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1.
Ab initio SCF-MO calculations of 14N quadrupole coupling constants are reported for HCN, HNC, CH3CN, CH3NC, NH3, NH2NH2, FCN, N2O, (CN)2, BrCN, pyridine and pyrazine. There is excellent correlation between calculation and experiment yielding Q = 1.503 ± 0.159 × 10?26 cm2 for the 14N nuclear quadrupole moment. Dunning sp basis sets are more than adequate for such calculations, STO/4G basis sets yielding almost identical results for pyridine and pyrazine. Unsuccessful attempts were made to correlate coupling constants with electronic population analysis indices.  相似文献   

2.
The rotational and centrifugal distortion constants of 2,6-difluoropyridine have been determined from the analysis of its microwave spectrum. The dipole moment of the molecule and the quadrupole coupling constants of the 14N nucleus have also been evaluated. The observed rotational constants indicate a distortion of the pyridine ring.  相似文献   

3.
When a polar liquid is subjected to an electric field, the dipoles obtain a small average orientation. At sufficiently high field strengths direct spin—spin dipolar and quadrUpolar electric field interactions may modify the NMR spetrum.NMR electric field experiments are reported for the proton, fluorine, and nitrogen NMR spectra of neat 2, 4, 6-trifluoronitrobenzene. The observed alignment values are smaller than those predicted on the basis of Onsager's theory.The 14N quadrupole coupling constant as been deduced from a comparison of the qUadrupolar and dipolar electric field effects.An upper limit of the absolute value of the anisotropy of the para-19F chemical shift has been inferred from the absence of a detectable displacement of the resonance on application of an electric field.  相似文献   

4.
The 14N and 2H quadrupole coupling tensors at both nitrogen and at all hydrogen sites, have been calculated by ab initio SCF MO methods, in a trimeric imidazole molecule having the geometry found in the solid state. The 14N changes produced at N(1)H by hydrogen bonding are correctly reproduced to a noteworthy degree of precision, as is the 2H quadrupole interaction at the same site. The changes in the values of the three principal components of the tensor, which have been inferred from NQR measurements when imidazole passes from the gas to the solid state, are supported by the calculations, both for N(1)H and N(3).  相似文献   

5.
The rotational spectra of 17O16O16O and 16O17O16O have been observed. The hyperfine structure has been analyzed to give the 17O quadrupole coupling and spin-rotation tensors for both species. Preliminary values of the molecular parameters are given.  相似文献   

6.
The 129I-Mössbauer spectra of several cis-diioda-and two hydridoiodo-platinum(II) complexes have been obtained at 4.2°K. The quadrupole coupling constants of the cis complexes vary systematically with the nature of the neutral ligands, indicating the operation of a Trans-influence. The values for the hydrides are very low, showing a large trans-influence for this ligand.  相似文献   

7.
The dipeptide cyclo(Asp-Pro) where the aspartic acid residue was 85% 13C enriched, was synthesized with the aim of analyzing its conformation in solution by using 1C-1H, 13H-1H and 13C-13C coupling constant parameters. The values of these couplings agree well with each other and show that the side chain of the aspartic acid residue adopts privileged conformations the proportions of which vary somewhat with pH, and more weakly, with a change in solvent. The 13C-13C interresidue coupling constants 3JCl'C2β and 3JCl'C2γ obtained after long accumulation of the signals of unenriched carbons, have different values; they show puckering in the pyrrolidine ring similar to that found in cyclo(Leu-Pro) in the solid state. It was concluded that 13C-13C coupling constants represent an excellent means of determining the side chain conformation (whenever the incorporation of an enriched amino acid into the peptide is possible) that will find applications particularly in the case of peptides with complicated proton spectra.  相似文献   

8.
199Hg NMR spectra are reported for the complexes [MeHgL]NO3 containing either two- (e.g. L = pyridine) or three-coordinate mercury (e.g. L = 2,2′-bipyridyl). For unidentate and bidentate ligands of similar basicity chelation with bidentate ligands to give three-coordinate mercury results in upfield shifts of 199Hg resonances from that of the linear complexes. For complexes of unidentate ligands shifts correlate with changes in base strength of the ligands, and methyl substitution in the 2 position of pyridine appears to result in an upfield shift of ca. 30 ppm. Effects of substitution in the 2 position are very strong in complexes of unidentate 2-benzylpyridine and 3,3′-dimethyl-2,2′-bipyridyl. Comparison of the 199Hg shifts with J(1H-199Hg) shows the coupling constant to be insensitive to substitution in the 2 position in linear complexes and is a function only of the ligand base strength.  相似文献   

9.
NQR spectra of 35Cl, 81Br and 127I in cyclopentadienyltitanium halides CpnTiHal4-n have been studied. Quadrupole coupling constants of the halogen atoms regularly increase with the increasing number of Cp rings in the molecule, which is apparently connected with the decreasing multiplicity of the TiHal bond. A sharp increase in the asymmetry parameters of the iodine atom on introduction of the Cp rings is evidence for an essential desymmetrization of the electron density in the molecule caused by this operation.  相似文献   

10.

