Molecular orbital of pyrrole

The frontier orbital argument, weak as it is, is clear in predicting attack at C-2. The n molecular orbitals of pyrrole are representative of all three—they have been shown earlier [see (Section 1.7.5) page 52], where i/j3 is the HOMO 4.53 (with a node running through the heteroatom, it is the same as i/j2 of butadiene). An estimate of the total n charge 4.54 can be calculated from the sums of the squares of the coefficients. 

Fig. 9. Bonding molecular orbitals of pyrrole-type heterocycles.

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