Background: Gaussian 09 program package was used to optimize the molecular
structures and calculate the vibrational wavenumber of cis and trans isomers of oligo
acetylene and functionalized oligo acetylene. The geometrical parameters of the more stable
conformers are reported and the total energies of the optimized structures were used to
calculate the cis-trans relative energies in gas and aqueous phases.
Objective: To carryout theoretical investigation of the conformational preference and
vibrational spectroscopy of mono-terminal substituted oligo acetylene with carboxylic acid
and 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 Equation
Formalism in the Polarizable Continuum Model was used as a solvation model for the
aqueous phase computations.
Results: The trans isomers of un-substituted and substituted oligo acetylene are found to be
more stable in both gas phase and aqueous phases. The order of stability in gas phase is as
follows: CnHn+1 (CO2H)> CnHn+1 (H2PO3)> CnHn+2, (n=3-5). Solvation results for the
substituted systems showed that the solvent effect on trans isomers of mono-substituted
phosphonic acid is higher than that of mono-substituted carboxylic acid and the solubility
increases with the increase in the number of monomer unit.
Conclusion: The use of B3LYP/6-31+G(d,p) method shows successful results for the
calculated properties of the studied systems which in agreement with results are reported in