An optically active cyclopropene as a mechanistic probe in cyclopropene photochemistry

1977 ◽  
Vol 55 (6) ◽  
pp. 979-985 ◽  
Author(s):  
James A. Pincock ◽  
Alexios A. Moutsokapas
Keyword(s):  
Triplet State ◽  
Optically Active ◽  
Excited Singlet ◽  
Mechanistic Probe

The photochemistry of methyl 1-methyl-2-phenylcyclopropene-3-carboxylate has been examined in both the racemic and optically active forms. In the excited singlet the cyclopropene is converted to 2-methoxy-5-methyl-4-phenylfuran whereas the triplet state dimerizes to a tricyclohexane derivative. Experiments with optically active cyclopropene ester demonstrate that photochemical racemization occurs about 2.5 times as fast as conversion to the furan product indicating that there is an intermediate vinyl carbene on the singlet surface. No racemization is observed in the triplet state.

Photolysis of ketene. I

1968 ◽  
Vol 46 (14) ◽  
pp. 2353-2360 ◽  
Author(s):  
A. N. Strachan ◽  
D. E. Thornton
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet State ◽  
Inert Gases ◽  
Inert Gas ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Increasing Temperature

Ketene has been photolyzed at 3660 and 3130 Å both alone and in the presence of the inert gases C4F8 and SF6. The quantum yield of carbon monoxide has been determined at both wavelengths as a function of pressure and temperature. At 3660 Å the quantum yield decreases with increasing pressure but increases with increasing temperature. At 3130 Å the quantum yield with ketene alone remains 2.0 at both 37 and 100 °C at pressures up to 250 mm. At higher pressures of ketene or with added inert gas the quantum yield decreases with increasing pressure. The results are interpreted in terms of a mechanism in which intersystem crossing from the excited singlet state to the triplet state occurs at both wavelengths, and collisional deactivation of the excited singlet state by ketene is single stage at 3660 Å but multistage at 3130 Å.

Triplet state quantum yields for some arom atic hydrocarbons and xanthene dyes in dilute solution

1967 ◽  
Vol 299 (1458) ◽  
pp. 348-353 ◽  
Keyword(s):  
Triplet State ◽  
State Formation ◽  
Heavy Atom ◽  
Quantum Yields ◽  
Triplet States ◽  
Dilute Solution ◽  
Perturbation Techniques ◽  
Excited Singlet ◽  
Xanthene Dyes ◽  
Extinction Coefficients

Quantum yields of triplet state formation and extinction coefficients of the triplet states have been determined by direct depletion methods for solutions of anthracene, phenanthrene, 1,2,5,6-dibenzanthracene, fluorescein, dibromofluorescein, eosin and erythrosin. The values obtained for the hydrocarbons are in reasonable agreement with those obtained by other workers using energy transfer and heavy atom perturbation techniques. In all cases which we have studied, the sum of the quantum yields of fluorescence and triplet state formation is equal to unity within the limits of experimental error, showing that radiationless transfer from the excited singlet to the ground state is negligible.

Comparison of resonance cars spectra of chrysene in the lowest excited singlet and triplet state

1980 ◽  
Vol 73 (1) ◽  
pp. 175-177 ◽  
Author(s):  
H.-J. Weigmann ◽  
K. Lenz ◽  
A. Lau ◽  
M. Pfeiffer ◽  
W. Werncke
Keyword(s):  
Triplet State ◽  
Excited Singlet
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