Examinations of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds. Part V

MI/FT-IR spectral data have been collected on selected types of organic compounds containing the carbonyl group. By the varying of the ratio of the matrix gas to the compound (M/E) as well as the matrix gas (Ar vs. Xe), the observed splitting of the carbonyl absorption band was attributed to both conformer isolation and aggregation in the matrix. The splitting of the carbonyl group of methyl acetate was attributed to aggregation, while conformer isolation was found to exist for phenyl acetate and trimethylacetaldehyde. The magnitude of the splittings found in this study, 3–30 cm⁻¹, is within the range of values found for other organic compounds. Band splitting was shown by (1) compounds that are linear and contain ≤5 carbons or (2) compounds that are branched and contain <5 carbons. Compounds having >5 carbons displayed only band broadening. Varying M/E ratios has been found to be a reasonable method by which to distinguish between conformer and aggregation. These data confirm the influence of sample phase and indicate that extreme care must be taken in the use of MI/FT-IR spectra as physical probes for structure determination.