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Influence of XCH2 and X2CH Rests upon Equilibrium Compositions Among Monosubstituted Bullvalenes and Cycloheptatrienes
Zeiger, Roland,Sarma, Keshab,Schroeder, Gerhard
, p. 2889 - 2894 (2007/10/02)
Cycloheptatrienylmethyl methyl ethers (5) and cycloheptatriene-carboxaldehyde dimethyl acetals (7) were equilibrated at 160-180 degC (1,5-H shift).While 7 approaches a statistical ("hydrogen-like") distribution of the CHX2 group, the methoxymethyl group of 5 strongly prefers position 1.In contrast, the NMR spectra of the analogous bullvalenes (2 and 9) indicate a nearly statistical distribution of CH2X, but not of CHX2.We conclude that electronic substituent effects on sigmatropic equilibria should not be generalized.
