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 language | English |
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Pages (from-to) | 12769-12786 |
Number of pages | 18 |
Journal | ACS OMEGA |
Volume | 6 |
Issue number | 19 |
Early online date | 7 May 2021 |
DOIs | |
Publication status | Published - 18 May 2021 |
Bibliographical note
Publisher Copyright:©
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.
Funders | Funder number |
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University of Bath |
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Dual source (Cu and Mo) Single Crystal Diffractometer (SuperNova)
Material and Chemical Characterisation (MC2)Facility/equipment: Equipment
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Electrospray Time-of-Flight Mass Spectrometer (Open-Access)
Material and Chemical Characterisation (MC2)Facility/equipment: Equipment