NMR Crystallography of Campho[2,3-c]pyrazole (Z′ = 6): Combining High-Resolution 1H-13C Solid-State MAS NMR Spectroscopy and GIPAW Chemical-Shift Calculations

详细信息    查看全文

• 作者：Amy L. Webber ; Lyndon Emsley ; Rosa M. Claramunt ; Steven P. Brown
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：September 30, 2010
• 年：2010
• 卷：114
• 期：38
• 页码：10435-10442
• 全文大小：339K
• 年卷期：v.114,no.38(September 30, 2010)
• ISSN：1520-5215

文摘

¹H-¹³C two-dimensional magic-angle spinning (MAS) solid-state NMR correlation spectra, recorded with the MAS-J-HMQC experiment, are presented for campho[2,3-c]pyrazole. For each ¹³C moiety, there are six resonances associated with the six distinct molecules in the asymmetric unit cell (Z′ = 6). The one-bond C−H correlations observed in the 2D ¹H-¹³C MAS-J-HMQC spectra allow the experimental determination of the ¹H and ¹³C chemical shifts associated with the separate CH, CH₂, and CH₃ groups. ¹H and ¹³C chemical shifts calculated by using the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach are presented. Calculations for the whole unit cell (12 × 29 = 348 atoms, with geometry optimization of all atoms) allow the assignment of the experimental ¹H and ¹³C chemical shifts to the six distinct molecules. The calculated chemical shifts for the full crystal structure are compared with those for isolated molecules as extracted from the geometry-optimized crystal structure. In this way, the effect of intermolecular interactions on the observed chemical shifts is quantified. In particular, the calculations are sufficiently precise to differentiate the small (<1 ppm) differences between the ¹H chemical shifts of the six resonances associated with each distinct CH or CH₂ moiety.