The Norrish Type II Photodecomposition of Di-n-Butyl Terephthalate

1971 ◽  
Vol 49 (17) ◽  
pp. 2916-2917 ◽  
Author(s):  
M. Day ◽  
D. M. Wiles
Keyword(s):  
Liquid Phase ◽  
Carboxylic Acid ◽  
Quantum Yields ◽  
Type Ii ◽  
Photochemical Rearrangement ◽  
Norrish Type ◽  
End Groups ◽  
Rearrangement Reaction

The liquid phase photolysis of undiluted di-n-butyl terephthalate yields 1-butene and carboxylic acid end groups as a result of a Norrish Type II photochemical rearrangement reaction. Quantum yields for the production of these two products have been determined and found to be [Formula: see text] and [Formula: see text] in vacuum and [Formula: see text] and [Formula: see text] in air.

scholarly journals Competition Between Cyclization and Unusual Norrish Type I and Type II Nitro-Acyl Migration Pathways in the Photouncaging of 1-Acyl-7-nitroindoline Revealed by Computations

2020 ◽  
Author(s):  
Pierpaolo Morgante ◽  
Charitha Guruge ◽  
Yannick P. Ouedraogo ◽  
Nasri Nesnas ◽  
Roberto Peverati
Keyword(s):  
Density Functional ◽  
Acyl Migration ◽  
Density Functional Theory Calculations ◽  
Computational Procedure ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Relative Quantum ◽  
Norrish Type ◽  
Migration Pathways

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

Photochemistry of alkyl esters of benzoylformic acid

1984 ◽  
Vol 62 (2) ◽  
pp. 386-391 ◽  
Author(s):  
M. V. Encinas ◽  
E. A. Lissi ◽  
A. Zanocco ◽  
L. C. Stewart ◽  
J. C. Scaiano
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Quantum Yields ◽  
Type Ii ◽  
Alkyl Esters ◽  
Hydrogen Atoms ◽  
Isopropyl Esters ◽  
Norrish Type ◽  
Competing Reactions

The photodecomposition of several alkylbenzoylformates has been examined using quantum yield and laser flash photolysis techniques. The Norrish Type II reaction is a major triplet deactivation path in all substrates having γ-hydrogen atoms. Representative triplet lifetimes are 670, 500, and 310 ns, for the methyl, ethyl, and isopropyl esters, respectively, in 1:4 chlorobenzene: n-heptane at 298 K. Product studies suggest that several competing reactions are involved in the decay of the 1,4-biradical; some of these lead to highly absorbing (and presumably quenching) products, that make it essential to extrapolate quantum yields to "zero conversion" conditions.

scholarly journals Competition Between Cyclization and Unusual Norrish Type I and Type II Nitro-Acyl Migration Pathways in the Photouncaging of 1-Acyl-7-nitroindoline Revealed by Computations

2020 ◽  
Author(s):  
Pierpaolo Morgante ◽  
Charitha Guruge ◽  
Yannick P. Ouedraogo ◽  
Nasri Nesnas ◽  
Roberto Peverati
Keyword(s):  
Density Functional ◽  
Acyl Migration ◽  
Density Functional Theory Calculations ◽  
Computational Procedure ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Relative Quantum ◽  
Norrish Type ◽  
Migration Pathways

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

scholarly journals Competition between cyclization and unusual Norrish type I and type II nitro-acyl migration pathways in the photouncaging of 1-acyl-7-nitroindoline revealed by computations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pierpaolo Morgante ◽  
Charitha Guruge ◽  
Yannick P. Ouedraogo ◽  
Nasri Nesnas ◽  
Roberto Peverati
Keyword(s):  
Density Functional ◽  
Acyl Migration ◽  
Density Functional Theory Calculations ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Migration Pathway ◽  
Norrish Type ◽  
Triplet Excited States ◽  
Migration Pathways

