Microwave spectrum, substitutional structure, and Stark and Zeeman effects in cyclopropenone

Abstract

mi of the concept of aromaticity, which is itself somewhat an artifact of inadequate structural description, suggest that such designations are not presently justifiable.Consideration of tropone as formally related to benzene by carbonyl insertion of 2-and 4-pyrone as similarly related to furan shows that insertion of a carbonyl group into these aromatic rings drastically suppresses the contribution of nonlocal effects to the molecular magnetic susceptibility.Extrapolation of these results beyond the present studies raises the questions of whether formal carbonyl insertion into other aromatic compounds will lead to a large suppression of aromatic character as judged by magnetic criteria and whether this suppression will be manifest in other criteria of aromatic character. Qualitative correlation between the magnetic, thermodynamic, spectroscopic, and calculational criteria of aromatic character is usually observed, but the interrelationships are sufficiently vague that it is not clear to what extent the present demonstration of a low degree of aromatic character for 1, 2, and 3 by magnetic criteria should be reflected in other criteria. For example, in considering the relationship between a suggested nmr-based quantitative criterion for aromaticity and the thermodynamic criterion for aromaticity, it was shown that in a thermo-dynamic comparison of the stabilization energy of Nmethyl-2-pyridone with 2-methoxypyridine the latter was found to be favored by only about 6 kcal/mol, while the nmr criterion suggested a much greater difference.2425 This lack of agreement could reflect failure (24) P.

Theoretical investigation of the photochemical reaction mechanism of cyclopropenone decarbonylation

“…This step commenced by the gradual shortening of the C1-C2 and C3-O bonds. Table 1 shows the results using the MP2 and B3LYP methods, which are in good agreement with previous theoretical [40][41][42] and experimental [39,40] studies. Our results indicate that an explanation for the non-dynamic electron correlation in the calculated stationary points on the reaction path of the decomposition of cyclopropenones should be considered.…”

Cyclopropenone (c‐H2C3O): A New Interstellar Ring Molecule

“…For propynal, the spectral line data were determined from a fit to the laboratory measurements of , Costain & Morton (1959), Takami &Shimoda (1976), andWinnewisser (1973). For cyclopropenone, the spectral line data were calculated from a fit to the laboratory frequencies reported by Benson et al (1973) and Guillemin et al (1990). For cyclopropene, the spectral line data were calculated from a fit to the laboratory measurements of , Stigliani et al (1975), Bogey et al (1986), and Vrtilek et al (1987).…”

1,2-Dimethyl-4,4-triafulvenedicarbonitrile

“…Similarly, the C=C distance changes from 1.338 A in 2,3-dimethylthiirene 1,1-dioxide (IVa) to 1.354 A in the diphenyl compound (IVb) (Ammon, Fallon & Plastas, 1976). The effect is quite dramatic in the cyclopropenones, in which there is ca 0.05 /k increase from cyclopropenone (1.302 A; Benson, Flygare, Oda & Breslow, 1973) to 2,3-diphenylcyclopropenone (1.349 /~; Tsukada, Shimanouchi & Sasada, 1974). Interestingly, the trend in C=C bond lengths in alkyl-and aryl-substituted alkenes is opposite to that observed in the three-membered-ring compounds.…”