ja5b11657_si_003.cif (297.78 kB)
Structure–Kinetics Correlations in Isostructural Crystals of α‑(ortho-Tolyl)-acetophenones: Pinning Down Electronic Effects Using Laser-Flash Photolysis in the Solid State
dataset
posted on 2016-02-05, 00:00 authored by Anoklase
J.-L. Ayitou, Kristen Flynn, Steffen Jockusch, Saeed I. Khan, Miguel A. Garcia-GaribayAqueous
suspensions of nanocrystals in the 200–500 nm size
range of isostructural α-(ortho-tolyl)-acetophenone
(1a) and α-(ortho-tolyl)-para-methylacetophenone (1b) displayed good
absorption characteristics for flash photolysis experiments in a flow
system, with transient spectra and decay kinetics with a quality that
is similar to that recorded in solution. In contrast to solution measurements,
reactions in the solid state were characterized by a rate limiting
hydrogen transfer reaction from the triplet excited state and a very
short-lived biradical intermediate, which does not accumulate. Notably,
the rate for δ-hydrogen atom transfer of 1a (2.7
× 107 s–1) in the crystalline phase
is 18-fold larger than that of 1b (1.5 × 106 s–1). With nearly identical molecular and
crystal structures, this decrease in the rate of δ-hydrogen
abstraction can be assigned unambiguously to an electronic effect
by the para-methyl group in 1b, which
increases the contribution of the 3π,π* configuration
relative to the reactive 3n,π* configuration in the
lowest triplet excited state. These results highlight the potential
of relating single crystal X-ray structural data with absolute kinetics
from laser flash photolysis.