Monitoring structural transformations in crystals. 5. A topotactic [2 + 2]-photodimerization reaction

Abstract

The structural changes in a crystal of 5-benzylidene-2-(4-chlorobenzyl)cyclopentanone during [2 + 2]-photodimerization were monitored by means of X-ray diffraction. It was observed that the monomers moved gradually from the position occupied in the crystal at the initial stage of the photoreaction and the dimers moved towards the position assumed at the final step. The movements of the molecules possess a rotational component. Moreover, with the progress of the phototransformation the monomers in the reacting pair gradually move closer and change their relative orientation to resemble more the product molecule. The behaviour of the molecules and also the variation of the cell constants for the studied compound were compared with data for 5-benzylidene-2-benzylcyclopentanone.

Monitoring structural transformations in crystals. 8. Monitoring molecules and a reaction center during a solid-state Yang photocyclization

“…In the case of the [2 + 2] photodimerization of 2-benzyl-5-benzylidenecyclopentanone, a small increase in unit-cell volume was observed during a short initial period of time, which was then followed by a continuous decrease (Nakanishi et al, 1980(Nakanishi et al, , 1981. For 5-benzylidene-2-(4-chlorobenzyl)cyclopentanone, a volume decrease from the beginning of the photodimerization could be seen (Turowska-Tyrk, 2003) and for 5-benzylidene-2-(4-bromobenzyl)cyclopentanone the unit-cell volume was constant during the entire reaction (Nakanishi et al, 1981). It should be emphasized that Fig.…”

“…A variety of techniques have been applied to studies in this field (Boldyreva, 1999) and among them X-ray structure analysis is one of the most effective. In recent years, papers on monitoring structural changes in crystals during photochemical reactions by means of X-ray structure analysis have started to appear (Fernandes & Levendis, 2004;Ohba & Ito, 2003;Turowska-Tyrk, 2001, 2003, 2004Turowska-Tyrk & Trzop, 2003). The above-mentioned papers deal with intermolecular reactions, namely [2 + 2] and [4 + 4] photodimerizations, and describe the movements of the reactant and product molecules during reaction.…”

Monitoring Photochemical Reactions in Single Crystals by X-ray Diffraction: Practical Aspects

“…The bigger energy, the faster the photochemical reaction is. There are known photochemical reactions which proceed in crystals in a homogeneous way independently of applied energy of UV-vis radiation (but the energy in the range of wavelengths for an absorption spectrum of a given compound) [16,17], including compound 1 studied in this paper. Taking into account the above two features, we can advise the use of a higher energy beam for such compounds.…”

Monitoring Structural Transformations in Crystals. Part 15. Structural Changes in Crystals Caused by UV Radiation Despite the Lack of a Photochemical Reaction

“…Although, the changes are small, they are statistically significant at the 3r level. For chemical reactions the changes in orientation of molecular fragments are usually much bigger, namely even ca 20° [5][6][7][9][10][11].…”

“…In the recent decade the papers on monitoring photochemical reactions in crystals by means of X-ray structure analysis have started to appear in the scientific literature [1][2][3][4][5][6][7][8][9][10][11][12]. Those papers have provided the knowledge on structural changes brought about by photochemical reactions, in particular in a reaction center and positions of molecules in crystals.…”