Regioselectivity in \alpha-Cleavage Reactions: Arylalkylcyclopropenethiones

Photoreactions of several arylalkylcyclopropenethiones (1b-e) have been investigated. The products formed have been rationalized on the basis of \alpha-cleavage as the primary photoprocess. The photochemical \alpha-cleavage is presumed to originate from the lowest excited $n\pi^*$ riplet state. A ioselective \alpha-cleavage reaction has been observed and this unusual regioselectivity is explained on the basis of close approach of the ground-state energy surface of the diradical/carbene, the primary intermediates, to the excited triplet-state surface of cyclopropenethiones. Reactions originating from both triplet and singlet thioketene carbene have been observed upon photolysis of arylalkylcyclopropenethiones

Regioselectivity in α - cleavage reactions: arylalkylcyclopropenethiones

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Solid-state Photochemistry of Nitro Compounds: Structure-Reactivity Correlations

The molecu lar structures of 1 -t - butyl- 3,5-dimethyl-2,4,6- trinitrobenzene, 1 - t - butyl-3,4,5- trimethyl - 2'6 -dinitrobenzene, and 1 -t-butyl-4-acetyl-3,5-dimethyl-,6-dinitrobenzene have been determined by single-crystal X-ray analyses with a view to establishing a structure-reactivity relationship in the photochemical intramolecular hydrogen-abstraction process in the solid state. The reactivity of these aromatic nitro compounds in the solid state has been rationalized in terms of relevant intramolecular geometrical parameters as well as intermolecular packing considerations

Structure-Reactivity Correlation of Photochemical Reactions in Organic Crystals: Intramolecular Hydrogen Abstraction in an Aromatic Nitro Compound

The molecular structure of 1,4- bis- (2-chloro-1 ,l -dimethylethyl) -2-nitrobenzene has been determined by X-ray crystallography. The single-crystal X-ray investigation, R=0.067, showed the compound to be monoclinic, space group $P2_1$, a=6.388(2), b = 13.848(4), $c=8.578(3) \AA$, $\beta=94.05(3)^0$. Structural analysis of 2-nitro-t-butylbenzenes which undergo intramolecular hydrogen abstraction in the solid state upon irradiation by U.V. light was carried out in connection with structure-reactivity correlation studies and X-ray crystallographic investigations. On the basis of intramolecular geometry and molecular packing considerations, it has been possible to identify the hydrogen atom abstracted preferentially in crystals of this compound. The benzene ring is found to exist in the boat conformation

Photodimerization of coumarins in the solid state

Photochemical dimerization of 7-methoxycoumarin occurs in the solid state to give high yields of a syn-head-to-tail dimer although the potentially reactive double bonds are not favourably oriented in the crystal of the monomer

Chloride sensing via suppression of excited state intramolecular proton transfer in squaramides

A new design strategy is described for chloride ion sensors based on suppression of excited state intramolecular proton transfer in squaramides as a fluorescence "turn on" mechanism