A New Mechanism for the Reaction of Carbenes with OH Groups

Pliego, Josefredo R.; Almeida, Wagner B. De

doi:10.1021/jp9838644

Cited by 46 publications

(62 citation statements)

References 37 publications

(76 reference statements)

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“…[6b] Indeed, three different mechanisms can be envisaged for this insertion reaction (Scheme 1): [8] (a) protonation to a carbenium ion, (b) a concerted cheletropic cycloaddition and (c) the OH group catalysis mechanism [9] in which alcohol (ether) formation occurs in only one step but in which the hydrogen atom and the hydroxy (alkoxy) group stem from two different molecules. The often discussed ylide mechanism (d) by which the carbene first attacks the oxygen atom and then rearranges by a proton transfer (Stevens rearrangement) is only relevant for reactive-electrophilic carbenes.…”

Section: Resultsmentioning

confidence: 99%

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

et al. 2008

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In the course of our investigation of the intermolecular reactions of foiled carbenes of the norborn-2-en-7-ylidene type, we have investigated the decomposition of methoxyoxadiazoline 1 in alcohols. Most of the reactions performed lead to products with an anti configuration confirming the participation of the double bond to the stabilization of the transition states. The thermal behavior of spirooxadiazoline 1 is quite different from the behavior of the parent 2-methoxy-2,5,5-trimethyl-∆ 3 -1,3,4-oxadiazoline. Photolysis of 1 leads to the carbene after prior formation of the diazo compound whereas thermolysis cleanly generates an extremely unstable carbonyl ylide 4 that immediately decomposes to the stabilizednucleophilic carbene 5 and methyl acetate without genera-

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Section: Resultsmentioning

confidence: 99%

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

et al. 2008

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“…Assuming carbene lifetimes to be <10 ns [48], an active carbene reagent of the molecular weight used in this study can diffuse isotropically ≤130 Å from its site of generation. Such distances are sufficient to increase quenching rates by bulk solvent and thus reduce yield.…”

Section: Restricting Diffusionmentioning

confidence: 99%

Amino Acid Insertion Frequencies Arising from Photoproducts Generated Using Aliphatic Diazirines

Ziemianowicz

Bomgarden

Etienne

et al. 2017

J. Am. Soc. Mass Spectrom.

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Abstract. Mapping proteins with chemical reagents and mass spectrometry can generate a measure of accessible surface area, which in turn can be used to support the modeling and refinement of protein structures. Photolytically generated carbenes are a promising class of reagent for this purpose. Substituent effects appear to influence surface mapping properties, allowing for a useful measure of design control. However, to use carbene labeling data in a quantitative manner for modeling activities, we require a better understanding of their inherent amino acid reactivity, so that incorporation data can be normalized. The current study presents an analysis of the amino acid insertion frequency of aliphatic carbenes generated by the photolysis of three different diazirines: 3,3'-azibutyl-1-ammonium, 3,3'-azibutan-1-ol, and 4,4'-azipentan-1-oate. Leveraging an improved photolysis system for single-shot labeling of sub-microliter frozen samples, we used EThCD to localize insertion products in a large population of labeled peptides. Counting statistics were drawn from data-dependent LC-MS 2 experiments and used to estimate the frequencies of insertion as a function of amino acid. We observed labeling of all 20 amino acids over a remarkably narrow range of insertion frequencies. However, the nature of the substituent could influence relative insertion frequencies, within a general preference for larger polar amino acids. We confirm a large (6-fold) increase in labeling yield when carbenes were photogenerated in the solid phase (77 K) relative to the liquid phase (293 K), and we suggest that carbene labeling should always be conducted in the frozen state to avoid information loss in surface mapping experiments.

