Linear relation between ultraviolet absorption transition energies and activation energies for thermal isomerization of cyclic olefins

Abstract

We have observed an unusually low-energy ultraviolet transition for bicyclo[2.1.0]pent-2-ene (1), +» 263 nm (e -~440).2•3 This highly strained bicyclic Table I. Ultraviolet Absorption Maxima and Activation Energies for Rearrangement of Cyclic Olefins a, cm'1 £a, Olefin Product Xmax, nm X 10'3 kcalmol'1 300" 33.3 ~22"•6

Structures of two cyclopropylcarbinyl cations

“…thiophene has been assigned to cyclopropene-3-thiocarbaldehyde (11) while the absorptions at 1950 and 1920 cm"1 have been assigned to 2,3-butadienthial (12). We have also photolyzed matrix-isolated C4D4 in which the 1150-cm"1 band remained essentially unchanged in agreement with its assignment to a thiocarbonyl absorption.…”

Phototransposition of carbon atoms in cyclopentadiene. Photoisomerization of cyclopentadiene to tricyclo[2.1.0.02,5]pentane

“…5 The NMR spectrum of 5 is similar to that of 3 except that the ring hydrogens of 5 are deshielded compared to those of 3, most likely a result of the electron withdrawing characteristics of the BF3 moiety. 11 In comparing the -allyl portion of the NMR spectrum of 3 to that of adduct 5 the chemical shifts of Hm (which are cis to ) and of 5 are lower field than those of 3, but the chemical shift of Ha of 5 is about the same as that of 3. If these shifts are due to through space effects then the orientation of the -bound allyl group is such that is pointing toward the complexed ring in each complex.…”

Dewar furan and Dewar thiophene: low-temperature matrix photolysis of furan and thiophene

“…(9) Popov, E. M.; Yakovlev, I. P.; Lubuzh, E. D.; Kogan, G. A. By analogy with the furan system the species responsible for the IR bands at 1150 and 855 cm"1 in the matrix photolysis of thiophene has been assigned to cyclopropene-3-thiocarbaldehyde (11) while the absorptions at 1950 and 1920 cm"1 have been assigned to 2,3-butadienthial (12). We have also photolyzed matrix-isolated C4D4 in which the 1150-cm"1 band remained essentially unchanged in agreement with its assignment to a thiocarbonyl absorption.…”