INFRARED STUDY OF TETRAALKYLUREAS IN DILUTE-SOLUTIONS

The nu-C = O frequency for tetraalkylureas (TAU) shifts to lower frequency, progressing in the series tetramethyl, tetraethyl, and tetrabutyl, and the strength of the intermolecular hydrogen bond between a CHCl3 proton and the C = O group increases, progressing in a series in the same order. The nu-C = O frequency decreases in the order hexane, carbon tetrachloride, and chloroform. The data indicate that TAU molecules exist in equilibrium with one, two, and three hydrogen-bonded complexes of CHCl3 and CCl4. These complexes, together with bulk dielectric effects of the solvent, account for the continual decrease in frequency as the mole % CCl4/C6H14, CHCl3/C6H14, or CHCl3/CCl4 increases.