Coverage dipolar interactions

BET monolayer surface coverage on -y-alumina is completely resolved, with separate resonances for each of the three types of carbon present. Within experimental error the line positions coincide with the values for liquid pyridine. The lines are noticeably broad (3-4 ppm). The use of N enriched (90%) material results in a partial reduction (approximately 30%) in linewidth relative to the isotopically normal (>99.7% N) spectrum, presumably because the N quadrupole effect interferes with MAS averaging of dipolar interactions. 

In addition to the information about structure, the carbon-13 CP-MAS NMR spectrum has also been shown to be useful for determining relative mobilities of various bonded moieties. The motion of the alkyl chain is reflected in the relaxation times of the various carbons. As the mobility in a certain part of the alkyl chain is increased, the relaxation time of the carbons in this part of the bonded organic moiety will increase due to less efficient dipolar interactions. In an early study it was concluded that motion increases up the alkyl chain from the surface to about the eighth carbon but after that point it remains relatively constant [25]. At uniform surface coverage it was determined that alkyl chains of C-6 or C-8 had the highest mobility [26]. Similar chain mobility studies were... 

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