Direct conversa'or 3 + 1.1 g (0.005 moI) 3 w a~ electrolyzed in 320 ml acetonitrile or 50% aqueous tetrahydrofuran in thc preescncc of 30 ml 40% tetrabutylammonium hydroxide as base and supporting electrolyte. I n tetrahydrofuran under the same experimental conditions as in methanol 130 mg (13%) 1 are obtained after workup and recrystallization. In acetonitrile the current intensity decreased during the electrolysis so t h a t thc voltage had to be risen to 80 V. The yicld was similar a5 in THF (~10%). Helv. 56, 272 (1973).
R . Taylm,Sum?nu?y. Thc scheme of 'through-spacc' and 'through-bond' interaction of (semi)localized orbitals, originally proposed by Hofjmaian, is reexamined in terms of SCF many-electron treatments. It is shown that the two types of interaction can be characterized by examining the corresponding off-diagonal matrix elements of the liartree-Fock matrices of the localized or the symmetry adapted localized orbitals and of the partially diagonalizcd Hartree-Fock matrices referring to 'precanonical orbitals'.The procedure outlined is applied to three practical examples using the semiempirical manyclectron treatments SPINDO, MIND0/2 and CNDO/2 : a) A reassessment of 'through-space' and 'through-bond' interaction in norbornadiene indicates, that the latter type of intcraction is also of importance for the orbital based mainly on the antisymmetric combination of thc localizcd n-orbitals. The differences in the predictions derived from the three models arc critically cxamincd.b) The competition between 'through-space' and 'through-bond' interaction in the series of bicyclic dhnes from norbornadiene to bicyclo[4.2.2]-dcca-7,9-diene and in cyclohexa-l,4-diene, i.e. their dependence on the dihedral anglc o is rccxamined. It is found that the rationalization for the orbital crossing near w = 130" dcduccd from PE. spectroscopic data can not be as simple as originally suggested and that thc 'relay' orbitals responsible for 'through-bond' intcraction affecting both the symrnctric and the antisymmetric combination of thc n-orbitals extend over the whole CC-a-systcm of the six membered ring. c) 'Through-bond' interaction of the two lone pair orbitals in 1,4-diazabicyclo[2.2.2]octane is found to bc large for their symmetric and the antisymmctric linear combination.The analysis quoted, draws attention to some of thc dangers involved in using semiempirid treatments for the interpretation of PE. data in terms of Koopmans' theorem, without due caution. E-=; (x-1 H ] x-} can then be evaluated by a second-order perturbation trcatntent as follows: %+ = (Hnc -i. Hbc)/li2 oc -(Sac + Stx),VZ Hc--' I (xC [ H [ x-} --(€lac -Hh,)/v2 OC' -. (Sac --Sa,)/l/Z T+ = @+I(&+ -4 z H~-/ ( E --BC)(1 1 An important consequence is that, ckpcncling on the relative sizes of H,,, and Hc,, one can have either z+ < r-or T + > T-. Whereas the former relationsliip lcacls again to the 'natural' sequence of the perturbed orbitals, iabove i+, an inverted sequence is obtained in the latter case, i.e. X; above ~1 .In general 'through-...
SummaryHigh resolution He (Ia) and He (IIa) photoelectron spectra of cubane are reported. The assignments of the bands to different states of the cubane radical cation are made on the basis of ab initio STO-3G and MIND0/3 calculations, using geometries optimized within each treatment. The vibrational fine-structure observed supports the proposed assignment. An open shell MIND0/3 model for ground state cubane radical cation suggests that the Jahn-Teller distorted system fluctuates between twelve equivalent structures of C,,-symmetry. Localized molecular orbitals derived from the STO-3G model of cubane indicate that the major feature which discriminates this molecule with respect to other hydrocarbons is the large interaction matrix element between the opposed CC-o-orbitals of each face.
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