Source: Dissertation Abstracts International, Volume: 57-02, Section: B, page: 1078.

Director: J. Michael McBride.

Photolysis of single crystals of (11-Bromoundecanoyl) (Decanoyl) Peroxide (BrUDP) at liquid helium temperatures generates two molecules of carbon dioxide and two primary radicals per decomposition site. Various reaction intermediates can be trapped in the ordered crystal environment by thermal annealing. The location and structure of the radical intermediates were investigated by electron paramagnetic resonance (EPR). By analyzing the structural change between successive intermediates the motion allowed by the crystalline environment can be determined. The movement of the radical intermediates is shown to be dependent on the packing between successive layers, even though these interactions are over 10 Angstroms from where the radicals were generated.

Steric isotope effects are shown to influence the motion of the radical carbons. Specific intermolecular $\beta$-hydrogens affect the motion the carbon dioxide dimer undergoes upon annealing, which in turn affects how the alkyl chains can move in response to the stress. The distinct motion caused by isotopic substitution leads to different intermolecular environments for the resultant radical pairs. The fate of the radical pairs is thus determined by the initial movement.

The primary radical carbon can abstract specific hydrogens from neighboring intact chains to generate a terminal methyl group and a new secondary radical. The geometry of these hydrogen abstractions was determined and the specificity of the reaction was verified in one example by studying a chiral, monodeuterated isotopomer of BrUDP.

Five unique radical pairs and six other radical species, either isolated radicals in different environments or weakly interacting radicals that have a large radical-radical separation, were studied. Eighteen isotopomers of BrUDP, either with carbon-13 or deuterium substitution, were prepared and analyzed to determine the radical motion.