AbstractThe 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and an acyl migration pathway, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish type I and a 1,6-nitro-acyl variation of a Norrish type II mechanism, which is reported here for the first time. We also found negligible energetic differences in the uncaging mechanisms of the 4-methoxy-5,7-dinitroindolinyl (MDNI) cages and their mononitro analogues (MNI). We traced the experimentally observed improved quantum yields of MDNI to a higher population of the reactants in the triplet surface. This fact is supported by a more favorable intersystem crossing due to the availability of a higher number of triplet excited states with the correct symmetry in MDNI than in MNI. Our findings may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.

scholarly journals Competition Between Cyclization and Unusual Norrish Type I and Type II Nitro-Acyl Migration Pathways in the Photouncaging of 1-Acyl-7-nitroindoline Revealed by Computations

2020 ◽  
Author(s):  
Pierpaolo Morgante ◽  
Charitha Guruge ◽  
Yannick P. Ouedraogo ◽  
Nasri Nesnas ◽  
Roberto Peverati
Keyword(s):  
Density Functional ◽  
Acyl Migration ◽  
Density Functional Theory Calculations ◽  
Computational Procedure ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Relative Quantum ◽  
Norrish Type ◽  
Migration Pathways

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and acyl migration pathways, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which is reported here for the first time. We also introduced a computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.<br>

Photochemistry of Ketones in Carbon Tetrachloride Solution

1973 ◽  
Vol 51 (9) ◽  
pp. 1435-1440 ◽  
Author(s):  
J. O. Pavlik ◽  
P. I. Plooard ◽  
A. C. Somersall ◽  
J. E. Guillet
Keyword(s):  
Energy Transfer ◽  
Carbon Tetrachloride ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Definitive Evidence ◽  
Carbon Tetrachloride Solution ◽  
Radiationless Energy Transfer ◽  
Norrish Type ◽  
Low Efficiency

Acetone, chloroacetone, 4-heptanone, 8-pentadecanone, 12-tricosanone, and dimethyl γ-keto pimellate were photolyzed at 3130 Å in carbon tetrachloride solution. The quantum yields of C2Cl6 formed, the decrease in Norrish type I and type II products, the copious yields of HCl and the Stern–Volmer quenching of ketone fluorescence by carbon tetrachloride provide definitive evidence for energy transfer which is rationalized by an exciplex mechanism of low efficiency. The excited [n,π*]1 state of the ketone forms a loose complex with the CCl4 and radiationless energy transfer leads to dissociation of the CCl4 in the primary chemical step.

scholarly journals Unusual Norrish Type I and Type II Nitro-Acyl Migration Transition State in the Photo-Uncaging of 1-Acyl-7-Nitroindolines Revealed by Computations

2020 ◽  
Author(s):  
Pierpaolo Morgante ◽  
Charitha Guruge ◽  
Yannick P. Ouedraogo ◽  
Nasri Nesnas ◽  
Roberto Peverati
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Acyl Migration ◽  
Density Functional Theory Calculations ◽  
Computational Procedure ◽  
Quantum Yields ◽  
Type I ◽  
Type Ii ◽  
Relative Quantum ◽  
Norrish Type

The 7-nitroindolinyl family of caging chromophores has received a lot of attention in the past two decades. However, it is not clear if they undergo cyclization or migration upon photo-uncaging to release the active compound. In this study, we performed state-of-the-art density functional theory calculations to fully understand the photo-uncaging mechanism and we compared the probabilities of all plausible pathways. We found that the key transition state in the lowest¬ energy pathway involves an acyl migration. It possesses the characteristics of a combined Norrish Type I and a 1,6-nitro-acyl variation of a Norrish Type II mechanism, which has not been previously reported. We also introduced a new computational procedure that allows the estimation of intersystem crossing rate constants useful to compare the relative quantum yield of substituted cages. This procedure may pave the way for improved cage designs that possess higher quantum yields and more efficient agonist release.<br><br>

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