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IX. 75)Sumvnavy. From PE.-spectroscopical studies the torsional angle p, of the N-phcnyl ring in isolated benzylideneaniline 1 has been found t o be dcfinitely srnallcr than p, = 90'. An approximate value q~ = 36" has been estimated which is e w n sniallcr than t h e one observed in the crystal (p, = 55") and suggested to prevail also in solutions of 1. 11 reevaluation of the gas phase optical spectrum of isolated 1 supports a torsional angle similar to that found in the other phases.Calculations of the most stable conformation of 1 as \re11 as of stilbene and azobenzene by the MINDO/3-tcchnique lead to torsional angles p, = 90" for both phenyl rings in all cases. These results are at variance with the experimental results ant1 suggcst t?iat MiND0/3-like its less advanced precursor MINDO/2 or likc CND0/2-is unreliable lor low cncrgy 12rocesscs involving rotation of n-systems connected by esscntial singlc bonds.I t is concluded that the n-energy of benzylideneaniline, likc that of stilhenti or azobenzene, \\auld favor a planar conformation. The increased torsional aiiglc: in 1 as compared to thc other two iso-conjugatc systems arises from a larger steric interaction between phenyland bridgcprotons.Introduction. -Crystalline benzylideneaniline (1) exhibitsin contrast to its iso-electronic and essentially planar analogues trans-stilbene (2) ~ 21 and tvans-azobenzene (3) [3] -an angle of twist cp = 5.5' of the S-plienyl-ring about the C-N essential single bond [4]. This deviation from planarity was already postulated on the basis of the marked differences between the optical spectra of 1 arid 2 or 3 [5] and by the resemblance of the optical absorption spectrum of 4, wliere planarity is enforced by bridging, to those of 2 and 3 [6]. That the angle of twist for 1 in solution is not too different from that in the solid is suggested by the similarity between its solution and its crystal reflectance spectrum i7]. A recent illuminating study employing deri\.atives of 1 and of the planar reference system 4 has indicated that the angle of twist varies markedly for different substituents in tlie $,$'-positions, 91 rn 0" being presumably realized for 'push-pull' substitution wliicli increases tlie bond order of the relevant C S p 2 --N s p~ bond ~ 81. -~~ -

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Bis( 1-methylcyclopropyl)acetylen (1 a) gibt mit verschiedenen Dichlorcarben-Reagenzien Gemische des acetylenischen Ketons 3 a und des Cyclopropenons 4a, wahrend Dicyclopropylacetylen (lb) neben den analog strukturierten Verbindungen 3b und 4b zusatzlich das Produkt 10 der Aufnahme von 2CC12 (Addition und formale Einschiebung in eine C -C-Bindung) liefert. Ahnlich gebaute aliphatische Alkine sind weniger reaktiv, nur mit dem CCI,-Reagens der PhasentransferKatalyse werden nennenswerte Umsetzungen zu 12a und b sowie 13a und b erreicht. -In seiner thermischen und Hydrolysebestandigkeit liegt das cyclopropylsubstituierte Cyclopropenon 4 b zwischen Diphenylcyclopropenon und dem sehr wenig reaktiven Di-tert-hutylcyclopropenon. Dipolmomente und Basizitaten der Cyclopropenone werden zusammgefaDt ; die cyclopropyltragenden Verbindungen sind die starksten Basen. Die Photoelektronenspektren einiger Cyclopropenone wurden gemessen, der SubstituenteneinnuB auf die Ionisationspotentiale der n-und a-Elektronen wird diskutiert.Cyclopropenone Chemistry, IX la)Chemical and Photoelectron Spectroscopic Properties of Cyclopropyl-substituted cyclopropenones Bis(1-methylcyc1opropyl)acetylene (1 a) reacts with various dichlorocarbene reagents to give mixtures of acetylenic ketone 3a and cyclopropenone 4a, while dicyclopropylacetylene (1 b) gives 10 in addition to 3 b and 4 b. 10 is formed by addition plus formal insertion into a C -C-bond by 2 moles of CCI,. Aliphatic alkynes of structures similar to l a are much less reactive, only the dichlorocarbene of phase transfer catalysis leads to conversions to 12a and b, and 1311 and b. -Cyclopropyl substituted cyclopropenone 4 b is thermally and hydrolytically more stable than diphenylcyclopropenone, though less so than di-tert-butylcyclopropenone. Dipol moments and basicities of cyclopropenones are tabulated. The compounds carrying cyclopropyl groups are the most basic ones.Photoelectron spectra of some cyclopropenones were measured. The influence of substituents on the ionization potentials of n-and rr-electrons is discussed.