Homolytic Rearrangements of Ketenimines to Nitriles:  Employments of Hammett Dual Parameters

Kim, Sung Soo; Liu, Bo; Park, Chul Hyun

doi:10.1021/jo971844c

Cited by 14 publications

(9 citation statements)

References 27 publications

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“…Highlights of Kinetic Data. Preparations of numerous substituted ketenimines followed the previous method . All the NMR spectra of ketenimines and nitriles match their structures.…”

Section: Resultsmentioning

confidence: 99%

“…Thermal isomerizations of ketenimines to nitriles − are known to take place via cage recombinations of radical pairs. Subsequently, the rates of isomerizations at 60 °C of various diphenyl N -(substituted benzyl)ketenimines were measured that follow excellent first-order kinetics. The rates are better fitted with Hammett dual correlations indicating concurrent contributions of 1 and 2 to the transition state (TS).…”

Section: Introductionmentioning

confidence: 99%

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Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Kim

Zhu

2000

J. Org. Chem.

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Rate constants (k(Y)) of the isomerizations of 11 diphenyl N-(substituted benzyl) ketenimines were measured at 40, 50, 60, and 70 degrees C. Activation parameters DeltaH()(Y) and DeltaS()(Y) were obtained using the Eyring equation. The relative rates (k(Y)/k(H)) were fitted into Hammett single correlations (log k(Y)/k(H) = rhosigma and log k(Y)/k(H) = rho(*)sigma(*)). The single correlations have been compared with Hammett dual correlations (log k(Y)/k(H) = rhosigma + rho(*)sigma(*) ). Separate treatments of para and meta substituents yielded even better correlations. Para substituents control the rates through spin-delocalizations and inductive effects. The former outweighs the latter when the latter exerts a modest but distinct influence on the rates. On the other hand, inductive effects are the "major" or the sole interactions triggered by meta substituents.

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“…Highlights of Kinetic Data. Preparations of numerous substituted ketenimines followed the previous method . All the NMR spectra of ketenimines and nitriles match their structures.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Kim

Zhu

2000

J. Org. Chem.

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“…After intensive literature searches we arrived at a set containing 24 reactions of molecules that are of typical size for organic chemistry and can be found in chemistry textbooks [56][57][58][59][60][61][62] or recent research papers. [63][64][65][66][67][68][69][70] It is shown in Fig. 1 and dubbed in the following and for future reference ISOL.…”

Section: The Isol Setmentioning

confidence: 99%

Effects of London dispersion on the isomerization reactions of large organic molecules: a density functional benchmark study

Huenerbein

Schirmer

Moellmann

et al. 2010

Phys. Chem. Chem. Phys.

139

163

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A benchmark set of 24 isomerization reactions of large organic molecules (consisting of 24 to 81 atoms) is presented (termed ISOL). The molecules are much larger than what is typically considered in thermochemical tests. To obtain reference isomerization energies, complete basis set (CBS) extrapolations at the (SCS)-MP2 level have been computed that are augmented by perturbative third-order corrections (SCS-MP3 and MP2.5 methods). Based on these carefully examined reference data, a diverse set of common density functionals varying from GGA to double-hybrid functional level with and without dispersion correction (DFT-D) is tested. Double-hybrid and the PBE0 hybrid functionals are found to be the methods of choice for the type of main group thermochemistry examined here. For all isomerizations with an average reaction energy of 22.7 kcal mol(-1) (in a range between 0.5 and 74.5 kcal mol(-1)), PBE0-D, B2PLYP-D and B2GP-PLYP-D yield mean absolute deviations of 2.5, 4.1 and 2.9 kcal mol(-1). Most importantly it is found that the use of a dispersion correction is essential if such large molecules are considered. For all DFT methods the MAD is lowered very significantly by 1.4-5.0 kcal mol(-1) when DFT-D is used. Intramolecular (mainly medium-range) London dispersion interactions account in some cases for more than 50% (41 kcal mol(-1)) of the isomerization energy even though the size of the systems remains unchanged. This study also demonstrates for the first time clearly that typical DFT errors are larger than expected (about 5 kcal mol(-1)) and that chemical accuracy (about 1 kcal mol(-1)) even for these electronically well-behaved molecules is currently not reached by DFT. We propose this new test set as a difficult challenge for electronic structure methods that claim to be routinely applicable to large molecules. We also suggest to use a distance range resolved dispersion energy as a diagnostic for problematic cases in DFT.

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“…The IR spectrum of 5 in CCl 4 at room temperature exhibited a weak but sharp band at 2011 cm -1 that remained unchanged for at least 24 h. Although this band might be attributed to a small amount of ketenimine 18 , such a product would not be expected to persist. , In a more determined effort to detect 18 , a degassed, sealed solution of 5 in hexane was heated at 40 °C with monitoring by UV. The azo band at 368 nm disappeared smoothly with no evidence of rising absorption at 290 nm, the expected λ max of a ketenimine.…”

Section: Resultsmentioning

confidence: 99%

Thermolysis of Acylazo O-Trimethylsilyl Cyanohydrins: Azoalkanes Yielding Captodatively Substituted Radicals

et al. 1998

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A new synthetic method has been developed for preparing azoalkanes bearing geminal α-cyano and α-trimethylsiloxy groups. While the symmetrical compound 5 decomposes near room temperature to afford, almost entirely, the C−C dimers, the unsymmetrical azoalkane 3 requires heating to 75 °C. The thermolysis activation parameters of 3 and 5 can be rationalized on steric grounds without invoking captodative radical stabilization. A 13C NMR product study of photolyzed 3 in the presence of TEMPO at 21 °C shows that the fate of caged [tert-butyl, 1-trimethylsiloxy-1-cyanoethyl (14)] radical pairs is disproportionation, 17%, cage recombination, 20%, and cage escape, 63%.

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Homolytic Rearrangements of Ketenimines to Nitriles: Employments of Hammett Dual Parameters

Cited by 14 publications

References 27 publications

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Effects of London dispersion on the isomerization reactions of large organic molecules: a density functional benchmark study

Thermolysis of Acylazo O-Trimethylsilyl Cyanohydrins: Azoalkanes Yielding Captodatively Substituted Radicals

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Homolytic Rearrangements of Ketenimines to Nitriles: Employments of Hammett Dual Parameters

Cited by 14 publications

References 27 publications

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ•) Constants for Spin-Delocalizations

Effects of London dispersion on the isomerization reactions of large organic molecules: a density functional benchmark study

Thermolysis of Acylazo O-Trimethylsilyl Cyanohydrins: Azoalkanes Yielding Captodatively Substituted Radicals

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Product

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Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations

Thermal Isomerizations of Ketenimines to Nitriles: Evaluations of Sigma-Dot (σ^•) Constants for Spin-Delocalizations