= Phosphoanhydride bond
A \b[phosphoanhydride bond] is the oxygen-bridged connection between phosphorus-containing groups in a phosphoric-acid anhydride, conventionally recognized as a $\mathrm{P-O-P}$ linkage. In <adenosine triphosphate>, the phosphate chain contains two such connections, whereas the attachment to the <ribose> is a <phosphate ester>. <Adenosine diphosphate> retains one phosphoanhydride connection. These distinctions concern connectivity, not simply the presence of phosphorus.<ATP in ChEBI>[CHEBI:15422, structure and SMILES]{ref}<ADP in ChEBI>[CHEBI:16761, structure and SMILES]{ref}
For an original connection count, draw the phosphate chain schematically as
$$
\text{adenosine}-P_\alpha-O-P_\beta-O-P_\gamma.
$$
The subscripts label the three phosphorus-containing groups, not bare phosphorus atoms bonded directly to <adenosine>. The two intergroup bridges are α–β and β–γ. A cleavage giving ADP and free <phosphate> leaves the α–β connection intact; a cleavage giving AMP and <diphosphate> leaves a phosphate–phosphate connection in the diphosphate product. Breaking one connection does not necessarily destroy every anhydride connection in the products.
The phrase “high-energy bond” must be read in the context of a complete <chemical reaction>. Isolated bond breaking requires an energy input; whether <hydrolysis> lowers <Gibbs free energy> depends on the full reactant/product states and conditions. A structural count alone supplies neither a reaction rate nor a free-energy change.<chemistry-2e-by-paul-flowers-and-others/7.5 Strengths of Ionic and Covalent Bonds>[Bond Strength: Covalent Bonds; bond dissociation requires energy]{ref} Calling every reaction that breaks a phosphoanhydride connection identical would erase the different chemical products and coupling possibilities.
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