Conformational Landscape of m-Anisic Acid and Its Complexes with Formic Acid

Abstract

Four conformers of m-anisic acid were observed in a supersonic expansion using Fourier transform microwave spectroscopy. These conformers correspond to different relative orientations of the acid and the methoxy groups and have their planar skeletons stabilized by resonance. When formic acid was present in the jet, the spectra of four m-anisic acid-formic acid heterodimer conformers were detected. The complexes are formed from the interaction of formic acid with each of the four observed conformers of m-anisic acid through the typical acid-acid sequential cycle with a double O-H•••O=C hydrogen bond interaction in a pseudo eightmembered ring arrangement. The four heterodimer forms retain the same four m-anisic acid conformational geometries and the same relative abundances of the m-anisic acid monomeric forms in the supersonic expansion. This proves that a kinetic mechanism dominates the formation of complexes in the jet.

2,2,3,3,3-Pentafluoro-1-propanol and its dimer: structural diversity, conformational conversion, and tunnelling motion

“…In a jet expansion, kinetically controlled processes are known to play a significant role in the formation of binary conformers. 50,51 We therefore also considered a different approach to estimate the abundances, which includes both kinetically and thermodynamically controlled processes. As discussed in the PFP monomer section, the barriers that separate different PFP conformers which have the same heavy atom frame but different OH orientations, are low and can be overcome in a jet expansion.…”

Rotational Spectroscopy of 2‐Furoic Acid and Its Dimer: Conformational Distribution and Double Proton Tunneling

“…Closely related to the current study are the reports of rotational spectroscopy of hetero‐ and homodimers of several carboxylic acids, such as the dimers of formic acid with itself, [14] with propiolic acid, [15,16] acetic acid, [17] and difluoroacetic acid, [18] o‐ and m‐anisic acid, [19,20] 3,3,3‐trifluoro‐2‐(trifluoromethyl)propanoic acid, [21] perfluorobutyric acid, [22] and benzoic acid, [23] as well as the acrylic acid homodimer [24] and acrylic acid‐difluoroacetic acid heterodimer [25] . It is interesting to note that double proton tunneling splittings were detected only in some [14–17,23,24] and not in others [19–22] including the THFA homodimer, whereas the tunneling splittings observed in difluoroacetic acid [18] and acrylic acid‐difluoroacetic acid heterodimer [25] were related to the internal rotation of the CHF 2 group. Generally, the rotational spectroscopic data of tunnelling splittings are high quality data for benchmarking different approaches, such as the instanton theory [26] and the simplified one‐dimensional approach, [27] for quantifying such splittings, a research topic of significant current interest.…”

“…Not surprisingly, researchers have applied several different types of spectroscopies, for example, laser induced fluorescence and IR spectroscopy, [12,13] as well as rotational spectroscopy, to examine double proton tunneling. Closely related to the current study are the reports of rotational spectroscopy of hetero‐ and homodimers of several carboxylic acids, such as the dimers of formic acid with itself, [14] with propiolic acid, [15,16] acetic acid, [17] and difluoroacetic acid, [18] o‐ and m‐anisic acid, [19,20] 3,3,3‐trifluoro‐2‐(trifluoromethyl)propanoic acid, [21] perfluorobutyric acid, [22] and benzoic acid, [23] as well as the acrylic acid homodimer [24] and acrylic acid‐difluoroacetic acid heterodimer [25] . It is interesting to note that double proton tunneling splittings were detected only in some [14–17,23,24] and not in others [19–22] including the THFA homodimer, whereas the tunneling splittings observed in difluoroacetic acid [18] and acrylic acid‐difluoroacetic acid heterodimer [25] were related to the internal rotation of the CHF 2 group.…”

A Scent of Peppermint—A Microwave Spectroscopy Analysis on the Composition of Peppermint Oil

“…Often, the rotational spectra of 13 C isotopologues of the molecules of interest can be recorded in natural abundance, allowing for an accurate structure determination. These powerful features of rotational spectroscopy were exploited and reported in numerous studies [17][18][19][20][21].…”