scholarly journals Multi-photon ionization and fragmentation of uracil: Neutral excited-state ring opening and hydration effects

2013 ◽  
Vol 139 (24) ◽  
pp. 244311 ◽  
Author(s):  
B. Barc ◽  
M. Ryszka ◽  
J. Spurrell ◽  
M. Dampc ◽  
P. Limão-Vieira ◽  
...  
Keyword(s):  
Excited State ◽  
Ring Opening ◽  
Photon Ionization

The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF2) with conjugated enones and en-esters

1993 ◽  
Vol 71 (6) ◽  
pp. 846-854 ◽  
Author(s):  
Yuan L. Chow ◽  
Shi-Sen Wang ◽  
Xian-En Cheng
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Ring Opening ◽  
Electron Donors ◽  
Head Orientation ◽  
Singlet Excited State ◽  
Methyl Substitution ◽  
Unsaturated Ketones ◽  
Dibenzoylmethanatoboron Difluoride

Dibenzoylmethanatoboron difluoride (DBMBF2), the BF2 complex of dibenzoylmethane, reacted from its singlet excited state with α,β-unsaturated ketones and esters to give 1,5-diketones by a [2+2] cycloaddition and ring-opening sequence in an analogous pathway to that observed in the photocycloaddition to olefins and dienes. The present photoreaction is unexpected since conjugated enones and en-esters are poor electron donors to comply with the previously proposed charge transfer requirement in DBMBF2 photoreactions. The photocycloaddition to these substrates was highly regioselective and stereoselective, giving the head-to-head orientation, which could be enhanced by α-methyl substitution; β-methyl substitution increased the alternate head-to-tail orientation. The photolysis of a mixture of DBMBF2 and a cyclic enone also caused the latter to dimerize to give head-to-head and head-to-tail dimers in significant yields. These photodimerizations were apparently caused by DBMBF2 sensitization. The mechanism of the sensitization is discussed.

Synthesis of nitropolychlorinated dibenzo-p-dioxins (NPCDDs) and their photochemical reaction with nucleophiles

1995 ◽  
Vol 73 (6) ◽  
pp. 826-834 ◽  
Author(s):  
Simona G. Merica ◽  
Nigel J. Bunce
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Linear Relationship ◽  
Nitro Group ◽  
Photochemical Reaction ◽  
Ring Opening ◽  
Sodium Ethoxide ◽  
Chemical Yield ◽  
Triplet Excited State ◽  
High Chemical

A series of nitropolychlorodibenzo-p-dioxins (NPCDDs) was synthesized by condensation between catechols and 2,6-dinitrohalobenzene derivatives. In the presence of sodium ethoxide in anhydrous ethanol, these underwent photochemical SN2Ar* substitutions meta to the nitro group in high chemical yield and moderate quantum yield. Both ring-opening and chloride replacement reactions were observed. The reactions involved the triplet excited state of the NPCDD, and showed a linear relationship between Φ−1 and [nucleophile]−1. Analogous reactions with KCN in methanol showed similar behaviour, but the products could not be isolated. Keywords: photosubstitution, SN2Ar*, dibenzo-p-dioxins.

Competition between ring-puckering and ring-opening excited state reactions exemplified on 5H-furan-2-one and derivatives

2020 ◽  
Vol 152 (6) ◽  
pp. 064301 ◽  
Author(s):  
Oliver Schalk ◽  
Joachim Galiana ◽  
Ting Geng ◽  
Tobias L. Larsson ◽  
Richard D. Thomas ◽  
...  
Keyword(s):  
Excited State ◽  
Ring Opening ◽  
Ring Puckering

ChemInform Abstract: EXCITED-STATE Σ SUCCINIMIDYL AND GLUTARIMIDYL RADICALS: REVERSIBLE RING OPENING

1983 ◽  
Vol 14 (11) ◽  
Author(s):  
R. L. TLUMAK ◽  
J. C. DAY ◽  
J. P. SLANGA ◽  
P. S. SKELL
Keyword(s):  
Excited State ◽  
Ring Opening

Excited-State Ring-Opening Mechanism of Cyclic Ketones: A MS-CASPT2//CASSCF Study

2015 ◽  
Vol 119 (15) ◽  
pp. 3569-3576 ◽  
Author(s):  
Shu-Hua Xia ◽  
Xiang-Yang Liu ◽  
Qiu Fang ◽  
Ganglong Cui
Keyword(s):  
Excited State ◽  
Ring Opening ◽  
Cyclic Ketones

Comparing a Photoinduced Pericyclic Ring Opening and Closure:  Differences in the Excited State Pathways

2007 ◽  
Vol 129 (27) ◽  
pp. 8577-8584 ◽  
Author(s):  
Björn Heinz ◽  
Stephan Malkmus ◽  
Stefan Laimgruber ◽  
Steffen Dietrich ◽  
Christine Schulz ◽  
...  
Keyword(s):  
Excited State ◽  
Ring Opening

The effect of central bond torsional mobility on the Rydberg state ring opening of alkylcyclobutenes

2003 ◽  
Vol 81 (6) ◽  
pp. 680-688 ◽  
Author(s):  
Bruce H Cook ◽  
William J Leigh
Keyword(s):  
Excited State ◽  
Absorption Band ◽  
Potential Energy ◽  
Ring Opening ◽  
Internal Conversion ◽  
Rydberg State ◽  
Energy Surface ◽  
Long Wavelength ◽  
Central Bond ◽  
Hydrocarbon Solution

The stereochemistry of the π,R(3s) excited state ring opening of a series of bicyclic alkylcyclobutenes has been studied in hydrocarbon solution with 228 nm excitation. In these compounds, the C=C bond is shared between the cyclobutene ring and a five-, six-, or seven-membered ancillary ring, which has the effect of restricting the torsional mobility about the central C—C bond in the isomeric diene products. It has previously been shown that monocyclic alkylcyclobutenes undergo stereospecific conrotatory ring opening upon excitation at the long wavelength edge of the π,R(3s) absorption band (228 nm), and nonstereospecific ring opening upon irradiation at shorter wavelengths (within the π,π* absorption band). Different behaviour is observed for the bicyclic systems studied in the present work. The bicyclo[3.2.0]hept-1-ene, bicyclo[4.2.0]oct-1-ene, and one of the bicyclo[5.2.0]non-1-ene derivatives yield nearly the same mixtures of E,E- and E,Z-diene isomers upon irradiation at 214 and 228 nm, with the product mixtures being heavily weighted in favor of the isomer(s) corresponding to disrotatory ring opening. The results may indicate that the stereochemical characteristics of the Rydberg-derived ring opening of alkylcyclobutenes depends on the ability of the molecule to twist about the "central" bond (i.e., the C=C bond in the cyclobutene) as ring opening proceeds. It is proposed that restricting the torsional mobility about the central bond activates internal conversion from the π,R(3s) to the π,π* potential energy surface, from which predominant disrotatory ring opening ensues.Key words: cyclobutene, Rydberg, ring opening, photopericyclic, electrocyclic.

Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization

2014 ◽  
Vol 140 (20) ◽  
pp. 204303 ◽  
Author(s):  
Camille Lévêque ◽  
Horst Köppel ◽  
Richard Taïeb
Keyword(s):  
Excited State ◽  
Ab Initio ◽  
Excited State Dynamics ◽  
Photon Ionization
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