Schwingungspektren und Kraftkonstanten von Phosphorverbindungen
ABSTRACT A short explanation is given for vibration spectra and force constants. The well known results of the different influences due to P–halogens-, P—O, P—S and P—C-bonds are treated. These are the following: (1) hybridization of the σ-bonds; (2) parts of d π –p π bonds; (3) the electronegativities of all bonded atoms; and (4) the ionic charge. Discussed in detail are the vibration-frequencies and force constants of P—N-valence bonds. The dependences of the hybridization, of the d π –p π -bonds and of the ionic charge are similar to the results of the other bonds, but much stronger. The influence of the electronegativities of the other bonded atoms is here not so clear; somewhat clearer is the effect on the force constants. The single P—N-bonds are strongly influenced by coupling with other valence vibrations. Similar effects are also observed at multiple P—N-bonds. These results are discussed. In consequence of the ‘free rotation’ a surplus of bands is found (rotation-isomers), normally in phosphorus compounds with the following groups: —O—R, —S—R and —CH 2 —R. A special form of the influence of ionic charges is found in the spectra of phosphonium ions. The changes of the spectra by the coordination of phosphorus(III) compounds is briefly discussed. Finally an attempt is made to show some relations between the results of the vibration spectra and the results of other spectroscopic methods, especially of n.m.r. spectroscopy. The importance of the facts described is directed towards analytical applications of vibration spectra. With these facts it is possible to construct the spectra of unknown phosphorus compounds.