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Branch, S. K.; Casy, A. F.; Lipczynski, A.; Ominde, E. M. A.
doi: 10.1002/mrc.1260240602pmid: N/A
The 13C NMR features of most β‐lactam antibiotics of the penicillin and cephalosporin groups in clinical use are presented and reviewed. Data on precursor and breakdown products are included in the survey, with particular reference to benzylpenicillin. Penicillin and cephalosporin spectra are discussed, and points of similarity and difference emphasized. The potential of the data for solving problems of analysis, stability, degradation and biological structure–activity relationships is summarized.
Samitov, Yu. Yu.; Danilova, O. I.; Unkovsky, B. V.; Boiko, I. P.
doi: 10.1002/mrc.1260240603pmid: N/A
The 1H and 13C NMR spectra of 50 methyl‐ and phenyl‐substituted tetrahydro‐1,3‐oxazines are presented and discussed. Conformational analysis based on the model of atom‐atom interactions in 3,5‐dimethyltetra‐hydro‐1,3‐oxazine shows that the free energy difference between the chair and twist forms is 21 kJ mol−1. The distortion of the ring, which adopts a chair conformation, is analysed by the R value method and by the ASIS effect. The use of geminal 2J(HH′) values in the heteroatomic moieties as a criterion of the ring conformation has been demonstrated. The equilibrium and activation parameters of the heterocycle and nitrogen inversion have been determined. A good correlation between the predicted and experimental chemical shift values, δc, has been obtained, and this is shown to depend on the spatial structure of the substituted tetrahydro‐1,3‐oxazine molecule; moreover, the influence of intermolecular associations on δc has been demonstrated. Conformational preferences and some peculiarities in the chemical shifts are explained in terms of interactions with the endocyclic β‐oxygen atom and the N‐methyl group.
doi: 10.1002/mrc.1260240604pmid: N/A
Methylmercuration of cytidine‐3′‐monophosphate is shown to occur at the N‐3 site, resulting in a substantial upfield shift in the 15N resonance of this nitrogen. For guanosine‐5′‐monophosphate the 15N NMR data show N‐1 to be the site of complexation of CH3Hg+ at pH 8. The large downfield shift observed for N‐1 as a result of this binding is explained in terms of a concomitant deprotonation phenomenon. Changes in 13C NMR chemical shifts on methylmercuration are less pronounced, but consistent with these binding sites.
Kolehmainen, E.; Laatikainen, R.; Král, V.
doi: 10.1002/mrc.1260240605pmid: N/A
The 1H NMR spectra of some aryl‐ and heteroaryl‐substituted methylenemalonaldehydes were measured and analysed. The long‐range proton–proton spin–spin coupling constants were used to estimate the conformational behaviour of the aryl group relative to the vinyl and aldehyde groups. The compounds serve as model compounds for styrenoic systems, and models for the conformational dependences of the ortho‐ and meta‐benzylic couplings are given.
doi: 10.1002/mrc.1260240606pmid: N/A
Electrophilic additions to 5,8‐dimethoxy‐1,4‐dihydro‐1,4‐ethanonaphthalene have produced a series of new products resulting from Wagner–Meerwein rearrangements. Proton and 13C NMR have been used to provide structure proofs for these molecules, which fall into two series of substituted benzobicyclooctanes. The full range of NMR techniques, i.e. lanthanide‐induced shifts (LIS), difference NOEs and 2D NMR, have been employed. Proton and carbon chemical shifts are reported, and also a brief description is given of the more complex experimental results.
