerization to a p-truxinic acid can occur. There is disorder of the carboxy hydrogen atom in (I) but it is localized in (11).THE structures of a cinnamic acid (I) and its hydrogenated derivative (11) were originally studied in this laboratory (1 1 (III by Patterson and Clark1 but atomic parameters were never published? only Fourier maps in projection. The cinnamic acids are of great interest because a solid-state photoreaction is possible in the crystal, and a cyclobutanedicarboxylic acid result^.^^^ The tram-cinnamic acids with ring substituents crystallize in one or more of three possible types: cc, p, or y. They may be distinguished by the product of their photoreactions (see Scheme).H02C Ph' o! 1 head-tl H02C -tail 1 p ( head-to-head 1 ,C 02 H Ph' KU 1 I cct r uxillic 1

Gramine was isolated from the leaves of Acer saccharinum L., JV,M-dimethyl-5-methoxytryptamine from the bark of Dictyoloma incanescens D.C., bufotenine from the seeds of Piptadenia colubrina Benth., and N, V-dimethyltryptamine from the roots of Mimosa hostilis Benth.Several plants which we have studied recently have, by coincidence, yielded indole alkaloids of simple structure. Four of these are described in the present paper.

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The presence of a bay-region methyl group in carcinogenic polycyclic aromatic hydrocarbons leads to considerable distortion in the molecule. This is illustrated in the structures, obtained by X-ray diffraction techniques, of 5,12- and 5,6-dimethylchrysene. The molecular distortions result from steric requirements, such as that the minimum H...H distance is 1.8 A and the minimum C...C distance is 2.90 A; distortions to accommodate these requirements may be both in-plane (by increasing the angles at carbon atoms in the bay-region from 120 degrees to approximately 124 degrees) and out-of-plane by torsion about certain bonds in the bay-region. It is shown that more in-plane distortions are found for 5-methylchrysene derivatives than for methylbenz[a]anthracene derivatives and this, it is suggested, results from the nature of the flexibility of the chrysene compared with the benz[a]anthracene fragment at the bay-region.

Dibenzylidene ketones are shown to form stoicheometric complexes with 1,3,5-trinitrobenzene wherein the molecular components are held together with C-He-0 hydrogen bonds. 7 This is true if the two-component entity is treated as a supermolecule. If, on the other hand, the entire crystal is treated as a supermolecule, many recognition sites will, in the limit, be directed outwards because each molecule is surrounded by many others.