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  Benzoxazine Oligomers: Evidence for a Helical Structure from Solid-State NMR Spectroscopy and DFT-Based Dynamics and Chemical Shift Calculations

Goward, G. R., Sebastiani, D., Schnell, I., Spiess, H. W., Kim, H. D., & Ishida, H. (2003). Benzoxazine Oligomers: Evidence for a Helical Structure from Solid-State NMR Spectroscopy and DFT-Based Dynamics and Chemical Shift Calculations. Journal of the American Chemical Society, 125(19), 5792-5800.

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Goward, G. R., Author
Sebastiani, Daniel1, Author           
Schnell, Ingo1, Author           
Spiess, Hans Wolfgang1, Author           
Kim, H. D., Author
Ishida, H.1, Author           
Affiliations:
1MPI for Polymer Research, Max Planck Society, ou_1309545              

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 Abstract: A combination of molecular modeling, DFT calculations, and advanced solid-state NMR experiments is used to elucidate the supramolecular structure of a series of benzoxazine oligomers. Intramolecular hydrogen bonds are characterized and identified as the driving forces for ring-shape and helical conformations of trimeric and tetrameric units. In fast MAS 1H NMR spectra, the resonances of the protons forming the hydrogen bonds can be assigned and used for validating and refining the structure by means of DFT-based geometry optimizations and 1H chemical-shift calculations. Also supporting these proposed structures are homonuclear 1H-1H double-quantum NMR spectra, which identify the local proton-proton proximities in each material. Additionally, quantitative 15N-1H distance measurements obtained by analysis of dipolar spinning sideband patterns confirm the optimized geometry of the tetramer. These results clearly support the predicted helical geometry of the benzoxazine polymer. This geometry, in which the N...H...O and O...H...O hydrogen bonds are protected on the inside of the helix, can account for many of the exemplary chemical properties of the polybenzoxazine materials. The combination of advanced experimental solid-state NMR spectroscopy with computational geometry optimizations, total energy, and NMR spectra calculations is a powerful tool for structural analysis. Its results provide significantly more confidence than the individual measurements or calculations alone, in particular, because the microscopic structure of many disordered systems cannot be elucidated by means of conventional methods due to lack of long-range order.

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Language(s): eng - English
 Dates: 2003
 Publication Status: Issued
 Pages: -
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 Table of Contents: -
 Rev. Type: -
 Identifiers: eDoc: 42687
Other: P-03-14
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Title: Journal of the American Chemical Society
  Alternative Title : J. Am. Chem. Soc.
Source Genre: Journal
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Pages: - Volume / Issue: 125 (19) Sequence Number: - Start / End Page: 5792 - 5800 Identifier: -