General Features of the X Part of an ABX Spin System in Isotropic and Liquid Crystalline Phases as Illustrated by the13C–{1H} Spectra of 2,2′-Difluorobiphenyl
✍ Scribed by M. Edgar; J.W. Emsley; M.I.C. Furby
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 301 KB
- Volume
- 128
- Category
- Article
- ISSN
- 1090-7807
No coin nor oath required. For personal study only.
✦ Synopsis
The 13 C-{ 1 H} NMR spectra of 2,2 -difluorobiphenyl dissolved and anisotropic samples. There are three factors which make in isotropic and liquid crystalline solvents have been obtained and these seemingly straightforward tasks more complex, and analyzed. They are examples of the X part of an ABX spectrum. more interesting.
It is shown that the spectrum of the isotropic solution yields J AX ,
The first factor concerns the analysis of the spectra of the J BX , J AB , d AB , and d X , but only if all the transitions are detected, isotropic samples. Thus, Weigert and Roberts (1) in 1971 and that intensities as well as frequencies of the transitions are described the ABX 13 C-{ 1 H} spectra given by the isotropic used in the analysis. It is demonstrated that for 2,2-difluorobiliquid samples of the three isomers of difluorobenzene, and phenyl this requires that for some of the carbons it is necessary showed that all the spectral parameters could be obtained to detect very weak transitions. For the spectra of liquid crystalline from the spectra, but only if all of the six theoretically possisolutions of ABX systems it is shown that the dipolar couplings ble lines, as given in Table 1, are detected, and that both D AX , D BX , and D AB are obtained only if these couplings are in a certain sensitive range of relative values. The sensitive range can the frequencies and the intensities of the lines are used in be adjusted by using variable angle sample spinning (VASS). It the analysis. Some of the 13 C-{ 1 H} spectra in these comis demonstrated that VASS spectra taken near the magic angle pounds did not show the six lines, and so ambiguities in their can be used to obtain the absolute signs of the scalar couplings. analysis were unavoidable at that time. The improvements in