title: 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.
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , 84105 Beer-Sheva, Israel.
authors.forename: Mark
authors.initials: M
authors.lastname: Sigalov
authors.affiliation: A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of Russian Academy of Sciences , 664033 Irkutsk, Russia.
authors.forename: Bagrat
authors.initials: B
authors.lastname: Shainyan
authors.affiliation: A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of Russian Academy of Sciences , 664033 Irkutsk, Russia.
authors.forename: Nina
authors.initials: N
authors.lastname: Chipanina
authors.affiliation: A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of Russian Academy of Sciences , 664033 Irkutsk, Russia.
authors.forename: Larisa
authors.initials: L
authors.lastname: Oznobikhina
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev , 84105 Beer-Sheva, Israel.
authors.forename: Natalia
authors.initials: N
authors.lastname: Strashnikova
authors.affiliation: A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of Russian Academy of Sciences , 664033 Irkutsk, Russia.
authors.forename: Irina
authors.initials: I
authors.lastname: Sterkhova