Solvent- and lanthanide-induced shifts in the exact solution of three-proton systems: Case study of 2-t-Butyl-2-cyano-3-phenylcyclobutanone

Abstract

An exact analysis was carried out for 1H NMR experimental spectra of the three protons attached to the four-membered ring of the title compound in various solvents (carbon tetrachloride, chloroform- d, benzene- d 6, acetone- d 6, all at 60 MHz, and chloroform- d at 80 MHz), then in presence of lanthanide-shift reagents Eu(fod) 3 · d 27 and Pr(fod) 3. Among the four, six, and in some cases eight real frequency solutions, only one is related unequivocally to the true spectral parameters obtained in CDCl 3 (at 60 MHz) δ H 1 = 4.41 ppm, δ H 2 = 3.81 ppm, δ H 3 = 3.44 ppm, J gem = −18.24 Hz, J cis = 10.07 Hz, J trans = 11.14 Hz. We propose that whenever one encounters possible alternatives for the choice of a true solution, the exact analysis of the solvent or lanthanide-induced-shift spectra represents a valid competing approach to the tickling technique.