Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260251001pmid: N/A

Krishnamurthy, V. V.; Casida, John E.

doi: 10.1002/mrc.1260251002pmid: N/A

The COLOC‐S pulse sequence (a modification of COLOC) provides rapid and selective long‐range correlation 2D NMR spectra. It combines the advantages of the COLOC and Freeman sequences. This modification is analysed in terms of the Product Operator Formalism, and its application is illustrated by spectral peak assignments of two insecticides, ryanodine and 1R, cis‐phenothrin.

Meyerhoff, Dieter J.; Nunlist, Rudi; O'Connell, John F.

doi: 10.1002/mrc.1260251003pmid: N/A

A NOESY‐type experiment with multiple mixing periods and acquisitions within a single pulse sequence was used to obtain a complete NOE correlation map of a small organic molecule. Incorporating multiple mixing periods and acquisitions into a single sequence can eliminate the need for repeating NOESY experiments with different mixing periods to observe dipolar exchange of considerably different rates or to determine exchange rates. The sequence has been applied to the molecular structure elucidation of cis‐8a‐vinyloctahydro‐3H‐2‐benzopyran‐3,7‐dione, a small organic molecule where the use of a single mixing period does not reveal all protons undergoing dipolar exchange.

Kamisako, Wasuke; Suwa, Kiyoko; Honda, Chie; Isoi, Koichiro; Nakai, Hiroshi; Shiro, Motoo; Machida, Katsunosuke

doi: 10.1002/mrc.1260251004pmid: N/A

Comparison of the 1H and 13C chemical shift data of bryonolic acid (D : C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) and its derivatives (13 species) revealed that the conformational features of these compounds in CDCl3 solution depend on whether the functional groups at C‐29 are trigonal, such as COOCH3, or tetrahedral, such as CH2OH. In order to study the conformational features of these two groups of compounds, vicinal coupling constants between the protons on the E rings of the methyl ester of D : C‐friedoolean‐8‐en‐29‐oic acid, D : C‐friedoolean‐8‐en‐29‐oic and its acetate were measured. Comparison of the results with the steric geometries to be expected from the molecular mechanics calculation for the E‐ring moieties of these derivatives in the S form (D‐E rings: boat‐boat form) and the F form (D‐E rings: chair‐chair form) led to the conclusion that the compounds having a trigonal functional group at C‐29 mainly adopt the S form, and those having a tetrahedral functional group at C‐29 are present as mixtures of the S and F form in equilibrium in the solutions.

Sohár, P.; Stájer, G.; Bernáth, G.

doi: 10.1002/mrc.1260251005pmid: N/A

The preferred conformations and, for the 3‐methyl‐substituted analogues also the configurations of the C‐3 atom, for 3‐unsubstituted and 3‐methyl‐substituted di‐exo‐ and di‐endo‐annellated oxazepinone derivatives fused with a norbornane or norbornene skeleton were determined by 1H and 13C NMR spectroscopy, including the use of DNOE measurements.

Xiaozeng, You; Weixiong, Wu

doi: 10.1002/mrc.1260251006pmid: N/A

The previously reported finite perturbation MNDO/GIAO method was ued to calculate nuclear magnetic shielding constants. A set of atomic MNDO parameters for nitrogen and oxygen was chosen by comparing calculated and experimental chemical shifts for compounds containing N and O atoms. The agreement of the trends within these compounds was satisfactory.

Barbarella, G.; Bertoluzza, A.; Tugnoli, V.

doi: 10.1002/mrc.1260251007pmid: N/A

The neutral and the protonated, positively charged, forms of 7‐methylguanosine have been characterized by 15N NMR in dimethyl sulphoxide. It is shown that in this solvent protonated 7‐methylguanosine gives specific interactions with cytidine at the same sites as those involved in the guanosine‐cytidine Watson‐Crick base‐pairs present in nucleic acids.

Arumugam, N.; Sundharavadivelu, M.; Sivasubramanian, S.; Wilson, D. A.

doi: 10.1002/mrc.1260251008pmid: N/A

1H NMR spectra of t‐3‐ethyl‐r‐2,c‐6‐diphenylpiperidine, t‐3‐ethyl‐r‐2,c‐6‐diphenyl‐4‐piperidone and several related compounds have been obtained in deuteriochloroform and deuteriotrifluoroacetic acid solutions, and compared with the spectra of their hydrochlorides in deuteriochloroform‐hexadeuteriodimethyl sulphoxide solutions. The effects of the structural changes 4‐CH2 → have been observed on the chemical shifts of ring and substituent protons, and on the non‐equivalence of the diastereotopic protons of the ethyl groups.

van Genderen, Marcel H. P.; Buck, Henk M.

doi: 10.1002/mrc.1260251009pmid: N/A

A new method is presented for the assignment of the NMR resonances of the diastereotopic protons in tetrahydrofur‐furyl and pyrrolidinylmethyl groups, based on the conformational transmission effect This effect describes the conformational changes produced by an increase of coordination from four to five of a phosphorus, silicon or germanium atom attached to the tetrahydrofurfuryl or pyrrolidinylmethyl moieties. The 1H NMR conformational analysis of these cyclic four‐ and five‐coordinated compounds yields two possible results, based on two assignments of the diastereotopic proton resonances. Comparison with the conformations of the analogous four‐ and five‐coordinated systems with acyclic 2‐methoxyethyl and dimethylaminoethyl groups (which lack diastereotopic protons) directly shows which assignment is correct, since a similar conformational transmission occurs in both the cyclic and the acyclic compounds.

Mitchell, T. N.; Nettelbeck, C.

doi: 10.1002/mrc.1260251010pmid: N/A

Multinuclear NMR data (1 H, 13 C, 119 Sn) have been obtained for almost all possible isomers of the composition Me3Sn(C3Hm)SnMe3 (m = 2, 4, 6) and Me3Sn(C4Hn)SnMe3 (n = 0, 2, 4, 6, 8). The coupling constants xJ(Sn, Sn) (x = 4, 5) are not linearly related to the corresponding coupling constants xJ(H, H), but are particularly large when tin‐carbon bonds can interact hyperconjugatively with carbon‐carbon double or triple bonds.