From rotational resolved spectra to an extended increment system of planar moments allowing ad-hoc conformational identification – Exemplification by the broadband microwave spectrum of [formula omitted]-hydroxyisobutyric acid

Abstract

The broadband microwave spectrum (10–25.5 GHz) of α-hydroxybutyric acid was recorded and analyzed. The resulting planar moment orthogonal to the molecular plane of symmetry was determined and compared with other molecules known from the literature. Subsequently, such out-of-plane contributions for a variety of other elements in tetrahedrally coordinated environments with different substituents were taken from the literature and compiled in a comprehensive form for the first time. This extension of the increment system described by Bohn et al. [J. Mol. Spectrosc. 325 (2016) 42–49], thus allowing an ad-hoc identification of planar conformers with the aid of experimentally derived rotational constants from rotationally resolved spectra.