Microwave spectra of two conformers of the (1R)-(–)-nopol monomer

[Display omitted] •The microwave spectrum of the nopol monomer has been collected.•Two conformers of nopol have been observed in the spectrum.•Computational calculations predict 27 low energy conformers of nopol.•Strong evidence supports the observed conformers are the 2 lowest energy geometries. The rotational spectrum of the (1R)-(-)-nopol monomer has been observed in the 6–18 GHz region using CP-FTMW spectroscopy. Transitions of two distinct conformers of the parent isotopologue have been observed and assigned. Density Functional Theory (DFT) calculations performed on the monomer predict nine distinct low-energy heavy atom geometries. The differences between these structures are attributed to changes in the orientation of two dihedral angles in the heavy atom R-CH2CH2OH functionalization, where R refers to the fixed bicyclic cage component of the molecule. Further optimization of these geometries found 27 distinct conformers associated with the hydroxyl hydrogen orientation. The rotational constants of the two lowest energy conformers were found to be in good agreement with the experimental constants of the two observed conformers and the predicted dipole moment components agree with the relative intensities of the observed transitions.