Ella B. Nadler

Hexamethyldisilane as a source of both trimethylsilyl and pentamethyldisilyl anions. Formation of a substituted pentamethyldisilyl stable enol

The reaction of dimesitylketene with MeLi/Me3SiSiMe3 gives in addition to the expected 2,2-dimesityl-l-trimethylsilylethenol, also the unexpected stable simple enol 2,2-dimesityl-l-pentamethyldisilylethenol.

The gas-phase ion chemistry of crowded, triaryl-substituted keto/enol pairs☆

Abstract The gas-phase ion chemistry of sterically crowded keto/enol pairs has been probed by using several experimental techniques in order to shed light on some highly remarkable mechanistic features of these systems. Labelling experiments prove that propene loss from ionized isopropyl trimesitylvinyl ether is a site-specific process by which, via a four-membered transition state, the ionized enol and not its tautomeric ketone is generated. Kinetic energy release measurements support earlier conclusions that enol cation radicals in a rate-determining step isomerize to (excited) ketones from which dissociations of the C(α)C(β) bond takes place. A correlation of the kinetic energy release, associated with this reaction, with the effects of substituents attached to the α-aryl group is not possible. Further, kinetic energy release measurements do not reflect the different behaviour of keto/enol tautomers in the reciprocal methyl/hydrogen migration. Similarly, the analysis of metastable ion spectra is not a means of distinguishing keto/enol forms; in contrast, for most pairs, a straightforward characterization is possible based on the analysis of collision-induced reactions.

Internal rotation in 2,2-dimesityl-1-trimethylsilylethenol

Abstract The intramolecular rotation of the two mesityl rings in 2,2-dimesityl-1-trimethylsilylethenol which leads to propeller enantiomerization is correlated. The ΔG c ‡ value for the enantiomerization is 1.11 kcal mol −1 , a value intermediate between those for the 1-isopropyl and 1-tert-butyl analogs.