Precise dipole moments and quadrupole coupling constants of the cis and trans conformers of 3-aminophenol: Determination of the absolute conformation

Abstract

The rotational constants and the nitrogen nuclear quadrupole coupling constants of cis-3-aminophenol and trans-3-aminophenol are determined using Fourier-transform microwave spectroscopy. We examine several $J=2\leftarrow 1$ and $1\leftarrow 0$ hyperfine-resolved rotational transitions for both conformers. The transitions are fit to a rigid rotor Hamiltonian including nuclear quadrupole coupling to account for the nitrogen nucleus. For cis-3-aminophenol we obtain rotational constants of A=3734.930 MHz, B=1823.2095 MHz, and C=1226.493 MHz, for trans-3-aminophenol of A=3730.1676 MHz, B=1828.25774 MHz, and C=1228.1948 MHz. The dipole moments are precisely determined using Stark effect measurements for several hyperfine transitions to ${\mu }_a=1.7735$ D, ${\mu }_b=1.5195$ D for cis-3-aminophenol and ${\mu }_a=0.5563$ D, ${\mu }_b=0.5376$ D for trans-3-aminophenol. Whereas the rotational constants and quadrupole coupling constants do not allow to determinate the absolute configuration of the two conformers, this assignment is straight-forward based on the dipole moments. High-level \emph{ab initio} calculations (B3LYP/6-31G^* to MP2/aug-cc-pVTZ) are performed providing error estimates of rotational constants and dipole moments obtained for large molecules by these theoretical methods.

9 pages, 4 tables, 3 figures (RevTeX)

References in corpus (1)

• Alternating Gradient Focusing and Deceleration of Polar Molecules

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