摘要:

AbstractThe13C chemical shifts of 209 naturally occurring and synthetic coumarin derivatives are listed and a number of methods for signal assignments are explained. Substituent effects on13C chemical shifts (SCS) in monosubstituted coumarins and non‐additivities of SCS in coumarins with more than one substituent are discussed in detai

ISSN:0030-4921    

DOI:10.1002/mrc.1270200202

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractA systematic study has been made of the effects of substituent induced chemical shifts in [(η5‐C5H5)(CO)3Mo(CH2C6H4R)] compounds. Both95Mo and13C NMR shifts in the aromatic ring are reported. The (η5‐C5H5)(CO)3MoCH2 group is a reasonably strong resonance donor (σR° = −0.21) and weak inductive donor (σI= −0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (rangec.40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this sp

ISSN:0030-4921    

DOI:10.1002/mrc.1270200203

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractErythroandthreoconfigurational assignments have been made for 11 β‐fluoro‐α‐amino acids or esters using the effect of complexation of the ammonium group by 18‐crown‐6 ether on the19F NMR parameters. For theerythroconfigurations,3J(HF) increases and a high‐field19F chemical shift is generally observed; these phenomena are accompanied by a decrease in3J(HH) and3J(CF). The opposite effects are observed for thethreoconfigurations. These observations can be explained by a change in the relative population of the conformers around the Cα‐Cβ bond on complexation of the ammonium group. This complexation impairs the interactions between the ammonium and fluorine groups and, concomitantly, the steric hindrance between the ammonium and R (methyl, phenyl or carboxylate) gr

ISSN:0030-4921    

DOI:10.1002/mrc.1270200204

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe easily obtained dimers of phosphole oxides, sulfides and methiodides give13C NMR spectra where carbons within three (sometimes four) bonds of each31P nucleus are doublets of doublets and thus constitute X in an AMX spectrum. Most of the spectra have been completely interpreted with the aid of spectral measurements at two magnetic fields. Saturation of the double bonds in dimers of methylphosphole–P(IV) derivatives causes the31P nuclei to have very similar chemical shifts, with Δν not adequately different from3J(PP) to give first‐order coupling. When both31P nuclei couple with a given13C, a second‐order (ABX)31C NMR spectrum is obtained. The presence of the effect is revealed by running the13C NMR spectra at high magnetic field;J(AX)+J(BX) is constant at all fields, but spacing between the lines of the multiplet varies. The spectrum of the oxide, with Δν/J=1.44 for the31P spectrum at 36.43 MHz, approaches first order character at 75 MHz; the methiodide spectrum (Δν/J=4.55) is second order at 15 MHz but clearly first order at 50 MHz, and the sulfide (Δν/J=5.6) is nearly first order at 15 MHz. [2 + 2]‐Photochemical intramolecular cyclization of the dimer oxides provides cage‐like structures where the31P nuclei are chemically equivalent, but magnetically non‐equivalent, making the13C signals have the characteristics of X in an AA

ISSN:0030-4921    

DOI:10.1002/mrc.1270200205

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractBecause of experimental and theoretical interest in long‐range1H19F and13C19F coupling constants between proximate atoms, a series ofN‐alkylfluoroquinolinium compounds was synthesized and the NMR parameters were accurately measured. By means of spin tickling and selective population inversion difference spectroscopy, the5J(HF) and4J(CF), which are associated with the proximate fluorine and methyl groups, were shown to be of the same (positive) sign as the directly bonded13C1H and vicinal1H1H coupling constants. InN‐methyl‐8‐fluoroquinolinium iodide (1a) and chloride (1b)5J(HF)=+8.8 and4J(CF)=+16.3 Hz, and inN‐ethyl‐8‐fluoroquinolinium iodide5J(HF)=+3.0,6J(HF)=+1.5,4J(CF)=(+)15.8 and5J(CF)=±5.2 Hz. Calculated molecular orbital results, which were based on the INDO‐FPT method and a molecular geometry from the x‐ray diffraction data for 1b, were in reasonable agreement with the4J(CF) values, but the5J(HF) values were of

