Alkenyl halides shifts 199

This chapter describes the photochemical C-X bond fission in alkene systems that have halogen atoms bonded to the carbon-carbon double bond. The substitution of halogen atoms in alkenes results in a red shift of the n,n absorption band because of the interaction between the lone pair on the halogen atom and the 7t-orbitals. > However, the UV absorption of aliphatic alkenyl halides, except for the iodides, lies in a region of short wavelength less than 254 nm (Table 11.1). Therefore, the majority of the alkenyl halides studied in these photolyses are the iodides. 

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