An unusually short intermolecular N - H...N hydrogen bond in crystals of the hemi-hydrochloride salt of 1-exo-acetamidopyrrolizidine

Minakshi Bhardwaj, Qianxiang Ai, Sean R. Parkin, Robert B. Grossman

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The title compound [systematic name: (1R∗, 8S)-2-acetamidooctahydropyrrolizin-4-ium chloride-N-[(1R, 8S)-hexahydro-1H-pyrrolizin-2-yl)acetamide (1/1)], 2(C9H16N2O)·HCl or C9H17N2O+·Cl-·C9H16N2O, arose as an unexpected product when 1-exo-acetamidopyrrolizidine (AcAP; C9H16N2O) was dissolved in CHCl3. Within the AcAP pyrrolizidine group, the unsubstituted five-membered ring is disordered over two orientations in a 0.897(5):0.103(5) ratio. Two AcAP molecules related by a crystallographic twofold axis link to H+ and Cl- ions lying on the rotation axis, thereby forming N - H...N and N - H...Cl...H - N hydrogen bonds. The first of these has an unusually short N...N separation of 2.616(2)Å: refinement of different models against the present data set could not distinguish between a symmetrical hydrogen bond (H atom lying on the twofold axis and equidistant from the N atoms) or static or dynamic disorder models (i.e. N - H...N + N...H - N). Computational studies suggest that the disorder model is slightly more stable, but the energy difference is very small.

Original languageEnglish
Pages (from-to)77-81
Number of pages5
JournalActa Crystallographica Section E: Crystallographic Communications
StatePublished - Jan 1 2020

Bibliographical note

Funding Information:
Funding for this research was provided by: The National Science Foundation (MRI-CHE1625732 to SRP), and by the University of Kentucky. QA acknowledges the NSF under Award DMR-1627428.

Publisher Copyright:
© 2020 International Union of Crystallography. All rights reserved.


  • crystal structure
  • short N - H...N hydrogen bond

ASJC Scopus subject areas

  • Chemistry (all)
  • Materials Science (all)
  • Condensed Matter Physics


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