scholarly journals Demethylation of an Allene Bearing Two Dimethoxythioxanthene Groups by Oxidation via a Vinyl Cation Intermediate

2010 ◽  
Vol 63 (12) ◽  
pp. 1638 ◽  
Author(s):  
Torahiko Yamaguchi ◽  
Shin-ichi Fuku-en ◽  
Shun Sugawara ◽  
Satoshi Kojima ◽  
Yohsuke Yamamoto
Keyword(s):  
Triplet State ◽  
Methoxy Group ◽  
Singlet State ◽  
Hydrogen Abstraction ◽  
Conjugate Acid ◽  
Vinyl Cation ◽  
Triplet Carbene

With the objective of preparing an isolable triplet carbene, we have carried out the oxidation of an allenic compound bearing two thioxanthene moieties (5). Relatively weak oxidants such as Ph3C+BF4 – gave 8, which is the conjugate acid of 5, as a result of a one-electron oxidation followed by hydrogen abstraction, whereas relatively strong oxidants such as SbCl5 furnished a dicationic ketal (9) as a consequence of oxidation and demethylation. Computations on the supposed dicationic intermediate suggest that the singlet state is more stable than the triplet state by 6.7 kcal mol–1 and that the reason for this peculiarity is because the singlet state is essentially a vinyl cation stabilized by a coordinating methoxy group.

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.

Sulfamoyl nitrenes: singlet or triplet ground state?

2018 ◽  
Vol 54 (48) ◽  
pp. 6136-6139 ◽  
Author(s):  
Yan Lu ◽  
Hongmin Li ◽  
Manabu Abe ◽  
Didier Bégué ◽  
Huabin Wan ◽  
...  
Keyword(s):  
Triplet State ◽  
Ground State ◽  
Singlet State ◽  
Minimum Energy ◽  
Closed Shell ◽  
Low Energy ◽  
Energy Minimum ◽  
Triplet Ground State ◽  
Crossing Point

Two prototypical sulfamoyl nitrenes R2NS(O)2–N (R = H and Me) in the triplet state were generated via the closed-shell singlet state by passing a low-energy minimum energy crossing point (MECP).

Reactions of trifluoromethyl radicals. V. Hydrogen abstraction from methyl acetate and methyl (2H3)Acetate

1980 ◽  
Vol 33 (7) ◽  
pp. 1437
Author(s):  
NL Arthur ◽  
PJ Newitt
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Methoxy Group ◽  
Methyl Acetate ◽  
Kinetic Isotope Effect ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Temperature Range ◽  
Kinetic Isotope ◽  
Acetyl Group

Hydrogen abstraction by CF3 radicals from CH3COOCH3 and CD3COOCH3 has been studied in the temperature range 78-242°, and data have been obtained for the reactions: CF3 + CH3COOCH3 → CF3H+[C3H5O2] �������������(3) CF3 + CH3COOCH3 → CF3H+CH2COOCH3������������ (4) CF3 + CD3COOCH3 → CF3D+CD2COOCH3������������ (6) CF3 + CD3COOCH3 → CF3H+CD3COOCH2������������ (7) The corresponding rate constants, based on the value of 1013.36 cm3 mol-1 S-1 for the recombination of CF3 radicals, are given by (k in cm3 mol-1 s-1 and E in J mol-1): logk3 = (11.52�0.05)-(35430�380)/19.145T ���� (3)logk4 = (11.19�0.07)-(34680�550)/19.145T ���� (4)logk6 = (11.34�0.06)-(46490�490)/19.145T ���� (6)logk7 = (11.26�0.05)-(36440�400)/19.145T ���� (7)At 400 K, 59% of abstraction occurs from the acetyl group, and 41 % from the methoxy group. The kinetic isotope effect at 400 K for attack on the acetyl group is 25, due mainly to a difference in activation energies.

Study of Chemically Induced Dynamic Nuclear Polarization of Aliphatic Aldehydes in D2O and other Solvents

1975 ◽  
Vol 53 (17) ◽  
pp. 2548-2557 ◽  
Author(s):  
Holger E. Chen ◽  
Michael Cocivera ◽  
Shiv P. Vaish
Keyword(s):  
Triplet State ◽  
Dynamic Nuclear Polarization ◽  
Nuclear Polarization ◽  
Hydrogen Abstraction ◽  
The Other ◽  
Excited Triplet State ◽  
Relative Importance ◽  
Aliphatic Aldehydes ◽  
Excited Triplet ◽  
Chemically Induced

The chemically induced dynamic nuclear polarization arising from irradiation of aliphatic aldehydes in D2O and various other solvents is reported. The aldehydes included acetaldehyde, propionaldehyde, isobutyraldehyde, and pivalaldehyde, and the solvents were benzene, acetonitrile, cyclohexane, methylcyclohexane, perfluoromethylcyclohexane, D2O, and D2O/acetonitrile. For propionaldehyde, the variation of c.i.d.n.p. with solvent can be explained by a variation of the relative importance of α-cleavage vs. hydrogen abstraction which occur via an excited triplet state. In addition, when D2O is the solvent, the c.i.d.n.p. provides information about secondary radical reactions not observed in the other solvents. For the other aldehydes, the nature of the solvent does not seem to affect the relative importance of α-cleavage vs. hydrogen abstraction. Acetaldehyde undergoes hydrogen abstraction whereas isobutyraldehyde and pivalaldehyde undgero α-cleavage via an excited triplet state.

Photoreactions of Simple Halonaphthalenes in Solution

1975 ◽  
Vol 53 (5) ◽  
pp. 688-693 ◽  
Author(s):  
Luis Octavio Ruzo ◽  
Nigel J. Bunce ◽  
S. Safe
Keyword(s):  
Electron Transfer ◽  
Triplet State ◽  
Singlet State ◽  
Abnormal Behavior ◽  
Quantum Yields ◽  
Transfer Processes ◽  
Electron Transfer Processes

The photolysis products and reaction quantum yields from a number of simple halonaphthalenes have been determined. Fluoronaphthalenes react from a singlet state to yield substitution products in nucleophilic solvents. Chloronaphthalenes and 1-bromonaphthalene afford mainly radical products (naphthalene and binaphthyls) through a triplet state, though some photonucleophilic substitution occurs with chloronaphthalene. Attempts at quenching lead to abnormal behavior, in that enhanced quantum yields for reaction are found with several potential triplet quenchers. Electron transfer processes are proposed to rationalize the observed products.

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