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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.
This is because according to Bent's rule, the C–F bond gains p-orbital character leading to high s-character in the C–H bonds, and H–C–H bond angles approaching those of sp 2 orbitals – e.g. 120° – leaving less for the F–C–H bond angle. The difference is again explained in terms of bent bonds. [3]
One example of the AX 2 E 2 geometry is molecular lithium oxide, Li 2 O, a linear rather than bent structure, which is ascribed to its bonds being essentially ionic and the strong lithium-lithium repulsion that results. [23]
(By Bent's rule, unoccupied orbitals for a main-group element are almost always of p character, since s character is stabilizing and will be used for bonding orbitals. As an exception, the LUMO of phenyl cation is an sp x ( x ≈ 2) atomic orbital, due to the geometric constraint of the benzene ring.)
Henry A. Bent (December 21, 1926 – January 3, 2015) [1] was a professor of physical chemistry who studied molecular orbitals to develop atomic hybridization and valence bond theories. [2] Bent's rule , which predicts the orbital hybridization of a central atom as a function of the electronegativities of the substituents attached to it, is ...
does. It has a completely different background and is a very succesful model in chemistry. A VSEPR, Bents rule cannont make quantitative predictions and for instance fails describing the big difference in bond angles between nitrogen and phosphorus halides in contrast to the small differences between P, As and Sb halides.
Structure of iodine heptafluoride, an example of a molecule with the pentagonal-bipyramidal coordination geometry.. In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid.
Bredt's rule is the empirical observation that such molecules only form in large ring systems. For example, two of the following norbornene isomers violate Bredt's rule, and are too unstable to prepare: Bridgehead atoms violating Bredt's rule in red. The rule is named after Julius Bredt, who first discussed it in 1902 [1] and codified it in ...