What is it about?
The preference for the gauche conformation around the C-C bond in poly(oxyethylene) (POE) has been debated for decades. One group declared that the gauche conformation (TGT) was intrinsically favored, which was referred to as the gauche oxygen effect. In contrast, other groups suggested that a high gauche population for the C-C bond was due to the 1,5 CH-O interactions across the C-C bond in the TGG' conformation. We have reconciled this discrepancy by re-examining the previous experimental data and determined that there is no gauche oxygen effect for POE. We also examined the 1,5 CH-O interaction in TGG' and found that although the interaction stabilizes TGG', it's still less stable than the trans (TTT).
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Why is it important?
1. The gauche oxygen effect has been proposed, discussed, argued, and debated since 1976 to date. During that period, there were back-and-forth public debates between several research groups, with one defending the effect and the others dismissing it. There is another article promoting the effect, published just this year. It's been exactly 50 years since its birth. Our article attempts to settle one of the longest debates in scientific history. Our re-examination of previous NMR analyses unambiguously demonstrates the absence of a discernible gauche oxygen effect. 2. We also elucidate the origin of the conformational stability around the C-C bond of PEO using the energy decomposition analysis. We conclude that the trans (TTT) conformation is more stable because the charge-transfer stabilization of TGT is insufficient to overcome the destabilizing deformation energy. Hence, the C-C bond conformation is determined by the interplay between stabilizing and destabilizing energy components, rather than by the gauche oxygen effect.
Perspectives
This subject was a part of my Ph.D. thesis work. I used NMR spectroscopy to determine the conformational energy around the C-C bond of POE. However, due to the limitations of the methodology at the time, we had to make some assumptions about individual coupling constants. It's been more than 40 years since then. Thanks to new computational tools now available, I was not only able to calculate the individual coupling constants without any assumptions at high accuracy, but also to elucidate the reason why the gauche is not as stable as originally proposed. Now I feel like I have finally finished my thesis.
ken tasaki
Read the Original
This page is a summary of: Revisiting the
gauche
oxygen effect in –[OCH
2
–CHRO]– (R = H/CH
3
): experimental reassessment and the..., Physical Chemistry Chemical Physics, January 2026, Royal Society of Chemistry,
DOI: 10.1039/d6cp00355a.
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