Diethylamine molecules can assemble into a helical chain held together by intermolecular hydrogen bonds. A 2018 study reported that this aggregate is more stable than competing cyclic arrangements, and proposed that two ethyl groups flanking the hydrogen-bonding site help produce the twist. The helix is formed by an assembly of molecules—not by a covalent spiral within a single diethylamine molecule.
What makes this a supramolecular helix?
A supramolecular structure is an organized assembly held together by interactions between separate molecules. In diethylamine, directional hydrogen bonding links molecules into a helical chain. That distinguishes the structure from a covalent helix, in which the spiral is part of one molecule’s chemical framework.
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The 2018 report contrasts this chain with cyclic aggregates commonly found among other small hydrogen-bonding molecules. Its claim is specific: the study found the diethylamine helix more stable than cyclic structures it considered. It does not establish that all other small molecules form rings or that diethylamine is the smallest helix-forming system under every possible definition.
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Why do diethylamine molecules twist instead of closing into a ring?
The role of the ethyl groups
Diethylamine has two ethyl substituents on either side of its hydrogen-bonding site. The authors’ structural explanation is that these groups help prevent the molecules from settling into a flat or cyclic arrangement, favoring a twist as the hydrogen bonds connect them. The proposed minimal feature is this pairing of ethyl groups with a directional hydrogen-bonding site.
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Size alone does not explain the shape
The reported comparison suggests that methyl groups are too small to induce the twist, while larger substituents can obstruct chain formation. A related study of diallylamine attributes helical twisting to a balance between hydrogen bonding and second-neighbor interactions between alkyl groups. These findings support an interaction-based explanation, not a universal rule that ethyl groups always create helices.
What evidence supports the stability claim?
The 2018 study reports structural studies alongside large-scale sampling simulations to support the conclusion that the helical aggregate is more stable than cyclic alternatives. The available article record does not provide a numerical energy difference or detailed simulation parameters, so the result should be described qualitatively rather than assigned a specific energy or treated as a measured record.
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The comparison is also not an exhaustive survey of every small hydrogen-bonding molecule. It establishes the reported behavior of diethylamine and offers a structural explanation for it, rather than proving a general hierarchy for all possible molecular aggregates.
Which paper reported the result?
Felix Hanke, Chloe J. Pugh, Ellis F. Kay, Joshua B. Taylor, Stephen M. Todd, Craig M. Robertson, Benjamin J. Slater, and Alexander Steiner published “The simplest supramolecular helix” in Chemical Communications, volume 54, issue 47, pages 6012–6015 (2018). The Royal Society of Chemistry lists its first publication date as 17 May 2018; the DOI is 10.1039/C8CC03295E. PubMed indexes the article as PMID 29796532.
A later related study, “The Helical Structure of Diallylamine in the Solid State,” appeared online on 22 November 2019 and in volume 50 (2020), pages 422–427. It offers context for how hydrogen bonds and interactions between more distant alkyl groups may contribute to helical twisting; it is not the original diethylamine report.
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