Analysis of Nitrocresols and Related Compounds by Gas Chromatography/Matrix-Isolation Infrared Spectrometry

Abstract

The capabilities of gas chromatography/matrix-isolation infrared (GC/MIIR) spectrometry for characterizing nitrocresols in air sample extracts were evaluated. The IR spectra of selected nitrocresols were recorded in an argon matrix, in a xenon matrix, in the vapor phase, and in dilute CCl4 solution. The MIIR spectra of the nitrocresols that do not undergo intramolecular hydrogen bonding exhibited split OH stretching bands. Several factors that might cause band splitting, including aggregation, solute–matrix interactions, and the isolation of conformers, were investigated. The presence of aggregates was indicated by a broad band assigned to intermolecular hydrogen bonding in the MIIR spectra of 3-and 4-nitrocresol isomers deposited in an argon matrix at a matrix-to-solute ratio ≤ 283:1. The split OH absorption bands persisted, however, when there was no evidence of aggregate formation. The complexity of the split OH stretching bands was also influenced by steric factors and by the choice of matrix gas. This result suggests that isolation of rotational isomers and solute-matrix interactions also contribute to the band splitting. The presence of the split OH absorption bands did not preclude the use of the GC/MIIR technique to identify several nitrocresols produced from the photooxidation of toluene and NO x.

2 Matrix isolation

“…First is a report of the analysis of nitrocresol mixtures from air. 6 Nitrocresols enter the atmosphere as a result of combustion processes, but most are secondary pollutants formed by photochemical reactions. They are considered to be particularly unpleasant pollutants because of their mutagenic properties.…”

“…In a CO-doped matrix (h 1 -C 5 H 5 N)Cr(CO) 5 is seen (the same product that is formed in room temperature solution); in an N 2 -doped matrix, addition of two N 2 molecules leads to (h 1 -C 5 H 5 N)Cr(CO) 3 (N 2 ) 2 . In solution a secondary photochemical process yields Cr(CO) 6 .…”

“…The lithium-silicon monoxide complex has been produced by codeposition of lithium atoms and SiO molecules with excess argon at low temperature. 146 The IR spectra of the molecule have been interpreted by observation of 6 Li/ 7 Li isotopic substitution and 28 Si/ 29 Si/ 30 Si isotopes in their natural abundance. The experimental observations have been backed up by density functional calculations.…”

“…The spectra in Fig. 17 show the n 2 region for LiSiO generated (a) from 7 Li atoms and (b) from 6 Li atoms.…”

“…17 Observed IR absorption spectrum in the n 2 region of Li + SiO. (a) 7 Li + SiO, (b) 6 Li + SiO. (Reprinted with permission from ref.…”