# Which is more acidic HOF or HOCl?

My attempt to the question: We know that more polar the $$\ce{O-H}$$ bond, the more acidic is the compound. According to electronegativity, the $$\ce{O-H}$$ bond of $$\ce{HOF}$$ should be more polar than $$\ce{O-H}$$ bond of $$\ce{HOCl}$$ since electronegativity order is $$\ce{F} > \ce{Cl}$$. But we should not miss another factor! That is the backbonding of 2p electrons (lone pairs) of oxygen with the 3d vacant orbital of chlorine. This is not possible in $$\ce{HOF}$$ due to the absence of vacant orbitals. Backbonding reduces (maybe, I do not know) electron density in oxygen and therefore polarity of $$\ce{O-H}$$ bond increases.

• For future reference, if deploying Latin script, do not skip spaces after the period. This renders recognition where a phrase ends and a new one starts easier. – Buttonwood Aug 29 at 20:19
• The 3d orbitals in 3rd row p block elements are not available for bonding, see any number of questions here, e.g. the first answer to chemistry.stackexchange.com/questions/13949/…. Thus there is no back bonding. – Ian Bush Aug 30 at 5:35