Microwave Spectra and Gas Phase Structural Parameters for N-Hydroxypyridine-2(1H)-thione

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2011-12, Vol.115 (50), p.14526-14530
• Main Authors: Daly, Adam M, Mitchell, Erik G, Sanchez, Daniel A, Block, Eric, Kukolich, Stephen G
• Format: Article
• Language: English
• Subjects: A: Molecular Structure, Quantum Chemistry, General Theory; Constants; Defects; Gas phases; Inertial; Quadrupole interaction; Rotational; Strength; Tautomers
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp2080385

The microwave spectrum for N-hydroxypyridine-2(1H)-thione (pyrithione) was measured in the frequency range 6–18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C5H4 32S14NOH, C5H4 32S14NOD, and C5H4 34S14NOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the 14N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ0 = −0.023 amu·Å2 for the C5H4 32S14NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O–H) = 0.93(2) Å, R(C–S) = 1.66(2) Å, and angle ∠(N–O–H) = 105(4)° for the ground state structure.