Ab Initio Calculations of Conformational Effects on 13C NMR by Dr. R. Born, Prof. H. W. Spiess (auth.)

By Dr. R. Born, Prof. H. W. Spiess (auth.)

The elucidation of the constitution of amorphous structures is likely one of the so much not easy difficulties of condensed-matter learn. Our lack of awareness in regards to the special constitution of disordered structures at the molecular point contrasts with the swiftly transforming into significance of such fabrics in technological know-how and expertise. reliable country NMR is of key value during this quarter, because it grants particular information regarding internuclear distances and torsional angles in crystals and glasses alike. universal examples of amorphous platforms are glassy polymers. There, structural info is encoded within the chemical shifts of 13C-NMR spectra.
This quantity offers a strong new method of resolve this data through combining polymer statistical types, quantum chemistry and good kingdom NMR. It studies the current cutting-edge, studies formerly unpublished effects, and exhibits methods for extra improvement within the future.

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Extra info for Ab Initio Calculations of Conformational Effects on 13C NMR Spectra of Amorphous Polymers

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12) The convergence N ---+ 00 was checked by varying N; for all systems investigated N ~ 10000 was by far sufficient. In the same way, it has been established that the use of longer chains with more (1000, 2000) monomeric units does not affect the results. As far as conformational statistics is regarded, the central part of a chain with 200 monomeric units does not deviate from the central part of a larger chain molecule. Endgroup effects are negligible. The probability distribution Eq. 13) which reflects the irrelevance of the direction from which the chain is seen.

The overall decrease of 15 with increasing I {}1 I + I {}4 I reflects the phenomenological y-gauche effect. Thus, the basic empirical finding is reproduced by theoretical investigations. On the other hand, for a fixed value of I {}1 I + I {}4 I a considerable spread in 15 is observed (horizontally aligned clusters). This spread is due to non-y-gauche contributions, and the figure shows that the phenomenological understanding of a y-gauche effect depending on {}1 and {}4 alone, is largely oversimplified.

The advent of high resolution multiple quantum solid state NMR spectroscopy [79, 80, 81, 82] should make it possible to use the dipolar coupling as a source of structural information and probe the local geometry in a direct way without extensive isotopic labelling [83,84]. 1 Atactic Poly(propylene) In this section, the method underlying the ab initio simulation of chemical shifts of amorphous polymers will be explained in some detail. In order to avoid a clumsy general notation, we will refer to the specific example of atactic poly(propylene) (aPP).

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