NMR and i.r. studies of the solvent effect on thioureas

Abstract

The solvent effect on the ν as and ν s NH stretching frequencies of the NH 2 group of N-methylthiourea and N,N-diphenylthiourea and on the proton chemical shift of the NH and NH 2 protons of N-methylthiourea was investigated in various solvents. The results were related to the donor and acceptor parameters of the solvents. Frequency shifts give good correlations with donor number alone, but better correlations were obtained with a two parameter relationship considering both donor and acceptor number. Frequency shift correlations with the the donor number show different slopes for solvents with low and high donor numbers, suggesting different behaviour of the solutes in such solvents. This can be interpreted as different grade of planarity of the molecule in solvents with low and high donor numbers.