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

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

It is shown that multiple quantum N.M.R. allows straightforward identification of networks of scalar coupled spins. The information obtained is particularly useful for the identification of magnetic equivalence when multiplet splittings are not fully resolved. The interpretation of multiple quantum spectra is based on a set of simple selection rules which restrict coherence transfer between multiple quantum and single quantum transitions.

Analysis of networks of coupled spins by multiple quantum N.M.R.

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

High resolution nuclear magnetic double and multiple resonance

The 1H, 199Hg and 13C spectra of the more common of the isotopic species occurring in natural abundance in mercury dimethyl have been studied. The proton spectra were observed directly whilst the 199Hg and 13C spectra were measured indirectly by a double resonance method involving observation in the proton region. A hitherto unreported long range coupling of magnitude 0·44±0·02 c/s was observed between the methyl protons and new values were obtained for the directly bonded 13C-H coupling, ± 129·6±0·1 c/s, and for the geminal 199Hg-12C-H coupling, ± 101·9±0·1 c/s. The relative signs of these couplings, together with the sign and magnitude of the directly bonded 199Hg-13C coupling, ±689±2 c/s, were determined by experiments on the 0·33 per cent abundant species H3 13C199Hg-12CH3. The magnitude of the 199Hg-13C coupling is discussed in terms of the correlation between reduced coupling constants and atomic number. The vicinal 13C-Hg-12CH3 coupling appears to be zero.

A Nuclear Magnetic Resonance Study of Mercury Dimethyl

In a nuclear magnetic resonance spectrum of the type AMX, the relative signs of the spin coupling constants J AM and J MX cannot be determined by double resonance experiments if J AX is unobservably small or zero, but the problem can be solved by the simultaneous application of three radio-frequency fields. This technique is described and demonstrated, and it is suggested that it should prove particularly useful for relating the signs of long-range spin coupling constants to couplings of known sign. Applied to the molecule of 3-bromothiophene-2-aldehyde, this experiment establishes that the long-range coupling to the aldehyde proton has the same sign as the vicinal coupling.

Determination of the signs of long-range proton spin coupling constants by nuclear magnetic triple resonance

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.

The relative signs of geminal and vicinal proton spin coupling constants

The high-resolution proton magnetic resonance spectrum of 2-carbomethoxy 5,6-dimethyl bezofuran has been obtained at 56·4 Mc/s. This N.M.R. (nuclear magnetic resonance) spectrum is complex since there are observable spin-spin coupled interactions between all the ring protons, between the protons of the 5 and 6 methyl groups and between the 4 and 7 protons and the protons of the 5 and 6 methyl groups. By taking advantage of solvent shifts and employing frequency-sweep spin decoupling techniques it was found that

K.A. McLauchlan

Papers

A Nuclear Magnetic Resonance Study of Mercury Dimethyl

Determination of the signs of long-range proton spin coupling constants by nuclear magnetic triple resonance

The relative signs of geminal and vicinal proton spin coupling constants

The high-resolution nuclear magnetic resonance spectrum of 2-carbomethoxy 5,6-dimethyl benzofuran