Poonia, Tamannavan Wijngaarden, Jennifer2024-06-052024-06-052023-06-08Poonia, T.; van Wijngaarden, J. Exploring the Distinct Conformational Preferences of Allyl Ethyl Ether and Allyl Ethyl Sulfide using Rotational Spectroscopy and Computational Chemistry. J. Chem. Phys. 2023, 158(22), 224301. DOI: 10.1063/5.01534791089-7690https://doi.org/10.1063/5.0153479https://hdl.handle.net/10315/42068This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Poonia, T.; van Wijngaarden, J. Exploring the Distinct Conformational Preferences of Allyl Ethyl Ether and Allyl Ethyl Sulfide using Rotational Spectroscopy and Computational Chemistry. J. Chem. Phys. 2023, 158(22), 224301. DOI: 10.1063/5.0153479 and may be found at https://doi.org/10.1063/5.0153479.The conformational energy landscapes of allyl ethyl ether (AEE) and allyl ethyl sulfide (AES) were investigated using Fourier transform microwave spectroscopy in the frequency range of 5-23 GHz aided by density functional theory (DFT) B3LYP-D3(BJ)/aug-cc-pVTZ calculations. The latter predicted highly competitive equilibria for both species including 14 unique conformers of AEE and 12 for the sulfur analog AES within 14 kJ mol-1. The experimental rotational spectrum of AEE was dominated by transitions arising from its three lowest energy conformers which differ in the arrangement of the allyl side chain while in AES, transitions due to the two most stable forms, distinct in the orientation of the ethyl group, were observed. Splitting patterns attributed to methyl internal rotation were analyzed for AEE conformers I and II, and the corresponding V3 barriers were determined to be 12.172(55) kJ mol-1 and 12.373(32) kJ mol-1, respectively The experimental ground state geometries of both AEE and AES were derived using the observed rotational spectra of the 13C and 34S isotopic species and are highly dependent on the electronic properties of the linking chalcogen (oxygen versus sulfur). The observed structures are consistent with a decrease in hybridization in the bridging atom from oxygen to sulfur. The molecular-level phenomena that drive the conformational preferences are rationalized through natural bond orbital (NBO) and non-covalent interaction (NCI) analyses. These shows that interactions involving the lone pairs on the chalcogen atom with the organic side chains favour distinct geometries and energy orderings for the conformers of AEE and AES.enArticle