Chem. J. Chinese Universities ›› 2022, Vol. 43 ›› Issue (6): 20220084.doi: 10.7503/cjcu20220084

• Analytical Chemistry • Previous Articles     Next Articles

1H NMR Study on the Conformation of Aromatic Amides Limited by Three-center Hydrogen Bonds

MIN Jing, WANG Liyan()   

  1. State Key Laboratory of Supramolecular Structure and Materials,College of Chemistry,Jilin University,Changchun 130012,China
  • Received:2022-02-12 Online:2022-06-10 Published:2022-03-17
  • Contact: WANG Liyan E-mail:wangliyan@vip.sina.com
  • Supported by:
    the National Natural Science Foundation of China(22193020)

Abstract:

We designed and synthesized nine N-aryl aromatic amides that could form three-center hydrogen bonds, and six N-aryl aromatic amides that could form two-center hydrogen bonds. Based on their one-dimensional 1H nuclear magnetic resonance(NMR) spectra in chloroform and dimethye sufoxide(DMSO), the de-shielding effects of carbonyl groups on βH and γH were analyzed separately. The conformational restriction of aromatic amides by three-center hydrogen bonds was evaluated by combining Δ(δβH) and Δ(δγH). It was disclosed that three aromatic amides [2-fluoro-N-(2-methoxyphenyl)benzamide, N-(2-fluorophenyl)-2-methoxybenzamide and 2-fluoro-N-(2-fluorophenyl)benzamide] display excellent planarization of molecular comformations at both sides of their carbonyl groups, which would have greater potential in constructing new foldamers. Furthermore, it was inferred that, when an NH group forms hydrogen bond with the second hydrogen-bond acceptor, the hydrogen bond between the NH group and the first hydrogen-bond acceptor would be weakened. In other words, for an aromatic amide with a three-center hydrogen bond, two hydrogen-bond acceptors contend with each other for the NH group, resulting in a balanced situation.

Key words: Three-center hydrogen bond, Aromatic amide, Conformation, Foldamer

CLC Number: 

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