By the way, this is the thisol ring of the Thiamine Pyrophosphate. And so we form a bond between this carbon and this carbon at the same exact time. This H ion that basically left is now picked up by this oxygen. So as this bond is being formed, the Pi bond is being broken and a Sigma bond is being formed between this oxygen and this H atom. And we form a tetrahedral intermediate molecule. Now, this tetrahedral intermediate molecule is not very stable.