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要旨

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 ← 1 and 1 ← 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 ¹⁴N nuclear spin. 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 μ_a = 1.7718 D, μ_b = 1.517 D for cis-3-aminophenol and μ_a = 0.5563 D, μ_b = 0.5375 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 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.