13C Spin-lattice relaxation times of piperidines. Molecular motions and interactions with solvents

Abstract

¹³ C Spin-lattice relaxation times have been measured for piperidine (1) and N-methylpiperidine (2) in several different solvents [CDCl₃, CD₃OD, D₂O, (CD₃)₂CO, C₆D₁₂, C₆D₅NO₂, and (CD₃)₂SO], and have been analysed in terms of anisotropic molecular motion. The results of these calculations show that these solvents can be divided into three types according to the hydrogen-bonded solute–solvent interaction involved: (i), C₆D₁₂, C₆D₅NO₂, and (CD₃)₂SO, which have no effect on molecular rotation; (ii), CDCl₃, CD₃OD, and D₂O, in which hydrogen-bonded interactions between solute and solvent molecules caused by the nitrogen lone-pair are expected (these affect the apparent size and anisotropy of the solute molecule, depending on the orientation of the lone-pair); and (iii), (CD₃)₂CO, in which the carbonyl group interacts with the solute NH proton.