Using the X-ray crystal geometry as input, the 13C NMR chemical shifts of benzo-9-crown-3 ether have been calculated via ab initio methods using a localized orbital local origin (LORG) approach. Reasonable agreement is found between the calculated values for an isolated molecule in the gas phase and those obtained in the 13C CPMAS NMR spectrum. Solid phase 13C spectra of the C7,10-d4 derivative confirm the existence of a 7.9 ppm shift difference between these sites in the solid, whereas in solution they are conformationally averaged to one resonance. The effects of C—H bond length variation on calculated 13C shifts have been explored.

We present here the single crystal X-ray structure of 1,2-dimethoxybenzene which reveals the methoxy groups to be trans and twisted out of the plane by -5.0 and 8.6". Using variable spinning rate I3C CP MAS NMR spectroscopy, the principal shielding tensors were measured for anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene and 1,3,5-trimethoxybenzene. From this work the principal elements were obtained for static benzene (c,, = 222, G~~ = 147 and 033 = 14) and for the substituent chemical shift of a planar methoxy group. The a6 initio tensors of 1,Zdimethoxybenzene were calculated by the GIAO and LORG methods using the X-ray data as input. The CP MAS spectrum of 1,3-dimethoxybenzene reveals that this molecule adopts the asymmetric planar conformation.

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature 1H1H COSY, 13C1H HETCOR, and DEPT 13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase 13C spectrum has many common features with the solid phase 13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on 13C shieldings are discussed in detail.

The X-ray crystal structure of the title material has been determined and the results are compared to previous findings for benzo-9-crown-3 itself. The 13C NMR spectrum in solution has been unambiguously assigned using COSY and HETCOR methods. The solid phase 13C spectrum has been obtained and the 7, 10-d4 derivative has been examined to aid in spectral assignments.

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