Matthew B. Zimmt

Magnetic Field and Magnetic Isotope Effects on the Products of Organic Reactions

Publisher Summary This chapter focuses on the magnetic field and magnetic isotope effects on the products of organic reactions. The chapter discusses reactions of radical pairs and examines the spin states of radical pair systems as archetypes. The crucial condition for observation of magnetic field effects is a competition between two processes: one of the processes must be magnetic field dependent and the other is magnetic field independent. As for magnetic field effects, magnetic isotope effects are generally very small or negligible in homogeneous solution, but may become significant in microheterogeneous environments, such as micelles. The chapter illustrates an example of a magnetic isotope effect involving 17 O, occurring in the thermolysis of endoperoxides of aromatic compounds. The decomposition of certain endoperoxides produces singlet molecular oxygen and the yield of singlet oxygen is magnetic field dependent. Such effects have been observed in many different kinds of chemical systems, and are readily interpreted in terms of the well-established principles of chemically induced magnetic polarization.

KETONE PHOTOCHEMISTRY ON SOLID SILICA. A DIFFUSE REFLECTANCE LASER FLASH PHOTOLYSIS STUDY

Abstract Using diffuse reflectance laser flash photolysis, the lifetimes of the triplet states of valerophenone and diphenylbutyrophenone adsorbed on solid silica have been determined to be 0.3 and 0.9 μs respectively. These lifetimes are at least two orders of magnitude greater than those found in homogeneous solution. Quenching of the triplet states by gas-phase oxygen and butadiene is observed.

Substituent and solvent effects on the lifetimes of hydrocarbon-based biradicals

Abstract Nanosecond transient absorption studies of the lifetimes (τ) of several substituted 1,n-diphenyl-1,n-diyls are reported in polar and non-polar solvents. A para-bromine substituent significantly shortens τ. Substitution of OH in the 1-position makes the lifetime highly solvent dependent. The substituent effect and the dependence of τ on biradical chain length is discussed in terms of spin-orbit coupling in the biradical.

Photoproduction of remarkably stable benzylic radicals in cyclodextrin inclusion complexes

Abstract Photolysis of cyclodextrin inclusion complexes of diastereomers of α,α′-dimethyldibenzyl ketone in the solid state resulted in stable benzylic radicals at room temperature. These radicals were characterized by their electron spin resonance (ESR) signals, emission and excitation spectra.

The observation of cidep from the photodecomposition of dibenzyl ketone in micellar solution

Abstract The photolysis of dibenzyl ketone (DBK) in sodium dodecyl sulfate micellar solution was studied using time-resolved ESR techniques. The CIDEP spectra observed are consistent with phenacyl-benzyl radical pair interactions with little, if any contribution from benzyl-benzyl radical pair interactions. There is a marked contrast in the CIDEP observed in homogeneous and micellar solution which cannot be explained simply by viscosity arguments.