Thomas Jefferson certainly acted in a way that was contrary to his political beliefs when he agreed to purchase the Louisiana Territory from France. However, this does not necessarily mean that he was a hypocrite. It is not necessarily the case that political leaders should stick fanatically to their principles even when it would be better for the country if they were to bend a little.
Jefferson believed in a strict construction of the Constitution. He and his political party believed more in states’ rights and less in the power of the national government. Therefore, they wanted the federal government to only be allowed to do things that the Constitution explicitly said it could do. In this case, there was nothing in the Constitution that said that the federal government could buy territory from any other country. In order to be true to his ideas about the Constitution, Jefferson should have pushed (as he thought about doing) for an amendment to the Constitution. However, he was persuaded that any delay might result in the US losing the chance to buy Louisiana. Therefore, he gave in and went against his ideals.
But is this hypocrisy? It seems more like wisdom to me. Ralph Waldo Emerson once said that “a foolish consistency is the hobgoblin of little minds.” In other words, it is only people with “little minds” that feel that they have to always stick to a set of ideas. A wiser person knows that there are times when exceptions to rules must be made. I would argue that it was good for Jefferson to betray his values when the result was so beneficial to the country.