Triple-resonance Techniques Research Articles

The application of laser-microwave double and triple resonance to a complex molecular system: Allylamine

Information relevant to the infrared spectrum and to the tunneling barrier in highly excited states has been obtained for allylamine from a series of laser-microwave double- and triple-resonance experiments. An extremely large number of double-resonance signals were observed in this molecule with the 10.8-μm, R(8), 13CO 2 laser line. From the extensive use of triple-resonance experiments this laser line was shown to be coincident with infrared transitions in two distinct rotameric forms of allylamine. In the two infrared transition systems analyzed the upper vibrational states proved to be badly perturbed. The use of the triple-resonance technique as an assignment aid under such circumstances is discussed. Rotational constants for two highly excited vibrational states of allylamine were obtained and in one case evidence is presented for a possible large effective lowering of the tunneling barrier. The center frequencies of the two vibrational bands concerned are calculated.

14N NMR studies of free radicals: Application to α,α-diphenyl-β-picrylhydrazyl (DPPH)

Using NMR, we establish that the 14 N hyperfine coupling, A N , of the -NO 2 groups in DPPH is −0.42 ± 0.05 G. This must correspond to the smallest splitting observed in the high-resolution EPR spectra of DPPH. We find that for such small 14 N splittings in free radicals, the NMR method has distinct advantages over ELDOR, ENDOR, and tripleresonance techniques.

13C NMR spectroscopic studies on the conformation during stepwise synthesis of peptides bound to solubilizing polymer supports

The C-13 {C-13-H-1} triple resonance technique allows constitutional and conformational studies on polypeptides bound to mono- and bi-functional solubilizing polyoxyethylene supports. High resolution shows distinct differences between random coil and α-helical conformations. This method is a valuable additional tool for control of the growing peptide during stepwise synthesis on soluble polymeric supports. Examples of partial sequences of the polypeptide antibiotic alamethicin and sequential analogs (Aib-Ala) n demonstrate the applicability for peptide polyoxyethylene esters with mean molecular masses between 2000 and 10,000.

Hyperfine structure and nuclear moments of99Ru and101Ru

The atomic-beam magnetic-resonance method in combination with the triple resonance technique has been used to determine the nuclear magnetic dipole moments of99Ru and101Ru. The moments are deduced fromrf transition measurements in the5F5 and5F4 states at magnetic fields between 770 and 2400 Oe. In order to reduce the part of the uncertainty of the moments which arises from the uncertainty of the hyperfine structure constants more precise values of the constants than those available up to now were determined from low field measurements. After making corrections for hyperfine and Zeeman interactions with neighbouring atomic states we obtain the following values for the magnetic dipole moments:μ 99=−0.6381 (51)μ N andμ 101=−0.7152 (60)μ N (uncorrected for diamagnetic shielding). The results of the present work combined with the results of an earlier hyperfine structure investigation in the5F multiplet are analysed with respect to the effective-operator formalism. From this analysis we obtain the following values for the electric quadrupole moments:Q 99=0.076 (7) b andQ 101=0.44 (4) b (uncorrected for Sternheimer shielding or antishielding).

Indirect observation of Bloch-Siegert shifts in 13C{ 1H} multiple-resonance experiments

Bloch-Siegert shifts imposed on the 1H resonance frequencies in 13{ 1H} single-frequency off resonance decoupling experiments have been indirectly observed by means of 13C-{ 1H} triple-resonance techniques using a sample of toluene. The observed shifts, which are several hundred hertz in magnitude, are in good agreement with those predicted by theory. A 13C{ 1H} quadruple-resonance experiment, which includes consideration of these Bloch-Siegert shifts, has been designed for the determination of the sign of 3J cα- P × 4J Hα- P in 2-isopropylphenyl diphenylphosphine. In general, 1H multiple-irradiation experiments prove extremely valuable in 13C NMR spectroscopy. However, these techniques require consideration of the Bloch-Siegert shifts, which may often be unusually large.

Microwave Spectrum of HCOOH in the vCH=1 Vibrational State Observed by Laser-Microwave Double and Triple Resonance

Application of laser-microwave double and triple resonance techniques to microwave spectroscopy of HCOOH in the CH stretching vibrational state is reported. The 3.39 µm output from a He–Ne Laser is Zeeman-tuned to saturate a rotation-vibration transition of HCOOH. The microwave transition from the upper state of the infrared transition is stimulated with a klystron and the resulting increase of the infrared absorption is detected. A technique of triple resonance is employed to observe microwave transitions which do not share a common level with the infrared transition. From the observed nineteen pure rotational transitions the rotational constants in the excited state are determined. Accuracy of the constants is limited by the effect of interactions between the vibrational states. The double and triple resonance effects for microwave spectroscopy of excited molecules are discussed by a rate equation approximation.

