Abstract
In complex scientific disciplines, such as chemistry, a command of the literature and an ability to recognize the common denominator of many apparently unrelated experimental observations often leads to the formulation of concepts and rules of broad applicability. One demonstration of how such a marriage of knowledge and intuition can bear offspring was given by Walsh, who, many years ago, recognized that many experimental facts, which were known at that time, could be explained in a self-consistent manner by assuming that the hybridization of a central atom (or core) depends on the electronic nature of the ligands attached to it and proposed the following rule: “If a Group X attached to Carbon is replaced by a more Electro-negative Group Y, then the Carbon Valency towards Y has more p Character than it had towards X”.1 We shall refer to this as Walsh’s rehybridization rule. In recent times, this rule, in one form or another, has been applied to a variety of interesting chemical problems by many, most notably by Bent2.
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References
Walsh, A.D., Disc. Faraday Soc. 1947, 2, 18.
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CH3)2O: Kimura, K.; Kubo, M., J. Chem. Phys. 1959, 30, 151.
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Epiotis, N.D.; Larson, J.R.; Eaton, H. “Unified Valence Bond Theory of Electronic Structure” in Lecture Notes in Chemistry, Vol. 29, Springer-Verlag; New York and Berlin, 1982.
The expression of the total energy of a system as a sum of the energies of the individual subsystems is the direct result of the neglect of electron- electron interaction of these subsystems. This is done only for qualitative purposes. Indeed, the Independent Bond Model MOVB theory can be rigorously implemented in a quantitative ab initio sense without neglecting the subsystem bielectronic interaction. However, this is not one of the aims of this work.
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The meaning of the wiggly double arrow is discussed in reference 6.
This is so because βtu and hmn are interfragmental resonance integrals.
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In a following paper, we shall see that F, O, and N actually have different hybridizations in the corresponding hydrides with N tending towards the sp3 and F towards the p mark of the scale, for the time being, the assumption that all three have the same hybridization (Table 1) is safe for the purposes of this paper.
For example, according to the Wolfsberg-Helmholz approximation, 3s is a stronger overbinder, while, according to the Pople approximation, employed in CNDO calculations, 3p exceeds 3s in overbinding ability. See: Pople, J.A.; Beveridge, D.L. “Approximate Molecular Orbital Theory”; McGraw-Hill: New York, 1970.
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Epiotis, N.D. (1983). The Induced Deexcitation Model. In: Unified Valence Bond Theory of Electronic Structure. Lecture Notes in Chemistry, vol 34. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-93239-7_1
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DOI: https://doi.org/10.1007/978-3-642-93239-7_1
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