Modeling the semi‐empirical electrotopological index in QSPR studies for aldehydes and ketones

Abstract

The semi-empirical electrotopological index, I SET , used for quantitative structure-retention relationship (QSRR) models firstly developed for alkanes and alkenes, was remodeled for organic functions such as ketones and aldehydes. The I SET values for hydrocarbons are calculated through the atomic charge values obtained from a Mulliken population analysis using the semi-empirical AM1 method and their correlation with the SET i values attributed to the different types of carbon atoms according to experimental data. For ketones and aldehydes the interactions between the molecules and the stationary phase are slowly increased relative to the hydrocarbons, due to the charge redistribution that occurs in the presence of heteroatoms. For these polar molecules the increase in the interactions was included in the calculation of the I SET values through the dipole moment of the whole molecule and also through an equivalent local dipole moment related to the net charges of the atoms of the C --O and HC --O functional groups. Our findings show that the best definition of an equivalent local dipole moment is clearly dependent on the specific features of the charge distribution in the polar region of the molecules (e.g. ketones and aldehydes), which allows them to be distinguished. Thus, the QSRR models for 15 aldehydes and 42 ketones obtained using the remodeled I SET were of good quality as shown by the statistical parameters. The ability of this remodeled index to include charge distribution and structural details opens a new way to study the correlations between the molecular structure and retention indices in gas chromatography.

Molecular Interactions in Chromatographic Retention: A Tool for QSRR/QSPR/QSAR Studies

“…An appropriate way to calculate the I SET was developed that takes into account the dipole moment exhibited by these molecules and the atomic charges of the heteroatoms and the carbon atoms attached to them (Souza et al, 2009a). By considering the stationary phase as non-polar material, the interactions are slowly increased relative to the corresponding hydrocarbons due to the charge redistribution that occurs in presence of the heteroatom.…”

“…The semi-empirical topological index (I ET ) allowed the creation of a new descriptor, the electrotopological index, I SET , which was recently developed by our group and applied to QSPR studies to predict the chromatographic retention index for a large number of organic compounds, including aliphatic hydrocarbons, alkanes and alkenes, aldehydes, ketones, esters and alcohols (Souza et al, , 2009a(Souza et al, , 2009b(Souza et al, , 2010. The new descriptor for the above series of molecules can be quickly calculated from the semi-empirical, quantum-chemical, AM1 method and correlated with the approximate numerical values attributed by the semiempirical topological index to the primary, secondary, tertiary and quaternary carbon atoms.…”

“…This new index, I SET , is able to distinguish between the cis-and trans-isomers directly from the values for the net atomic charges of the carbon atoms that are obtained from quantumchemical calculations . For polar molecules like aldehydes, ketones, esters and alcohols, the presence of heteroatoms like oxygen changes considerably the charge distribution of the corresponding hydrocarbons, leading to a small increase in the interactions between the solute and the stationary phase (Souza et al, 2009a(Souza et al, , 2009b(Souza et al, , 2010). An appropriate way to calculate the I SET was developed, taking into account the dipole moment exhibited by these molecules and the atomic charges of the heteroatoms and the carbon atoms attached to them.…”

Development of semi‐empirical electrotopological index using the atomic charge in QSPR/QSRR models for alcohols

“…As in the case of ketones, aldehydes [30] and esters [31] we have included the above-mentioned points by calculating the retention index as in Equation (1), also using Equation (2) for heteroatoms, but including slight alterations that incorporated the effects of the dispersive dipolar interactions. For alcohols, the major effects in the charge distribution are due the presence of the oxygen atom and they occur at the site of and close to their neighbor (adjacent carbon atoms).…”

“…In order to obtain a molecular descriptor not directly related to the chromatographic retention indices (RI) but based on values calculated by quantum mechanics, a new semi-empirical electrotopological index (I SET ) was developed [29][30][31]. This new approach takes into account the dipole moment exhibited by these molecules as well as the atomic charges of the heteroatoms and the carbon (www.interscience.wiley.com) DOI: 10 atoms attached to them through the definition of an equivalent local dipole moment.…”