Microwave spectra, structures and dipole moments of 4H-pyran-4-one and its sulphur analogues

Abstract

Microwave spectra have been measured for the planar molecules 4H-pyran-4-one (I), 4H-pyran-4thione (11), 4H-thiapyran-4-one (111) and 4H-thiapyran-4-thione (IV). Extensive isotopic data for I, I1 and IV enable precise, complete structures to be calculated. There is little structural evidence for enhanced aromaticity in these molecules.The high, almost constant, values for the dipole moments near 4 D, previously indicated from solution measurements on I, I1 and IV, have been confirmed and the values more closely defined.Vibrational satellite spectra indicate the lowest frequency fundamentals in these molecules to be out-of-plane motions near 100 cm-'.

Vibrational spectroscopy and ab initio MO study of the molecular structure and vibrational spectra of α- and γ-pyrones

“…Table 1 shows the HF/6-31G p calculated equilibrium molecular geometries for the studied compounds. The previously reported structural data [4,5] are also presented in this table. Despite the fact that the different sets of data are not directly comparable, it can be noticed that, for both molecules, the calculated values show a good general agreement with the experimental values, and improve over the previously reported theoretical data [6±10].…”

“…In turn, the molecular structure of g-pyrone was obtained in the gaseous phase by microwave spectroscopy (r s structure) [5] and later on studied both by semiempirical and ab initio Hartree±Fock level calculations [6±10], the latter undertaken with the relatively modest 3-21G and 4-21G split valence basis sets. The infrared and Raman spectra (at T 310 and 328 K, respectively) of melted g-pyrone and also the infrared spectrum of the gas was presented in Ref.…”

A physical Study on the Aromaticity of 4H-Pyran-4-one, 9H-Xanthen-9-one, and related sulphur Compounds

“…Some of its physico chemical data also are consistent with a slight aro matic character (see [4] and [5] for relevant referen ces). 9H-xanthen-9-one appears to be aromatic, fol lowing its diamagnetic susceptibility [6], Since the aromaticity of 4H-pyran-4-one can be related to contribution of the valence structure (IV) which contains a benzene-like rc-sextet, the ( 0 ...C = 0 ) interaction moment may give some in formation in this respect (vide infra).…”

“…This is supported by their dipole moments (1.75 4H-pyran-4-one 2-a, 4H-pyran-4-thione 2'-a and 4H-thiopyran-4-thione 2'-b are all planar molecules in the gaseous phase [5], as well as is 9H-xanthen-9-one 3-a in the crystalline state [39]. By analogy, Table 2.…”

Protonation of 4 H-Pyran-4-one and its Sulfur Analogues. MNDO Study

“…All calcu lated structures are found to be planar possessing C2v symmetry. The available experimental data [23] 0340-4811 / 84 / 0300-281 S 01.3 0/0. -Please order a reprint rather than making your own copy.…”