摘要:

AbstractThe13C data of several new amino protecting groups of the urethane structure are reported. The speeds of acidolytic cleavage are correlated with the13C parameters.

ISSN:0030-4921    

DOI:10.1002/mrc.1270170302

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractAssignments of the13C NMR resonances for some cassane diterpenoids have been made. The data have proved to be a useful tool for the stereochemical examination of the caesalpins.

ISSN:0030-4921    

DOI:10.1002/mrc.1270170303

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractCarbon‐13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol andepi‐friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revis

ISSN:0030-4921    

DOI:10.1002/mrc.1270170304

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectral data for a series of symmetrical 2,6‐disubstituted adamantanes (O, CH2, CH3, OH, OCOCH3) are presented. The substituent effects on13C chemical shifts are additive, except for carbons 2 and 6 in 2,6‐adamantanedione. The non‐additivity of the substituent effect in the diketone can be interpreted in terms of a through‐space interaction of the carbonyl π‐electrons; the additivity in the other derivatives indicates that there is no appreciable interaction between

ISSN:0030-4921    

DOI:10.1002/mrc.1270170305

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractBy the use of the1H1H and1H31P coupling constants in two analogues of aspartic acid i.e. 3‐amino‐3‐phosphonatopropionic and 3‐amino‐3‐(methylphosphinato) propionic acids, it was shown that the six parameter formulation for the evaluation of mole fractions of three staggered ethanic rotamers is not necessarily better than the two parameter formulation in this system. The results allowed the recommendation of the following values for the two vicinal proton parameters i.e.J(HH)g=2.3,J(HH)t=13.9 and for the two vicinal proton‐phosphorus parameters i.e.J(HP)g=4

ISSN:0030-4921    

DOI:10.1002/mrc.1270170306

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractNo significant steric effects are observed in the proton and carbon resonance spectra of 2,2′,4,4′,6,6′‐hexa‐t‐butylazobenzene, a very distorted molecule in the

ISSN:0030-4921    

DOI:10.1002/mrc.1270170307

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstract13CT1ρvalues measured for isobutylamine, diethylamine, pyrrolidine, piperidine and triethylamine yield one‐bond14N13C coupling constants and14N spin‐lattice relaxation times. A decrease of1J(14N13C) was observed in sterically hindered secondary

ISSN:0030-4921    

DOI:10.1002/mrc.1270170308

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractNitrogen‐15 NMR spectra of 11 ketenimines have been taken both at the natural‐abundance level of15N and with the aid of15N‐labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone‐pair. Furthermore, there is a rough parallelism between the13C shifts of the terminal carbons and the15N

ISSN:0030-4921    

DOI:10.1002/mrc.1270170309

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe selective population transfer method has been applied to the study of a secondary amide and of the corresponding iminium salt. Important signal‐to‐noise enhancements were accessible in both fully coupled and proton decoupled15N and13C spectra. Moreover, the resolving power of the method was exploited for the accurate determination of long range15N1H coupling constants. Experiments in which the selective inversion of transitions pertaining to the15N satellite spectrum of multiplets which themselves constitute the13C satellite spectrum of the main proton resonances could be carried out. The influence of a change from the amide to the iminium structure on the magnitudes and the signs of various15N1H and15N13C coupling constants is discus

ISSN:0030-4921    

DOI:10.1002/mrc.1270170310

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe proton NMR spectra of 14 actinomycins and the13C NMR data for four of these compounds were compared with those of actinomycin D. These compounds differ from actinmycin D by the replacement of one or both proline residues by sarcosine, azetidine‐2‐carboxylic acid, 4‐ketoproline, orcisortransisomers of 4‐hydroxy‐, 4‐chloro‐ or 4‐methylproline. In those (aniso) compounds in which one proline residue is replaced, the possibility of isomerism was considered, since replacement could be located in either the α‐ or β‐peptide. Except for the sarcosine case, for which both isomers have been isolated, theaniso‐actinomycins gave spectra in which the presence of a second isomer was undetectable. Attempts to utilize the NMR data to determine which peptide contained proline, and which its congener, produced the tentative conclusion that in these compounds there is a biosynthetic preference for replacement of the β‐peptide proline residue. In comparing conformationally dependent NMR parameters for the various actinomycins, the most obvious variations appeared in the proline congener α‐proton splittings. Some of these (forcisisomers of 4‐chloroproline and 4‐methylproline) reflected different pyrrolidine ring geometries to that of proline, while others (for the correspondingtransisomers) did not. Only minor differences were apparent in the conformations of othe

ISSN:0030-4921    

DOI:10.1002/mrc.1270170311

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY