Resolving a long-standing ambiguity: the non-planarity of gauche-1,3-butadiene revealed by microwave spectroscopy
Martin-Drumel, Marie-Aline
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https://hdl.handle.net/2142/91253
Description
Title
Resolving a long-standing ambiguity: the non-planarity of gauche-1,3-butadiene revealed by microwave spectroscopy
Author(s)
Martin-Drumel, Marie-Aline
Contributor(s)
Stanton, John F.
Ellison, Barney
Baraban, Joshua H.
Buckingham, Grant
Eibenberger, Sandra
Patterson, David
McCarthy, Michael C.
Issue Date
2016-06-20
Keyword(s)
Structure determination
Abstract
The preferred conformation of \textit{cis}-1,3-butadiene (CH$_2$=CH$-$CH=CH$_2$) has been of long-standing importance in organic chemistry because of its role in Diels-Alder transition states. The molecule could adopt a planar \textit{s-cis} conformation, in favor of conjugations in the carbon chain, or a non-planar \textit{gauche} conformation, as a result of steric interactions between the terminal H atoms.
To resolve this ambiguity, we have now measured the pure rotational spectrum of this isomer in the microwave region, unambiguously establishing a significant inertial defect, and therefore a \textit{gauche} conformation. Experimental measurements of \textit{gauche}-1,3-butadiene and several of its isotopologues using cavity Fourier-transform microwave (FTMW) spectroscopy in a supersonic expansion and chirped-pulse FTMW spectroscopy in a 4 K buffer gas cell will be summarized, as will new quantum chemical calculations.
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