The carboxyl group attached to the end of the molecule (COOH) acts as a terminal acidic group. Normally, an acid is andy substance that, when mixed with water, dissociates and produces hydrogen ions (H+). These hydrogen ions desperately want to combine with another element or molecule that has an electron to offer to fill the absence of that electron in its outer electron shell. So the carboxyl group acts as a group with a positive charge overall, seeking to attach itself to another element or, in this case, carbon chain, that has an electron to offer in terms of fulfilling the same requirement. Carbon atoms have the ability of catenation, which means they can form bonds with each other and form chains up to fifty carbon atoms long. Such compounds are commonly referred to as organic compounds, and the study of such substances is called organic chemistry.