Structure refinement and molecular packing of p-chloro-trans-cinnamic acid and β-(p-chlorophenyl)propionic acid

Abstract

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

A predicted new type of directional noncovalent interaction

“…These results show that the Group V atoms in some (not all) molecules do indeed have regions of positive electrostatic potential on their outer surfaces, approximately along the extensions of the ROX bonds; see also Figures 1 and 2. The deviations average about 20°, similar to what was observed in the crystallographic data for molecules containing covalently-bonded Group VII atoms or sulfur [17][18][19][20][21][22]. Just as for Groups VI and VII [11][12][13][14][15][16], these positive regions become more likely and stronger as the polarizability of the Group V atom increases and its electronegativity decreases, and as the R group is more electron withdrawing.…”

Topochemical studies. XIII. Structures of 3-bromocinnamic acid and 3-chlorocinnamic acid

“…Photodimerization occurred between these double bonds in both crystals (Kanao, Kashino & Haisa, 1990). The structure of 4-chlorotrans-cinnamic acid, which is similar to (2), has been reported (Glusker, Zacharias & Carrell, 1975).…”

Electrostatic versus Nonelectrostatic Effects in DNA Sequence Discrimination by Divalent Ions Mg2+ and Mn2+

“…The representative structural parameters are summarized in Table 1. Despite the difference between the ionic radii of the Mn 2+ and Mg 2+ ions, 0.80 Å vs 0.65 Å, 71 the length of the metal-base contacts are surprisingly similar in the inner-shell complexes of the two metal ions, with deviations less than 0.07 Å between them. In outer-shell complexes the metal ion has little impact on the distance between the water molecules coordinated directly to the base and the contacting base atoms.…”