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Extended Huckel (Hoffmann) calculations have been performed for the ' lateral shift ' syn-anti-isomerization of seven simple imine derivatives H&=N-X (X = H, Me, NH2. OH, F. CI. and Br). The energy-barrier values obtained are in satisfactory agreement with the experimental data (except those for X = CI or Br). The computed ' reduced overlap population ' for the N-X bond, and the ' gross atomic population ' values for the nitrogen atom, together with previous data show that our hypothesis about the influence of the N-bonded substituent is valid : i.e., the isomerization energy barrier isgreatest for substituents with a strong -/ (inductive) but no -M (mesomeric) effect.THE rate and mechanism of syn-anti isomerization of imine systems (I) has been investigated re~ently.l-~ Huckel lo first suggested, and Curtin a and Staab 2e recently described more exactly, that the intercon- R'x R>=d (I) 1 (a) G. Ostrogovich and F. Kerek, Studii picerceta'ri Chim.

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the CND0/2 and nb-initio calculationsra1, which show the reliability of the approximation chosen.In the 'H-NMR spectrum of the cation [C,H,]' Olah eta/.r3J found at room temperature one single signal which was split at lower temperatures. These authors -100' Table. Localized three-center molecular orbitals. \ I I Linear combination coefficients Atom i Function i [C,H,]+ ~ B,H, 1 B,H,, ab lriitio [8] [a] C', B' 0.1995 0.0404 H 0.0404 0 0 0.4208 0.3632 ' 0.2143 Localized proportion (%) 96.1 [a] The linear combination coefficients of C N D O calculations refer to orthogonalized (Lowdin) atomic orbitals and thus their absolute values in bonding molecular orbitals aregreater than thecorresponding coefficients in ab-initio calculations which refer to ordinary nonorthogonal atomic orbitals. assigned the structure of a o-complex to the solvated cation. According to our calculations the %-complex should be more stable in the gas phase. This need not contradict our results since 7t-and o-complexes can differ considerably in their solvation energies and in their interaction with the counter-ion. Recently Helgstrand[" reported CND0/2 calculations on the o-complex of [C,H,]'. This author's results agree well with ours, especially as regards bond angles and CH distances.We have been able to prepare the levorotatory form of 3-methyl-l-(p-diethylaminophenyl)-2-phospholene I-oxide ( I ) via its salt with (+)-9-camphorsulfonic acid. To thebest of our knowledge this is the first resolution of a chiralic phosphacyclic compound ['].Methylene chloride solutions of ( I ) [ * , 31 (16.5 mmol in 10ml) and (t )-9-carnphorsuIfonic acid (previously dried in vacuum over P,O, ; 16.2mmol in 160ml) were thoroughly mixed and the solvent subsequently removed in vacuum. The residual syrup was dissolved in 75 ml boiling benzene and the hot solution rendered slightly turbid by addition of 3-4ml n-heptane. By very slow and careful cooling, approximately 4.1 g of the camphorsulfonate of ( I ) could be obtained. After double recrystallization from benzene with a little n-heptane the specific rotation and melting point were constant ([a];'= -40.3' (benzene); m.p. 103-104°C). The difference between the UV spectrum (in cyclohexane) of compound ( I ) (A,,, = 277 nm ; log E = 4.45) and that of the salt (I.,,, = 281 nm ;log E = 3.03) shows that an ammonium (and no phosphonium) salt is present.