摘要:

AbstractDetailed1H NMR studies ofmstetraphenylchlorins (H2TPC), new amino‐ and hydroxypyrroline substitutedmstetraphenylchlorins andmstetraphenylisobacteriochlorins (H2TPisoB) are presented and discussed. The results obtained are consistent with the general aspects of the ring current models as applied to the parent porphyrins. According to proton chemical shifts a gradual reduction in the magnitude of the ring current is observed in the ordermstetraphenylporphyrin (H2TPP)>H2TPC>mstetraphenylbacteriochlorin (H2TPB)>H2TPisoB. The1H NMR spectra show chemical non‐equivalence of the pyrroline ring protons due to adjacent substituents, and effects of steric constraints on the aminoalkyl substituents due to the close vicinity to themesophenyl rings. The non‐equivalence of the methylene protons of the pyrroline ring produces geminal coupling between the two methylene protons and vicinal coupling with the adjacent pyrroline proton, more pronounced in H2TPCOH and in . Restricted configuration of the methylene groups in the ethyl groups of H2TPCC(H)(CH3)N(CH2CH3)2produces observable geminal coupling between the methylene protons.1H NMR reveals the difference between two types ofmesophenyls in the chlorins, and three types ofmesophenyls in isobacteriochlorins, as reflected in the chemical shifts of theo‐phe

ISSN:0030-4921    

DOI:10.1002/mrc.1270150102

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe15NMR chemical shifts were measured of a number ofN‐substituted formamides and acetamides at the natural abundance level. The ratios of thecisandtransisomers for severalN‐alkylformamides were also determined. Substituent effects on the15N chemical shifts of formamides are compared with those of some other nitrogen‐containing compounds. There is a consistent pattern of behavior of the one bond spin–spin coupling constants [1J(15NH)] wherein thetransisomers ofN‐alkylformamides are larger than those of thec

ISSN:0030-4921    

DOI:10.1002/mrc.1270150103

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe1H spectrum of (15N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3‐dioxane, 1,4‐dioxane, D2O, acetonitrile and pyridine‐d5at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG≠, for hindered rotation about the central CN bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG≠(298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3‐dioxane and 70.1 kJ mol1in 1,4‐dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D2O, acetonitrile and pyridine‐d5. The free energy of activation and the internal chemical shift are discussed on the basis of solvent‐amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molec

ISSN:0030-4921    

DOI:10.1002/mrc.1270150104

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractJ(13C1H) coupling constants for some methyl‐ and aminopyrimidines have been determined by13C NMR. Both the one‐bond and long‐bond and long‐range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the3J(C‐i,H) coupling constants between a ring carbon C‐i and the ring protons are larger than the2J(C‐i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons:3J(C,Me). These general rules are very useful for the assignment of resonances in complex13C spectra of pyrimidines and seem to be valid for other 6‐membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on1J(CH) for monosubstituted pyrimidines allows the estimation of1J(CH) for polysubstituted pyrimidines with a ver

ISSN:0030-4921    

DOI:10.1002/mrc.1270150105

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstract13C chemical shifts obtained under uniform conditions for selected compounds containing secondary aliphatic fragments were employed in a linear regression analysis. Two‐parameter relationships describing the substituent effects in the saturated framework were calculated, and the usefulness of such calculations is discussed. Finally, coefficients for linear relationships in primary and secondary alkyl derivatives are compare

ISSN:0030-4921    

DOI:10.1002/mrc.1270150106

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe NMR variable temperature behaviour ofN‐aroyl‐ andN‐thioaroyl‐N′‐piperonylpiperazines was investigated. The largest chemical shift separation between the exchanging methylene groups, and the highest energy barrier, is found for the thioamide compounds. Results from semi‐empirical calculations are qualitatively in line with the experimental findings, revealing that the higher barrier in the thiocarbonyl compounds compared with the carbonyl compounds is mainly connected with differences in the energies of ground states, rather than in those of transition states, of these molecules. The effect of the nature of the heterocyclic ring containing the amidic nitrogen atom on the barrier height is a

ISSN:0030-4921    

DOI:10.1002/mrc.1270150107

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe1H and31P NMR spectra of the phenyl ester of dichlorophosphoric acid dissolved in Merck nematic phase IV have been recorded and analysed. The values of the dipole dipole couplings have been discussed in terms of several different geometric models. Non‐planarity of C‐1, O, P and the phenyl ring must be assumed in order to account for the results; a twist angle of 49° was f

ISSN:0030-4921    

DOI:10.1002/mrc.1270150108

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe lanthanide shift reagent (LSR)/1H NMR study of some 7‐chloro‐5‐phenyl‐2,3‐dihydro‐1H‐1, 4‐benzodiazepines shows that these compounds exist in CDCI3solution as two pseudo‐boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1‐substituent: this effect may be the result of the greater basicity of 4‐N when the 1‐N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1‐ to 4‐N through the fused benzene ring. The detection of H‐9/1‐Me through space spin‐spin coupling in medazepam (7‐chloro‐1‐methyl‐5‐phenyl‐2,3‐dihydro‐1H‐1,4‐benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of3J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer

ISSN:0030-4921    

DOI:10.1002/mrc.1270150109

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe olefins Ph2P(X)CHCHR [X=lone pair, O, S, Ch3I; RCh3, ph, P(X)ph2] have been prepared and their1H,13C and31P NMR spectra measured.trans3J[P(IV)C] (range 18.3–25.7 Hz) is greater thancis3J[P(IV)C] (range 6.9–11 Hz) but this relationship does not hold for P(III) compounds. In the31P spectra theEisomer absorbs to higher field than theZisomer for P(III) and P(IV) compounds. The1H data are in accord with previous results; average substituent shielding coefficients for ph2P(X) substituted alkenes are r

ISSN:0030-4921    

DOI:10.1002/mrc.1270150110

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe relationship between vicinal NMR proton–proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on3J(HH); second, empirical correlations between the parameters governing the conformation of β‐D‐furanosides (taken from an analysis of 178 crystal structures) were used to define proton–proton torsion angles as a function of the pseudorotation parametersPand Φm; and, third an iterative least‐squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′‐cyclic nucleotides, a base‐stacked ribonucleotide, 2′‐anhydroarabinonucleosides, α‐D‐2′,2‐O‐cyclouridine, 2′‐ and 3′‐aminosubstituted ribonucleosides, 2′‐ and 3′‐deoxyribonucleosides. The present results confirm that the conformational properties found in the so

ISSN:0030-4921    

DOI:10.1002/mrc.1270150111

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY