1,3-Dipolar cycloadditions. Part XVII: Experimental and theoretical spectroscopic investigations of <i style="">C</i>-aryl-<i style="">N</i>-methyl nitrones

Abstract

Detailed experimental and theoretical spectroscopic studies of <i style="">C</i>-aryl-<i style="">N</i>-methyl nitrones have been reported. The optimized geometries have been calculated by DFT/B3LYP level of theory with 6-31+G(d,p) basis set. The theoretically computed frontier orbital energy gaps and TDDFT calculations (calculated at B3LYP level with 6-31+G(d,p) basis set) of <i style="">C</i>-phenyl-<i style="">N</i>-methyl nitrone in different solvents are in good agreement with the UV spectral absorptions. This agreement reveals that the FMO energies can be well utilized to rationalize the observed regioselectivities of this and related nitrones in 1,3-dipolar cycloadditions and also their relative reactivities compared to other 1,3-dipoles. The fundamental vibrational modes of <i style="">C</i>-phenyl-<i style="">N</i>-methyl nitrone have been assigned by comparing the theoretical (calculated at B3LYP level with 6-311++G(d,p) basis set) and experimental frequencies. The thermodynamic parameters (which are generally used to rationalize the observed stereo- and regioselectivities of 1,3-dipolar cycloadditions of nitrones) have been calculated for <i style="">C</i>-phenyl-<i style="">N</i>-methyl nitrone at 6-311++G(d,p) level of theory. The preferred configuration and conformation predicted by theoretical ¹H NMR studies of <i style="">C</i>-aryl-<i style="">N</i>-methyl nitrones coincides with that obtained from the dipole moment measurements and experimentally recorded ¹H NMR chemical shifts.