Walsh rules

For example, the well known Walsh rules 52 for molecular geometries were first based on simple molecular orbital arguments depending on orbital overlap and the difference between s and p atomic energies. Pearson 51 re-interpreted them from a symmetry point of view as the following example will show. 

Below are five illustrative examples of the explanatory power of classical physics in structural chemistry. In these examples, classical electrostatic interactions are used with the electron-domain representation of molecules to explain or to derive The New Walsh Rules , the Langmuir-Pauling and Hendricks-Latimer Occupancy Rule, the s-character Rule, the Methyl Group — Tilt Rule, and the Octet Rule. 

The New Walsh Rules. Rules such as the rule that covalent molecules with three heavy atoms ( heavy atom = any atom other than hydrogen) and 18 valence-shell electrons are bent, while with 16 valence-... 

Table 10 The shape of AH2 molecules predicted by Walsh rules"...

Most data for geometries of excited states stem from theoretical arguments or calculations. Qualitative concepts such as the Walsh rules (cf. Buenker and Peyerimhoff, 1974) have proven very useful. Another valuable... 

An obvious consequence of the Bent-Walsh rule is that bond lengths a and bond angle a should be correlated. Unortunately this has never been found due to too low precision in bond lengths determination [82], However, if instead of bonds lengths a the differences A = b - a are taken, then the mutual correlation appears [83] as shown in Fig. 23. 

The dependence A vs a works since in the subtraction part of the experimental error cancel out, and hence the dependence predicted by the Bent-Walsh rule may be observed. It is worth mentioning that the line described by A vs a relationship for p-homo-disubstituted benzene derivatives may be a good reference line for the situations in which there is no x-electron cooperative effect. For p-X-Y-disubstituted derivatives, if X and Y differ significantly by their electron accepting/donating abilities, the appropriate points in this graph are shifted down, as shown in Fig. 24. 

Undoubtedly, the model presentation of fulfilling the Bent - Walsh rule may be a convenient way of a quantitative estimation of through resonance effect compared with the reference interactions which are inductive (or due to electronegativity) in nature. 

Table 11 The shape of AB2 molecules predicted by Walsh rules ...

A bent structure (C2v symmetry), predicted by the Walsh rules [1], was obtained by experimental and theoretical studies (see also pp. 232/4). 

The Walsh rules predict C2V symmetry for the amide ion just as for the isoelectronic water molecule [1]. Experimental results confirm the theoretical predictions ... 

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