Cyclobutene photochemistry. Substituent and wavelength effects on the photochemical ring opening of monocyclic alkylcyclobutenes

1990 ◽  
Vol 68 (11) ◽  
pp. 1988-1997 ◽  
Author(s):  
William J. Leigh ◽  
Kangcheng Zheng ◽  
K. Brady Clark
Keyword(s):  
Ring Opening ◽  
Energy State ◽  
Wavelength Dependence ◽  
Uv Spectra ◽  
Solution Phase ◽  
Light Sources ◽  
Orbital Symmetry ◽  
Cis And Trans Isomers ◽  
193 Nm ◽  
Cis And Trans

The photochemical ring opening of cis- and trans-3,4-dimethyl-, 1,3,4-trimethyl-, and 1,2,3,4-tetramethylcyclobutene (1, 3, and 4, respectively) has been investigated in hydrocarbon solution with 193 nm and 214 nm light sources. Ring opening is non-stereospecific in all cases at both wavelengths. The ratio of dienes formed by the formally allowed to formally forbidden pathways in the photolysis of these compounds is highest (ca. 2) for the trimethylcyclobutenes, and approximately 1 for both cis and trans isomers of the di- and tetramethylcyclobutenes with 193 nm excitation. The diene distributions from photolysis of all compounds but cis-3 show slight wavelength dependence. Gas- and solution-phase UV absorption spectra are reported for 3 and 4, and indicate that there are at least three singlet excited states accessible in the 185–230 nm region in these molecules. The π,R(3s) state is the lowest energy state in the gas phase in 3 and 4. The results verify that orbital symmetry factors do not play a role (or a consistent one, at least) in controlling the stereochemistry of the reaction, but they do not allow a firm assignment of the excited state(s) responsible for ring opening. Direct photolysis of these compounds also results in fragmentation to yield Z-2-butene (from cis-3 and 4) or E-2-butene (from trans-3 and 4) in addition to propyne or 2-butyne. The 2-butenes are formed with greater than 90% stereospecificity in all cases. The structures of the four 3-methyl-2,4-hexadiene isomers obtained from photolysis of 3 have been assigned on the basis of 1H NMR spectroscopy and the results of thermolysis of the two cyclobutene isomers. Keywords: cyclobutene, photolysis, Rydberg, orbital symmetry, far-UV, solution phase, UV spectra.

Cyclobutene photochemistry. Adiabatic photochemical ring opening of alkylcyclobutenes

1996 ◽  
Vol 74 (6) ◽  
pp. 951-964 ◽  
Author(s):  
William J. Leigh ◽  
J. Alberto Postigo ◽  
K.C. Zheng
Keyword(s):  
Ring Opening ◽  
Quantum Yields ◽  
Light Sources ◽  
Trans Isomers ◽  
Excited Singlet ◽  
Orbital Symmetry ◽  
Cis And Trans Isomers ◽  
Product Distributions ◽  
Reaction Proceeds ◽  
Cis And Trans

The photochemistry of the cis and trans isomers of a series of dimethylbicyclo[n 2.0]alk-(n + 2)-enes (n = 2–5) (bicyclic cyclobutene derivatives in which the C=C bond is shared by the two rings) in pentane solution is described. Irradiation of these compounds using monochromatic 193- or214-nm light sources results in ring opening to yield the corresponding 1,2-bis(1-ethylidene)cycloalkanes (C4–C7) in high chemical and quantum yields. In all cases, the reaction proceeds with a high (70–90%) degree of disrotatory stereoselectivity. Quantum yields for direct cis,trans photoisomerization of the isomeric E,E-and E,Z-1,2-bis(1-ethylidene)cycloalkanes have also been determined. The product distributions from irradiation of the cyclobutenes are wavelength dependent, but for 214-nm excitation the isomeric diene distributions obtained from cyclobutene ring opening agree fairly closely with those calculated from the quantum yields for cis,trans photoisomerization of the isomeric dienes on the assumption that the process involves purely disrotatory ring opening to yield a single diene isomer in the lowest excited singlet state. The results are consistent with an orbital-symmetry-controlled, adiabatic mechanism for ring opening. Key words: photochemistry, cyclobutene, electrocyclic, adiabatic, conical intersection, orbital symmetry.

Photoresponsive Properties of a Azobenzene-Based Polyacrylamide Copolymer

2011 ◽  
Vol 189-193 ◽  
pp. 4346-4349
Author(s):  
Yi Ping Zhao ◽  
Yu Xin Zhang ◽  
Qing Song Zhang ◽  
Li Chen
Keyword(s):  
Aqueous Solution ◽  
Free Radical ◽  
Uv Spectra ◽  
Molar Ratio ◽  
Trans Isomers ◽  
Reversible Transformation ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Azobenzene Groups ◽  
Poly Acrylamide

A novel copolymer of poly(acrylamide-co-acrylamido azobenzene) consisting of acrylamide (AAm) and acrylamido azobenzene (AAAB) was synthesized via a free-radical polymerization route by using 2,2’-azobisisobutyronitrile (AIBN) as initiator. The investigation of UV spectra of the copolymer aqueous solution that exposed to UV irradiation revealed that p(AAm-co-AAAB) possessed good UV photoresponsive properties. The photoresponsibility was proposed to stem from reversible transformation between cis and trans isomers of azobenzene groups in the side chains. The concentration and molar ratio of copolymer have some influence on the photoresponsive behaviors.

