A quantative relationship exists between the structrue and physical properties of organic compounds.The molecular structrue of the examined compounds is selectively described by a molecular distance-edge（MDE）vector.The physical properties of alkanes such as boiling points

density at 25℃

refractive index at 25℃

heat capacity at 300K

Gibbs energy

enthalpy at 300K are estimated with satisfactory results by a novel modified back- propagation neural network method based on the above MDEvectot.