¹³C NMR Spectroscopic and Density Functional Theory (DFT), <i>ab Initio</i>, and IGLO Theoretical Study of Protonated Cycloalkylcarboxylic Acids (Carboxonium Ions) and Their Acyl Cations (Oxocarbenium Ions)

Abstract

A series of protonated cycloalkylcarboxylic acids (carboxonium ions) and their corresponding acyl cations (oxocarbenium ions) were investigated in FSO 3 H−SbF 5 −SO 2 ClF solution by 13 C NMR spectroscopy. The ions were also studied by density functional theory (DFT) and ab initio and IGLO theoretical methods. The study shows that the various cycloalkyl groups have little effect on the 13 C NMR chemical shift of the carbocationic carbons of the ions. Charge calculations show that the delocalization into the cycloalkyl group is greater for the oxocarbenium ions than for the carboxonium ions. This is consistent with the greater electronic demand in oxocarbenium ions wherein one adjacent oxygen atom effects stabilization.