Chemisty Research Journal

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Investigating the Van Der Waals Equation “A” and “B” Parameters for Hydrocarbons (C1 to C24) by Computational Modelling

In the present work, it is performed a computational chemistry study involving hydrocarbons, from C1 (methane) to C24 (tetracosane), in order to correlatethe a and bparameters of van der Waals equationswith polarizability and molecular volume, as well another molecular parameters.The computations were performed usingSpartan´14 (version 1.1.8) by a Density Functional (DFT) method (B3LYP level, 6-31G* basis set, 6-31G* optimized geometry, in vacuum). Linear relationship between a andpolarizability, as well as b and volume, are observed. The energies of frontier molecular orbital (εHOMO, εLUMO), energy band gap (εLUMO-εHOMO), electronegativity (χ), chemical potential (𝜇), global hardness (η), global softness (S), and global electrophilicity index (ω) were calculated.  It is verified that the values of energy gap, and, mainly, η, S and ω (this last one, mainly) suffers very small variations or no variations at all, to higher hydrocarbons. So, as the number of carbons increases, the parameters that can be related with attractive and repulsive forces (and related, of course, with a and b values, both related, in a last reasoning, with the higher or lower deformability of the electron clouds), tends to a “stabilization”, making the linear relationship no longer so pronounced.

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