Molecular structures and crystal packings of 2-styrylquinoxaline derivatives
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Molecular Structures and Crystal Packings of 2Styrylquinoxaline Derivatives L. G. Kuz’minaa, A. G. Sitinb, E. N. Gulakovac, O. A. Fedorovac, E. Kh. Lermontovaa, and A. V. Churakova a
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia email: [email protected] b Mendeleev University of Chemical Technology of Russia, Miusskaya pl. 9, Moscow, 125047 Russia c Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow, 119991 Russia Received March 16, 2011
Abstract—The crystal and molecular structures of 2styrylquinoxaline derivatives with different substituents in the styryl fragment are determined. The degree of planarity of the molecules studied varies in a very wide range, from 1.7° to 33.5°. In the ethylene fragment, the double bond is essentially localized. The bicycle pedal disordering of the ethylene fragment is found in the crystals of the methoxy and oxyacetyl derivatives of 2styrylquinoxaline. None of the packings contains packing motifs favorable for the photocycloaddition (PCA) reaction with single crystal retention. The crystal packings of these compounds and that of 2(4meth ylstyryl)quinoxaline are characterized by a stacking motif of the headtohead type, which eliminates the possibility of PCA taking place with single crystal retention but is suitable for this reaction in polycrystalline films. The crystal packing of 2(3,4dimethoxystyryl)quinoxaline does not contain elements with stacking interactions. DOI: 10.1134/S1063774511050166
requires the prearrangement of a pair of ethylene groups in the form of a dimer with a parallel orienta tion of double bonds and a distance between them not exceeding 4.2 Å (Schmidt criterion). Only a few of crystal packings can afford such a mutual arrangement of molecules in crystal; therefore, it is important to study their variation in related compounds and make an effort to reveal what factors determine the forma tion of the packing necessary for PCA. With this pur pose, the structures of four styrylheterocycles of the quinoxaline series, in which substituents of different shapes change the external contours of molecules but differ little in the effect that the electron has on the dis tribution of the πelectron density in the ethylene fragment, were studied by Xray diffraction.
INTRODUCTION This work continues our studies of molecular and crystal structures of styrylheterocycles and corre sponding styryl dyes [1–9]. These compounds of the general formulas Het–CH=CH–Ar and [Het+– CH=CH–Ar]X– (where Het is a nitrogencontaining heterocycle and X– is a counterion), respectively, are able to enter into the reaction of [2 + 2] photocycload dition (PCA) under irradiation with light of the visible or near UV region. The PCA reaction affords cyclob utane derivatives, which are difficult to prepare by alternative synthetic procedures. However, the PCA reaction is of interest mainly because it offers the pos sibility
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