PEDA descriptor

A comparison of the substituent effects in monosubstituted tetrazole systems and benzene derivatives has been presented (2011T(67)6316). For this purpose the pEDA index (2009JPOC(22)769), defined as the sum of the occupation of 2p orbitals at aU atoms of the ring minus 6, has been used as a substituent descriptor. In aU three cases (substituted benzenes, IH- and 2H-tetrazole derivatives) the pEDA index, which ilLustrates the Tc-electron transfer from the substituent to the ring or vice versa, is weU correlated with constants. A more detailed analysis revealed that the dependence of 2pj, occupancies at the carbon atoms of benzene in either ortho- or para-positions on pEDA values are represented by linear trends with cc= 0.971 and 0.968, respectively. In contrast, the same correlation for the carbon atom in the meta-position is worse cc= —0.791) and with a small... 

Indeed, a heteroatom embedded into a ring certainly affects its c- and TC-electron system. Such incorporation effects can be evaluated by CT-electron-donor-acceptor descriptor [sEDA(II)] and ir-Electron-donor-acceptor descriptor [pEDA(II)] characteristics, which have been developed especially for unsaturated five- and six-membered cycles with heteroatoms (2012JOC2608), or their later modification for fused heterocycles, sEDA(III) andpEDA(III) (2015JP0290). 

To study the difference between ir-electron systems of hetero- and car-bocycles, the pEDA(II) descriptor (2012JOC2608), which measures heteroatom incorporation effects on the ir-electron system, is very helpfirl. Using natural bond orbital (NBO) analysis, it is possible to estimate the changes in population of a- and ir-electron in a given system (2009JP0769), that is, the amount of electrons shifted to or withdrawn ftom the ir valence orbitals of the core molecule by the heteroatom/heteroatomic group. The obtained... 

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