Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations † : Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert -cumyl and 1-aryl-1-cyclopentyl carbocations—correlation of the data by a new set of substituent constants, σ C+
Year: 1980
Type: article
Abstract: The cationic carbon substituent chemical shifts (DeltadeltaC(+)) for nine representative meta-substituted tert-cumyl carbocations are correlated satisfactorily by the sigma(m) (+) substituent constants (slope rho+ = -18.18, correlation coefficient r = 0.990). However, the substituent chemical shifts (DeltadeltaC(+)) for the corresponding para derivatives are not correlated by the sigma(p) (+) substituent constants. The possibility of developing a set of substituent constants capable of correlating such (13)C NMR shifts was examined. The slope of the line defined by the meta substituents (rho+ = -18.18) was utilized to calculate sigma(C+) constants for both meta and para substituents. The utility of these constants was then tested by their ability to correlate the (13)C NMR shifts in the cations for a different system, the 1-aryl-1-cyclopentyl cations. Indeed, these sigma(C+) values correlate very well with the DeltadeltaC(+) values, yielding rho(C+) = -16.84, r = 0.999.
Institution: Purdue University West Lafayette
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2050122243