Hydrogen bonding of cyclopentadithiophenones and fluorenone in trifluoroacetic acid. A study of the electronic absorption, 1H, and 13C nuclear magnetic resonance spectra
Abstract
The electronic absorption bands of cyclopentadithiophenones and fluorenone show large shifts towards longer wavelengths when the solvent is changed from cyclohexane to CF3CO2H. 1H and 13C n.m.r. spectra of these ketones in CDCl3 and CF3CO2H differ considerably. These observations point to strong hydrogen bond formation between the carbonyl oxygen atom and the solvent. Taking hydrogen bond formation into account by changing the core parameters of the oxygen atom, PPP calculations satisfactorily predict the bathochromic shifts of the electronic absorption bands. The calculated change in electron density at a particular carbon atom correlates well with the change in 1H and 13C n.m.r. chemical shifts as measured in CDCl3 and CF3CO2H.