Before revision:  We first illustrate our approach with a simple toy model and then we apply it to study the C7 _{eq to C7 _{ax transition of alanine dipeptide.
After revision:  We first illustrate our approach in simple cases, and compare with the results of the instanton theory. Then we apply our method to study the C7 _{eq to C7 _{ax transition of alanine dipeptide.