W. M. Coleman

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part X

The characteristics of the OH stretching absorptions in a series of catechols, resorcinols, hydroquinones, and diols have been documented with the use of matrix isolation Fourier transform infrared spectroscopy. Steric and electronic effects were described and found to agree with published results on the vapor-phase studies on the same compounds. The positions of the OH absorptions were shown to fall within a window set on the high energy side by the vapor-phase results and on the lower energy side by solid-state/solution results. The very low full width at half-height values unique to the matrix experiment allowed for the observance of absorption bands not yet seen before in the vapor-phase or solid-state studies. These new bands confirm the presence of intramolecular interactions not previously documented. The data as a whole do indicate that extensive intermolecular interactions do occur at very low loadings on the cryogenic disk (10 ng) for compounds containing polar substituents.

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds, Part I

Data are presented that describe the IR spectra of organic compounds obtained under matrix isolation conditions. Among the types of compounds examined are amides, lactones, lactams, esters, acids, alcohols, and phenols. Trends, as a function of structure, established in vapor-phase IR are shown to exist under MI conditions. The frequency (cm−1) of the stretching absorption for hydroxyl groups and carbonyl groups associated with the types of compounds listed above under MI conditions is shown to be intermediate between the vapor-phase position (highest energy) and the solid-solution position (lowest energy). In some cases the three phases differ by as much as 300 cm−1 (OH group in carboxylic acids) and by as little as 15 cm−1 (carbonyl group in carboxylic acid esters).

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part VII

A series of lactones and lactams have been examined by matrix isolation Fourier transform infrared spectrometry. The values for the carbonyl absorption bands fall between those reported for the same compounds in the vapor phase and solid state. Multiple absorption bands are found in the region of carbonyl absorption for compounds examined under the matrix isolation phase. Ring strain has a dramatic effect on simplifying the complexity of the spectra. Little or no aggregation effects are observed for either the lactones or lactams under accepted operating parameters. The effects of substituents on these systems are comparable to those found in the vapor-phase and solid-state data.

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part II

Matrix-isolated (MI) Fourier transform infrared spectra have been collected on a series of aliphatic ketones. The values for the carbonyl absorptions maxima are intermediate between vapor-phase (VP) and solid-state solution (SS) phases. The data reveal a stereochemical influence on the position of the ketone carbonyl absorption when the carbons that are in the alpha position with respect to the carbonyl group contain alkyl snbstituents vs. protons. Steric bulk causes the frequency of the absorption to decrease. The position of the ketone carbonyl absorption was also shown to decrease as the carbonyl group migrated toward the center of a long straight-chain hydrocarbon backbone. Stereochemical influences due to ring strain were also documented. Unsaturation, located in the alpha position with respect to the carbonyl, was shown to reduce the absorption frequency. The trends found in this MI study are comparable to those previously documented from VP and SS studies. In two cases wherein very bulky substituents were located in the alpha position with respect to the carbonyl, a splitting of the carbonyl absorption was observed. Studies are underway to test for a general trend in and to uncover an explanation for this phenomenon.

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part III

Matrix-isolated (MI) Fourier transform infrared spectra (FT-IR) have been collected on a series of esters and ketones. The values for the carbonyl absorption are intermediate between the values for vapor-phase (VP) and solid-state (SS) phases. The spectra reveal a splitting or broadening of the carbonyl absorption in the majority of cases for both compound types. The splitting, on the order of 5 to 10 cm−1, does not appear to be a function of concentration at ≤20 ng on the cryogenic disk. The splitting is also not unequivocally due to steric hindrance about the carbonyl group. Compounds with liner as well as branched substituents display spectra having split carbonyl absorptions. Isolation of molecules within multiple types of matrix sites is advanced as the predominant cause of the splitting phenomenon. Implications and consequences of the observed splitting are discussed.

Examinations of the matrix isolation fourier transform infrared spectra of organic compounds: Part XII

Matrix isolation Fourier transform infrared spectra (MI/FT-IR), mass spectra (MS), carbon-13 Nuclear Magnetic Resonance (13C-NMR) spectra, condensed-phase infrared spectra, and vapor-phase infrared (IR) spectra are presented for a series of terpene compounds. Subtle differences in positional and configurational isomers commonly found with terpenes could be easily detected by the MI/FT-IR spectra. The results are comparable in some aspects to those obtainable from 13C-NMR and thin-film IR; however, most importantly, they are acquired at the low nanogram level for MI/FT-IR, as compared to the milligram level for the other techniques. These results represent an advance in the technology available for the analysis of complex mixtures such as essential oils containing terpene-like molecules.

Examination of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part VI

Matrix-isolated (MI) Fourier transform infrared spectra (FT-IR) have been collected on a series of aldehydes and acids. The values for the carbonyl absorption are intermediate between the higher values for vapor-phase (VP) and lower values for solid-state (SS) phases. Substituent effects on aromatic rings induce shifts in carbonyl absorptions in the same manner as found in VP and SS studies. The magnitude of the shifts is approximately the same for all three phases. The spectra reveal a splitting or broadening of the carbonyl absorption for both aldehydes and acids. The size of the molecule affects the degree of band broadening. In certain cases discrete conformers appear to have been isolated in the matrix.

Examinations of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part IX

A series of β-diketones and alkenes have been examined by matrix isolation Fourier transform infrared spectroscopy. The matrix experiment readily detects the presence of extensive keto-enol tautomerization in selected β-diketones. Certain absorption bands in the IR could be used to estimate the extent of the tautomerization. The data gathered on the alkenes found their absorption bands to occur in the same regions (±5 cm−1) as those found for VP and SS phases. Minimal nearest-neighbor (aggregation) interactions were found. These results are in contrast to those found for aldehydes, ketones, and acids of similar chain lengths.

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.

Examinations of the Matrix Isolation Fourier Transform Infrared Spectra of Organic Compounds: Part XI

Matrix isolation Fourier transform infrared information has been presented on a series of aliphatic amines, anilines, and amides. The absorptions associated with NH stretches are found at essentially the same energies in both the vapor phase (VP) and matrix isolation (MI) phase. Both the VP and MI values are found at higher energy than the solid state (SS) phase. The similarity of the values for the MI and VP phases is a departure from results found previously for other types of organic compounds. The carbonyl absorptions for the amides (MI) were found to be intermediate between the VP (high) and SS (low) values. This is consistent with established trends for other carbonyl containing compounds. The absorptions for carbonyl groups for the majority of the compounds appear as split absorptions on the order of 20 cm−1 peak to peak. These split absorptions were ascribed to intramolecular hydrogen bonding and rotational conformer isolations. Minor aggregation effects were found to occur as band broadening effects when the ratio of matrix gas (argon) to analyte dropped below 1000:1.