To convert a nitrogen containing compound to a hydrocarbon, remove the N from the formula and replace it with one C and one H. Thus, pyridine, C5H5N, becomes C6H6, which has four degrees of unsaturation. because nitrogen in its several oxidation states is odd, a CHN compound with an odd number of nitrogen atoms must have an odd number of hydrogens. Since halogens have an odd valence, they can be considered along with nitrogen. Compound C5H4NCl has an even number of hydrogens.
Try the following:
Information provided by: http://classes.yale.edu