Abstract  

Density-functional theory calculations have been performed to investigate the properties of the electronic structures of silicon–carbon-doped boron nitride nanotubes (BNNTs). The geometries of zigzag and armchair BNNTs were initially optimized and the quadrupole coupling constants subsequently calculated. The results indicate that doping of B and N atoms by C and Si atoms has more influence on the electronic structure of the BNNTs than does doping of B and N atoms by Si and C atoms. The changes of the electronic sites of the N atoms are also more significant than those of the B atoms.  相似文献   

11.
The 13C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on 13C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.  相似文献   

12.
13C-NMR spectra of fluorinated molecules are difficult to observe under conventional broad-band proton decoupling. The large coupling constants involved make polarization transfer between fluorine and carbon, using INEPT or DEPT experiments very effective while broad band fluorine decoupling collapses the multiplet pattern.  相似文献   

13.
B. Kirste  H. Kurreck  K. Schubert 《Tetrahedron》1980,36(13):1985-1991
Proton and non-proton ENDOR studies are reported on isotopically labelled Coppinger's radical (galvinoxyl) and on N-Coppinger's radical in isotropic solutions and in liquid-crystalline mesophases. The hyperfine coupling constant shifts have been measured over the temperature range of the nematic mesophase and an analysis of the shifts in terms of anisotropic hyperfine tensors and ordering parameters is given. A short phenomenological discussion of the 13C and14N ENDOR response is presented. Several methods for the sign determination of hyperfine coupling constants are discussed. Finally, a survey of the ENDOR spectroscopy on galvinoxyl type biradicals is given.  相似文献   

14.
The microwave spectrum of N2D4 has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the 14N nuclei are Xaa = 4.23 ± 0.04 MHz, Xbb = 1.98 ± 0.05 MHz, and Xcc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N2D4 and N2H4 the barrier to inversion of a single amino group is computed to be 5.00 kcal mol?1.  相似文献   

15.
Linear complexes [MeHgL]NO3 (L = substituted pyridine) have been prepared and their 1H and 199Hg NMR spectra measured and compared with other complexes of this series reported previously. The coupling constant J(1H?199Hg) correlates directly with pKa and with the gas phase enthalpy of ionization [ΔGi(g)] of LH+; with J(1H?199Hg) decreasing with increasing pKa or ΔGi(g). The chemical shift, δ, for 199Hg does not correlate with either pKa or ΔGi(g). Complexes without substituents in the 2 position of pyridine have δ199Hg ca. 80–100 ppm downfield from MeHgNO3, those with one methyl group in the 2 position ca. 125–150 ppm, and those with methyl groups in the 2 and 6 position (or benzyl or 3′-methylpyridyl groups in the 2 position) ca. 160–200 ppm downfield from MeHgNO3. The coupling constant J(1H?199Hg) is found to be more useful than δ199Hg in determination of solution structures of MeHg(II) complexes of this type of ligand.  相似文献   

16.
The rotational spectra in the vibrational ground states of (H2O, HC14N) and (H2O, HC15N) have been assigned in the frequency range 6–19 GHz. Values of rotational constants (BO, CO) and centrifugal distortion constants (ΔJ, ΔJK) have been determined for both species, while the 14N-nuclear quadrupole coupling constants xaa and xbb have been established for the first. Observations concerning additional hyperfine structure arising from H,H nuclear spin-nuclear spin coupling in the H2O subunit suggest that (H2O,HCN) has a pair of equivalent protons and is effectively planar in the zero-point state. Observed spectroscopic constants are consistent only with the arrangement H2O…HCN, with r(O…C) = 3.1387 Å.  相似文献   

17.
The IR spectra of cis- and trans-[Pt(pyridine)2X2] (X = Cl, Br, I, SCN) are discussed. Distinction between the vPt—N and vPt—X bands is based on their relative sensitivities to 15N-labelling and deuteration of the pyridine ring, to halogen substitution and to 15NCS-labelling. Two vPt—N and two vPt—X bands are observed in the cis-complexes as required for C2v symmetry. The D2h symmetry of the trans-complexes requires one vPt-N and one vPt—X band but additional bands are observed and are ascribed to coupling between vPt—N and vPt—X.  相似文献   

18.
INDO–MO calculations have been performed on the ESR hyperfine coupling constants of the pyridinyl radical and the radical anions of pyrimidine, quinoline, isoquinoline, acridine and benzcinnoline. The nuclear spin coupling constants and the 14N nuclear quadrupole coupling constant of pyridine have also been calculated. In general, calculated values are in satisfactory agreement with the experimental data.  相似文献   

19.
Stefan Berger 《Tetrahedron》1978,34(20):3133-3136
2-Azabicyclo(2.2.2)octan-3-One 1, N-isopropylpivaloylamide 2 and 4-azatricyclo(4.3.1.13,8)undecan-5-one 3 have been prepared with a 15N label. The amides were reduced to the corresponding amines 2-azabicy-clo(2.2.2)octane 4, N-isopropyl-N-neopentylamine 5 and 4-azatricyclo(4.3.1.13,8)undecane 6. The 13C spectra of these compounds and their hydrochlorides were measured and the 15N13C spin coupling constants interpreted in terms of their conformational dependence.  相似文献   

20.
Rotational spectra have been assigned for the 82Kr, 83Kr, 84Kr, and 86Kr isotopic species of the KrHF and KrDF van der Waals molecules by using pulsed microwave Fourier transform spectroscopy in a Fabry—Perot cavity with a pulsed supersonic nozzle molecular source. The rotational, centrifugal distortion, nuclear spin—spin, and nuclear quadrupole coupling constants are used to determine the structure and obtain intramolecular potential binding information. The 83Kr nuclear quadrupole coupling constants are 10.28 ± 0.08 MHz and 13.83 ± 0.13 MHz for KrHF and KrDF respectively. The electric field gradient at the krypton nucleus is calculated from the coupling constant and the known nuclear quadrupole moment and explained by Sternheimer shielding and formation of the van der Waals bond. There is a negligible charge transfer in the KrHF bond.  相似文献   

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