Asymmetric photodestruction

The first possibility is ruled out by the observation that asymmetric photodestruction by irradiation with CPL is much slower than asymmetric photocyclization. Moreover, it results in an optical activity of opposite sign in comparison with the optical activity observed in asymmetric photocyclization of the corresponding 1,2-diarylethylene. Finally, the optical yield and the wavelength of the CPL required for different precursors of [8]-helicene are different and the latter does not show any connection with the CD-Spectrum of [8]-helicene 6S). 

Asymmetric photodestruction is observed if the product formation is fast compared to deactivation and enantiomerization in the excited state and if the reactants are considered (Sec. II.B). 

In asymmetric photodestruction the interest concentrates on the reactants. They, again, absorb at different rates, and different concentrations of R and S are created. Product formation is treated in Sec. II.C, but this is not of interest in this context. The reactions of R and S may be mono- or bimolecular, k 2 and kD2 of Scheme may be identical or different, the products PR and Ps may or may not be optically active or even be identical molecules. The rates of product formation just influence the magnitude of the quantum yield < >. However, the... 

Partial photoresolution by asymmetric photodestruction can be used to determine the chiroptical constants of the pure enantiomer of the reactant, without their separation. A hint to this is found in the paper of Balavoine et al. [40], a detailed development of this concept has been published by the Rau group [12,73]. By the combination of e and CD data at the irradiation wavelength, with the... 

Asymmetric photodestruction can be used as a method to achieve high enantiomeric excess values. As the g factors are generally small, this is only reached at a large where, according to Fig. 5, most of the starting material has disappeared. So Fig. 6 in some way is deceptive. The optical yield in reference to the starting material can be defined by... 

This curve mimics the 0(t) curve (e.g., Fig. 5B). The optical yield is a maximum at the maximum of the 0 — t curve, i.e., at 63% photodestruction for k < 1,5. Examples are trans-3,5-diphenyl-pyrazoline 15 with Prei( max) = 1.1% [ 332 — 0.058, ee(Tmax) = 3%] or the spiropyrazoline 1 with Prei(Tmax) = 1 7% g = 0.096, ee(Tmax) = 4.3%]. Indeed, most papers published on cpl photochemistry for these reasons deal with asymmetric photodestruction. Balavoine et al. [40] reached 20% ee at 99% destruction for camphor 16 even higher ee of 30% was reached for frawtf-bicylco. Olnonane-S-one 17 [76,77]. Emeis et al. [78] reported that 17 also shows circularly polarized luminescence with gem = 0.035... 

Xmax) = 4.3%]. Indeed, most papers published on cpl photochemistry for these reasons deal with asymmetric photodestruction. Balavoine et al. [40] reached 20% ee at 99% destruction for camphor 16 even higher ee of 30% was reached for rra/i.y-bicylco[4.3.0]nonane-8-one 17 [76,77]. Emeis et al. [78] reported that 17 also shows circularly polarized luminescence with gem = 0.035 [79]. 

Asymmetric photoreactions by circularly polarized light (CPL) are induced through the preferential excitation of one enantiomer. The chiral information is introduced by a physical source of chirality that renders this approach most effective in terms of chiral amplification. Asymmetric photodestruction causes a racemic mixture to be enantiomericaUy enriched when one enantiomer is consumed more rapidly by CPL. Photoderacemization creates an enantiomericaUy enriched reaction mixture when one enantiomer... 

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