Nuclear Overhauser enhancement properties

Spin-lattice relaxation times of carbon-13 in different polypropylene stereosequences differ slightly while nuclear Overhauser enhancements are almost identical (1.8-2.0) [533] isotactic sequences display larger Tx values than the syndiotactic stereoisomers. Other vinyl polymers behave correspondingly [534]. Carbon-13 spin-lattice relaxation times further indicate that dynamic properties in solution depend on configurational sequences longer than pentads. The ratio 7J(CH) 7J(CH2) varies between 1.6 to 1.9 thus, relaxation can be influenced by anisotropic motions of chain segments or by unusual distributions of correlation times [181],... 

Within a molecule, a nucleus is characterized by its magnetic properties and electronic environment and by the following consequent parameters associated with the corresponding NMR signals chemical shift, coupling constants, relaxation rates,15 and nuclear Overhauser enhancement (NOE).1617 All these values may be used to extract qualitative or quantitative information about the structure, the conformation, and the behavior of molecules in solution. 

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