Orbital symmetry control in the nitrone-oxaziridine system. Nitrone photostationary states

Splitter, Janet S.; Su, Tah-mun; Ono, Howard; Calvin, Melvin

doi:10.1021/ja00745a057

Cited by 64 publications

(39 citation statements)

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“…19,20 The photoirradiation studies on nitrones can be primarily summarized into 2 important observations; the cis-trans isomerization reactions of nitrones occur thermally or through triplet excited states in presence of photosensitizers, 21,22 while their normal photo-excitation involves singlet excited states which subsequently forms oxaziridines and other photo-products, such as amides. 19,20 The photoirradiation studies on nitrones can be primarily summarized into 2 important observations; the cis-trans isomerization reactions of nitrones occur thermally or through triplet excited states in presence of photosensitizers, 21,22 while their normal photo-excitation involves singlet excited states which subsequently forms oxaziridines and other photo-products, such as amides.…”

Section: Introductionmentioning

confidence: 99%

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

Saini

Chattopadhyay

2015

RSC Adv.

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This comprehensive spectroscopic analysis of a-(2-naphthyl)-N-methylnitrone has proposed its photochemical oxaziridine formation and thermal E-Z isomerization mechanisms. The activation energy for the conversion of the unstable non-planar E isomer to the stable planar Z-isomer is found to be 23.7 kcal mol À1 at the CASSCF/6-31G* level of calculation. A transition state with a negative frequency of 350 cm À1 is likely to be responsible for this process. Both CASSCF and ONIOM-based studies have revealed that the nitrone-oxaziridine photochemical conversion involves non-radiative decay channels which include biradicaloid conical intersection (CI) points through Hula-twist and terminal one-bond-flip motions, situated at 35-40 kcal mol À1 below the first excited singlet state (S 1 ). Following the directions of their gradient-difference vectors, the optimized oxaziridine geometries are obtained. The nature of the low-lying singlet-singlet transitions of these a-naphthyl N-methylnitrones is found to be similar to that of the conjugated non-polar polyenes, and differs appreciably from our previously studied longchain conjugated nitrone systems. The fluorescent S 1 state with a radiative lifetime of nanosecond order is populated by the weak upward S 0 -S 1 transition (transition moment: 0.3 Debye) and through the decay of the S 2 state, which eventually gets involved in the S 0 /S 1 conical intersections.

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Section: Introductionmentioning

confidence: 99%

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

Saini

Chattopadhyay

2015

RSC Adv.

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“…In few cases, some unstable (E)-nitrones have been generated by irradiation of the Z isomers. 14 The mechanistic investigation of this widely used oxidation process has been studied to some extent. 10 In our continuing studies 9,10 to investigate the regiochemistry and mechanism of oxidation of unsymmetrical secondary hydroxylamines to nitrones, we report here a systematic study of the oxidation of various Nbenzy1-N-alkylhydroxylamines 1-4 and their deuterated counterparts [ 2 H 2 ]1-4 using mercury(II) oxide and p- Scheme 1 Scheme 2 benzoquinone (p-BQ) as oxidants (Scheme 2).…”

Section: Introductionmentioning

confidence: 99%

Regiochemistry and mechanism of oxidation ofN-benzyl-N-alkylhydroxylamines to nitrones

Hassan

Wazeer

Saeed

et al. 2000

J. Phys. Org. Chem.

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“…Several other examples are * For correspondence also there, where N-alkyl-α-arylnitrones were reported to give more stable oxaziridines on photo-irradiation in comparison to the N, α-diarylnitrones. 1,2 Photoexcitation studies on conjugated long-chain nitrones have also given similar indications. The chemopreventive N-methyl retinylnitrone 6 w a sf o u n dt oc o n v e r t slowly to stable oxaziridine under the exposure to room light.…”

Section: Introductionmentioning

confidence: 87%

“…The nitrone-oxaziridine photochemical conversion has been experimentally attempted by several groups in the last few decades. Photo-irradiation study on nitrones reported in the last century by Splitter et al 1,2 is considered to be one of the most significant contributions in this field. In contrast to the photochemical conversion to oxaziridine, the cis-trans isomerization reactions of nitrones were found to occur thermally or in presence of photosensitizers, such as uranine, eosine, iodine, etc.…”

Section: Introductionmentioning

confidence: 99%

A computational investigation of the photochemical oxaziridine and amide conversion process of open-chain conjugated nitrone with electron-withdrawing trifluoromethyl group on nitrogen

Saini

Chattopadhyay

2015

J Chem Sci

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This computational study investigates the photo-excitation process and subsequent photoproduct formation steps through non-radiative deactivation channels in open-chain conjugated N-substituted nitrone systems (model compounds of corresponding retinylnitrones) having electron-withdrawing groups on nitrogen. Calculations mostly based on CASSCF/6-31G* and CASMP2/6-31G* level of theories on a representative system with N-trifluoromethyl substituent have predicted initial photo-excitation to a planar singlet state. This photochemical path is subsequently followed by a barrierless non-radiative channel towards the lowest-energy conical intersection (CI) geometry having a terminal CNO kink, and situated at 30 kcal/mol below the planar excited state. Following the direction of its gradient difference (GD) vectors, an oxaziridine-type species (R C−O = 1.38 Å, R N−O = 1.53 Å, < CNO= 55.8 •) appears at 3-6 kcal mol −1 below the ground state nitrone system through a transition state (along its reverse direction of minimum-energy path), situated on the reaction pathway. This species with an elongated NO bond seems to be heading towards an amide geometry. On the other hand, in the opposite GD vector direction a proper oxaziridine geometry has been obtained with a much shorter NO bond distance (R N−O = 1.42 Å).

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Orbital symmetry control in the nitrone-oxaziridine system. Nitrone photostationary states

Cited by 64 publications

References 0 publications

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

Regiochemistry and mechanism of oxidation ofN-benzyl-N-alkylhydroxylamines to nitrones

A computational investigation of the photochemical oxaziridine and amide conversion process of open-chain conjugated nitrone with electron-withdrawing trifluoromethyl group on nitrogen

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