Intramolecular Hydrogen Bonding in Benzoxazines: When Structural Design Becomes Functional

KAN ZHANG; PABLO FROIMOWICZ; HATSUO ISHIDA

CHEMISTRY-A EUROPEAN JOURNAL

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2016 vol. 22 p. 2691 - 2707

0947-6539

The future evolution of benzoxazines and polybenzoxazines as advanced molecular, structural, functional, engineering, and newly commercial materials depends to a great extent on a deeper and more fundamental understanding at the molecular level. In this contribution, the field of benzoxazines is briefly introduced along with a more detailed review of ortho-amide-functional benzoxazines, which are the main subjects of this article. Provided in this article are the detailed and solid scientific evidences of intramolecular five-membered-ring hydrogen bonding, which is supposed to be responsible for the unique and characteristic features exhibited by this ever-growing family of ortho-functionalized benzoxazines. One-dimensional (1D) 1H NMR spectroscopy was used to study various concentrations of benzoxazines in various solvents with different hydrogen-bonding capability and at various temperatures to investigate in detail the nature of hydrogen bonding in both ortho-amidefunctionalized benzoxazine and its para counterpart. These materials were further investigated by two-dimensional (2D) 1H?1H nuclear Overhauser effect spectroscopy (NOESY) to verify and support the conclusions derived during the 1D 1H NMR experiments. Only highly purified single-crystal benzoxazine samples have been used for this study to avoid additional interactions caused by any impurities.