Coupling pattern in NMR

Mann, B. The Analysis of First-Order Coupling Patterns in NMR Spectra, Journal of Chemical Education, 72 (1995) 614. 

Thus the patterns of hyperfine splittings observed in EPR spectra provide direct information about the numbers and types of nuclei with spin coupled to the electrons this information is exactly analogous to that obtained from coupling patterns in NMR spectra. The magnitudes of the hyperfine couplings can indicate the extent to which the unpaired electrons are delocalized, while g values could also show whether unpaired electrons are based on transition-metal atoms or on adjacent ligands. Another example is described in the online supplementary material for Chapter 5 (hyperfine splitting), and many other examples of the application of EPR to chemical problems are described in a series of annual reports [5]. 

The 400 MHz 111 NMR spectrum of 17 (Fig. 1) shows characteristic 3/(H,H) coupling constants for the non-equivalent syn and anti oriented /l-CH2-hydrogens to the x-methine-hydrogen which are useful for the assignment of the stereochemistry. The connectivity and the coupling pattern, in particular the diagnostically valuable AMM X-spin system formed by III H (syn), Ha were analyzed by H,C-COSY and H,H-COSY45 NMR spectra. 

In the presence of potential ligands for lithium, f-butyllithium was found to be a dimer in diethyl ether-<7 0, a mixture of dimers and monomers in TIIIw7 0 and entirely monomeric when complexed to PMDTA. All these results are derived from one bond 13C—6Li coupling patterns in 13C NMR spectra, needless to say with NMR determined at low temperature, >160 K, since the reagent rapidly deprotonates all these ligands at higher temperatures. 

Kozik, M. Baker, L. C. W. Blue Electron Distributions in Diamagnetic Reduced Heteropolytungstates. Insights Concerning Conduction Pathways and Spin Coupling Patterns. 183W NMR Chemical Shift Calculations. In Polyoxometalates from Platonic Solids to Anti-retroviral Activity Pope, M. T. Muller, A., Eds. Kluwer Academic Publishers Dordrecht, 1994, pp 191-202. 

Canadensolide (6.18) is an antifungal metabolite of Penicillium canadense that was reported in 1968. Its dilactone structure was established by a combination of spectroscopic and chemical methods. Thus the presence of the exocyclic methylene was suggested by the IR data and established by ozonolysis to give formaldehyde whilst the presence of the vicinal diol as part of the dilactone was indicated by the coupling pattern in the NMR spectrum and confirmed by hydrolysis and cleavage of the resultant diol with sodium periodate to give valeraldehyde (pentan-l-al). There is a similarity between these metabolites and avenaciolide (6.19), a metabolite of Aspergillus avenaceus. 

Identification of unknown compounds NMR spectroscopy provides the forensic analyst with one of the most powerful techniques for identification of unknown compounds. The full range of structural elucidation techniques of modern spectrometers is available. First, the analyst obtains a high-resolution proton (NMR) spectrum in an appropriate deuterated solvent. The chemical shifts and integration in the spectrum give an indication of the types (aliphatic, olefinic, aromatic, etc.) and relative numbers of protons present in the molecule. The appearance of the coupling patterns in the molecule often provides very useful structural information. If the identity of the unknown cannot be determined from the results of the NMR study alone, the analyst next obtains information. The NMR spectrum gives a count of the number of nonequivalent carbon atoms, as well as the types of carbon (aliphatic, aromatic, carbonyl, etc.) present in the unknown. The number of protons attached to each carbon may... 

The J-coupling patterns in spectra can help to elucidate chemical structure, but they also comphcate the spectrum. Spectral-editing experiments allow such interactions to be observed in a controlled way. One such technique, DEPT (ifistortionless enhancement by polarization transfer), edits the spectrum based on scalar coupUng the pulse sequence is depicted in Fig. 15. DEPT is actually a set of three experiments, with tip angles, /, of 45°, 90°, and 135°. In NMR, appropriate addition and subtraction of the resulting subspectra separate the contributions from methyl, methylene, and methine carbons quaternaries are not observed. 

Table 4. n NMR chemical shifts and coupling patterns (in parentheses) T = triplet, Q = quintet and M = multiplet. 

The AA BB coupling pattern in the P NMR spectra of 22-27 were analysed, and the resulting coupling constants indicated that the basic structural features observed for these species in the solid state are also preserved in solution [57-60]. 

The long-range coupling of 2.2 Hz which appears in A and B, two quaternary C atoms in the NMR spectrum with appropriate shifts (5c = 76.6 and 83.0) and the two double-bond equivalents (molecular formula C TZ/oO) suggest that a CC triple bond links the two structural fragments. Hence the compound is identified as hex-3-yn-l-ol (C) in accordance with the coupling patterns. 

Tree diagram (Section 13.12) A diagram used in NMR to sort out the complicated splitting patterns that can arise from multiple couplings. 

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