Intermolecular Effects and Relaxation Behaviour

The high degree of resolution in the CP/MAS NMR spectra also permits the analysis of the relaxation behaviour of individual carbon atoms. The T1 relaxation is seldom solely determined by a single motion of a single intermolecular interaction. Nevertheless, if the dominant source is known, T1 can provide useful information. As an example the relaxation behaviour of celluloseacetate in both acetone solution and in the solid state will be discussed. The experimental data in Table 2 give chemical shifts and relaxation T1 information for the above system 21 . 

By the comparison of T1 relaxation data in solution and in the solid state it is realised that the relaxation time increases disproportionally when going from solution to 

1) The chemical shifts are for the solid state spectra obtained by the CP-MAS technique and referred to hexamethyl benzene (132.3 ppm compared to TMS). 

2) The chemical shifts are obtained from the spectra of the T1 measurements in relation to the signal for the methyl carbon (20.6 ppm). The T1 measurements were performed using the inversion recovery (IR) method (180 deg. (12.7 us)-tau — 90 deg. (6.1 us)) with MAS 2200 scans were collected and the pulse delay time was veryshort, + 10 sec. 

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