385. Topochemistry. Part III. The crystal chemistry of some trans-cinnamic acids

Abstract

The crystal structures of substituted cinnamic acids can be divided into three groups (a,P,y) according to their cell dimensions. These structure groups coincide with the three types of photochemical behaviour reported in Part I1 : dimerisation to (1) a-truxillic or (2) @-truxinic acid, and (3) lightst ability.X-Ray analyses of members of the a-and @-classes indicate that in these photo-active structures the conformation of the dimers can be correlated with the packing arrangement of nearest-neighbours in the monomer lattice : dimerisation takes place a t >C=c( separations of 3-6-4-1 and preserves in the (molecular) symmetry of the cyclobutane derivative the (crystallographic) symmetry element relating nearest-neighbour monomers. The separation between y = C < of 4-7-51 in the light-stable y-structures is interpreted as too long for dimerisation to be possible.

Aspects of spontaneous separation of enantiomers in two- and three-dimensional crystals

“…This concept was taken advantage of to perform asymmetric synthesis within enantiomorphous mixed crystals of cinnamide/cinnamic acid 28 and cinnamide/␤-thienylacrylamide, 29 via solid-state dimerization 30 between host and guest molecules, yielding chiral cyclobutane products.…”

Fotoquímica de chalconas fluoradas no estado sólido

“…Durante a primeira parte do século XX, vários pesquisadores iniciaram a sistematização dos resultados da dimerização no estado cristalino a partir do estudo da fotoquímica de ácido cinâmico e derivados. Somente após os anos 60, com o aparecimento de técnicas de difração de raios-X, foi possível a Schmidt e colaboradores avançarem no entendimento dos processos de fotodimerização no estado cristalino, para os quais foram estabelcidas regras importantes, denominadas de regras topológicas [5][6][7][8] . De acordo com os princípios topoquímicos, as reações no estado sólido se processam com um mínimo de movimento atômico, o que implica que só serão esperadas reações de dimerização em compostos apresentando ligações olefínicas se as ligações duplas estiverem paralelas e orientadas de forma correta sob o ponto de vista estereoquímico.…”

Organic Solid-State Reactions

“…The synthesis of [7]-ladderanes according to this technique appears, therefore, unlikely. It should, however, be tried to synthesize [5] of Scheme 20 in a solid ethanol matrix at 10 K yielded the elusive diazetidine (thermal reversion at room temperature) with four nitrogen atoms in series, but only biphotonically with multi megawatts per square centimeter laser pulses at 248 nm [82c]. Similarly, the internal hetero [4 + 2]-cycloaddition of the highly photoresistant illuminant and optical brightener cyano-triazole in Scheme 20 required multi megawatts per square centimeter pulsed biphotonic laser irradiation (308 nm) in an ethanol glass at 56 K to give the thermally labile pentacycle [82c].…”

“…The photodicarbonylative synthesis of tetra-t-butyl-tetrahedrane uses the solid state of the 2,2-dimethyl-n-pentane (8 : 3) glass with embedded tetra-t-butyl-cyclopentadienone at −196 ∘ C. The irradiation with low-pressure Hg lamps (253.7 nm) for 77 h followed by chromatography provides the tetra-t-butyl-tetrahedrane (35% yield, mp 135 ∘ C with decomposition). It forms via the intermediate tetra-t-butyl-cyclobutadiene [176a] or tetra-t-butyl-tricyclo[5.0 2,4 .0 3,5 ] pentanone-1 [176b] photolysis. Promising biphotonic tetrahedrane syntheses by excimer-laser irradiation in MTHF or EE matrix at 93 K with Kaupp [82c] using less crowded, tri-t-butyl-or tetramethyl-cyclopentadienones were not pursued after the monophotonic success with the tetra-t-butyl system.…”

“…The term topochemistry of Kohlschütter [4] describes an alkaline hydrolysis of a KAl(SO 4 ) 2 crystal to Al(OH) 3 gel. It was copied in 1964 to more than strangely mean that molecular and atomic movements within crystals were restricted to <2.7 Å distances [5]. Hype developed with this obviously redefined hypothesis of "topochemistry."…”