摘要:

Various types of topochemical [2+2] photocycloaddition behaviors are described focusing on the recent results of a series of alkyl pyridylethenylcinnamate derivatives. Highly stereo regular polymerization and “absolute” asymmetric synthesis were achieved by using crystal-lattice controlled [2+2] photocyclo-additions. Product control by employing co-crystallization of solvent molecules and a low temperature photo irradiation technique is demonstrated in the topochemical photoreactions of diolefin molecules. A methodology for the synthesis of highly strained compounds, [2.2]paracyclophane derivatives, in the crystalline state is also described.

ISSN:1058-725X    

DOI:10.1080/10587259208032112

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The two carbonyl groups in 1,8- cyclohexadecanedione (1a) are separated by eight methylene groups on one side and six on the other, thus giving rise to two nonequivalent γ-hydrogen atoms for abstractionviathe Norrish type II reaction. X-ray crystallography reveals that, in the solid state, the γ-hydrogen atom on the longer methylene chain is more favorably situated for abstraction than that on the shorter chain, both in terms of abstraction distance (2.72 Å vs 2.99 Å) and angular relationship. In accord with this analysis, photolysis of diketone 1a in the solid state leads exclusively to a single cyclobutanol diastereomer resulting from abstraction of the stereo electronically favored hydrogen atom. In contrast, irradiation of compound 1a in solution affords a complex mixture of all six possible type II cyclization and cleavage products resulting from non-selective abstraction of both γ-hydrogens. The solid state results are interpreted in terms of the crystallographically determined conformation of diketone 1a, which favors stereoselective cyclization over cleavage.

ISSN:1058-725X    

DOI:10.1080/10587259208032113

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We have studied bimolecular photoreactions between (a) 1-methy1-2,4,5-triphenylimidazole and benzophenones, (b) indole and naphthalene or phenanthrene, and (c) 6-cyano-1,3-dimethyluracil and acenaphthylene or phenanthrene, both in the solution and solid phases. Different products (or product distributions) were obtained in the two phases and the reactions were usually more selective in the solid state than in solution.

ISSN:1058-725X    

DOI:10.1080/10587259208032114

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In earlier work (1–3) we tried to establish correlations between molecular size or shape and crystal structure descriptors for organic crystals containing C,H,N and O atoms, without fully developed hydrogen bonds. Samples of 391 hydrocarbon, 590 oxohydrocarbon, and 458 azahydrocarbon crystal structures, retrieved from the Cambridge Structural Database (4), were used. Of course size and shape alone are important for crystals which are built under the action of purely isotropic, or at least scarcely directional, intermolecular forces; ideally, for non polar substances like hydrocarbons. In fact, in crystals containing O or N atoms, a rather large number of C-H… X (X=O or N) attractive interactions were detected through a search of the spurious repulsions that result from their treatment as pure van der Waals contacts. These interactions are now recognized as weak hydrogen bonds, and also display some angular selectivity: Figure 1 shows that C=O… H angles for carbonyl compounds cluster in the 110–140° range for R(O… H) < 3Å.

ISSN:1058-725X    

DOI:10.1080/10587259208032115

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

X-ray oscillation photographs reveal both diffuse and discrete scattering for alkanone guest molecules within inclusion compounds of 5-undecanonehrea grown from methanol. Guest molecules that give rise to diffuse scattering are ordered only along the channel axis, whereas those guest substructures that give rise to discrete scattering are ordered in three dimensions. Precession photographs and diffractometry show that within domains containing three dimensionally ordered guests, the offset (denoted δg) between the heights of guest molecules in adjacent channels is exactly zero. These guests therefore share overall hexagonal symmetry with the host, as do a large number ofn-alkanones of varying chain length and symmetry properties. Although side by side ordering optimizes dipole-dipole interactions between alkanones in adjacent channels, the large inter channel distance (8.22Å) and the lack of symmetry in 5-undecanone suggest that other factors could influence guest molecule ordering. A careful diffractomemc study from -24°C to +20°C reveals that 5-undecanone/urea is a commensurate system in which the periodic repeats of the host and guest structures follow the relationship 3ch= 2cg. Both dipole-dipole interactions and commensurability of host and guest are thought to contribute to the ordering of guests in this system.

