Bent's rule

Shape of water molecule showing that the real bond angle 104.5° deviates from the ideal sp3 angle of 109.5°.

In chemistry, Bent's rule describes and explains the relationship between the orbital hybridization and the electronegativities of substituents.[1][2] The rule was stated by Henry A. Bent as follows:[2]

Atomic s character concentrates in orbitals directed toward electropositive substituents.

Valence bond theory gives a good approximation of molecular structure. Bent's rule addresses disparities between the observed and idealized geometries.[3] According to Bent's rule, a central atom bonded to multiple groups will rehybridize so that orbitals with more s character are directed towards electropositive groups, and orbitals with more p character will be directed towards groups that are more electronegative. By removing the assumption that all hybrid orbitals are equivalent, Bent's rule leads to improved predictions of molecular geometry and bond strengths.[4][5] Bent's rule can be justified through the relative energy levels of s and p orbitals. Bent's rule represents a modification of VSEPR theory for molecules of lower than ideal symmetry.[6] For bonds with the larger atoms from the lower periods, trends in orbital hybridization depend strongly on both electronegativity and orbital size.

  1. ^ Weinhold, F.; Landis, C. L. (2005), Valency and Bonding: A Natural Donor-Acceptor Perspective (1st ed.), Cambridge: Cambridge University Press, ISBN 978-0-521-83128-4
  2. ^ a b Bent, H. A. (1961), "An appraisal of valence-bond structures and hybridization in compounds of the first-row elements", Chem. Rev., 61 (3): 275–311, doi:10.1021/cr60211a005
  3. ^ Foster, J. P.; Weinhold, F. (1980), "Natural hybrid orbitals", J. Am. Chem. Soc., 102 (24): 7211–7218, doi:10.1021/ja00544a007
  4. ^ Alabugin, I. V.; Bresch, S.; Gomes, G. P. (2015). "Orbital Hybridization: a Key Electronic Factor in Control of Structure and Reactivity". J. Phys. Org. Chem. 28 (2): 147–162. doi:10.1002/poc.3382.
  5. ^ Cite error: The named reference Jonas-1996 was invoked but never defined (see the help page).
  6. ^ Alabugin, I. V.; Bresch, S.; Manoharan, M. (2014). "Hybridization Trends for Main Group Elements and Expanding the Bent's Rule Beyond Carbon: More than Electronegativity". J. Phys. Chem. A. 118 (20): 3663–3677. Bibcode:2014JPCA..118.3663A. doi:10.1021/jp502472u. PMID 24773162.