Original scientific paper

Rules Governing the Effects of Substituents upon Alternant Conjugated Hydrocarbons

Viktorija Gineityte ; Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania

Abstract

Explicit algebraic expressions are derived and analyzed for the common charge-bond order
matrix and for the related representation matrix of non-canonical molecular orbitals (NCMOs)
of substituted alternant hydrocarbons (AHs) in terms of entire blocks of the common Hückel
Hamiltonian matrix of parent AHs and thereby of adjacency matrices of graphs of their C-skeletons.
Rules governing the effects of substituents upon electronic structures of hydrocarbons are
established and supplement the classical results describing the electronic structures of AHs and
of their perturbed analogues. In particular, two additive components are revealed within the effect
of substituent upon an AH, namely the charge transfer between the above-mentioned subsystems
and the intersubset polarization inside the AH [cf. the well-known partition of the basis
set of 2pz AOs of carbon atoms of AHs into two subsets]. The principal rule governing the
first component involves division of the total transferred population equally between the two
subsets of AOs of the AH. The intersubset polarization is shown to be governed by the second
order analogue of the rule of alternating polarity. Finally, a single principal electron-accepting
(donating) orbital is revealed among NCMOs of the parent AH for systems containing an electron-
donating (accepting) substituent, viz., the initially-vacant (occupied) NCMO attached to
the site of substitution is shown to play this role. The results obtained are illustrated by substituted
benzenes as examples.

Keywords

alternant conjugated hydrocarbons; adjacency matrix of molecular graph; charge-bond order matrix; non-canonical molecular orbitals; substituted benzenes; alternating polarity

Hrčak ID:

31137

URI

https://hrcak.srce.hr/31137

Publication date:

15.11.2008.

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