Matrix-isolation infrared spectroscopy of organic phosphates

Matrix-isolation infrared spectra of trimethyl phosphate (TMP), triethyl phosphate (TEP), and tri-n-butyl phosphate (TBP), in argon and nitrogen matrices, are reported for the first time. The peak widths of the sharpest features in our matrix-isolated spectra are typically 2 cm-1, compared with peak widths of 40 cm-1 seen in liquids for these compounds. Comparison with the vapor-phase spectrum of TMP reported earlier indicates that TMP is trapped in two different conformations in these matrices. Similar spectra were also obtained for TEP. Our matrix-isolated spectra indicate that the intramolecular hydrogen bonding (which is believed to be responsible for the lowering of the P=O frequency in the C3, conformer relative to the C3 conformer in these compounds) is stronger in TEP than in TMP. In the case of TBP, the peak widths were larger (8-10 cm-1) than those obtained for TMP and TEP. This observation is probably due to a distribution of conformers that may be trapped in the matrix, as a result of the increased alkyl chain length in TBP.