The paper shows that if the distribution is defined on a manifold with the special smooth structure and does not depend on the vertical coordinates, then the Schouten curvature tensor coincides with the Riemannian curvature tensor. The Schouten curvature tensor is used to write the Jacobi equation for the distribution. This leads to studies on second-order optimality conditions for the horizontal geodesics in subRiemannian geometry. Conjugate points are defined by the solutions of the Jacobi equation. If a geodesic passed a point conjugated with its beginning then this geodesic ceases to be optimal