Improper hydrogen C-H...O bonds cause self-association of alpha, beta-enaminoketones containing fluorosubstituted alkyl groups.
Concentration- and temperature-dependent IR, NMR and dipole-moment studies on 4-N,N-dimethylamino-1,1,1-trifluoro-3-buten-2-one and two of its higher homologues showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel "closed" dimers are formed with a network of improper intermolecular C-H...O hydrogen bonds. Quantitative analysis of the 1H NMR data yielded delta H0 = -17.6 kJ mol-1 and delta S0 = -46.9 J deg-1 mol-1. The interactions observed are the strongest among those involving a C-H group reported so far. The complex described here is the first example of a cyclic complex stabilized by two improper C-H...O hydrogen bonds. The conclusions drawn from the solution and solid-state data were confirmed by ab initio calculations.
Wójcik
Jacek
J
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, ul. Pawińskiego 5a, 02-106 Warszawa, Poland. jacekw@ibb.waw.pl
Kamienska-Trela
Krystyna
K
Pecul
Magdalena
M
Bartoszak-Adamska
Elzbieta
E
Vdovienko
Siergiej I
SI
Gerus
Igor I
II