Theoretical Study of Mono-terminal Functionalized Oligo Acetylene [CnHn+2X] (n=3-5, X= - COOH, and - PO₃H₂) in Gas and Aqueous Phases

摘要

Background: Gaussian 09 program package was used to optimize the molecularstructures and calculate the vibrational wavenumber of cis and trans isomers of oligoacetylene and functionalized oligo acetylene. The geometrical parameters of the more stableconformers are reported and the total energies of the optimized structures were used tocalculate the cis-trans relative energies in gas and aqueous phases.Objective: To carryout theoretical investigation of the conformational preference andvibrational spectroscopy of mono-terminal substituted oligo acetylene with carboxylic acidand phosphonic acid groups in gas and aqueous phases.Methods: Computations were performed using Density Functional Theory adopting Becke-3–Lee–Yang–Parr (B3LYP) with the 6-31+G(d,p) standard basis set. The Integral EquationFormalism in the Polarizable Continuum Model was used as a solvation model for theaqueous phase computations.Results: The trans isomers of un-substituted and substituted oligo acetylene are found to bemore stable in both gas phase and aqueous phases. The order of stability in gas phase is asfollows: CnHn+1 (CO2H)> CnHn+1 (H2PO3)> CnHn+2, (n=3-5). Solvation results for thesubstituted systems showed that the solvent effect on trans isomers of mono-substitutedphosphonic acid is higher than that of mono-substituted carboxylic acid and the solubilityincreases with the increase in the number of monomer unit.Conclusion: The use of B3LYP/6-31+G(d,p) method shows successful results for thecalculated properties of the studied systems which in agreement with results are reported inliterature.