Magnetic Resonance in Chemistry

Bigam, G. E.; McClung, R. E. D.; Nakashima, T. T.; Angelov, C. M.; Cavell, R. G.

doi: 10.1002/(SICI)1097-458X(199708)35:8<502::AID-OMR118>3.0.CO;2-7pmid: N/A

Anomalous APT spectra are reported for an organophosphorus compound containing methylene 13C nuclei coupled to two 31P nuclei. Strong coupling effects in these ABX spin systems are shown to account for the anomalous phases and intensities of the APT spectra by density matrix simulations. © 1997 John Wiley & Sons, Ltd.

Reynolds, William F.; Yu, Margaret; Enriquez, Raul G.; Leon, Ismael

doi: 10.1002/(SICI)1097-458X(199708)35:8<505::AID-OMR130>3.0.CO;2-Kpmid: N/A

Although the potential advantages of f1 forward linear prediction for the processing of multi‐dimensional NMR spectra are well established, this method is surprisingly little used for 2D spectra used for organic structure determination. A detailed investigation of the advantages and limitations of f1 forward linear prediction for this purpose is reported. This is a reliable technique which is particularly useful for 1H‐detected 13C–1H shift correlation spectra, allowing up to 16‐fold linear prediction of the 13C axis of HSQC spectra. In general, the use of linear prediction allows one to obtain comparable 2D spectra in one quarter of the time or double the sensitivity in a comparable time relative to similar spectra without linear prediction. The one exception is the absolute value COSY spectrum, where linear prediction beyond a factor of two gives poor results. Linear prediction is generally superior to zero filling as a time‐saving technique, although the difference between the two approaches disappears as the f1 data point resolution approaches the natural linewidth. By contrast, f2 forward linear prediction is not recommended. © 1997 John Wiley & Sons, Ltd.

Hansen, Poul Erik; Bolvig, Simon

doi: 10.1002/(SICI)1097-458X(199708)35:8<520::AID-OMR132>3.0.CO;2-Rpmid: N/A

The interesting deuterium isotope effects of gossypols have been reinvestigated and the very large two‐bond isotope effect, 2ΔC‐6(OD), is ascribed to electric field effects. Common to the investigated compounds is the presence of intramolecular hydrogen bonds. A feature strongly related to the strength of the intramolecular hydrogen bond is intermolecular OH exchange. Electron‐attracting substituents at the 3‐ and 5‐positions of 2‐hydroxyacyl aromatics increase the acidity of the 2‐OH proton and therefore the intermolecular exchange, but not the hydrogen bond strength, whereas alkyl groups ortho to the intramolecularly hydrogen bonded OH prevent the OH group from swinging out and therefore prevent intermolecular exchange. Conformational equilibria were studied in 2‐hydroxy‐3‐nitro‐6‐methoxyacetophenone. Surprisingly, the form with the weaker intramolecular hydrogen bond to the nitro group is dominant at ambient temperature, whereas it is the opposite at 160 K. For 2‐hydroxy‐5‐methyl‐3‐nitroacetophenone a similar pattern is seen, but with much less of the form having hydrogen bonding to the nitro group at ambient temperature. 2‐Acetyl‐1, 8‐dihydroxy‐3,6‐dimethylnaphthalene is involved in tautomerism of the enolic β‐diketone type and large deuterium isotope effects on the 13C and OH chemical shifts are observed. © 1997 John Wiley & Sons, Ltd.

Chan, Tze‐Ming; Osterman, Rebecca M.; Morton, James B.; Ganguly, Ashit K.

doi: 10.1002/(SICI)1097-458X(199708)35:8<529::AID-OMR120>3.0.CO;2-7pmid: N/A

The complete assignments of 1H and 13C data for Sch 27899 are described. The compound is an oligosaccharide antibiotic belonging to the class everninomicin. It has a molecular mass of 1629. The assignments are based on 2D HMQC, HMQC‐TOCSY and HMBC experiments. © 1997 John Wiley & Sons, Ltd.