ISSN:1058-725X    

DOI:10.1080/10587259208032116

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The hydrogen bonding interactions of 6:1 cyclamers composed of 1,3-diones in their enol forms and both fluoro- and perfluorobenzene have been examined by the AM1 molecular orbital method. These structures are analogous to those found experimentally in cocrystals of benzene with these diones. The fluorobenzne host-guest complexes are predicted to be stable, but the perfluorobenzene complexes are not. However, it is unlikely that the stabilization of fluorobenzene in the cocrystal would be greater than the interaction between molecules of fluorobenzene in solution.

ISSN:1058-725X    

DOI:10.1080/10587259208032117

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Cholic acid affords polymorphic crystal forms. The molecular assemblies have a guest-dependent bilayered structure. Insertion and replacement of guest molecules between the layers took place with retention of the crystalline state. The intercalation phenomena give us an opportunity to understand a structure-property relationships in organic solids.

ISSN:1058-725X    

DOI:10.1080/10587259208032118

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A new host series for crystalline inclusion complexes, which were designed on the basis of linearly condensed polythiophenes as a rigid backbone, were prepared. The host guest (DMSO) composition and the conformation of the host molecule in the inclusion crystals exhibited a novel dependence on the number of the condensed thiophene rings.

ISSN:1058-725X    

DOI:10.1080/10587259208032119

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Triphenylacetic acid is isomorphous with the published structure of triphenylchloromethane (I). It crystallizes in the trigonal system, space group P3, witha=b=14.105(3)Å,c=13.121(2)ÅV=2261(1)Å3,Z=6 at 175K. The structure was solved by direct methods and refined toR(F0)=0.062. We determined the structures for two triclinic polymorphs of triphenylchloromethane,IIandIII. The three forms were obtained from pentane evaporated at room temperature. PhasesIandIIIwere isolated from particular solvent systems. Crystal data (II): triclinic system, space group P3, witha=13.028(1)Å,b=13.559(2)Å,c=13.969(3)Å, α=117.67(1)°, β=92.67(1)°, γ=91.43(1)°,V=2179.9Å3,Z=6 at 228K. The structure was solved by direct methods and refined toR(F0)=0.045. Crystal data (III): triclinic system, space group P3, witha=14.1562(4)Å,b=21.3190(7)Å,c=13.0654(5)Å, α=99.92(3)°, β=92.68(3)°, γ=106.15(2)°,V=3712(2)Å3,Z=10 at 248K. The structure was solved by direct methods and refined toR(Fo)=0.064. A batch of crystals from pentane showed three peaks in the DSC thermogram at 99°C (III), 108°C (II), and 111°C (I). PhaseIIImelts without being transformed to phaseIIor phaseI. PhaseIIcould not be isolated for calorimetric studies.

ISSN:1058-725X    

DOI:10.1080/10587259208032120

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The strength of the transannular N→B interaction in the substituted cycloboronate 1,3,5-trioxa-6,8-diaza-2,4-diboracyclooctane1can be controlled both by varying the Lewis basicity of the ring nitrogen atoms and by modifying the steric factors dependent on the nature of the nitrogen substituents (by changing R). Examples of the structural types displaying varying degrees of transannular bonding have been prepared and characterized by X-ray analysis. A simple six-membered cycloboronate structure4containing one boron atom is formed when the basicity of the aminal nitrogen atom is reduced and the boronic acid residue is sterically hindered [R = C(CH3)2CN and Ar = 2,4,6-(CH3)3C6H2]. The bicyclo[3.3.0]octane structure3is obtained when R = simple alkyl and Ar = phenyl. A structural type between1and2is realized when R = C(CH3)2CN and Ar = Ph.

ISSN:1058-725X    

DOI:10.1080/10587259208032121

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor