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A quantitative study of alkyl radical reactions by kinetic spectroscopy. IV. The flash photolysis of azopropanes
Author(s) -
Adachi Hiroyuki,
Basco Norman
Publication year - 1981
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550130404
Subject(s) - chemistry , radical , flash photolysis , reaction rate constant , disproportionation , isopropyl , excited state , singlet state , photodissociation , photochemistry , spectroscopy , analytical chemistry (journal) , medicinal chemistry , kinetics , organic chemistry , physics , quantum mechanics , nuclear physics , catalysis
The flash photolysis of azo‒ n ‒propane and of azoisopropane has been studied by kinetic spectroscopy. Transient absorption spectra in theregion of 220–260 nm have been assigned to the n ‐propyl and isopropyl radicals. For the n ‐propyl radical, ϵ max = 744 ± 39 l/mol cm at 245 nm and the rate constants for the mutual reactions were measured to be k c = (1.0 ± 0.1) × 10 10 l/mol sec (combination) and k d = (1.9 ± 0.2) × 10 9 l/mol sec (disproportionation). For the isopropyl radical, ϵ max = 1280 ± 110 l/mol cm at 238 nm, with k c = (7.7 ± 1.6) × 10 9 l/mol sec and k d = (5.0 ± 1.2) × 10 9 l/mol sec The rate constant for the dissociation of the vibrationally excited triplet state of the azopropanes into radicals was measured from the variation in the quantum yield of radicals with pressure. For azo‐ n ‐propane k d T= (6.6 ± 1.3) × 10 7 sec −1 , and for azoisopropane k d T= (1.6 ± 0.4) × 10 8 sec −1 . Collisional deactivation of the vibrationally excited singlet and triplet states was found to occur on every collision for n ‐pentane; but nitrogen and argon were inefficient with a rate constant of 1.1 × 10 10 l/mol sec. Spectra observed in the region of 220–260 and 370–400 nm areattributed to the cis isomers of the parent trans ‐azopropanes. These are formed, as permanent products, in increasing amounts as the pressure is increased.