Electronic and geometrical structures of cyclopropanes. Part 2. Photoelectron spectra and electronic structures of halogenocyclopropanes. Linear correlation of ionization energies with C-C bond lengths.
PE spectra of six chloro-(1-6), four bromo-(7-10) and two iodocyclopropanes (11, 12) have been measured and analyzed using semiempirical PM3 and DFT B3LYP calcns. The spectra are dominated by strong ionizations of electrons from the halogen atoms. The first IP of all chloro derivs. has a rather const. value of 10.22-10.32 eV. The same holds for the bromo (IP1: 9.90-9.94 eV) and the iodo derivs. (IP1: 9.13-9.15 eV). In the central region of the spectra, ionizations related to the Walsh orbitals wA (IP: 11.2-14.2 eV) and wS (IP: 11.6-13.9 eV), which interact to different extents with n orbitals of the halogens, are found. A linear relationship, DIPw = 0.375 Dr + 0.165, between DIPw (in eV), the difference of the IPs related to the Walsh orbitals wS and wA of the three-membered ring, and Dr (in pm), the difference of vicinal and distal C-C bond lengths, is established.
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