ELECTRONIC-STRUCTURE OF HALOALKANES - A HIGH-RESOLUTION PHOTOELECTRONSPECTROSCOPIC STUDY

High resolution He(I) photoelectron spectra (PES) of a number of bromo - and iodoalkanes have been measured. Linear relationships between ion ization energies (E(i)) and 1/n (where n is the number of carbon atoms in the chain) describe the trends reasonably well if n = 1 is exclude d for dihaloalkanes. This property (i.e. line slopes) when joined with the alternation of halogen lone pair bandwidths within a given spin-o rbit doublet, can be used to provide a fully empirical assignment of t he four non-bonding orbital ionizations of dihaloalkanes. The interact ions between the halogen lone pair orbitals and the alkane sigma orbit als dominate in dihaloalkanes for which n greater-than-or-equal-to 2, while through-space interaction is important only in dihalomethanes (n = 1). Vibrational fine structures were used to infer the existence of hyperconjugative effects.