Rulev, Alexander Yu.; Mokov, Alexander S.; Krivdin, Leonid B.; Keiko, Natalia A.; Voronkov, Mikhail G.

doi: 10.1002/(SICI)1097-458X(199708)35:8<533::AID-OMR108>3.0.CO;2-2pmid: N/A

1H and 13C NMR spectra of N,N‐disubstituted α‐amino‐α,β‐unsaturated aldehydes and their azomethines and enammonium salts were studied. The spectra reflect the degree of p–π conjugation between the nitrogen lone pair and the π‐electrons of the carbon–carbon double bond. In this respect, the title 2‐aminoenals are shown to be in an intermediate position between α‐unsubstituted aminoalkenes and α,β‐unsaturated aldehydes. The degree of conjugation depends on the nature of the amine moiety and the activating group. © 1997 John Wiley & Sons, Ltd.

Rochet, Patrick; Lancelin, Jean‐Marc

doi: 10.1002/(SICI)1097-458X(199708)35:8<538::AID-OMR122>3.0.CO;2-3pmid: N/A

The major polyene antibiotic macrolide isolated from Streptomyces filipinensis, filipin III, was reinvestigated in DMSO solution using homonuclear and heteronuclear correlation spectroscopy. In addition to several corrections to previous 1H NMR assignments, the nine exchangeable hydroxylic protons were structure‐specifically assigned together with 13C NMR lines using proton‐detected HSQC spectroscopy. The magnitudes of the 3J proton–proton couplings indicated a probable constrained geometry of the macrocyclic lactone. © 1997 John Wiley & Sons, Ltd.

Waisser, Karel; Kuneš, Jiří; Kubicová, and Lenka; Buděšínský, Miloš; Exner, Otto

doi: 10.1002/(SICI)1097-458X(199708)35:8<543::AID-OMR126>3.0.CO;2-5pmid: N/A

The 1H, 13C and 19F NMR spectra of 3′‐ and 4′‐substituted 3‐ and 4‐fluorobenzanilides and thiobenzanilides are reported. According to the 19F substituent‐induced shifts (SCS), transmission of substituent effects through the NHCS group is less efficient than that through NHCO groups. On the other hand, in thioanilides a greater part of the substituent effect remains on the functional group itself, as follows mainly from 13C SCS of the central carbon. An explanation is possible in terms of the greater polarizability of sulfur, which accommodates charge better than oxygen. Comparison with the isomers studied previously reveals that transmission depends slightly on the direction. It is more efficient through the NHCX group than through the CXNH group: the nitrogen atom as donor interacts more strongly than carbonyl with the substituent effects of acceptor groups. © 1997 John Wiley & Sons, Ltd.

TASHTOUSH, HASAN; AL‐TALIB, RUFAIDA SUBAIHI AND MAHMOUD

doi: 10.1002/(SICI)1097-458X(199708)35:8<549::AID-OMR131>3.0.CO;2-1pmid: N/A

1,3,5‐Tris(5‐substituted‐1,3,4‐oxadiazol‐2‐yl)benzenes were prepared by the dehydration of the corresponding hydrazides. The structures of these compounds were elucidated by IR, 1H and 13C NMR spectroscopy. © 1997 John Wiley & Sons, Ltd.

BERESNEVIČIŪTĖ, K.; BERESNEVIČIUS, Z.; MIKULSKIENĖ, G.; KIHLBERG, J.; BRODDEFALK, J.

doi: 10.1002/(SICI)1097-458X(199708)35:8<553::AID-OMR109>3.0.CO;2-Ypmid: N/A

The 13C NMR spectral data for 18 dihydropyrimidinediones and their 2‐thio analogues are presented. The influence of substituents on the shielding of neighbouring atoms was analysed and the resonances were unambiguously assigned. 13C NMR spectroscopy was shown to be useful for structural determination of dihydropyrimidinediones and thioanalogues and allowed the facile distinction of otherwise similar compounds from the two classes. © 1997 John Wiley & Sons, Ltd.