Irradiation mixed crystals

A dimer portion can be prepared exclusively from the mixed crystal by controlling the wavelength of irradiating light (>410nm) and isolated by preparative thin-layer chromatography. The high-performance liquid chro-... 

Shortly after, Doetschman and Hutchison reported the first example of a reactive carbene in the crystalline solid state, by preparing diphenylcarbene from diphenyldi-azomethane in mixed crystals with 1,1-diphenylethylene 84 (Scheme 7.23). When the mixed crystals were irradiated, carbene 85 was detected by electron paramagnetic resonance (EPR) and the disappearance of the signal was monitored to determine its kinetic behavior. Two reactions were shown to take place under topochemical... 

Radical formation in a mixed crystal system of cytosine monohydrate doped with small amounts of thiocytosine (ca. 0.5%) was investigated on order to gain insight into hole transfer in a well-defined crystalline system.31 Also of interest was whether the protonation state of the thiocytosine radical(s) was the same as that of the cystosine radical(s). Crystals were X-irradiated (ca. 30 kGy) and ESR and ENDOR spectra recorded at ca. 15 K. After irradiation, many types of free radicals were formed. Among these, the low field resonance from a sulfur centered radical (42), with g-tensor (2.132, 2.004, 2.002), was clearly visible. Radical 42 constituted approximately 10% of the total cohort of radicals formed in the crystal and is apparently the only sulfur-centred radical observed in this experiment. Six weakly coupled protons were observed, two of which are shown... 

X-ray irradiation of single crystals of anthracene peroxide (33, Scheme 23) gives mixed crystals of anthraquinone (34) and anthrone (35), with retention of the shape of the original crystal [118]. This transformation has been monitored by... 

Achiral butadienes 143 and 144 formed chiral mixed crystals (substitutional solid solutions) of space group P2 l lx by cooling the melts of both components or on crystallization from ethanol solution. A single large-sized mixed crystal 143144 was pulverized and irradiated resulting in [2 + 2] photocycloaddition, thereby giving the optically active heterodimers 145 as well as the achiral homodi-... 

If these mixed crystals are irradiated, however, at 400 nm where only the anthryl groups absorb a small photosensitation can be observed. Neither of the two models have been fully established experimentally to date. 

Figure 6. A change with time of H- and D-atom concentrations (in arbitrary units) after cutoff of /-irradiation of mixed crystal Dj-HD (15.6 mol %) at 4.2 K determined by the reaction HD -I- D- H -I- Dj.

Asymmetric Photodecarboxylations - Acridine and diphenylacetic acid are both achiral molecules, but despite this fact the two compounds self-assemble to form dextro- and /aevo-rotatory chiral mixed crystals from acetonitrile solution. Irradiation of either the dextro- or /aevo-rotating crystals causes a stereospecific decarboxylating condensation, which yields excess of (+)- or (—)-(68), respectively, with about 35% ee. ... 

This is the first example of topochemical copolymerization in which the copolymer formation is completely substantiated on the basis of direct evidence from spectroscopic and preparative techniques. The same mixed crystal is also obtained through crystal-crystal contact by simple grinding of two monomers with an amalgamator. Irradiation of the resulting mixed crystal gives a crystalline linear copolymer (rjjnh = 0.6 dlg" ) having the same structure. 

Experimental details.716 Grating of a hologram on a single crystal made of 119 was achieved using an He Ne laser (632.8 nm 50 mW) (Special Topic 3.1) for both writing and reading. Crystallographic data were obtained for monomer, dimer and mixed crystals that were isolated after different irradiation times. 

The mixed crystals of lb (46 mg, 0.2 mmol), 2 (39 mg, 0.4 mmol), and xanthone (10 mg, 0.05 mmol) prepared by crystallization were ground for 10 min and sandwiched between two Pyrex glass plates and irradiated for 24 h under nitrogen atmosphere at room temperature. The reaction solid was washed with CHCI3 (5 mL) to remove the starting materials and the resulting solid was fdtered to give 3b (40 mg, 52% yield), which was recrystallized from MeCN. 

Similarly, a heterodimer was formed as a major product upon irradiation of mixed crystals which had been prepared by cocrystallization of Cl- and Me-substituted 2-benzyl-5-benzylidenecyclopentanones (Scheme 2) [24]. As a consequence of cocrystallization, the photoinert chloro compound (X = Br, Y = Cl) has been induced to adopt both the crystal structure and molecular conformation of the photoreactive methyl derivative (X = Br, Y = Me). 

