Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds

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

doi:10.1590/s0103-50531998000200011

Cited by 7 publications

(6 citation statements)

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“…[16] In contrast, nucleophilic carbenes do not even add to the oxygen atom of C=O double bonds. [17] In regard to the decomposition of oxadiazoline 13, computations were performed at the B3LYP/6-31G(d) level of theory. It is found that diastereomer 13b is more stable than 13a by about 1.3 kcal/mol.…”

Section: Investigation Of the Reaction Mechanismsmentioning

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: Investigation Of the Reaction Mechanismsmentioning

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 some situations the carbene does not present strong absorption bands and cannot be observed. In these cases the pyridine probe technique has been utilized. − ,, In addition to experimental studies, ab initio calculations have become an important tool to predict and understand carbene reactivity. − …”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4]8,11 In addition to experimental studies, ab initio calculations have become an important tool to predict and understand carbene reactivity. [18][19][20][21][22][23][24][25][26][27][28][29] Carbenes are usually generated in a closed shell singlet state upon photolysis of a photochemical precursor. 1,11,30,31 While many carbenes have singlet ground states, several others have triplet multiplicity in their lowest electronic state.…”

Section: Introductionmentioning

confidence: 99%

Singlet−Triplet Gap, and the Electronic and Vibrational Spectra of Chlorophenylcarbene: A Combined Theoretical and Experimental Study

Pliego¹,

Almeida²,

Celebi³

et al. 1999

J. Phys. Chem. A

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Minimum energy structures of singlet and triplet chlorophenylcarbene, a prototypical carbene, were computed. The singlet-triplet energy separation was predicted to be 7.84 and 7.70 kcal/mol at the UCCSD(T)/6-31+G* and QCISD(T)/6-31+G** levels of theory, respectively, after zero-point correction. This is slightly larger than that predicted by the CAS(6,6) (4.5 kcal/mol), local spin density approximation (5.6 kcal/mol), and the BLYP (7.3 kcal/mol) methods with the 6-31G* basis set reported by Trindle et al. The UV-vis and IR spectra of chlorophenylcarbene were analyzed with the aid of the CASPT2/CASSCF(10,10) and the B3LYP/ 6-31G* levels of theory, respectively. The UV-vis and IR spectra of chlorophenylcarbene were assigned on the basis of these calculations. The ab initio calculations predicted the existence of strong absorption bands in the UV and a weak band in the visible in good agreement with published spectra. The long (750 nm) wavelength band corresponds to electron promotion from the lone pair σ (HOMO) to the π* (LUMO). On the basis of the calculated harmonic frequencies, we cannot assign the 1244 and 1600 cm -1 IR bands observed in an argon matrix to chlorophenyl carbene. The most intense IR band (1225 cm -1 ) corresponds to the symmetric C-C stretch of the carbene and aromatic carbon. The asymmetric and symmetric C-C-Cl stretches are assigned to the bands observed at 847 and 739 cm -1 , respectively.

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“…The carbon−oxygen π bond breaks down, and the formation of an ylide with biradical characteristics takes place . The carbonyl ylides of methylene, difluorocarbene, and dihydroxycarbene with formaldehyde also exhibit biradical characteristics. − In the reaction of dichlorocarbene with CN groups, dipolar and biradical species can be formed, although the biradical form is thermodynamically and kinetically more stable . Based on these studies, the electrophilic properties of carbenes should be looked at with caution, since in general these species prefer to form biradical structures rather than dipolar ones.…”

Section: Introductionmentioning

confidence: 99%

A New Mechanism for the Reaction of Carbenes with OH Groups

Pliego

Almeida

1999

J. Phys. Chem. A

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The reaction pathway for the 2H2O + CCl2 reaction through a cyclic five-atom transition structure was studied using ab initio molecular orbital theory. The MP2 method in conjunction with the DZP basis set was used for geometry optimizations, and single point energy calculations were performed at MP2 and MP4 levels with the cc-pVDZ and cc-pVTZ basis sets. The solvent effect on the activation free energy was evaluated by Monte Carlo statistical mechanics calculations. The new mechanism has a high rate constant, and we predict a lifetime of seven nanoseconds for dichlorocarbene in aqueous solution. We have proposed that this mechanism occurs for the reaction of dichlorocarbene with water, and possibly may be involved in many reactions of carbenes with alcohols. We have also shown that it can explain the following experimental facts: (a) alteration of the product isotopic effect on addition of a second alcohol, (b) difference between product and kinetic isotopic effects, and (c) no linear dependence of the observed rate constant for carbene decay on alcohol concentration.

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Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds

Cited by 7 publications

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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

Singlet−Triplet Gap, and the Electronic and Vibrational Spectra of Chlorophenylcarbene: A Combined Theoretical and Experimental Study

A New Mechanism for the Reaction of Carbenes with OH Groups

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Thermodynamics of Ylide Formation from Carbenes and Carbonyl Compounds

Cited by 7 publications

References 0 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

Singlet−Triplet Gap, and the Electronic and Vibrational Spectra of Chlorophenylcarbene: A Combined Theoretical and Experimental Study

A New Mechanism for the Reaction of Carbenes with OH Groups

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Product

Resources

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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