The order of acidity in organic compounds is primarily determined by the stability of the conjugate base formed after the loss of a proton. This is influenced by the electronegativity and resonance effects of the atoms involved in the compound.
The higher the electronegativity of an atom, the more stable its conjugate base will be. This is because electronegative atoms are better at stabilizing negative charges, making it easier for them to accept a proton and become an acidic compound.
Resonance is the distribution of electrons within a molecule, and it can greatly influence the stability of a compound's conjugate base. Molecules with more resonance structures will have more stable conjugate bases and therefore be more acidic.
The strength of a bond can also affect the order of acidity. Generally, the weaker the bond between a proton and an atom, the more easily the proton can be removed and the more acidic the compound will be.
The size of atoms can also play a role in the order of acidity. As the size of an atom increases, its ability to stabilize a negative charge decreases. This means that larger atoms will have less stable conjugate bases and therefore be less acidic compared to smaller atoms.