Furan−Formic Acid Dimers:  An ab Initio and Matrix Isolation Study

Abstract

The dimers formed by formic acid (FA) and furan are investigated by ab initio methods and matrix isolation spectroscopy. Nine complexes with binding energies between -3.91 and -0.82 kcal/mol (MP2/6-311++G(d,p) + ZPE + BSSE) are identified. Another five weaker bound complexes are localized at lower level of theory only. The binding in the furan-FA dimers can be described in terms of OH...O, C=O...H, HO...H, CH...O, OH...pi, and CH...pi interactions. Therefore, the furan-FA complexes are classified in two types: (1) the dimers where the OH hydrogen of formic acid interacts with the furan molecule and (2) the dimers where the main interactions of FA with the furan molecule are via the less acidic CH hydrogen. Duning's and Pople's triple and double basis sets were used to study the dependence of the geometries and energies of the complexes from the basis set. BSSE (basis set superposition error) counterpoise corrections (CP) were included during the geometry optimizations of all dimers at the MP2/6-31G(d,p) level of theory. Matrix isolation spectroscopy allowed us to record the IR spectrum of aggregates between FA and furan. By comparison of the experimental IR spectrum with calculated IR spectra of a variety of complexes, it was possible to identify the most stable furan-FA dimer as the major product of the aggregation.

Photoisomerization and Photochemistry of Matrix-Isolated 3-Furaldehyde

“…48 The observed bands of the 3FA photoproducts are collected in Table S7. The assignments were made taking into account literature data for these species isolated in argon matrices 54,[57][58][59][60] and also results of calculations made in the present study at the B3LYP/6- Figure 9). The characteristic absorptions due to CO are observed in the 2120-2140 cm -1 range: the most intense band at 2138 cm -1 corresponds to weakly interacting or well-isolated monomeric CO, whereas the lower intensity bands indicate that part of the CO molecules did not diffuse from the original cage where they were formed and interact with other species resulting from fragmentation of 3FA.…”

Ab initio and matrix isolation study of the acetylene–furan dimer

“…2) Table 5 Bond critical point properties (in au) for complexes with CHÁ Á ÁO Fu and OHÁ Á ÁO Fu interactions, respectively and distance between the proton donor group (Y = C in furan-acetylene and Y = O in furan-formamide) of the complex (r Y-H in Å ) and its increment (Dr Y-H in Å ) with respect to the isolated monomer geometries of argon at 10 K. In highly diluted matrices mainly the monomers -acetylene and furan -are observed by IR spectroscopy. The monomers are easily identified by comparison with the literature data and pure samples of matrix-isolated acetylene [62,[67][68][69] and furan [21]. This also allows to identify complexes of furan and acetylene with water, a frequent contaminant in the matrices.…”

“…2) [21] and the acetylene-furan dimer structures B and A is striking. The formic acid-furan structure F is stabilized by the interactions of the oxygen atom and the a-hydrogen atom of furan with formic acid, similar to the acetylenefuran structure B (Figs.…”

“…Recently some of us presented combined theoretical and experimental studies on the interactions of formic acid with acetylene and formic acid with furan [19][20][21]. Therefore, the investigation of the interactions between acetylene and furan is a logical next step to provide a deeper insight into weakly interacting complexes.…”

Density Functional Theory Study of the Oligomerization of Carboxylic Acids

“…placed at the centre of a cube of defined side length, and extensively applied to study the microhydration and noncovalent interaction of molecular complexes. [38][39][40][41][42][43]…”