Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270130401pmid: N/A

Besserre, D.; Coffi‐Nketsia, S.

doi: 10.1002/mrc.1270130402pmid: N/A

Measurements of the 13C chemical shifts of 2‐alkoxy‐1,3,2‐dioxaphospholanes have allowed the determination of the contribution of the substituent to the α‐, β‐ and γ‐carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constants J(31P13C) and the existence of linear correlations between the shifts of carbon atoms in the P‐alkoxy groups and the degree of substitution of the observed carbon or of its neighbours.

Khin, Tun; Duangthai, S.; Webb, G. A.

doi: 10.1002/mrc.1270130403pmid: N/A

INDO parameterized calculations of nJ(19F15N) are reported where n=1, 2, 3, 4 and 5. The calculations are performed within the sum‐over‐states perturbation and self‐consistent perturbation frameworks. In general, satisfactory agreement between both sets of calculated results and the available experimental data is obtained. All of the 1 J(19F15N) and 4J(19F15N) couplings can be of either sign. Most of the couplings considered are dominated by the contact contribution but the non‐contact interactions can be very important in certain cases.

Imagawa, Takeshi; Haneda, Akira; Kawanisi, Mituyosi

doi: 10.1002/mrc.1270130404pmid: N/A

The 13C NMR spectra of methyl 2‐pyrone‐3‐, 4‐, 5‐ and 6‐carboxylates were studied and the substituent effects on the 2‐pyrone ring were compared with those of some model compounds. 1H NMR spectra were also recorded and discussed. The long range 13C, 1H coupling constants were obtained, discussed and proved useful in signal assignments.

Runsink, Jan; Günther, Harald

doi: 10.1002/mrc.1270130405pmid: N/A

13C, 1H coupling constants for biphenylene have been obtained from the analysis of the 13C NMR spectrum of the natural abundance α‐13C‐ and β‐13C‐isotopomers. The various mechanisms responsible for the observed results are discussed.

Carleer, Robert; Anteunis, Marc J. O.

doi: 10.1002/mrc.1270130406pmid: N/A

Three series of substituted silaalkanes, (i) SiH3CH2X, (ii) MeSiH2CH2X and (III) Me2SiHCH2X, have been prepared (X=Cl, Br, I, NMe2, OMe, SMe), and the shifts and coupling constants extracted from their 1H NMR spectra. Coefficients averaged over three rotameric states can be obtained from the first series which are used for the correction of coupling constants resulting from the presence of the electronegative substituents X. With the aid of the Karplus‐Conroy angular dependence of the interproton coupling constants in silaethane† fragments, corrected for electronegative substitution, approximate rotameric populations in series ii and iii were obtained. Except for X=NMe2, there is always a preference for a synclinal X/CH3 relationship, even for sandwiched situations (series III).

Subbotin, O. A.; Sergeyev, N. M.; Chlopkov, V. N.; Nikishova, N. G.; Bundel, Yu. G.

doi: 10.1002/mrc.1270130407pmid: N/A

The conformational equilibrium constants for isomeric methylcyclohexanols (cis‐ and trans‐1,2‐, 1,3‐ and 1,4‐methylcyclohexanols) have been determined from peak area measurements in the completely proton decoupled low temperature 13C NMR spectra of the individual conformers. The 13C chemical shifts are discussed in terms of the additive model.

Rodríguez, Mario; Bertrán, José Fernández

doi: 10.1002/mrc.1270130408pmid: N/A

Evidence from the coupling constants and solvent shifts of the protons in cedranone rules out the boat and chair conformations of the cyclohexanone ring. Linear correlation of the solvent shifts of the C‐15 methyl protons of cedranone with those of the α‐methyl groups of fenchone indicates a nearly planar conformation of the cedranone ring. Site factor analysis of the ASIS effect of the methyl protons of cedranone provides conclusive evidence of a quasi‐chair conformation of the 6‐membered ring.

Schneider, Hans‐Jörg; Freitag, Wolfgang; Hoppen, Volker

doi: 10.1002/mrc.1270130409pmid: N/A

Intrinsic temperature dependencies of 13C NMR shifts in alkanes bearing one polar C‐αX bond are determined with neopentyl and 4‐tert‐butylcyclohexyl derivatives as conformationally homogeneous model compounds. The increased shiedling for C‐α at higher temperatures can be related to a C‐α—X bond length increase and, for less polarizable CX bonds, essentially to a decrease of solvent polarity on raising the temperature. The use of temperature dependent 13C shifts in conformationally mixed compounds for the determination of the equilibrium constants, K, is evaluated with n‐propyl halides; the computer fit of the unknown conformer shifts and the conformational enthalphy difference, δH° to the time averaged shifts yields δH° values which, although converging rather broadly, are in general agreement with literature data. In compounds with higher conformational barriers, such as methoxy‐ and bromocyclohexane, low temperature signal integration yields accurate δG° values; inclusion of shifts above coalescence, however, yields unreliable δH° and δS° parameters. This can only partially be remedied by application of temperature shift corrections obtained from parent t‐butylcyclohexyl compounds.

Greenaway, Frederick T.; Dabrowiak, James C.; Grulich, Robert; Crooke, Stanley T.

doi: 10.1002/mrc.1270130410pmid: N/A

Using the carbon assignments of bleomycin A2 as well as those of a series of model compounds, the 13C NMR assignments of the antitumor antibiotic tallysomycin (TLM) have been made. With the aid of the carbon assignments the metal binding properties of the new antibiotic toward Zn(II) have been investigated.