Bond energy term values

The heat of formation of tin tetraethyl is quoted by Long and Norrish i, and they obtain E G -Sn) =81 kcal. This is based on Zc = 190 kcal, a value of 50 9 kcal for the heat of atomization of tin, and an excitation energy of 113 2 kcal to the appropriate excited state. Reduced to ground state atoms, and taking our values of heats of atomization E G - Sn) becomes 45 kcal. The same result is obtained using the bond energy term values given here. 

H. A. Skinner and G. Pilcher, Bond energy term values in hydrocarbons and related compounds, Quart. Rev. 17, 264 (1963). 

V. Metal-Carbon Bond Energy Term Values.96... 

The C—H bond energy term value in CH4 is uniquely determined by dividing the total heat of atomization equally between the four bonds, i.e.,... 

Bond energy term values do not bear a simple relation to bond dissociation energies, and are not necessarily numerically identical with them on the contrary, the two measures often differ by substantial amounts. The widespread acceptance of E values as an index of bond strength continues nonetheless, largely as a matter of expediency due to the lack of more direct information. 

Bond Energy Term Values and Allen Parameters of Metal-Carbon... 

Skinner HA, Pilcher G. Bond-Energy Term Values in Hydrocarbons and Related Compounds. Quart Rev Chem Soc. 1963 17 264-288. 

The standard deviation between experimental and calculated heats of reaction are between 0.5 and 1 kcal/mol for those classes of compounds where enough experimental heats of formation are available to allow a full parameterization. For those classes of compounds where insufficient heats of formation are known to allow the determination of all parameters for 1,2- and 1,3-interactions, an estimate can be given for the bond energy terms which are the dominating parameters. Even here, therefore, a reasonable value for the reaction enthalpy is available. 

AH°t) and the sum of bond-energy terms ( °b) of the species under consideration. Here, Nab stands for the number of equivalent bonds having E°b. The bond-energy terms are obtained from a set of reference compounds. The heat of atomization is evaluated from the difference of the heat of formation of the constituent atoms and the species under consideration (2). The procedure depends on the reliability of the heat of formation of the individual molecules. In cases where experimental values exist it is not necessary to have recourse to computational methods. However, the heats of formation of many molecules which are of interest in the context of captodative substitution are not known experimentally. 

In view of the fact that bond energy terms have usually been calculated for 25° G, the heats of atomization are given for this temperature. Thus the numerical value quoted for the atom A is A/y (A) at 25° C. The discussion of each value is subheaded by the atomic number of the element concerned thus Section 8.2.2.14 refers to silicon. 

NUMERICAL VALUES OF THERMOCHEMICAL BOND ENERGY TERMS IN POLYATOMIC MOLECULES... 

Numerical values of thermochemical bond energy terms, derived from heats of atomization of molecules, are given in this chapter. An attempt is made to assess the reliability of the experimental information on which they are based. Only molecules for which an unambiguous valence bond structure can be written are discussed so that the question of empirical resonance energies is not treated. 

NUMERICAL VALUES OF THERMOGHEMIGAL BOND ENERGY TERMS... 

Skinner et al. deduced the average value of Z)(B-0) in these compounds to be 110 5 kcal, in reasonably good agreement with the above bond energy term. 

The uncertainty in the heat of atomization of carbon introduces uncertainty in the absolute values of its bond energy terms. The following discussion will, however, be concerned largely with differences, where this difficulty does not arise. 

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