Flexi Says: Van der Waal forces are a type of weak intermolecular forces that are dependent on the distance between atoms or molecules. These forces arise from interactions between uncharged atoms. These forces can have an effect on certain properties like boiling points of branched or unbranched isomers. The boiling points of the alcohols increase as the number of carbon atoms increases. However, long, unbranched isomers have stronger Van der Waal's forces compared to the branched isomers. Due to this, branched isomers have lower boiling points.