Hydrogen bond dissociation energy

Table 1.1 Carbon-Hydrogen and Heteroatom-Hydrogen Bond Dissociation Energies (D in kJ morI)a °...

The addition of several ligands to the metal system can reverse relative metal methyl and metal hydrogen bond dissociation energies. For example, reaction 5 is observed to be a last exothermic process,... 

Steele, W. C., L. D. Nichols, and F.G. A. Stone The Determination of Silicon-Carbon and Silicon-Hydrogen Bond Dissociation Energies by Electron Impact. J. Amer. chem. Soc. 84, 4441—4445 (1962). 

Problem 10.3 The carbon-hydrogen bond dissociation energy for benzene (112 kcal) is considerably larger than for cyclohexane. On the basis of the orbital picture of benzene, what is one factor that ntay be responsible for this What piece of physical evidence tends to support your answer Hint Look at Fig. 10.4 and )see Sec. 5.4.)... 

The thermodynamic stabilization was determined from the barrier to rotation, by thermochemical methods,and from thermolysis studies of bis(cyclopropylalkyl)diazenes, and found to be approximately 1.9 kcal mol . The value of the carbon-hydrogen bond dissociation energy, DH (cyclopropylmethyl-hydrogen), deduced from this is 98.5 kcal mol , which may be compared with the DH (ethyl-hydrogen) value of 100 kcal mol This demonstrates that there is a small but chemically significant interaction between the orbital containing the unpaired electron (SOMO) and orbitals of the C -C, bond. 

Direct hydrogen atom abstraction occurs less frequently from the nucle-obases, despite the expected modest carbon—hydrogen bond dissociation energy of the carbon—hydrogen bonds in the methyl groups of thymidine and 5-methyl-2 -deoxycytidine due to resonance stabilization of the incipient radicals. The respective radicals are also formed by deprotonation of the nucleobase radical cations, intermediates involved in electron transfer that are produced via one-electron oxidation. Amine radicals are also postulated as intermediates produced from the spontaneous decomposition of chloramines that arise from reactions of nucleosides with hypochlorous acid." " However, the majority of nucleobase radical intermediates arise from the... 

Further research into the reaction mechanism revealed that the reaction rate was correlated with the electron structure of the sulfoxide the more electropositive sulfoxides were the better oxygen donors. Excellent correlation of the reaction rates with the heterolytic benzylic carbon-hydrogen bond dissociation energies indicated a hydride abstraction mechanism in the rate-determining step to yield a carbocation intermediate. The formation of 9-phenylfluorene as by-product in the oxidation of triphenylmethane supports this suggestion. Further kinetic experiments and NMR showed the formation of a polyoxometalate-sulfoxide complex before the oxidation reaction, this complex being the active oxidant in these systems. Subsequently, in a similar reaction system, sulfoxides were used to facilitate the aerobic oxidation of alcohols [29]. In this manner, benzylic, allyUc, and aliphatic alcohols were all oxidized to aldehydes and ketones in a reaction catalyzed by Ke jn-type... 

In this way a hydrated H3O ion is formed with an exceptionally strong hydrogen bond (dissociation energy about 100 kJ mol ). A similar mechanism is valid in transport of OH ions, which also occurs along the hydrogen bridges ... 

Singleton, D.L., R.S. Irwin, and R.J. Cvetanovid (1977), Arrhenius parameters for the reactions oxygen( P) atoms with several aldehydes and the trend in aldehydic carbon-hydrogen bond dissociation energies. Can. J. Chem., 55, 3321-3327. 

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