Ions and excitations in organic radiation chemistry. The gamma radiation induced reactions of 1, 3-cyclohexadiene. The radiation induced isomerization of 1, 2-diphenylpropene in cyclohexane
PART I: Irradiation of 1,3-cyclohexadiene with γ rays leads to dimerization, either in benzene solution or in the neat liquid. Relative amounts of the products vary widely with reaction conditions but the composition of the mixtures can be expressed as consisting of variable amounts of two groups. O...
| Summary: | PART I: Irradiation of 1,3-cyclohexadiene with γ rays leads to dimerization, either in benzene solution or in the neat liquid. Relative amounts of the products vary widely with reaction conditions but the composition of the mixtures can be expressed as consisting of variable amounts of two groups. One set of products corresponds to those formed in thermal dimerization and the other has the distribution found in photodimerization induced by triplet sensitizers. Formation of the "thermal" dimers is inhibited by 2-propanol, a cation scavenger, and promoted by electron scavengers, so a cationic mechanism is postulated. The other, "photo" dimers,are presumably formed from triplet diene. Ring cleavage to give 1,3, 5-hexatriene is also observed and attributed to an excited singlet state of 1,3-cyclohexadiene. Since ring opening is not affected by electron scavengers whereas "photo" dimers are quenched, it is inferred that excited singlets are formed in primary excitation processes and that triplets are largely produced by charge neutralization. In benzene solution charge and excitation transfer from the solvent are involved in the production of diene products. A chain dimerization also seems to be present in benzene solution.
PART II: The cis and trans isomers of 1,2-diphenylpropene are isomerized in cyclohexane by irradiation of solutions with γ radiation. At low solute concentrations both isomers appear to react through the triplet state of the 1,2-diphenylpropene which is formed by charge neutralization. At higher alkene concentrations and especially at low radiation doses a cationic chain reaction contributes to cis→trans isomerization. The value for isomerization of the trans isomer at high solute concentration gives a G for solute triplet of 4.4.
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