Bond Energies, Lengths, and Dipoles

Part A of Table 1.4 shows all the acyclic C4-C6 hydrocarbons and a number of the Cg hydrocarbons. A general trend is discernible in the heats of formation data. Branched-chain hydrocarbons are more stable than straight-chain hydrocarbons. For example, the AH for n-octane is -49.82 kcal/mol, whereas the most highly branched isomer possible, 2,2,3,3-tetramethylbutane, is the most stable of the octanes, with a AH of -53.99 kcal/mol. Similar trends are observed in the other series. 

Part B of Table 1.4 gives heats of formation for the C4, C5, and some of the alkenes. A general relationship is also observed for the alkenes The more highly substituted the double bond, the more stable the compound. There are also other factors that enter into alkene stability, trans-Alkenes are usually more stable than cw-alkenes, probably largely because of increased nonbonded repulsions in the cis 

Empirical Electronegativities for Some Organic Functional Groups  

A review of the use of heats of hydrogenation for evaluation of the enthalpy of organic molecules is given in J. L. Jensen, Prog. Phys. Org. Chem. 12, 189 (1976). 

For more detailed discussions, see L. E. Sutton, in Determination of Organic Structures by Physical Methods, Vol. 1, E, A. Braude and F. C. Nachod (eds.). Academic Press, New York, 1955, Chap. 9 V. I. Minkin, O. A. Osipov, and Y. A. Zhdanov, Dipole Moments in Organic Chemistry, Plenum Press, New York, 1970. 

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During the last decade of the twentieth century, creation and testing of functionals provided gainful employment for the many theoretical chemists who were interested in the development of DFT as an accurate method for use in electronic structure calculations. The chapter on DFT in Cramer s book provides not only descriptions of different types of functionals but also information on how well each performs in calculating energies, bond lengths, and dipole moments for several different test sets of molecules. 

The CNDO and IN DO methods give accurate bond angles and fairly accurate bond lengths and dipole moments, but poor dissociation energies. 

Important properties of the chemical bond include its length, dissociation energy, order, and dipole moment. 

The active space used for both systems in these calculations is sufficiently large to incorporate important core-core, core-valence, and valence-valence electron correlation, and hence should be capable of providing a reliable estimate of Wj- In addition to the P,T-odd interaction constant Wd, we also compute ground to excited state transition energies, the ionization potential, dipole moment (pe), ground state equilibrium bond length and vibrational frequency (ov) for the YbF and pe for the BaF molecule. 

Quantitative structure-physical property relationships (QSPR). There are two types of physical properties we must consider ground state properties and properties which depend on the difference in energy between the ground state and an excited state. Examples of the former are bond lengths, bond angles and dipole moments. The latter include infrared, ultraviolet, nuclear magnetic resonance and other types of spectra, ionization potentials and electron affinities. 

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