The 1H NMR Spectroscopic Effect of Steric Compression Is Found in [3.3.1]Oxa- and Azabicycles and Their Analogues

Ziyu Zeng, Gabriele Kociok-Kohn, Tim Woodman, Michael Rowan, Ian Blagbrough

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7 Citations (SciVal)

Abstract

The through-space 1H NMR effect of steric compression by the lone-pair electrons of O- and N-atoms is shown in synthetic [3.3.1]oxa- and azabicycles. The electrons of the compressed proton bond are pushed away by the repulsive force generated by the lone-pair electrons of the heteroatom. There is a corresponding significant increase in the chemical shift of the compressed proton. The intensity of this deshielding effect is related to the proximity and overlap of the lone-pair or compressing atom. The steric compression decreases when the lone-pair electrons of the heteroatom and the compressed proton are not directly overlapped, for example, in [4.3.1]- and [3.2.1]azabicycles. Steric compression is also caused by a proton, deuterium, or an ethyl group close in space to the compressed proton. The protonated [3.3.1]azabicycle adopts a true-boat/true-chair conformation in its crystal lattice, but in solution the conformation is true-chair/true-chair.
Original languageEnglish
Pages (from-to)12769-12786
Number of pages18
JournalACS OMEGA
Volume6
Issue number19
Early online date7 May 2021
DOIs
Publication statusPublished - 18 May 2021

Bibliographical note

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Funding

This study was partly funded by the University of Bath. The NMR and MS equipment and the X-ray diffractometer were provided by the Material and Chemical Characterization Facility at the University of Bath.

FundersFunder number
University of Bath

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