THE CARBONYL STRETCHING BANDS IN THE INFRARED SPECTRA OF UNSATURATED LACTONES

Certain types of unsaturated lactones exhibit two bands in the region of the spectrum associated with the C=O stretching vibrational mode. This is observed both in the infrared and Raman spectra.The infrared spectra of 23 simple saturated and unsaturated lactones have been examined in an attempt to determine the structural features with which this carbonyl band splitting is associated. It appears to be common to most unsaturated five- and six-membered ring lactones in which the double bond is conjugated with the carbonyl group, though one well-established exception has been observed. The relative intensities of the two bands are extremely sensitive to changes in the polarity of the solvent; they also vary reversibly with temperature but are independent of concentration.The splitting of the C=O stretching band is attributed to an intramolecular vibrational effect similar to that which occurs in cyclopentanone and in certain Δ2-cyclopentenone derivatives. Its possible dependence on Fermi resonance with the overtone of a lower lying fundamental vibration is discussed.Similar effects occur in other types of carbonyl compounds, such as benzoyl chloride and cyclic five-membered ring anhydrides, and care is needed to distinguish carbonyl band splitting of this kind from that associated with equilibria between conformational isomers.

Magnetic moments of copper(II) complexes

Magnetic moments of octahedral, tetrahedral, square planar, trigonal planar, and trigonal pyramidal Cu(II) complexes have been discussed theoretically including the orbital contribution on the basis of the molecular orbital theory. It has been shown that the orbital contribution of electrons to the magnetic moment is expected only in tetrahedral, trigonal planar, and trigonal pyramidal complexes. The effective magnetic moment of tetrahedral Cu(II) complexes has been estimated to be about 2.2 at room temperature and that of tri-coordinated Cu(II) complexes to be higher than the spin-only value. The hypothesis of electron promotion to a 4p level in Cu(II) complexes has been criticized.