Molecular Structure and Photoinduced Intramolecular Hydrogen Bonding in 2-Pyrrolylmethylidene Cycloalkanones

Abstract

The structures of pyrrolylmethylidene derivatives of 2,3-dihydro-1H-inden-1-one (3), 3,4-dihydro-naphthalen-1(2H)-one (4), and cycloalkanones (5-7) were studied for the first time in the solid state and solution by NMR, IR, and UV spectroscopies supported by DFT quantum mechanical calculations. It was shown that all studied compounds except cycloheptanone derivative 7 both in crystal and in solution exist in the form of dimers where single E or E,E configuration with respect to the exocyclic C═C bond is stabilized by intermolecular hydrogen bonds N-H···O═C. UV irradiation at a wavelength of 365 nm of MeCN or DMSO solutions of 3-6 results, depending on the exposition time and solvent, partial to complete isomerization to the Z or Z,E isomers (in the case of 6, also the Z,Z isomer). The NMR and IR spectroscopy data show the existence of a strong intramolecular hydrogen bond N-H···O═C in the Z moieties of isomerized compounds. The studied compounds are protonated by trifluoroacetic acid at the carbonyl oxygen, in spite of the reverse order of basicity and nucleophilicity of the carbonyl group and the pyrrole ring. Investigation of the behavior of compound 6 with respect to acetate and fluoride anions allows one to consider it as a potential fluoride sensor.

Synthesis, Vibrational (IR), Thermal analysis and Quantumchemical Study of a Series of Cyclic Chalcones

“…However, these frequencies appear coupled to the close ν C=C bond. The decreased ν C=O intensity in compound 3 compared to 1 , further support the notion that charge transfer is weakening the C=O bond, which leads to reduction in the band's intensity and a blue shift to lower energy with considerable mixing with ν C=C stretching …”

Molecular Structure, Intramolecular Hydrogen Bonding, Solvent‐Induced Isomerization, and Tautomerism in Azolylmethylidene Derivatives of 2‐Indanone

“…[22] However, hydrogen bonding is not the only factor determining the relative stability of the 3-Z,E and 3-E,E isomers. Although being more sterically strained, it is strongly stabilized by two intramolecular hydrogen bonds that are not destroyed even by such a strong base as DMSO, as follows from the fact that the Z,Z-isomer remains most stable irrespective of the presence of solvent either as a continuum or as discrete molecules.…”

“…[18][19][20] 2-Indanone-based dienones 2 have been used as building blocks for the synthesis of biologically active compounds. [22] It was shown that all studied compounds except cycloheptanone derivative (n = 3) both in crystal and in solution, exist in the form of dimers in which the E-or E,E-configuration with respect to the exocyclic C=C bond is stabilized by N-H···O=C intermolecular hydrogen bonds. Recently, we studied pyrrolylidene derivatives of 1-indanone and bis-pyrrolylidene derivatives of cycloalkanones (1, Ar = 2-pyrrolyl, n = 1-3).…”

Potassium 3-oxo-2,3-dihydro-1H-inden-4-olate: Formation, molecular and electronic structure

“…the ability to isomerize under UV irradiation [9e11]. Recently, we have shown that pyrrolylidene 1-indanone and -1-tetralone, which under normal conditions exist as E-isomers, when irradiated, isomerize to the Z-isomers possessing intramolecular hydrogen bond [12].…”

“…The reaction was carried out under the conditions successfully used for the reaction of 1-H-pyrrol-2-carbaldehyde with 1-indanone, that is, by reflux in ethanol in the presence of potassium hydroxide [12]. However, instead of the desired product of condensation, the potassium salt of the starting indanone 3-K was isolated.…”