Knowledge Bank

Rotational spectra of the heterocyclic rings 3-hydroxytetrahydrofuran and tetrahydrothiophen-3-one have been recorded using a Fourier-transform microwave spectrometer. Spectra of the $\mathrm{<mrow\; data-mjx-texclass="ORD">34</mrow>}S$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ isotopomers were recorded in natural abundance. The a-, b-, and c-type transitions observed for each species were fit to a Watson A-reduction Hamiltonian, which led to the rotational constants $A=4272.6617(9)$, $B=2764.5523(7)$, and $C=2250.1361(4)$ MHz for 3-hydroxytetrahydrothiophene and $A=5623.697(1)$, $B=2431.3551(4)$, and $C=1801.4946(4)$ MHz for tetrahydrothiophen-3-one. Ring-puckering conformations were determined from fitting the rotational constants as well as from Kraitchman calculations of the atomic coordinates. Ab initio calculations at the $MP2/6-31+G\ast \ast$ level support the experimental structures.