Methylenes formation

Energy-resolved rate constant measurements near the threshold for diplet methylene formation from ketene have been used to provide confirmation of the fundamental hypothesis of statistical transition state theory (that rates are controlled by the number of energetically accessible vibrational states at the transition state).6 The electronic structure and aromaticity of planar singlet n2-carbenes has been studied by re-election coupling perturbation theory.7 The heats of formation of three ground-state triplet carbenes have been determined by collision-induced dissociation threshold analysis.8 The heats of formation of methylene, vinylcarbene (H2C=CHCH), and phenylcarbene were found to be 92.2 3.7, 93.3 3.4, and 102.8 33.5 kcal mol-1, respectively. 

Table IV. Comparison of Methylol Loss, Methylene Formation, and Phenol Substitution as Percentage of Methylol Consumed after 6 Hours and 100 °C at Various pH...

The tremendous advantage of this method of methylene formation over the various other procedures is that it is capable of producing optically pure material through the addition of an enantiomer of (methyl-... 

The methylene compound 26 forms much faster iu the preseuce of 2,4-dimethylpheuol (21) thau by self-reaction. However, the relative rate of methylene formation does not... 

In conclusion, the group VIII metals may be classified according to their increasing capacities to form metallocarbenes, and it is worth mentioning again that the above classification Pd < Pt < Ir < Ni < Co, parallels that suggested by the multiple exchange of methane for adsorbed methylene formation (90). 

An example of the inferences that have been drawn is as follows. Methylene formation in the reactions of recoiling carbon atoms was deduced from comparison of product distributions from recoil experiments with those obtained from singlet state CH2 (16yl7). The hexanes produced from the reactions of recoiling atoms with n-pentane were... 

Figure IX-E-15. Quantum yield of singlet methylene formation as a function of wavelength in the photodecomposition of ketene at low pressures.

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