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“…A study of the solvent effect on these systems by free energy perturbation is available from the literature 24,25 and we have adopted the structures optimized at MP2/DZP level of ab initio theory of those reports. Figure 1 shows the transition states TS1 and TS2.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

“…[18][19][20][21][22][23] In this report, we will present a study of the relative importance of G cav and G dr for two reaction systems where results of free energy perturbation calculation are available. 24,25 Our calculations were done using both the Claverie-Pierotti method 16,21 and the Pierotti formula 16 to evaluate the cavity formation contribution and the Floris and Tomasi approximation [26][27][28] for the dispersion-repulsion terms. A comparison with free energy perturbation calculations allows us to verify the accuracy of the cavity term alone for the nonelectrostatic contribution to the activation free energy.…”

Section: Introductionmentioning

confidence: 99%

The role of nonelectrostatic solvation to chemical reactions in liquid phase

Pliego¹

2005

J. Braz. Chem. Soc.

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A importância de cada termo de solvatação não eletrostática, mais especificamente, formação de cavidade e dispersão-repulsão, para reações químicas em fase líquida foi analisada tomando como exemplo a reação de uma e duas moléculas de H 2 O com CCl 2 . O cálculo do efeito do solvente para estas reações em solução aquosa, via perturbação de energia livre, está disponível na literatura e foi usado para comparação. Neste trabalho, utilizamos a fórmula de Pierotti e o método de ClaveriePierotti para computar o valor da contribuição de formação de cavidade, enquanto que o termo de dispersão-repulsão foi calculado pelo método de Floris e Tomasi. Nossos resultados mostram que o termo de cavidade é o mais importante, sendo que o termo de dispersão-repulsão corresponde de 25% a 35% do termo de cavidade. Além disso, observamos que a aplicação direta da fórmula de Pierotti para a energia livre de cavidade é mais acurada do que o método de Claverie-Pierotti para este sistema.The relative importance of cavity formation and dispersion-repulsion contributions to the activation free energy of chemical reactions in liquid phase is discussed, taken as example the reaction of one and two H 2 O molecules with CCl 2 in aqueous solution. The solvent effect on these systems was investigated by free energy perturbation in previous publications. In the present report, were used the Pierotti scaled particle theory and the Claverie-Pierotti method to compute the free energy of cavity formation, while the dispersion-repulsion contribution was determined by the Floris and Tomasi method. We have found that the cavity term is the most important nonelectrostatic contribution of the solvent to the activation free energy, while the dispersion-repulsion contribution accounts for 25% to 35% of that term. In addition, we have observed that the direct Pierotti formula is more accurate than the Claverie-Pierotti method for the present system. Keywords: solvent effect, continuum model, reaction kinetics IntroductionThe important role of the solvent on the outcome and kinetics of chemical reactions is well established. 1-14 Usually, the electrostatic solute-solvent interaction is the most important contribution of the solvent to the free energy of solvation ( G el ), mainly in polar media and in situations where ionic species are involved. The nonelectrostatic contribution ( G nel ) is regarded as playing a minor role, but it is important for a fine turning of the solvation process modeling. This contribution can be separated in two terms: free energy of cavity formation ( G cav ) and dispersionrepulsion contribution ( G dr ). Thus, the full solvation free energy of a molecule can be written as:An important question to be analyzed is the level of importance of each nonelectrostatic term. It is known that both nonelectrostatic contributions can be relatively large and have opposite signals, leading to a small G nel . However, for a chemical process in solution, the variation of the solvation free energy ( G * solv , from the reactants to the transition ...

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A New Mechanism for the Reaction of Carbenes with OH Groups

Cited by 46 publications

References 37 publications

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

Amino Acid Insertion Frequencies Arising from Photoproducts Generated Using Aliphatic Diazirines

The role of nonelectrostatic solvation to chemical reactions in liquid phase

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A New Mechanism for the Reaction of Carbenes with OH Groups

Cited by 46 publications

References 37 publications

2‐Methoxy‐Δ3‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ3‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

Amino Acid Insertion Frequencies Arising from Photoproducts Generated Using Aliphatic Diazirines

The role of nonelectrostatic solvation to chemical reactions in liquid phase

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2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound

2‐Methoxy‐Δ³‐1,3,4‐oxadiazoline, a Multipurpose Precursor for the Generation of a Carbene, an Ylide, or a Diazo Compound