Noncovalent Interactions between Aromatic Heterocycles and Carboxylic Acids: Rotational Spectroscopy of the Furan–Formic Acid and Thiophene–Formic Acid Complexes

Abstract

The binary molecular complexes formed between the aromatic heterocycles furan and thiophene with formic acid were investigated using pulsed-jet Fourier transform microwave spectroscopy and quantum chemical computations. For both of the complexes, rotational spectra of the lowest energy isomer were detected and assigned. Rotational spectroscopic results and density functional theory calculations support that the preferred conformation of the furan–formic acid complex is characterized by a relatively strong O–H···O and a weak C–H···O hydrogen bonds while the O–H···π and C–H···O hydrogen bonds stabilize the thiophene–formic acid complex. Natural bond orbital analysis further proves the experimental observation, suggesting that the strength of the O–H···O­(furan) interaction is about two times stronger than that of O–H···π­(thiophene). The symmetry adapted perturbation theory analysis reveals that electrostatic interaction is dominant in stabilizing the two complexes and that dispersion becomes significant in the thiophene–formic acid complex compared to furan–formic acid.

Organocatalyzed Synthesis of Bicyclic γ‐Lactam Derivatives via Asymmetric Conjugate Addition of Cyclic β‐Keto Esters to Benzoyl Acrylonitriles

“…Cyanoenones 2 m and 2 n bearing heterocycles, such as furan and thiophene, were also good substrates, affording bicyclic γ‐lactam derivatives 4 m and 4 n in good to high yields with excellent enantioselectivities. We guess that excellent stereoselectivity of 4 m is due to additional formation of hydrogen‐bond between catalyst C9 and furan ring in 2 m [14] . Although the reaction of 1 c with 2 o bearing a pyridine ring also smoothly proceeded to provide adduct 3 o in a high yield with excellent stereoselectivity, the hydrolysis of the cyano group in 3 o did not proceed under the same reaction conditions using the Pd(NO 3 ) 2 catalyst [13] .…”

Unveiling the Noncovalent Interactions between Formamide and Heteroaromatics: Microwave Spectroscopy of the Formamide Complexes with Furan and Thiophene

“…Conversely, the π-electron of thiophene exhibits a preference for forming N–H···π or O–H···π hydrogen bonds with FM, formic acid, or water. The secondary interactions between FM and thiophene are identified as O···π interactions, while a CO···H–C hydrogen bond is observed as the secondary interaction between thiophene and formic acid …”

“…73,74 an formic acid. 37 In all of these complexes, the oxygen atom of furan is the preferred proton acceptor for the N−H or the O−H group, and the planar conformation is more stable than those formed by π-type hydrogen bonds. Conversely, the π-electron of thiophene exhibits a preference for forming N−H•••π or O−H•••π hydrogen bonds with FM, formic acid, or water.…”

“…The secondary interactions between FM and thiophene are identified as O•••π interactions, while a C�O•••H−C hydrogen bond is observed as the secondary interaction between thiophene and formic acid. 37 NBO analysis provides valuable insights into intermolecular orbital donor−acceptor interactions in the complexes. The results derived from calculations performed at the B3LYP/augcc-pVTZ level of theory suggest that the stability of the FM− furan complex is predominantly attributed to the interaction between the lone pairs of oxygen in furan and the N−H antibonding orbitals in FM, leading to a second-order perturbation stabilization energy (E 2 ) of approximately 15.2 kJ/mol.…”

Noncovalent interactions of aromatic heterocycles: rotational spectroscopy and theoretical calculations of the thiazole–CF4 and thiazole–SF6 complexes

“…Hydrogen bonds are usually the preferred interaction topologies in water or formic acid complexes with thiazole, 15,16 pyridine and its derivatives, [17][18][19][20] and thiophene derivatives. [21][22][23] The np* or pp* interactions overwhelm HBs in the formaldehyde complexes with pyridine 24 or benzofuran. 25 Both np* and CHÁ Á ÁN and CHÁ Á ÁO interaction topologies were observed for the formaldehyde-thiazole complex.…”