https://spin.niddk.nih.gov/bax/lit/508/16.pdf

Investigation of complex networks of spin-spin coupling by two-dimensional NMR

A theory is developed to explain high‐resolution nuclear magnetic resonance spectra observed in the presence of a second weak rf field at ω2. When ω2 is set on a nondegenerate transition frequency and the rest of the spectrum recorded by sweeping the frequency of the investigating rf field, any transitions that have an energy level in common with the perturbed transition will be split into doublets. If magnetic field inhomogeneities exceed the natural linewidth, the line profile of the doublets gives information about the ordering of the three energy levels involved. Good agreement with the theory has been obtained in experiments on two‐spin and three‐spin proton systems where the energy‐level diagram is already known. The method has been used to establish the ordering of the energy levels of the ABC system of protons in methyltrivinylsilane and the analysis has been completed by two independent methods. Some of the special effects which arise when double‐resonance spectra are recorded by sweeping the magnetic field have been examined and discussed.

Use of Weak Perturbing Radio‐Frequency Fields in Nuclear Magnetic Double Resonance

Geminal and Vicinal Proton-Proton Coupling Constants in Organic Compounds

The A2B2 proton resonance spectra given by 1,2-disubstituted ethanes are reported and analysed A large number of these spectra are examples of the ‘deceptively simple’ type of spectra which do not give explicit values of the coupling constants In those cases which are not of this type, it is shown that the average coupling constant, ie 1/3(J t + 2J g), can be obtained from such spectra, even though the individual vicinal coupling constants are dependent on the percentage of the rotational isomers, and thus change with solvent, etc This change with solvent is discussed, and the results show that in many 1,2-disubstituted ethanes the gauche isomer is the more stable isomer Also, the results suggest that, in many of the compounds investigated, the dihedral angle between the substituents in the gauche isomer differs appreciably from 60° The values of the average coupling constant obtained from these systems are combined with measurements of this coupling in other substituted ethanes to investigate the 

The proton magnetic resonance spectra of some substituted ethanes

An implementation of the Deutsch-Jozsa algorithm on a three-qubit NMR quantum computer

The 60 Mc/s proton resonance spectrum of 2,3-dibromopropionic acid is reported and analysed as an ABC system. The relative signs of the geminal and vicinal coupling constants observed have been determined by the double irradiation method and confirmed by experiments at 15·086 Mc/s. The two types of coupling constant are found to have opposite signs and to be large, the geminal one being ∓9·9 c.p.s. and the vicinal ones ±10·8 c.p.s. and ±4·6 c.p.s.

K.G.R. Pachler

Papers

The relative signs of geminal and vicinal proton spin coupling constants