Raman spectroscopy and molecular mechanics in the investigation of molecular structure: calcium, strontium, barium and copper(l1) monochloroacetates

Abstract -Molecular mechanics is used to provide information on the stable conformations of the monochloroacetic acid molecule. In the most stable form, the C-C1 is in the COO plane (syn), while in the other form (gauche) the C1-C-C=O dihedral angle is in the 131O region. Thus in the syn form, the bond dipoles associated with the C-C1 and CEO bonds are approximately aligned, leading to a C=O bond stronger than in the less stable conformer and, by consequence, to a larger C-0 stretching frequency for this form. The Raman spectra of Ca, Sr, Ba and Cu(I1) monochloroacetates in crystalline phases have been recorded and interpreted to assess the relative importance of the mutual interactions of the metal-metal and metal-ligand bonds and the nature of the metal-metal bond in these systems. The preferred conformations around the Ca-C single bond of the coordinating monochloroacetic acid molecules have also been studied and correlated with our previous theoretical and experimental results on the pure acid