29939-31-9Relevant articles and documents
Structures of Pyridines Obtained in the Aluminum Bromide Mediated Cyclocongregation of Acetylenes with Cyanoformates
Wedinger, R.,Hogeveen, H.,Noble, W. J. le
, p. 1338 - 1341 (1984)
It is shown that the product of the title reaction with tert-butylacetylene and ethyl cyanoformate is not ethyl 3,5-di-tert-butyl-2-picolinate as reported in the recent literature but rather the 4,5-isomer.Varying yields of the 4,6-isomer are also obtained.The NMR spectra described for the 3,5-dimethyl analogue likewise suggest a misassignment of structure in that case.A revised mechanism is tentatively given for these reactions.
Steric effects on the proton-transfer equilibria of ketones, sulfoxides, and phenols
Bagno, Alessandro,Boso, Renato L.,Ferrari, Nicola,Scorrano, Gianfranco
, p. 1507 - 1515 (2007/10/03)
The proton-transfer equilibrium of several bases and acids, including some sterically hindered ketones, sulfoxides, and phenols, has been investigated by means of the determination of the thermodynamics of the equilibrium, NMR 13C relaxation measurements, and quantum chemical calculations. The analysis of such data yields information about the steric effects on basicity or acidity and about the underlying reasons for the anomalous behavior of species having a sterically hindered basic or acidic site. Thus, it is demonstrated that the anomalously low basicity of two sterically hindered ketones (tBu2CO and PhCOtBu) is enthalpic in origin and stems from steric hindrance to the solvation of their protonated forms. No such effect is found for analogous sulfoxides, whereas phenols display a more complex behavior.
