Quantitative applications of ¹H and ³¹P chemically induced dynamic nuclear polarization

Chemically Induced Dynamic Nuclear Polarization (CIDNP) spectroscopy has
been widely used for many years for study of mechanisms of reactions that involve
free radical pairs. Unlike Electron Spin Resonance (ESR) spectroscopy CIDNP provides
an information on radicals that have been already reacted to paramagnetic
species bringing the power of NMR into determination and identification of reaction
pathways, yields and environmental effects. Since been discovered in year 1969
CIDNP was mostly applied in purely qualitative mechanistic studies where the simple
rules developed by Kaptein allowed to deduce number of important reaction
parameters. The quantitative application of CIDNP was rather difficult since there
were sometimes no other experimental evidence to be compared especially within
the cases where ESR failed. With the fast development of different theoretical calculation
procedures which can provide rather precise knowledge on geometry, electron
spin distribution and various magnetic properties of free radicals(g-factors, hyperfine
coupling constants), CIDNP finds a new broad field of use especially where other
physico-chemical methods are not successful by different reasons.
Being a variety of Nuclear Magnetic Resonance (NMR) spectroscopy CIDNP is
limited by the same drawbacks - bad time resolution (usually microseconds) and
poor sensitivity. Despite that it can follow the radical processes that are by far too
fast to be observed ESR spectroscopy - the most straightforward method to observe free radicals. The rate of fastest radical reactions that can be observed by CIDNP
is determined by the rate of intersystem crossing which is about 10−10 −10−9s. The
information on free radical properties and properties of the paramagnetic products of
the reaction is then stored within the longitudinal relaxation time of the particular
nuclei which is typically 1 - 10s. That very important information includes spin
distribution, radical concentration, rotation diffusion and magnetic properties of
radicals and rates of reactions. Within the certain conditions it can be extracted by
the analysis of CIDNP spectra.
The two different novel quantitative and semiquantitative applications of Chemically
Induced Dynamic Nuclear Polarization combined with density functional quantum
mechanical calculations and NMR studies are the subject of the present thesis.
First application is of almost pure fundamental interest whereas the second finds its
use in industry.