The theory of vibrational effects on the nuclear shielding and spin-rotation constants for a diatomic molecule is outlined. Corrections for these effects are calculated theoretically for both IH and 19F nuclei in the HF molecule. The theoretically calculated isotopic shift for 19F shielding between DF and HF is in good agreement with the zero pressure experimental value, 2.5±0.5 ppm. The shielding for the vibrating molecule at 300 0 K is computed from the theoretically calculated value for ITFG and the experimentally measured spin-rotation constant, as (
The 19F and lH resonances for gaseous hydrogen fluoride were measured over the range from low pressure to saturated vapor. In each spectrum, only a single line is observed, which shows an unusually large and monotonic change in chemical shift with HF density. The monomer chemical shifts were determined by extrapolation, to zero total pressure, of data for mixtures with various foreign gases. The 19F chemical shifts, in parts per million relative to SiF4 gas at zero pressure, are HF(g, monomer): 46.85±0.35 ppm, DF(g, monomer): 49.35±O.35 ppm, HF(liq, cylinder): 25.53±O.04 ppm. The lH shifts relative to CH 4 gas at zero pressure are HF(g, monomer): -2.1O±0.20 ppm, HF(liq, cylinder): -8.67±0.02 ppm. These data are for 34°C, but the extrapolated monomer shifts appear to be practically independent of temperature. The absence of spin-spin splittings, and the observation of only a single averaged resonance in HF-DF mixtures, proves that there are rapid monomer-breaking exchange processes in the vapor. This is evidence for the presence of a ring polymer.
The rigid-lattice second moment of the 19F nuclear magnetic resonance of XeF2 has been measured as a function of the external magnetic field. The experimental shielding anisotropy | Δσ | = 105 ± 10 × 10−6 does not agree closely with a value of σ⊥ − σ‖ = − 506 × 10−6 previously calculated using a localized orbital model. The field-independent rigid-lattice second moment is ∼ 0.4 G2 larger than that calculated from crystallographic data, probably because of large amplitude vibrations in XeF2. The temperature dependences of the second moment and of the spin–lattice relaxation time are also reported.
3.0 (aromatic protons). The dibromide 10 was contaminated with 7 and was easily converted to this substance by dehydrobromination with boiling ethanolic potassium hydroxide.The properties and reactions of 3 provide clear evidence for the assigned structure. At least one of the double bonds must have the trans configuration, in view of the presence of a strong band at 958 cm-1 in the infrared spectrum and the observed J value of 17 cps in the nmr spectrum. The di-trans stereochemistry is excluded by the complexity of the olefinic pattern of the nmr spectrum. The mono-trans configuration 3 is confirmed by the fact that H5 and H6 (see 8) in the adducts are (rans-oriented (J = 14-19 cps). The corresponding protons in the precursor 5 are therefore also trans, the stereochemistry expected to be formed from the mono-trans compound 3 by a thermal disrotatory cyclization process.4,11,16 On the other hand, all-c/s-1,2:3,4: 7,8-tribenz[10]annulene or the corresponding di-/ram compound should have given c/s-fused adducts. 3,11,16 It appears that the ten-membered ring in 3 is nonplanar and does not represent a delocalized ten--electron system. A reason for the greatly increased stability of 3, as compared with [10]annulene itself,3,4 is presumably that the isomerization to the 9,10-dihydronaphthalene derivative in this case involves disruption of the cyclic delocalization of a benzene ring. 391 (1965).
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