Gas Electron Diffraction Study of the 193-nm Laser-Induced Interconversion between Cis- and Trans-1,2-Dichloroethylene

1987 ◽  
Vol 41 (4) ◽  
pp. 631-635 ◽  
Author(s):  
D. L. Monts ◽  
J. D. Ewbank ◽  
K. Siam ◽  
W. L. Faust ◽  
D. W. Paul ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Diffraction Study ◽  
Chemical Reactions ◽  
Electron Diffraction Study ◽  
Gas Electron Diffraction ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
193 Nm ◽  
Cis And Trans

Gas electron diffraction (GED) data were recorded of 193-nm irradiated cis- and trans-1,2-dichloroethylene. The interconversion between the cis-and trans-isomers and the formation of chloroacetylene can be inferred from the diffraction intensities. The experiments demonstrate the utility of GED in the study of chemical reactions.

1992 Merck–Frosst Award Lecture Orbital symmetry and the photochemistry of cyclobutene

1993 ◽  
Vol 71 (2) ◽  
pp. 147-155 ◽  
Author(s):  
William J. Leigh
Keyword(s):  
Ring Opening ◽  
Rydberg State ◽  
Uv Light ◽  
Light Sources ◽  
Unusual Behavior ◽  
Orbital Symmetry ◽  
Direct Photolysis ◽  
High Degree ◽  
Π State ◽  
Theoretical Results

Direct photolysis of alkyl-substituted cyclobutene derivatives in solution with monochromatic far-UV light sources results in competing ring opening to the corresponding substituted 1,3-butadiene derivatives and fragmentation to the corresponding alkene and alkyne via formal [2 + 2] cycloreversion. The excited states leading to the two types of products have been identified. Cycloreversion occurs stereospecifically and arises as a result of excitation of the π,R(3s) Rydberg state, which is of comparable energy to the π,π* state in alkylcyclobutenes. In spite of its stereospecificity, the reaction is nonconcerted; evidence is presented to suggest that it occurs by a mechanism involving [1,2] migration (ring contraction) to yield a cyclopropylcarbene intermediate, which then fragments to yield the alkyne and alkene. The stereochemistry at C3 and C4 in the starting cyclobutene is retained in the alkene produced in the reaction. Ring opening proceeds nonstereoselectively (from the π,π* singlet state) in well over a dozen systems that have been investigated, and possible mechanisms to account for this are discussed. It is proposed that orbital symmetry plays a role in the reaction, but only in the early stages of ring opening. Bicyclic cyclobutene derivatives in which the cyclobutene double bond is located across the [0] bridge undergo ring opening with a high degree of disrotatory stereoselectivity. Possible reasons for this unusual behavior are discussed in light of recent ab initio theoretical results.

scholarly journals Identification of Anthocyanin Compounds in Butterfly Pea Flowers (Clitoria ternatea L.) by Ultra Performance Liquid Chromatography/Ultraviolet Coupled to Mass Spectrometry

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4539
Author(s):  
Nguyen Minh Thuy ◽  
Vo Minh ◽  
Tran Ben ◽  
My Tuyen Thi Nguyen ◽  
Ho Ha ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Ultra Performance Liquid Chromatography ◽  
Negative Ion ◽  
Trans Isomers ◽  
Clitoria Ternatea ◽  
Flower Extract ◽  
Cis And Trans Isomers ◽  
Butterfly Pea ◽  
Cis And Trans

Butterfly pea flower have great sensory attraction, but they have not yet been used widely in Vietnam. Extracts of butterfly pea flowers can be used conveniently as a natural blue colorant for food products. In this study, the identification of anthocyanin compounds in butterfly pea flowers was performed by UPLC coupled with a UV and Mass spectrometer instrument. Positive and negative ion electrospray MS/MS chromatograms and spectra of the anthocyanin compounds were determined. By analyzing the chromatograms and spectra for each ion, five anthocyanins were identified in the butterfly pea flower extract; these were delphinidin-3-(6”‐p-coumaroyl)-rutinoside, cyanidin 3-(6”-p-coumaroyl)-rutinoside, delphinidin-3-(p-coumaroyl) glucose in both cis- and trans- isomers, cyanidin-3-(p-coumaroyl-glucoside) and delphinidin-3-pyranoside. Additionally, based on their intensity, it was determined that cyanidin-3-(p-coumaroyl-glucoside) was the most abundant anthocyanin, followed by cyanidin 3-(6”-p-coumaroyl)-rutinoside, delphinidin-3-(p-coumaroyl-glucoside), delphinidin-3-(6”-p-coumaroyl)-rutinoside and delphinidin-3-pyranoside. In this study, cyanidin derivatives were discovered in butterfly pea flower extract, where these compounds had not been detected in previous studies.

Unveiling the coexistence of cis- and trans-isomers in the hydrolysis of ZrO2: A coupled DFT and high-resolution photoelectron spectroscopy study

2020 ◽  
Vol 153 (24) ◽  
pp. 244308
Author(s):  
Ali Abou Taka ◽  
Mark C. Babin ◽  
Xianghai Sheng ◽  
Jessalyn A. DeVine ◽  
Daniel M. Neumark ◽  
...  
Keyword(s):  
High Resolution ◽  
Photoelectron Spectroscopy ◽  
Spectroscopy Study ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Hydrolysis Of
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