Bent's rule

https://doi.org/10.1351/goldbook.BT07000
In a molecule, smaller bond angles are formed between electronegative @[email protected] since the @[email protected], to which the @[email protected] are attached, tends to direct bonding hybrid orbitals of greater p character towards its more electronegative substituents.
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1926 [Terms] [Paper]