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SOME CORRELATIONS BETWEEN SPECTROSCOPIC AND PHOTOCHEMICAL PROCESSES *
Author(s) -
Pitts J. N.,
Foote J. K.,
Wan J. K. S.
Publication year - 1965
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1965.tb09746.x
Subject(s) - chemistry , radiolysis , photochemistry , benzene , radiation chemistry , toluene , photodissociation , ionizing radiation , irradiation , chemical reaction , radical , organic chemistry , physics , nuclear physics
— By applying the modifier ‘Space’ to the terms ‘Photochemistry’ and ‘Spectroscopy’ one implies a concern with electromagnetic radiation of wavelengths less than that found at the earth's surface (i.e., Λ≤23000Å) and with energetic particles, particularly electrons. It has been observed that for certain classes of organic compounds useful empirical correlations exist between reactions induced by electron impact, non‐ionizing ultraviolet radiation and ionizing radiation. These correlations allow qualitative or semi‐quantitative predictions of specific reactions and/or reaction mechanisms which will occur during photolysis or radiolysis, based on known optical or mass spectra. As an example of the above approach, we have shown that, in accord with recent spectroscopic evidence, benzene and toluene do not significantly react photochemically in their first absorption band (at ˜ 2500Å); however, they react with a quantum yield approaching unity in their second and third absorption bands (at ‐20008Å and 1850Å respectively). The products of this decomposition are primarily carbon and/or polymer which deposit on the cell windows, however, small yields of stable products have been isolated (i, e., φc 2 h 2 =0.01 for benzene; φ, C 6 H 6 =0.05 for irradiation of toluene). Another example of this extrapolation from one technique to another deals with the correlation of cyclic elimination reactions observed in the mass spectra, photochemistry and radiation chemistry of various classes of organic compounds. Classic examples of this type of reaction are the photolytic and radiolytic elimination of olefins from esters and ketones having a hydrogen γ to the carbonyl group (i.e., the elimination of ethylene from ethyl acetate and of propylene form methyl n ‐butyl ketone). Based on mass spectral correlations with the above reactions, the same type of elimination should be expected from a great number of compounds which contain hydrogens γ to unsaturated groups (i.e., C=O, C≡N, C=C, etc.). In those cases where the photochemistry or radiation chemistry of these compounds have been studied, an intramolecular cycloelimination of olefin has been observed to be an important process. It is suggested that mass spectra are a useful diagnostic tool for at least gross predictions in ‘space photochemistry’ and ‘space photobiology’, as well as in considering reactions of importance under primitive earth conditions.