Chapter 3 - Alkyl Carbon-Hydrogen Vibrations

Abstract

This chapter discusses alkyl carbon-hydrogen molecular vibrations and looks at how these molecular vibrations are affected by their surrounding chemical environment. The n-alkane protons form weak intermolecular hydrogen bonds with the free pair of electrons on the Cl atoms of the CCl4 and/or CDCl3 solvent system, and an explanation is needed to determine the frequency behavior of these four molecular vibrations in going from solution in CCl4 to solution in CDCl3. CH2 modes vibrate, the protons obtain a weak positive charge and the carbon atom obtains a weak negative charge. This is the so-called dipole moment change during the molecular vibrations. Therefore, the n-alkane protons would form weak intermolecular hydrogen bonds with the free pair of electrons on the Cl atoms of the CCl4 and CDCl3 solvent system. The Cl atoms of CCl4 would be expected to be more basic than those for CDCl3 due to the fact that the D atom attracts electrons from the Cl atoms.