Nudelman, N. S.; Cerdeira, S. B.
doi: 10.1002/mrc.1260240607pmid: N/A
The 1H and 13C NMR spectra of 3‐nitro‐, 5‐nitro‐ and 3,5‐dinitro‐2‐methoxypyridines have been determined. The results show the preferred cis conformation for the 2‐methoxy group, and the importance of steric repulsion between the oxygen atom of this group and those of the o‐nitro group which hinders conjugation in the 3‐nitro‐substituted derivatives. Similar steric inhibition of resonance is observable with 2‐N‐butylamine‐, 2‐N‐cyclohexylamine‐ and 2‐(N‐piperidyl)‐substituted nitropyridines, whose 1H and 13C NMR spectra were also determined. In the case of the secondary amines, a hydrogen bond between the amino proton and the 3‐nitro group was clearly detected. 1H and 13C NMR spectra of 2,6‐dinitro‐, 2,4‐dinitro‐ and 2,4,6‐trinitro‐2‐R‐benzenes (R = OCH3, NHC4H9, NH‐cyclo‐C6H11, NC5H10) were also recorded and compared with those of the pyridine derivatives. The electronic aza and nitro group effects are comparable if conjugation of the nitro group is not hindered.
Pisipati, V. G. K. M.; Rao, N. V. S.; Muralikrishna, V.; Premchand,
doi: 10.1002/mrc.1260240608pmid: N/A
ESR and optical absorption studies are described for a number of ternary copper(II) compounds formed with substituted amino acids and different aliphatic polyamines, giving rise to two different immediate environments around copper(II), [3N, O] and [2N, 2O]. The ESR measurements were carried out in different solvents such as dimethyl sulphoxide, dimethylformamide and pyridine at room and liquid nitrogen temperatures. Molecular orbital coefficients were estimated assuming an axial symmetry. The parameter χ, proportional to the hyperfine constants, was estimated and shows a variation with solvent. The χ values in a solvent were found to be lower than the corresponding average values reported in the solid state for a particular type of environment. The solvent effect and the influence of the 4s character in the ground state are discussed. The hyperfine line widths in solution are estimated using Kivelson's theory. The disagreement between theoretical and experimental line widths are discussed.
Gray, Gary M.; Redmill, Keith A.
doi: 10.1002/mrc.1260240609pmid: N/A
It is possible to use multinuclear NMR spectroscopy to measure both the steric and electron donor/acceptor properties of the P‐donor ligands in Mo(CO)4[(R2″PO)2YRR′] complexes [R2″=Ph2, OCH2CMe2CH2O; YR = P(O), Si(Me); R′ = alkyl, haloalkyl, aryl]. The 13C, 29Si, 31P and 95Mo NMR data for some Mo(CO)4[(R2″PO)2YRR′] complexes [R2″ = Ph2, OCH2CMe2CH2O; YR = P(O), Si(Me); R′ = alkyl, haloalkyl, aryl] are presented and the factors affecting both the chemical shifts and coupling constants are discussed. The linear correlations between the chemical shifts of the cis and trans CO 13C, the 29Si, the 31P and the 95Mo resonances of the R2″ = Ph2 complexes and those of the similar resonances of the R2″ = OCH2CMe2CH2O complexes are also discussed.
doi: 10.1002/mrc.1260240610pmid: N/A
Poor correlations are normally observed between the chemical shifts of the various NMR‐active nuclei in Mo carbonyl complexes of group 15 ligands as the group 15 atom substituents are varied. It is possible to observe good chemical shift correlations and to develop relationships between chemical shift and changes in electron density due to variations in the group 15 atom substituents, provided that this variation does not change the cone angles of these ligands. This is the case for complexes of the type cis‐Mo(CO)4(py‐R)2 (py‐R = 3‐ or 4‐substituted pyridine). Good to excellent linear correlations are observed between the chemical shifts of the cis and trans CO 13C and 17O resonances and the 95Mo resonances in these complexes, and between these chemical shifts and the CO infrared stretching force constants of the complexes. Good to excellent correlations also occur between either the chemical shifts or the CO infrared stretching force constants and either the Taft σm/σp or σR and σ1 parameters. These correlations provide significant insights into the relationship between the electron donor/acceptor abilities of the pyridine ligands and the NMR and infrared spectra exhibited by the cis‐Mo(CO)4(py‐R)2 complexes.
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