Photochemical .alpha. cleavage of ketones in solution. VI. Substituent effects on the photochemical .alpha. cleavage of deoxybenzoin

Lewis, Frederick D.; Hoyle, Chv; Magyar, J. G.; Heine, H.-G.; Hartmann, Willy

doi:10.1021/jo00892a025

Cited by 45 publications

(17 citation statements)

References 7 publications

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“…The migration of the acyl unit is facilitated by the inherent formation of the stabilized acyl radical, typically formed within classical Norrish 52 type I alpha cleavages of excited carbonyl of ketones (Figure 3, part a). [53][54][55][56] The (Figure 3, part b). 52,56 In order to better understand this migration pathway, we computed the energy for an ethyl group migration (in place of the acetyl) and noted that it was higher in energy (21.3 kcal/mol, Figure 3 part c), Ulg, respectively.…”

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“…Calculated bond lengths (in Å) and bond angles (degrees) in the cyclization and migration transition structures (TSs). the acyl unit is facilitated by the inherent formation of the stabilized acyl radical, typically formed within classical Norrish52 type I alpha cleavages of excited carbonyl of ketones (Figure3, part a) [53][54][55][56]. The 1,6-acyl migration effectively embodies type I and type II Norrish reactions in which the acyl undergoes an acleavage as it transfers to the O radical of the nitro unit similar to the g-H abstraction by triplet carbonyl in Norrish type II positioned at a 1,6-relationship (Figure3, part b).…”

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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

Morgante¹,

Guruge²,

Ouedraogo³

et al. 2020

Preprint

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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>

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confidence: 99%

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

Morgante¹,

Guruge²,

Ouedraogo³

et al. 2020

Preprint

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“…The migration of the acyl unit is facilitated by the inherent formation of the stabilized acyl radical, typically formed within classical Norrish 55 type I alpha cleavages of excited carbonyl of ketones (Fig. 5a) [56][57][58][59] . The 1,6acyl migration effectively embodies characteristics of both Norrish type I and type II reactions in which the acyl undergoes an α-cleavage as it transfers to the O radical of the nitro unit similar to the γ-H abstraction by triplet carbonyl in Norrish type II positioned at a 1,6-relationship (Fig.…”

Section: Resultsmentioning

confidence: 99%

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

Morgante

Guruge

Ouedraogo

et al. 2021

Sci Rep

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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 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.

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“…The reaction rate constants are not correlated with the stability of the radicals produced after the cleavage process, indicating a transition state geometry close to that of the triplet. 9, 11 The reactivity is controlled by the steric effects, 11 the electronegativity of the substituents on the benzoyl group 12 and the negative partial charge on the carbon atom of the carbonyl group in the transition state. 15 In the tunnelling theory, no activation energy is needed: the electron reaches the potential energy surface of the radicals from the triplet surface by a tunnel effect.…”

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confidence: 99%

Theoretical and experimental study of the Norrish I photodissociation of aromatic ketones

Dietlin

Allonas

Defoin

et al. 2008

Photochem Photobiol Sci

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A set of selected acetophenone derivatives was investigated using absorption and emission spectroscopy, laser flash photolysis and DFT calculations. The triplet state lifetimes and the activation energy of the cleavage reaction were measured. Computed triplet-triplet absorption spectra were found in very good agreement with the experimental ones. Bond dissociation energies, activation energies, partial charges, ground state geometries were calculated. The transition state theory TST was successfully used to calculate the cleavage rate constants: a very good correlation was found between the experimental and the calculated values. It is found that the entropy change influences the preexponential factor. This study also points out the role of the partial charges in the transition state, although this effect alone does not account for the reaction rate constants.

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Photochemical .alpha. cleavage of ketones in solution. VI. Substituent effects on the photochemical .alpha. cleavage of deoxybenzoin

Cited by 45 publications

References 7 publications

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

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

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

Theoretical and experimental study of the Norrish I photodissociation of aromatic ketones

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