What is it about?

Although the amide functional group is weakly ionizable, there have been serendipitous discoveries of amide salts. To facilitate their systematic design, we sought to identify the preference of 12 possible synthons in oxygen protonated amide structures. An analysis of a total of 81 protonated amide crystal structures retrieved from the Cambridge Structural Database and 12 new protonated amide structures prepared by us, revealed that ∼86% of these structures involving charge assisted short strong hydrogen bonds, including ∼54% of the hydrogen bridged dimers formed between protonated and neutral amide. The probability of forming hydrogen bridged dimers increases in the order of primary amide < secondary amide < tertiary amide.

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Why is it important?

We describe a systematic approach for preparing salts of weakly ionizable amide groups.


Applications of this approach have the potential to expand the solid-state landscape of biologically important molecules, e.g., drug molecules.

Professor Changquan Sun
University of Minnesota

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This page is a summary of: Synthon preference in O-protonated amide crystals – dominance of short strong hydrogen bonds, CrystEngComm, January 2013, Royal Society of Chemistry,
DOI: 10.1039/c3ce41271g.
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