ChemInform Abstract: STUDIES OF ORGANOPHOSPHORUS SELENIDES BY HETERONUCLEAR MAGNETIC TRIPLE RESONANCE

AbstractDie "Se‐chemischen Verschiebungen in den Titelverbindungen (I) werden gemessen.

Studies of organophosphorus selenides by heteronuclear magnetic triple resonance

A heteronuclear magnetic selective triple resonance technique for the determination of chemical shifts in incomplete spin systems is described and applied to the measurement of 77Se chemical shifts in Organophosphorus selenides. The results indicate that the dipolar form makes a major contribution to the phosphorus–selenium bond, but π-bonding between phosphorus and selenium is also important. The 31P–77Se spin coupling constants are negative and can be interpreted in terms of the inductive effect of the substituents of the phosphorus atom.

Measurement of longitudinal relaxation times for spin-decoupled protons

Description of an experimental method for the determination of the longitudinal relaxation time for spin-decoupled protons by a modified version of the saturation recovery technique reported by Van Geet and Hume (1965). The described method should facilitate relaxation studies of chemically shifted protons (or fluorines) and can be applied to more complicated spin systems with the aid of triple resonance and noise-decoupling techniques.

Determination of chemical shifts by heteronuclear magnetic triple resonance: the nature of the phosphorus–selenium bond in organophosphorus selenides

A novel heteronuclear triple resonance technique is used to obtain 77Se chemical shifts in organophosphorus selenides, and to show that the dipolar form of the phosphorus–selenium link is predominant.

Long range coupling constants in monosubstituted methyl and aldehydo pyridines

Abstract Double and triple resonance techniques are used to determine the magnitude of long range coupling constants in mono-substituted aldehydo and methyl pyridines. Relative sign information is obtained for two of the molecules. The coupling behaviour of the exocyclic group is shown to be consistent with long range coupling constants in other molecules.

Instrumentation and Measurement of Nuclear Magnetic Triple Resonance Including 14N Resonance

SUMMARYA bridge-type high-resolution NMR spectrometer has been modified to yield a triple-resonance spectrometer which decouples two kinds of interaction, 14N-1H and 1H-1H. The instrumentation of this modification is described in detail. The conditions for decoupling the UN interaction with proton were investigated experimentally, especially the dependence of the proton resonance resolution on both power and frequency of the rf field corresponding to the UN resonance. It is pointed out that the resonance frequency of the 14N nucleus can be measured with high accuracy using this double-resonance technique. The triple-resonance technique was applied to pyrrole, and was successful in obtaining the finely resolved spectrum and in attributing the spin-spin couplings to the interactions between specified groups of proton.

DOUBLE AND TRIPLE RESONANCE EXPERIMENTS ON 2-BROMO-5-CHLOROTOLUENE: SIGNS OF THE RING AND RING-METHYL PROTON COUPLING CONSTANTS

Tickling and decoupling (triple resonance) techniques show that the ortho, meta, and para proton coupling constants have the same sign in 2-bromo-5-chlorotoluene. If the ortho coupling in the ring is positive, then decoupling experiments show that the methyl proton couplings to the ring protons in the ortho and para position to the methyl group are negative, while that to the meta position is positive. These signs are in agreement with the σ–π exchange polarization mechanism.

The analysis of complex nmr spectra by multiple resonance techniques

The complete analyses of complex proton nmr spectra by double and triple resonance techniques are illustrated for AA′BB′MM′XX′ and ABCDMXY systems. The single resonance spectra of cis-4-cyclohexene-1,2-dicarboxylic anhydride and 1-methyl- cis-4-cyclohexene-1,2-dicarboxylic anhydride consist of so many overlapping multiplets that individual features are unrecognizable. However, by multiple resonance techniques it is possible to obtain good estimates for all the coupling constants and chemical shifts for these molecules.

Dynamic polarisation in a three-spin system

The dynamic polarization due to the Overhauser effect in a system of three spins S, I/sub 1/, and I/sub 2/ was observed using double and triple resonance techniques. Measuremerts were made on the signal enhancement of the nuclear magnetic resonance of the C/sup 13/-nuclei (I/sub 2/) of the solvent in natural abundance in a solution of the free radical 1,3-bisdiphenylene-phenyl- allyl in benzene and perdeuterobenzene while saturating the electron (S) and both the electrons and the protons simultaneously. This system is used to calculate theoretically in first approximation the interaction between the electrons and protons, neglecting the comparatively small numbers of the C/sup 13/-spins, and in second approximation the polarization of the C/sup 13/-spins due to their interaction with the electrons and with the protons. (H.D.R.)