Wavelength effects in the photolysis of ketones: Stereoisomerization and magnetic isotope [sup 13]C/[sup 12]C separation. A probe for adiabatic versus diabatic trajectories during bond dissociation

Journal Article · Thu Jan 14 00:00:00 EST 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100104a017· OSTI ID:6389559

Step, E N ^[1]; Tarasov, V F; Buchachenko, A L ^[2]; Turro, N J ^[3]

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1. Columbia Univ., New York, NY (United States) Inst. of Chemical Physics, Moscow (Russian Federation)
2. Inst. of Chemical Physics, Moscow (Russian Federation)
3. Columbia Univ., New York, NY (United States)

The [sup 13]C enrichment in the photolysis of three ketones, dibenzyl ketone (DBK), (S)-(+)-[alpha]-methyldeoxybenzoin (MBD), and d,1-2,4-diphenylpentan-3-one (DPP), along with photostereoisomerization of the latter two ketones was studied in SDS micelles as a function of the wavelength of the excited light. Following the radical pair paradigm, triplet radical pairs (RP) of the corresponding acyl and benzyl radicals are generated during the photolysis of these ketones and are the key intermediates responsible for the stereoisomerization of MDB and DPP and for the [sup 13]C enrichment of starting ketones. Two parameters, the recombination probability of the primary RP (P[sub r]) and the efficiency of [sup 13]C enrichment ([alpha]), which are not quantum yields, do not depend on the amount of light adsorbed by the ketones, and can be measured with high accuracy by measuring only chemical yields, were employed as mechanistic probes. The magnitude of both P[sub r] and [alpha] for the photolysis of MDB in micelles and the magnitude of [alpha] for the photolysis of DBK in micelles and in viscous glycerol solution decrease as the energy of the exciting light increases. On the other hand, for DPP no wavelength dependence is found for P[sub r] and only a small wavelength dependence is found for [alpha]. The results are examined in terms of adiabatic or diabatic trajectories of the dissociation of the bond which produces the radical pair. 49 refs., 5 figs., 8 tabs.

• OSTI ID: 6389559
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 97:2; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
KETONES
PHOTOLYSIS
BENZYL RADICALS
DISSOCIATION
EFFICIENCY
ENRICHMENT
MICELLAR SYSTEMS
PROBABILITY
RADICALS
REACTION INTERMEDIATES
RECOMBINATION
STEREOCHEMISTRY
TRAJECTORIES
ARYL RADICALS
CHEMICAL REACTIONS
DECOMPOSITION
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
400500* - Photochemistry
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation