Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260270701pmid: N/A

Karavai, Vladimir P.; Gaponik, Pavel N.; Ivashkevich, Oleg A.

doi: 10.1002/mrc.1260270702pmid: N/A

The 1H and 13C NMR spectra of several meta‐ and para‐substituted 1‐phenyltetrazoles have been recorded, and the observed chemical shifts used for (i) the evaluation of σp, σm, σI, σR and σR°, the Hammett and Taft values of the 1‐tetrazoyl group, and (ii) the transmission of the electronic effects of the meta and para substituents on the phenyl ring to the tetrazole carbon and hydrogen atoms.

Watkins, C. L.; Krannich, L. K.; Kanjolia, R. K.; Srivastava, D. K.

doi: 10.1002/mrc.1260270703pmid: N/A

13C and 1H NMR spectral data for a homologous series of tertiary arsines (R3As, where R = Me, Et, n‐Pr and Ph), aminoarsines and arsonium and aminoarsonium salts are reported and discussed. In nearly all cases, quaternization of the tertiary arsine to its corresponding arsonium or aminoarsonium salt causes a decrease in the magnitude of δc. These results are compared with those from an analogous study on the quaternization of tertiary phosphines, R3P. A discussion of the factors that affect the relative magnitudes of δc and R3As and R3P is given. Hammett‐Taft dual substituent parameter analysis was used to show that the positive charge on the arsenic in the atomatic quaternary salts is delocalized by an inductive mechanism. The 1H NMR spectra of the n‐propyl‐ and phenyl‐containing compounds are non‐first order. The δH and nJ(HH) values were determined by iterative computer analysis. Likewise, the nJ(CH) values for the phenyl carbons of [Ph3AsNH2]Cl and [Ph3AsNHMe]Cl were determined from the coupled 13C NMR spectra.

Perry, Nigel B.; Blunt, John W.; Munro, Murray H. G.

doi: 10.1002/mrc.1260270704pmid: N/A

The 1H NMR spectra of the antibiotic cycloheximide in CDCl3 and CD3OD have been assigned. Analyses of coupling constants and difference NOE spectra showed different conformations in these two solvents, due to changeover between intra‐ and inter‐molecular hydrogen bonding. The twist boat cyclohexanone found in the solid state was not detected in solution. The results are compared with the solution and solid‐state conformations of the antitumour agent sesbanimide A.

Thomas, Ruthanne D.; Ellington, Donald H.

doi: 10.1002/mrc.1260270705pmid: N/A

A 13C spin‐echo technique with gated 6Li decoupling has been developed for the selective observation of different alkyllithium aggregates, (RLi)n. The spectral editing technique is based on the fact that both the multiplicity of the 13C resonance and the magnitude of the observed 13C6Li coupling are a function of the number of coupled 6Li nuclei. The method was shown to differentiate between three types of tert‐butyllithium‐6Li: dimers, fluxional tetramers and non‐fluxional tetramers.

Kalchhauser, H.; Krishnamurty, H. G.

doi: 10.1002/mrc.1260270706pmid: N/A

The assignment of the 1H and 13C NMR spectra of macrocyclic biphenyl ethers isolated from Garuga gamblei King was performed by 2D NMR techniques. An erroneous assignment given in the literature for one of the compounds was corrected. The use of shift increment systems and a 13C NMR data base demonstrated the applicability of these methods even in the case of very unusual structural elements. The conformation of the compounds in solution is discussed with the help of arguments derived from coupling constants and intramolecular anisotropy effects.

Ragg, Enzio; Mondell, Rosanna; Garbesi, Anna; Colonna, Francesco P.; Battistini, Carlo; Vioglio, Sergio

doi: 10.1002/mrc.1260270707pmid: N/A

2D 31P/1H correlation spectroscopy has been used to assign individual phosphates in the self‐complementary DNA fragment d(CGTACG), which is present in solution as a B‐DNA type double helix. 31P chemical shift variation with temperature and with the base sequence has been studied, and evidence is given of a steric clash between purines in the minor groove, affecting the chemical shift of the innermost TpA phosphate. For this hexanucleotide there is a good correlation of 31P shifts with both the helical twist (∑1) and roll angle (∑2) Calladine‐Dickerson sum functions. Different types of linear correlations, also including data from other nuclotides, have been performed. The results show that it is more appropriate to consider the change in chemical shifts as it occurs during melting rather than the actual 31P shifts. An interesting correlation was also found between 31P chemical shifts and P,H‐3′ coupling constants.

Kallinowski, Georg; Vogt, Walter

doi: 10.1002/mrc.1260270708pmid: N/A

13C chemical shifts and 31P, 13C spin‐spin coupling constants are reported for six model phosphinates and eight synthetic phosphinolipids. The complex spectra of the synthetic phosphinolipids could be assigned from increments and couplings derived from the model compounds. Based on these investigations the 3J(PC) couplings of 7–15 Hz indicate a preferential trans orientation of the respective head‐group carbon relative to the phosphorus. This behaviour is similar to that of natural phosphatidylcholine lipids.

Macías, F. A.; Massanet, G. M.; Rodríguez‐Luis, F.; Salvá, J.; Fronczek, F. R.

doi: 10.1002/mrc.1260270709pmid: N/A

The 13C NMR data of several khellactone derivatives are reported. 1H NMR‐based stereochemical criteria are evaluated, and a new criterion based on 13C NMR is proposed to establish the relative configuration at C‐3′ and C‐4′ using ΔδC‐3′ between trans and cis isomers and Δδgem(Me)2 values. The structure of trans‐4′‐methylkhellactone was determined by x‐ray analysis.

Bernstein, Michael A.

doi: 10.1002/mrc.1260270710pmid: N/A

The INEPT experiment which uses selective 1H pulses (INAPT) was used to assign quaternary carbon NMR signals in trisubstituted alkenes. Given that 3J(CH) across the double bond is usually larger for the trans than the cis disposed nuclei, experimental conditions may be chosen such that more polarization transfer is effected in the case of the trans nuclei. We applied this approach to two important pharmaceutica Is, cyclobenzaprine and ami‐triptyline, and some structurally related compounds. In each case the INAPT experiment quickly afforded a stereochemical assignment. Assignments were corroborated with the data from two‐dimensional selective hetero‐nuclear J‐resolved and heteronuclear nuclear Overhauser effect experiments.