Interactions among permanent dipoles such as carbonyl groups (Fig. 2-5a) are much weaker than ionic interactions. A permanent dipole also induces a dipole moment in a neighboring group by electrostatically distort- ing its electron distribution (Fig. 2-5b). Such dipole–induced dipole interac- tions are generally much weaker than dipole–dipole interactions. At any instant, nonpolar molecules have a small, randomly oriented di- pole moment resulting from the rapid fluctuating motion of their electrons. This transient dipole moment can polarize the electrons in a neighboring group (Fig. 2-5c), so that the groups are attracted to each other. These so- called London dispersion forces are extremely weak and fall off so rapidly with distance that they are significant only for groups in close contact