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.

The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes

1985 ◽  
Vol 63 (7) ◽  
pp. 1424-1430 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers
Keyword(s):  
Ground State ◽  
Internal Conversion ◽  
Rydberg State ◽  
Singlet State ◽  
Hydrogen Shift ◽  
Geometric Isomerization ◽  
Trans Isomerization ◽  
Show Evidence ◽  
Structural Isomerization ◽  
Π State

We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.

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.

Higher excited singlet state of diphenylacetylene in solution phase

1993 ◽  
Vol 209 (4) ◽  
pp. 397-402 ◽  
Author(s):  
Yoshinori Hirata ◽  
Tadashi Okada ◽  
Tateo Nomoto
Keyword(s):  
Singlet State ◽  
Solution Phase ◽  
Excited Singlet State ◽  
Excited Singlet

Stereochemistry and chiroptical properties of 1,3-dialkylaziridinones (α-lactams). Chiral rules for the nonplanar amide chromophore

1994 ◽  
Vol 72 (2) ◽  
pp. 279-286 ◽  
Author(s):  
G. V. Shustov ◽  
A. V. Kachanov ◽  
I. I. Chervin ◽  
R. G. Kostyanovsky ◽  
A. Rauk
Keyword(s):  
Rydberg State ◽  
Singlet State ◽  
Structural Features ◽  
Molecular Orbital Calculations ◽  
Cd Spectra ◽  
Trans Isomers ◽  
Excited Singlet ◽  
Chiroptical Properties ◽  
Tert Butyl ◽  
Cotton Effects

Structural features, configurational stability, and chiroptical properties of the nonplanar amide group in α-lactams were investigated by means of ab initio (6-31 + G*) molecular orbital calculations on (1R)-aziridinone 1, (1R)-1-methylaziridinone 2, (1R,3R)-3-methylaziridinone 3, (1R,3R)-1,3-dimethylaziridinone 4a, its cis diastereomer (1S,3R)-1,3-dimethylaziridinone 4b, and (1R,3R)-3-tert-butyl-1-methylaziridinone 5, and by experimental CD spectra of 1-tert-butyl- and 1-(1′-adamantyl)-substituted 3(R)-3-tert-butylaziridinones 6 and 7. The nitrogen inversion barriers of 4a and 4b are 2.8 and 1.6 kcal mol−1, respectively. The lowest excited singlet state of all of the aziridinones is a valence state (the nO–πCO* transition); the second is a Rydberg state (the nN–3s transition). The signs of the first and second Cotton effects in the CD spectra of the compounds 6 and 7 coincide with the calculated ones for 1 and 2 and the trans isomers 3, 4a, and 5. According to the calculated and experimental data for aziridinones 1–7 as well as to the well-known data for other nonplanar amides, the sign of the first Cotton effects is determined by the intrinsic chirality of the nonplanar amide chromophore and obeys a spiral rule. For cases where the chromophore has the conformation around the N—C(O) bond, which is close to the antiperiplanar, a reverse octant rule is proposed.

The Gold Porphyrin First Excited Singlet State¶

2002 ◽  
Vol 76 (1) ◽  
pp. 47 ◽  
Author(s):  
Joakim Andréasson ◽  
Gerdenis Kodis ◽  
Su Lin ◽  
Ana L. Moore ◽  
Thomas A. Moore ◽  
...  
Keyword(s):  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet
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