4. When comparing organic compounds within the same family, adding carbon atoms to the chain decreases the polarity. For example, methyl alcohol (CH3OH) is more polar than propyl alcohol (CH3CH2CH2OH). This is because hydrocarbons are nonpolar, and increasing the length of a carbon chain makes the compound more hydrocarbon-like. The general rule of thumb is that each polar group (groups containing nitrogen or oxygen) will allow up to 4 carbons to be soluble in water.
5. As mentioned earlier, the force of attraction between polar molecules is dipole-dipole interaction. A special case of dipole-dipole interaction is hydrogen bonding. Hydrogen bonding is a possibility when a compound possesses a hydrogen atom bonded to a nitrogen, oxygen, or fluorine atom. It is the attraction between this hydrogen atom and a nitrogen, oxygen, or fluorine atom in another molecule. Hydrogen bonding may occur between two molecules of the same compound or between molecules of different compounds.