ISSN:0030-4921    

DOI:10.1002/mrc.1270200206

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

Abstract77Se NMR chemical shifts and1J(SeC) coupling constants were measured for nine organic selenium compounds: 4,5,6,7‐tetrahydro‐,4′,4′,6,6‐tetramethylspiro[1,3‐benzoxaselenole‐2,1′‐cyclohexane]‐2′,4,6′‐trione and closely related derivatives, bis(2‐hydroxy‐4,4,6,6‐tetramethyl‐3‐oxo‐1‐cyclohexenyl) selenide and derivatives, and 1,5,5‐trimethyl‐7‐selenabicyclo[2.2.1]heptane‐2,3‐dione. The chemicalshifts ranged from −107 to 595 ppm from the external dimethyl selenide standard. The bridged selenabicycli

ISSN:0030-4921    

DOI:10.1002/mrc.1270200207

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractCarbon‐13 chemical shift assignments are reported for benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives, where X=CH(OAc)CH3substituted at positions 2‐7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C‐3, arising from theperiinteraction of H‐3 and the 4‐ethyl acetate substituent. Carbon‐13 relaxation times (T1) and nuclear Overhauser enhancements (η) have been measured for benzo[b]thiophene and its derivatives, and the contributions of dipolar,TDD1, and spin rotation,TSR1, relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin‐lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution toT1, and can form the basis for spectral assignments, as in 1‐phenylethyl acetate. Long‐range13C1H coupling constants were observed both between ring carbons and between ring carbons with ring side‐chain hydrogens. These results have been used for the structure determ

ISSN:0030-4921    

DOI:10.1002/mrc.1270200208

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe1H NMR parameters of the NCH2O protons in the spectrum of perhydropyrrolo[1,2‐c][1,3]oxazine show its existence in solution at room temperature in theO‐insidecis‐fused conformation.rel‐(3aS,6aS,6bR,10aS,11aS)‐6a‐Methylperhydroindolo[3,2,1‐i,j]benzoxazine andrel‐(3aS,6aS,6bS,10aR,11aS)‐6a‐methylperhydroindolo[3,2,1‐i,j]benzoxazine are shown to adoptcis‐ andtrans‐fused conformations, respectively, for the corr

ISSN:0030-4921    

DOI:10.1002/mrc.1270200209

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

Abstract1H,13C and77Se NMR spectra of 2‐carboxyphenyl methyl selenoxides, 2‐carboxyphenyl phenyl selenoxides, their sodium salts and related compounds have been measured to determine their structures in solution. The77Se NMR chemical shifts and theJ(77Se,13C) values were found to be particularly useful in distinguishing between selenuranes and selenoxides. The downfield shifts of 286‐536 and 587‐667 ppm from selenoanisoles are characteristic of the corresponding selenuranes and selenoxides, respectively. The couplings were 61‐65 and 77‐81 Hz for the selenuranes and selenoxides, respectively. The effects of salt formation on the NMR parameters are also discussed. The results show that the carboxylic acids have the cyclic selenurane structure, whereas the salts are acyclic

ISSN:0030-4921    

DOI:10.1002/mrc.1270200210

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of pureexo‐2‐norbornyltrimethylstannane and a mixture of theexo‐ andendo‐isomers have been recorded.1H–13C polarization transfer spectra have been obtained and require the previously reported assignments for C‐3 and C‐4 in theexo‐isomer to be reversed. The reported assignments for theendo‐isomer are correct. The new assignment for C‐4‐exo[withJ(119Sn,13C) vic=12 Hz, instead of the previously assignedJ(vic)=23 Hz], has a very minor effect on the nature of the Karplus curve [for3J(119Sn,13C)]

ISSN:0030-4921    

DOI:10.1002/mrc.1270200211

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY