Nuclear Magnetic Resonance Spectrometry

Hindered rotation in N-methylthiourea

“…Nuclear magnetic resonance studies of the rotational barrier about the central C-N bond in amides and thioamides have indicated that the energy barrier is greater than for a normal C-N bond because of electron delocalization.2-6 Furthermore, several authors have reported that the rotational barriers in thioamides are higher than for amides.4-8 However, the determination of kinetic parameters for the interconversion of geometrical isomers of amides and thioamides by nmr spectroscopy has been a controversial subject.6•9-11 Several authors have discussed and presented comparative results pertaining to the various nmr methods employed to obtain energy barriers to restricted rotation about the C-N bond in amides.5•9 •12 In spite of the errors involved in comparing results obtained by the various nmr techniques, solvent and concentration effects seem apparent in these systems. [10][11][12][13][14][15][16] In connection with a research program in our laboratories, we have studied by the nmr technique the behavior of N-methylthiourea (MTU)16 and N-methylurea in a few nonpolar and polar solvents at various temperatures in order to determine whether hindered rotation is present in these molecules and whether any solvent interactions exist. The results and conclusions of these studies are given below.…”

Nuclear Magnetic Resonance Studies of Ions in Pure and Mixed Solvents

“…While nmr is not a panacea for the solution of all chemical problems, its prominence in chemical investigation is shown by the fact that nmr was referred to in some respect in one out of every six publications occurring in the chemical literature of the United States in 1964 (218).…”

High resolution NMR spectroscopy and some examples of its use

“…A review of analytical applications of NMR, ineluding 700 references, was compiled by Lustig and ~oniz (7). Examples of quantitative analysis by NMR have appeared in pharmaceutical chemistry.…”

“…Some good sources of information on NMR for lipid chemists are the following: Basic theory and practice (2); Practical discussion (3); Comprehensive text (4); Application to fatty acids and esters (1); Application to organic compounds and drugs (5) ; Application to sugars (6) ; Analytical uses (7) ; Recent developments (8); Index to NMI~ spectra in the literature (9); Collection of NMR spectra of organic compounds (10).…”