NMR-Untersuchungen über inter- und intramolekulare Wechselwirkungen in substituierten Trifluormethylphenylisocyanaten,Fluorphenylisocyanaten, in Fluoranilin und Fluornitrobenzol

The temperature and solvent concentration (carbon tetrachloride) dependence of the chemical shifts of the fluorine and proton signals of substituted trifluoromethylphenylisocyanate, fluorophenylisocyanate, fluoroaniline and fluoronitrobenzene are investigated. The temperature effect on the chemical shifts of the fluorine signals of the ortho-substituted trifluoromethylphenylisocyanate originates from the intramolecular interaction of the trifluoromethyl groups and the ortho-substituents, resulting in an increase of the chemical shifts with rising temperature. The temperature dependence of the electron distribution of meta- and para-substituted trifluoromethylphenylisocyanates is mainly attributed to intermolecular interactions, causing a decrease of the chemical shifts of fluorine signals with increasing temperature. The protons of the investigated compounds, being localized on the ‘molecular surface’, show a temperature dependence of the chemical shifts due to the van der Waals effect. Increasing the amount of the solvent (carbon tetrachloride) leads to a weakening of the anisotropy effect and causes an increase of the chemical shifts of the fluorine and proton signals of all investigated compounds.