Photolysis of some alkyl-1-pyrazolines

1968 ◽  
Vol 46 (21) ◽  
pp. 3305-3313 ◽  
Author(s):  
Ralph Moore ◽  
Anupama Mishra ◽  
Robert J. Crawford
Keyword(s):  
Excited Singlet ◽  
Direct Photolysis ◽  
Cis And Trans ◽  
Singlet Methylene

The direct and photosensitized photolysis of six methylated-1-pyrazolines is described. Examination of the products suggests that direct photolysis leads to an excited singlet trimethylene, whereas a triplet is produced on benzophenone photosensitization. The trimethylene produced from 4 and 5 is related to the intermediates produced on addition of triplet methylenes to cis- and trans-2-butene. Evidence is presented to support the claim that no intermediate is involved in the addition of singlet methylene to cis-and trans-2-butene.

Collisional deactivation of singlet methylene in the photolysis of ketene

1969 ◽  
Vol 47 (18) ◽  
pp. 3345-3353 ◽  
Author(s):  
R. A. Cox ◽  
K. F. Preston
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Ground State ◽  
Inert Gases ◽  
Inert Gas ◽  
Quantum Yields ◽  
Electronic Relaxation ◽  
Excited Singlet ◽  
State Formula ◽  
Singlet Methylene

An investigation has been made into the effect of inert gas additions on product quantum yields for the photolysis at 2800 and 2490 Å of mixtures of ketene and oxygen and for the photolysis at 2800 Å of mixtures of ketene and carbon monoxide. Concentration ratios of O2 (or CO) to CH2CO were chosen so that the reaction of CH2(3Σg−) with CH2CO could be ignored and C2H4 formation could be attributed entirely to the reaction[Formula: see text]Quenching of the C2H4 quantum yield by inert gases was interpreted in terms of collisional deactivation of CH2(1A1) to the ground state[Formula: see text]and rate constant ratios k2/k1 have been determined for a number of gases: He (0.018), Ar (0.014), Kr (0.033), Xe (0.074), N2 (0.052), N2O (0.10), CF4 (0.047), C2F6 (0.11), and SF6 (0.045). It has been assumed that collision-induced intersystem crossover in excited singlet ketene makes an insignificant contribution to the observed quenching effects, but it has not been possible to verify this assumption experimentally. The mechanism of collision-induced electronic relaxation of singlet methylene is discussed in the light of the results.

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.

The solution-phase photochemistry of 2-trifluoromethylnorbornene

1990 ◽  
Vol 68 (11) ◽  
pp. 1961-1966 ◽  
Author(s):  
N. Nguyen ◽  
B. E. Harris ◽  
K. B. Clark ◽  
W. J. Leigh
Keyword(s):  
Rydberg State ◽  
Singlet State ◽  
High Energy ◽  
Sigmatropic Rearrangement ◽  
Solution Phase ◽  
Excited Singlet ◽  
Direct Photolysis ◽  
Additional Support ◽  
193 Nm ◽  
Π State

The photochemistry of 2-trifluoromethylnorbornene in pentane solution has been investigated. Direct photolysis with 193 nm light yields 1-trifluoromethyl-2-norcarene in 90% yield, due to formal [1,3]-sigmatropic rearrangement, in addition to three other minor products. Chlorobenzene-sensitized photolysis affords photoreduction products, principally exo- and endo-2-trifluoromethylnorbornane and decane isomers, in addition to several products of higher molecular weight. On the basis of comparisons of the photochemistry of this compound to that previously reported for norbornene and 2-cyanonorbornene, as well as spectroscopic evidence, it is suggested that the lowest excited singlet state (the photoreactive state in solution) in 2-trifluoromethylnorbornene is the π, π* state. The results indicate that trifluoromethyl substitution has the effect of significantly raising the energy of the π,R(3s) Rydberg state in simple alkenes, without altering the high energy (ca. 6.5 eV) or the localized character of the alkene π, π* state. Furthermore, they lend additional support to the view that the carbene-derived products typically formed upon photolysis of alkenes in solution are derived from π,R(3s) excitation. Keywords: Rydberg, photolysis, far-uv, alkene, solution phase, singlet, triplet.

Trypanocidal Structure-Activity Relationshipfor Cis- and Trans-methylpluviatolide

Planta Medica ◽  
2008 ◽  
Vol 74 (03) ◽  
Author(s):  
R Silva ◽  
J Saraiva ◽  
S Albuquerque ◽  
C Curti ◽  
PM Donate ◽  
...  
Keyword(s):  
Structure Activity ◽  
Cis And Trans
Sign in / Sign up

Export Citation Format

Share Document