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In complete agreement with experimental results ab initio molecular orbital calculations predict that ionized hydroxy(methyl)carbene, [CH,COH] +, does not only exist as a stable C,H,O*+ isomer but also serves as the key intermediate in the isomerization-dissociation processes of the cation radical of gaseous vinyl alcohol.

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significant, and showed no trend with dielectric constant. Thus, it appears that solvent effects are not important in those cases in which there are no changes in rotamer population^.^^ ConclusionsGood correlations of the orthobenzylic coupling constants in methyl aromatic compounds and unsaturated compounds (having vinylic methyl groups) are found with the *-bond order q, the square of q, and the mutual atom-atom polarizability A~~. However, the linear dependence on 4 (which has no theoretical basis) gives values which are much too high in the region of very low bond orders.In the extension of the study to molecules in which both conformational and bond order effects are important to the Job, it is found that the generalization of the relationship of coupling constant to A to include angular factors gives results which are in very gooi'agreement with the experimental results. The agreement is an improvement on the results based on the IND-0-FPT methodS4 and is much better than the correlation with qz. It seems likely that the inadequacy of the latter is due to the overestimation of J".The experimental and theoretical results presented here provide an important method for obtaining useful structural information in complex molecules. (X = H), 10239-86-8; 49 (X = CH,), 84959-62-6; 49 (X = CH(CO,CHS),), 84944-79-6; 49 (X = C&5), 84944-80-9; 84944-83-2; 49 (X = OH), 84944-84-3; 49 (X OCOCH,), 84944-85-4; 50 (X = H), 4208-97-3; 50 (X = CHS), 84944-86-5; 50 (X = CH-(C02CH,)2), 84944-87-6; 50 (X = C,H5), 84944-88-7; 50 (X = NH,), = OH), 84944-91-2; 50 (X = OCOCHS), 84944-92-3. 49 (X = NH2), 84944-81-0; 49 (X = Br), 84944-82-1; 49 (X = CI), 84944-89-8; 50 (X = Br), 29094-68-6; 50 (X = Cl), 84944-90-1; 50 (X Supplementary Material Available: Data concerned with general experimental procedures, synthesis of compounds, and spectral analyses (1 12 pages). Ordering information is given on any current masthead page.Abstract: The molecular ions of the methyl esters of chloro-, bromo-, dichloro-, and dibromoacetic acids undergo unimolecular elimination of C 0 2 in the gas phase. Collisional activation (CA) mass spectrometry suggests that the resulting [M -C02]+. ions possess novel types of hypervalent structures, Le., CHSXCH2+. and CH3XCHX+. (X = C1, Br). MNDO and ab initio calculations show that the methylmethylenechloronium radical ion CH3CICH2+. and the isomeric chloroethane cation radical CH3CH2CI+. exist in a potential minimum. MNDO predicts that CH3C1CH2+. is more stable than CH3CH2C1+. by 10.1 kcal mol-', whereas according to 6-31G' and UMP2/6-31G* CHSCH2C1+. is more stable by 9.1 and 6.4 kcal mol-', respectively. CzHSX+* (X = C1, Br) ions obtained after COz elimination from

Die unimolekulare Eliminierung von Br bzw. NO; aus den Radikalkationen der Titelverbindungen 1 und 2 gehorcht nicht einem einstufigen Reaktionsverlauf unter Erzeugung eines substituierten a-Acylcarbenium-lons 3. Markierungsexperimente und MNDO-Rechnungen legen einen Mechanismus nahe, bei dem die Dissoziation der C -X-Bindung durch einen intramolekularen H-Transfer von der NCH,-zur C = 0-Gruppe eingeleitet wird. Dies fUhrt zur Zwischenstufe 4, die schlieRlich zu 5 weiterzerftillt. Die mechanistischen Details der unimolekularen Zerfallsreaktionen von 5 unter Ethylen-Verlust zu 13 und Keten-Abspaltung zu 17 werden eingehend diskutiert. MassSpectrometric Investigation of Nitrogen Compounds, X X X I Expcrimental and Theoretical Investigatlons on the Dissociative Ionlzatlon of a-Nitro-and a-Halo-substituted Dimethylamides of Acetic Acid. Pseudo-simple Cleavage Reactions of Gaseous Calion RadicalsThe unimolecular elimination of Br' (and NO$ from the cation radicals of the title compounds 1 and 2 cannot be described as a simple one-step process giving rise to the formation of the substituted a-acylium cation 3. Both experiments and MNDO calculations clearly indicate that the cleavage of the C-X bond is preceded by an intramolecular hydrogen migration, whereby a hydrogen from the NCH, group is transferred to the carbonyl oxygen. It is the intermediate 4 from which the actual dissociation takes place, thus generating 5. The mechanistic details of the process of both ethylene and ketene loss from 5 generating 13 and 17, respectively, are discussed in detail.Die 7@eV-Massenspektren von Brom-(1) und Nitroessigsthre-dimethylamid (2) enthalten neben anderen Fragmenten (Tab. 1) ein Uberraschend intensittitsstarkes Signal bei m/Z 86. Dieses Bruchstilck, das durch unimolekulare Eliminierung des Substituenten X' (X = Br, NO3 aus den jeweiligen MolekUl-Ionen entsteht, kann nicht in einer einstufigen Reaktion M + * -+ 3 + X' (Schema 1) erzeugt worden sein. Mit einem Chem. Ber. //4(1981)