This is a total misunderstanding of the Union. First of all, the consitutional convention and the states subsequent ratification post-date the formation of the union. The Union began with the articles of association in 1774. When you create a corporation, which is a seperate legal person, the inception of it is filed with your secretary of states office under articles of association. At this point, the corporation comes into being. It is a single entity.

This entity (the Union) later declared independence...entered into a form of government called the articles of confederation...then dissolved that and replaced it with a new constitutional form of government...but it is and always has been one entity. A state can no more secede from the union than a hand or a foot can decide to secede from the body. Their are many parts, but they are all one body. One nation. Indivisible.