We present computational analyses, methodological advances, and heuristic conclusions applied on a series of polyaromatic systems condensed in the shape of regular triangles, carrying spin, because of topological reasons. A new clue about the classification of title systems in three equivalency classes is presented. A conjugated hydrocarbon having n-hexagonal rings at one edge, carrying n − 1 unpaired electrons, will be called n-triangulene in the generalization of the experimentally known structures with n = 2 (phenalenyl) and n = 3 (triangulene). To be distinguished from most of the previous computational approaches, done by density functional theory, we challenged the problem in the key of valence bond (VB) paradigm in both ab initio and phenomenological manners. The Heisenberg spin Hamiltonian was used to simulate the computed spectrum of VB states for the phenalenyl radical (n = 2), predicting with the fitted parameters the effective VB description of n = 3 triangulene and other related systems. The outcome has practical importance in the prospects of spin chemistry because the VB ab initio calculations are prohibitive beyond the n = 2 case. The results are made transparent to the chemical intuition using the language of resonance structures.

New possibilities for estimating octanol/water partition coefficients (logP) and the water solubility (S w ) were investigated using Kovàts retention indices (I) obtained from GLC retention data for 132 volatile organic compounds belonging to 7 different chemical classes (hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters and halogen compounds). Application of the multilinear regression method led to six equations, all involving index I, as follows: (i) direct correlation logP vs. I (eq.1); (ii) logP vs. I , molar refractivity, and surface tension (eq. 2); (iii) logP vs. I and structural characteristics (eqs. 3, 4 and 6); (iv) logP vs. the I/S w ratio (eq. 5). Excepting eq. 1 (which showed relatively weak correlations), eqs. 2 -6 can provide reliable values for logP and for logS w as proved by the significant statistical parameters. The general models presented through eqs. 2 -6 may also be applied in estimation of other biological and/or ecological important properties, which are linearly dependent on the logP or log S w values. By generalization, a new calculation method is suggested (eq. 7), in order to allow the estimation of logP or logS w in terms of the number of bonds and the Kovàts retention index.

A QSPR study was realized in order to predict the Retention Times (RT) determined from interaction between two types of solutes (alcohols and esters) and six Stationary Phases (SPs), five of them specials (1a -e) and a classical one (OV-25), by correlating the adjusted RTs, t 0 R determined for each SPs at temperature between 70 and 140 8C with the values of molecular descriptors implemented in CODESSA program. New topological indices R AF (for alcohols) and D A (for esters) derived from local invariants of chemical graphs of alcohols and esters determine an increase in predictive power of models where these descriptors have been used.

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