Lanthanide-induced shifts in the carbon-13 nuclear magnetic resonance spectra of some ketones, alcohols, and amines. An analysis of contact, pseudo-contact, and complex-formation contributions to the observed shifts

Abstract

The lanthanide-induced shifts in the carbon-13 n.m.r. spectra of some ketones, alcohols, and amines are reported. The shifts produced upon complex formation with diamagnetic La(dpm)₃ are relatively large for carbonyl carbons of ketones, and significant for oxygen-bonded carbons of alcohols, and carbons α to the C–N bond of primary amines (C–C–N); appropriate corrections must therefore be made to the measured shifts produced by paramagnetic lanthanide ions. Contact contributions to the ¹³C shifts in the compounds examined are generally larger in amines than alcohols or ketones, pseudo-contact shifts normally being dominant in the last two classes of compound. For quantitative structural ¹³C work with shift reagents, Yb(dpm)₃ is recommended as it minimises contact contributions without causing adverse line broadening.