The formula #C_nH_(2n+2)# is important. Try it for hexanes, #n=6#, heptane, #n=7#, methane. Are the formulae consistent?
Of course halogens substitute for hydrogen, i.e. #C_nH_(2n+1)X#. Each #2# hydrogens less than the saturated formula, #C_nH_(2n+2)# corresponds to an olefinic bond, i.e. #C=C, C=N, C=O#, OR a ring junction. Is it consistent for cylcohexane?
For compounds containing nitrogen, subtract #NH#; try it for prussic acid, #HC-=N#, clearly #3""^@# of unsaturation. The degree of unsaturation is a very useful parameter to characterize an organic formula. An example is one of the simplest organic molecules, #C_6H_6,# benzene. Given my spray, this has 4 degrees of unsaturation. And indeed benzene has the equivalent of #3# #"double bonds"# and a ring. Try this treatment with toluene, acetone, ethylene, acetylene, as well as say decane, and decene, and cyclohexane. If you have any queries, state them here.