On the other hand, cocrystallization or grinding together of 12a and S-ethyl 4-[2-(2-pyrazinyl)ethenyl]thiocinnamate (12b) forms a 45 55 molar mixed crystal (a solid solution), which upon UV irradiation gave a crystalline random copolymer (Scheme 10) [14]. 

Ethyl and propyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamates (13a and 13b) also form a mixed crystal of various compositions. Irradiation of mixed crystals having 70 30 to 5 95 13a/13b afforded unsymmetric monocyclic dimers 14 and tricyclic [2.2]paracyclophane-type dimers 15 quantitatively, whereas each homocrystal gave the corresponding symmetric dimer 16 (Scheme 11) [15,16]. 

Asymmetric Proton Transferfrom Alkane Radical Cations to Alkanes An Experimental Study in y-Irradiated Mixed Alkane Crystals... 

The molecular interpretation is again based on the crystal structure of the starting material (Figure 22). The molecules 13 are almost perpendicular on (100) (front), perpendicular on (010) (top), and flat on (001) (left). There is enough room on both sides to partially rotate for photodimerization in the orientations found and to move upward [010], This does form volcanoes with pillars and leaves craters (Figure 216). Those features must consist of mixed crystals out of 13 with 14, 15, and 16 admixed. From there mixed phases rich in products will be formed upon continuation of the irradiation forming the features in Figure 21c. However, the details of the secondary processes cannot yet be assessed. Local spectroscopy measurements (Sections IX and X) will have to look at the distribution of chemical compositions and nanometric Laue facilities (which are yet to be developed) at the local crystallinity. However, for the initial photochemical reaction it has... 

Koshima and his co-workers have studied the reactivity of co-crystals of acridine and 1-phenyIpropionic acid. This work is analogous to that described last year for the reactivity of acridine with diphenylacetic acid. The present study is summarized in Scheme 2. Again irradiation brings about decarboxylation of the propionic acid and the resulting radical bonds to the acridine. The yields of the compounds and their optical activities are shown below the appropriate structures. When acridine and the acid are irradiated in acetonitrile solution racemic (71) is formed along with the dimer (72). A review of the photochemistry in two-component and mixed crystals systems has been published. ... 

An Interesting example of the role of the exclmer as Intermediate comes from the system l-(2,6-dlchlorophenyl)-4-phenylbuta-dlene. Irradiation of a mixed crystal of this compound together with the corresponding 4-thlenyl derivative gives dimers by a (2n + 2tr) photocycloaddltlon reaction. The products are homo-dlmers of the phenyl and of the thienyl derivatives, and hetero-dimers. The two heterodimers formed are enantiomeric and, because the crystal Is of chiral structure, they are formed In different yields (54). Thus Irradiation of a single crystal has been found (55) to lead to a 70% enantiomeric excess. 

Whereas most reactions of singlet arenes and aryl olefins with secondary amines result in N-H addition, there are exceptions to this generalization. Cookson et al. reported that irradiation of 1-phenylcyclohexene in isopropylamine yielded a mixture of N-H and a-C-H adducts. Gilbert and co-workers ° found that the reaction of benzene with dimethylamine yields N-H adducts, whereas pyridine reacts with diethylamine to yield the substitution product 11, which presumably is formed by aromatization of the a-C-H adduct. Irradiation of stilbene and indole in mixed crystals yields both N-H and C-H adducts, product ratios being dependent upon the reactant ratio. Investigation of the reactions of 9-cyanophenanthrene with primary and secondary... 

Phosphorus. Silicon. The reaction of PH3 with recoil P atoms (from the irradiation of PH3 with thermal neutrons) yields considerable quantities of PH3 via H abstraction details are given in Section 1.3.1.5.1.5, p. 215. The measured relative efficiency of the H abstraction in irradiated PH3 and PF3 was used to consider the likely reaction mechanism in [65]. A reaction of PH3 (from adding Ca3P2 to the solution) with recoil was also considered in order to explain the formation of 30 10% of when KCl crystals [66] or KCl-CaCl2 mixed crystals [67, 68] were irradiated with protons (635 to 660 MeV) and dissolved in water. The H abstraction between and PH3 might have occurred at the surface of the dissolving crystals however, a formation of PH by secondary reactions was also considered to be conceivable [66 to 68]. 

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