Variational Nature, Integration and Properties of Newton Reaction Path Josep Maria Bofill,1 Wolfgang Quapp,2 1 Departament de Química Orgànica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, and Institut de Química Teòrica i Computacional de la Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain 2 Mathematical Institute, University of Leipzig, Johannisgasse 26, Postfach 10 09 20, D-04009 Leipzig, Germany November 2010 Abstract: The Distinguished Coordinate Path and the Reduced Gradient Following Path or its equivalent formulation, the Newton Trajectory, are analyzed and unified using the Theory of Calculus of Variations. It is shown that their minimum character is related with the fact that the curve is located in a valley floor. In this case we say that the Newton Trajectory is a reaction path with the category of minimum energy path. In addition to these findings a Runge-Kutta-Felhberg algorithm to integrate these curves is also proposed.