No abstract

a), R = C&, ;( 6 ) . R = P-CH,-(:& On reaction of ( 1 ) with CO at -78°C we obtained a carbonylation product that was different from (3). With bromine at -78°C this afforded the same degradation products as (3) : aryl bromide, aroyl bromide, and CpzZrBrz. A comparison of the spectral properties (Table 1) indicates a stereoisomer of (3). The unusual position of the CO stretching vibration band in the IR spectrum and the absorption of the acyl carbon in the 13C-NMR spectrum at remarkably low fieldr5] indicate the presence of a qz-aroyl ligand in this complex. On the basis of these data and the isomerization to (3) we ascribe the structure (2) to the product. not, as has repeatedly been p~s t u l a t e d [~" *~"~ 71, take place at the central position between the two o-bonded ligands to give (4)[*' but, in accordance with calculations by Hoffinandgal and spectroscopic investigations by Dahl[9b1, via a further route to the product (5).

The title compound (1) is prepared in situ from 5-methylenebicyclo[2.2.0]hex-2-ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X-ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C,H:hypersurface and can be obtained photochemically from other isomeric ions or by a McLufferty rearrangement. The enthalpies of formation of 1, its precursor and the corresponding radical ions are compared to the most recent data available for other C,H, isomers and their ions. It is shown that the thermodynamic stability of 1 + is closer to that of toluene cation than concluded on the basis of earlier results.Introduction. -Although the gas-phase interconversion of toluene and cycloheptatriene molecular ions, which is often accompanied by extensive C-and/or H-scrambling, has attracted continuing interest over the last two decades [ 11, its reaction mechanism has not been fully elucidated. It was, however, recognized that the molecular ion of 5-methylene-1,3-cyclohexadiene (1 ') may play a key role in this process [2]. It is, for example, almost certainly involved in the HJH, exchange in toluene radical cations, and is probably an intermediate in the toluene radical cation (2 + )+cycloheptatriene radical cation (3+) interconversion (Scheme 1) [3].

Die hochgespannten neuen Xylol‐Isomere (1) und (2) sind interessante Objekte für mechanistische Studien. (1) isomerisiert thermisch zu (3) und (4), (2) bildet in n‐Heptanlösung (1) [und dieses wenig (3) und (4)], in der Gasphase entstehen dagegen (3) und (4) auch direkt aus (2). Überraschend ist die Bildung von (5).

Decomposition of 5-Norbornene-2-diazonium Ions. Derivatives of Bicyclo[3.l.l]hept-2-enePhotolysis of 5-norbornen-2-one tosylhydrazone (4) in aqueous sodium hydroxide afforded 4% of 3-norpinen-2-01 (3) in addition to 5-norbornen-2-01 (5, 10%) and nortricyclanol(6,86%). 3 arises from 5-norbornene-2-endo-diazonium ions (2) as shown by the nitrous acid deamination of the epimeric amines 1 and 7. 3-Norpinen-2-one (12) was isolated by oxidation of the deamination products followed by preparative g.1.c. 3 and 12 were synthesized independenrly from norpinan-2-one (9) via sulfenylation and sulfoxide pyrolysis. The norbornene + norpinene rearrangement is slightly enhanced by 1 -OCH3. The deamination of l-methoxy-5-norbornen-2-endo-amine (14) produced 10% of 12, as compared to 5.6% of 3 from 1. sylhydrazon (4) in Natronlauge/l,2-Dimethoxyethan. Die GC-Analyse der Produkte zeigte nur 5-Norbornen-2-01 (5) und Nortricyclanol (6). Nach katalytischer Hydrierung fanden wir neben 6 und 2-Norbornanol (aus 5 ) auch 1.2% 2-Norpinanol, das vermutlich aus 3-Norpinen-2-01 (3) entstanden war. Die Bildung von 3 durch Wanderung von C-7 erschien demnach unbedeutend. Kationische Umlagerungen von