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.

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.

scholarly journals TiCl3 as a New Catalyst for the Imino Diels-Alder Reaction

2006 ◽  
Vol 1 (9) ◽  
pp. 1934578X0600100
Author(s):  
Narayan V. Mayekar ◽  
Sandip K. Nayak ◽  
Subrata Chattopadhyay
Keyword(s):  
Ambient Temperature ◽  
Alder Reaction ◽  
Diels Alder ◽  
Trans Isomers ◽  
Effective Catalyst ◽  
Diels Alder Reaction ◽  
Cis And Trans Isomers ◽  
Reaction Proceeds ◽  
Cis And Trans

Titanium(III) chloride was found to be an effective catalyst for the imino Diels-Alder reaction between an imine (generated in situ) and an activated alkene in acetonitrile at ambient temperature. The reaction proceeds smoothly to afford the corresponding adduct as a mixture of chromatographically separable cis- and trans isomers in moderate to good yields.

The Photochemistry of a Dihydropyridazine

1973 ◽  
Vol 51 (11) ◽  
pp. 1729-1736 ◽  
Author(s):  
P. De Mayo ◽  
M. C. Usselman
Keyword(s):  
Triplet State ◽  
Ring Opening ◽  
Quantum Yields ◽  
Trans Isomers ◽  
Absorption Bands ◽  
Cis And Trans

Irradiation of a 5,6-dihydropyridazine in either the n → π* or π → π* absorption bands results in ring-opening to the two isomeric diazatrienes expected of a concerted, electrocyclic process. Population of the triplet state of the dihydropyridazine by sensitization also results in ring-opening, but much less efficiently. The quantum yields of the two processes were found to be 0.40 ± 0.04 and 0.07 ± 0.01, respectively. The primary photoproducts, cis,cis- and cis,trans-4,5-diazatriene, isomerize thermally at temperatures greater than 20° to the trans,cis and trans,trans isomers.

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

PREPARATION OF ERUCIC AND NERVONIC ACIDS LABELLED WITH CARBON-14

1957 ◽  
Vol 35 (8) ◽  
pp. 757-760 ◽  
Author(s):  
K. K. Carroll
Keyword(s):  
Enoic Acid ◽  
Nervonic Acid ◽  
Malonic Ester ◽  
Ester Synthesis ◽  
Trans Isomers ◽  
Carbon 14 ◽  
Cis And Trans Isomers ◽  
Cis And Trans

The malonic ester synthesis of nervonic acid (tetracos-15-enoic acid) has been modified so that the product consists of pure cis rather than a mixture of cis and trans isomers. The modified synthesis has been used for the preparation of C14-labelled erucic and nervonic acids.

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