Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270020501pmid: N/A

Deb, K. K.; Bloor, J. E.; Cole, T. C.

doi: 10.1002/mrc.1270020502pmid: N/A

The proton magnetic resonance spectra of 1,4‐benzodithiin and 1,4‐benzodioxin have been fully analyzed. The effects of the substituent heteroatoms on the chemical shifts of the various protons in the two molecules have been discussed.

Naegele, Walter; Wendisch, Detlef

doi: 10.1002/mrc.1270020503pmid: N/A

Im Zuge der Konfigurations‐ und Konformationsuntersuchungen an substituierten Cyclohexanen wurden 220 MHz‐Spektren von di‐ und trisubstituierten Verbindungen gemessen. In vielen Fällen gestattet die höhere Frequenz eine weitgehende Zuordnung aller Ringprotonen. Spezielle Eigenheiten der Spektren werden diskutiert.

Friebolin, H.; Keilich, G.; Siefert, E.

doi: 10.1002/mrc.1270020504pmid: N/A

Am Beispiel der Cellulosederivate wurde gezeigt, wie es mit Hilfe der PR‐Spektroskopie—speziell bei einer Meßfrequenz von 220 MHz—möglich ist, in Polysacchariden zwischen einer Hexose und Pentose zu unterscheiden, die Konfiguration und die Konformation des Monomerbausteins im Polymeren sowie die Art der glycosidischen Bindung zu bestimmen. Voraussetzung für diese Untersuchungen sind die Acetyl‐, Benzoyl‐ oder Methylderivate des Polysaccharids, wobei der Polymerisationsgrad bei den Acetaten und den Methyläthern Pw < 200, bei den Benzoaten sogar Pw < 100 sein sollte.

Lehmann F., Pedro A.

doi: 10.1002/mrc.1270020505pmid: N/A

PMR studies of a series of 2,4‐ and 2,6‐ dinitrophenyl‐ and 2,4‐dinitronaphthyl‐ aryl ethers strongly indicate the existence of preferred conformations. Extensive conjugation of the ether linkage with the dinitro ring, resulting in their coplanarity, is an important stereochemical influence. In the ensuing skew conformation the dinitro ring is positioned in such a way that the 6‐substituent is proximal to the other ring. In the case of the 2,4‐dinitrophenyl ethers (1) this is the 6‐proton, which shows the expected shielding due to the ring current in the other ring. In the 2,6‐dinitrophenyl‐(2) and 2,4‐dinitronaphthyl‐(3) ethers, this is a nitro group, twisted out of coplanarity to fit over the other ring, whose magnetic anisotropy is reflected in the shielding experienced by the 6′‐protons. When there is a 2′‐substituent present the ring which bears it twists in such a way as to bring the 6′‐proton closer to the proximal nitro‐group, explaining the greater shielding observed in these cases. Variable temperature studies provided further evidence in favor of these conformations since no significant changes were observed from −55° to + 155°, even for compounds with four substituents flanking the ether linkage. Nevertheless, the compounds studied here are not frozen in these conformations, but probably inter‐convert via concerted rotation with others.

Deb, K. K.; Cole, T. C.; Bloor, J. E.

doi: 10.1002/mrc.1270020506pmid: N/A

A study, using NMR techniques, of the propensity of complex formation of silver ions with hydrocarbons and heterocyclic compounds containing nitrogen, oxygen and sulphur is described. The results are compared with similar data using 1,3,5‐trinitrobenzene as an acceptor. The differences in the two sets of data are interpreted in terms of localized and delocalized interactions in the formation of weak complexes.

Thomas, W. A.; Griffin, G. E.

doi: 10.1002/mrc.1270020507pmid: N/A

The 1H and 19F spectra of a variety of mono‐ and di‐ fluorinated pyridines are examined, and compared with the corresponding spectra of the pyridinium ions. The magnitudes and signs of the 1H19F coupling constants are in general in accord with those observed for the corresponding 1H1H couplings, with an exaggerated range. Large changes in the NMR parameters are observed on protonation of the nitrogen, 3J(HF) changing sign in some of the α‐fluoropyridine derivatives.

Cooper, M. Ashley; Manatt, Stanley L.

doi: 10.1002/mrc.1270020508pmid: N/A

Newly determined and accurate data for the magnitudes of cis vinyl proton‐proton spin‐spin coupling constants in cis‐dialkylethylenes and cycloalkenes have been obtained. With these new data and also values taken from the recent literature, it has proved possible to make a critical determination of the correlation between 3J(HH) and CCH bond angles in ethylenic systems. It is suggested that it is possible to obtain accurate estimates of bond angles using NMR coupling constants, even though much more data will be required to fully substantiate this proposal. Whereas cis‐3J(HH) decreases rapidly with increasing CCH bond angles, evidence is presented that the opposite is the case for trans‐3J(HH). A brief theoretical discussion of these trends in coupling constants is given.

doi: 10.1002/mrc.1270020509pmid: N/A

doi: 10.1002/mrc.1270020510pmid: N/A