Conformational and vibrational study of di‐n‐propyl and di‐i‐propylphosphonates by MM/QM method

Abstract

ABSTRACT:A conformational search by MM/QM methods was realized for the din-propyl and di-i-propylphosphonates. The normal mode frequencies and corresponding vibrational assignments were examined theoretically using the hybrid functional B3LYP and the 6-31G* basis set, and were compared with the experimental spectra. It was possible to arrive at an accurate spectral assignment without the utilization of scaling factors including the region between 1,200 and 850 cm Ϫ1 , which is the most complicated spectral region for the assignment.

Conformational and vibrational study of di‐n‐butyl and di‐sec‐butylphosphonates by MM/QM method

“…In the region <300 cm −1 , the different torsional modes along the CC, CO, and PO axes were identified as well. These results agree with those obtained for DNP and DIP 5.…”

“…For DNB, this mode is coupled to the δ (PH) and CH twisting. These results agree to those for DNP and DIP 5.…”

“…Several experimental works 18, 19 assigned bands in the region 1311–1243 cm −1 to PO stretching. In our last works 4, 5, these modes were calculated at 1381 (AM1), 1401 (HF), and 1284 cm −1 (B3LYP) for di‐ n ‐propylphosphonate (DNP), and 1368 (AM1), 1395 (HF), and 1281 cm −1 (B3LYP) for di‐ i ‐propylphosphonate (DIP) with mean deviation of 2% for the DFT method.…”

“…Besides, there is no systematic study concerning the identification and full assignment of the vibrational spectra of these compounds in the literature. Recently, our group has been carrying out systematic work with the goal of calculating the vibrational spectra of di‐ n ‐propyl (DNP) and di‐ i ‐propylphosphonates (DIP) by a set of theoretical levels: semiempirical (AM1) and ab initio [restricted Hartree–Fock (RHF)/6‐31G*] 4 as well as density functional theory (DFT) (B3LYP/6‐31G*] 5. Although conformational analysis and electronic correlation effects were not taken into account, the AM1 and RHF/6‐31G* methodologies showed good results for band assignment, once scaling factors are properly used.…”

“…However, due to the highly coupled vibrational normal modes and the vicinity of bands in the region of 1200–850 cm −1 , deviations between the calculated and the experimental wavenumbers may lead to dubious assignment. A study of the di‐ n ‐propyl and di‐ i ‐propylphosphonates by the MM/QM method 5, based on conformational search and the vibrational spectra calculated by DFT methods, led to results that are surely better than the previous ones, mainly because of the better description of the electronic state of the system. However, uncertainties for assignments in the region between 1200 and 850 cm −1 may still persist.…”