Structure of the β-form of p-formylcinnamic acid, C10H8O3, a photodimerizable crystal

Abstract

Abstract. Mr= 176.2, monoclinic, P2~/n, a = 6.261(2), b=4.825(1), c=27.614(9)A, t= 91.54 (2) ° , V=833.9(4) A 3, Z=4, D_=1.40, D x = 1.403 Mg m -a, 2(Cu Ka) = 1.5418/~', # = 0.88 mm -~, F(000) = 368, T= 298 K. Final R = 0.058 for 1286 unique observed reflexions. Nearly planar molecules are piled up along the short b axis to form a parallel plane-to-plane stack. The b-axial length is just the shortest intermolecular distance between reactive double bonds, indicating that the double bonds related by the b translation would react to form a cyclobutane ring with a mirror symmetry. This conforms with the experimental results, though 4.825 A is the longest separation so far found for solid-state photodimerization. Since the plane-to-plane perpendicular distance between reactive molecules is fairly short (3.888A), it may be concluded that the topochemical behaviour is better understood by 1r-interactions between reactive molecules than by the distances between functional groups.

Structural Aspects of the β‐Polymorph of (E)‐4‐Formylcinnamic Acid: Structure Determination Directly from Powder Diffraction Data and Elucidation of Structural Disorder from Solid‐State NMR

“…± The structure reported here for the b-phase of 1 is completely in line with the structural characteristics reported for other b-phase derivatives of (E)-cinnamic acid. This work has, thus, resolved the structural controversy that has surrounded this material, and establishes that, contrary to a previous report [23], the b-phase of 1 is not structurally anomalous among photoreactive (E)-cinnamic acid crystals. The elucidation of the structural disorder involving the orientation of the formyl group in this material highlights the advantages of tackling such issues by applying both diffraction-based techniques and solid-state NMR spectroscopy in conjunction with one another.…”

“…The crystal structure reported to be the b-phase of 1 was, thus, widely accepted [17] [24 ± 30] as a structurally anomalous b-type (E)-cinnamic acid derivative, with an unprecedentedly (and uniquely) large value for the shortest distance between the CC bonds of potentially reactive molecules. However, it was shown subsequently [31] that the powder X-ray-diffraction pattern calculated using the crystal structure reported [23] to be the b-phase of 1 was actually in agreement with the experimental powder X-raydiffraction pattern of the photostable g-phase, establishing that the crystal structure reported to be the b-phase of 1 was actually that of the g-phase. This structure, therefore, did not represent a structurally anomalous photoreactive (E)-cinnamic acid derivative as the distance (4.825 ä) between the CC bonds of potentially reactive molecules is within the well-established range for g-type crystals.…”

“…The structure of a crystal of 1 grown by vacuum-sublimation techniques has been reported previously [23], and was claimed to represent the crystal structure of the bphase. If this claim were correct, this crystal structure would be of considerable interest among b-type (E)-cinnamic acid derivatives since the shortest distance between the CC bonds of potentially reactive molecules of 1 in this structure is 4.825 ä.…”

[2+2] Photodimerization and photopolymerization of diphenylhexatriene crystals utilizing perfluorophenyl–phenyl stacking interactions

“…Although we cannot, of course, entirely exclude the possibility that the reaction of 3 takes place from some structural defects in the crystal, it may be possible that molecule 3 is irradiated to move in the crystal, making the intermolecular cycloaddition possible. Also for the several exceptions to the 4.2 Å -rule reported up to now, the molecular movements in the excited states (or the dynamic preformation of excimers in the crystal lattice) are suggested [1,10,[35][36][37][38].…”

Solvent‐Free Photosynthesis of Cyclobutanes: Photodimerization of Crystalline Olefins

“…The center-to-center distance for the two sets of dimerizable bonds are 3.8 and 4.4Å, the latter being outside the presently accepted limit. The most unusual case reported so far is p-formylcinnamic acid (4) 33,48 . This crystal, possessing a b-axis of 4.825Å, dimerizes in the solid state to yield a mirror symmetric dimer.…”