Intermediate field case, effect

We shall start with the so-called intermediate-field case. In many of the ionic complexes of the 3group elements, while the free ion energies due to the Coulomb repulsion between electrons have the order of magnitude of 10 to 10 cm, energies of the cubic crystal field are of the order of 10 cm. So we can treat the effect of the latter as the perturbation acting on the multiplet terms characterized by definite values of L and S. 

Also, rearrangement in many cases would be difficult because of the crystal field stabilization effects. But it could be possible that somewhere, when this bond had lengthened sufficiently, this group X could slip in and as Dr. Langford indicated, we would then have an intermediate, or transition state, or something which would have these two groups partially bonded. 

In such cases, the more acidic hydrogen is removed. Since acidity is related to the field effect of Z, it can be stated that an electron-attracting Z favors removal of the ortho hydrogen while an electron-donating Z favors removal of the para hydrogen. The second factor is that the aryne, once formed, can be attacked at two positions. The favored position for nucleophilic attack is the one that leads to the more stable carbanion intermediate, and this in turn also... 

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