Elements of Unsaturation: Heteroatoms Halogens replace hydrogen atoms in hydrocarbons,so when calculating unsaturations,count halides as hydrogen atoms. Oxygen does not change the C:H ratio,so ignore oxygen in the formula. Nitrogen is trivalent,so it acts like half a carbon.Add the number of nitrogen atoms when calculating unsaturations. Chapter 7 10 Chapter 7 10 Elements of Unsaturation: Heteroatoms • Halogens replace hydrogen atoms in hydrocarbons, so when calculating unsaturations, count halides as hydrogen atoms. • Oxygen does not change the C:H ratio, so ignore oxygen in the formula. • Nitrogen is trivalent, so it acts like half a carbon. Add the number of nitrogen atoms when calculating unsaturations