A compound’s molecular formula is a derivative of its molecular weight (which was determined independently) and elemental analysis. The notion of the degree of unsaturation of an organic compound is derived simply from the tetravalency of carbon. Any compound whose chemical formula has two hydrogen less than the maximum number possible (2n+2) must have one ring or one double bond. The Degree of Unsaturation is the rings plus the total number of multiple bonds. The molecular formula is abridged to CnHm and the Degree of Unsaturation Formula is given by
The degree of unsaturation designates the number of π bonds or rings that the compound is comprised of. For hydrocarbons that are compounds comprising of only hydrogen and carbon the degree of unsaturation formula is
Degree of unsaturation = Total number of rings + Total number of double bonds + (2 x total number of triple bonds)
The formula for degree of unsaturation is articulated like this, if the molecular formula is given,
Problem 1: Find out the degree of unsaturation for ethylene whose molecular formula is C2H4.
Answer: Molecular formula for ethylene = C2H4
Problem 2: Calculate the degree of unsaturation for benzene.
Answer: Benzene has one ring and three double bonds. The structure of benzene is
Using the formula a hydrocarbon which is saturated and has six carbons has the formula C6H14.