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Steric numbers of 7 or greater are possible, but are less common. The steric number of 7 occurs in iodine heptafluoride (IF 7); the base geometry for a steric number of 7 is pentagonal bipyramidal. [10] The most common geometry for a steric number of 8 is a square antiprismatic geometry.
Sterimol parameters are built upon the Corey-Pauling-Koltun atomic models, which take into consideration the Van der Waals radii of each atom in the molecule. Unlike most other steric parameters such as A-value, Taft parameters and Tolman cone angle, which group all the spatial information into a single cumulative value, Sterimol parameters consist of three sub-parameters: one length parameter ...
Despite having the same atoms and number of bonds, methylcyclopentane is higher in energy than cyclohexane. This difference in energy can be attributed to the ring strain of a five-membered ring which is absent in cyclohexane. Experimentally, strain energy is often determined using heats of combustion which is typically an easy experiment to ...
In addition to Taft's steric parameter E s, other steric parameters that are independent of kinetic data have been defined. Charton has defined values v that are derived from van der Waals radii . [ 9 ] [ 10 ] Using molecular mechanics , Meyers has defined V a values that are derived from the volume of the portion of the substituent that is ...
A-values can help predict the steric effect of a substituent. In general, the larger a substituent's A-value, the larger the steric effect of that substituent. A methyl group has an A-value of 1.74 while tert-butyl group has an A-value of ~5. Because the A-value of tert-butyl is higher, tert-butyl has a larger steric effect than methyl. This ...
The steric factor, usually denoted ρ, [1] is a quantity used in collision theory. Also called the probability factor , the steric factor is defined as the ratio between the experimental value of the rate constant and the one predicted by collision theory.
The invariance properties of molecular descriptors can be defined as the ability of the algorithm for their calculation to give a descriptor value that is independent of the particular characteristics of the molecular representation, such as atom numbering or labeling, spatial reference frame, molecular conformations, etc. Invariance to molecular numbering or labeling is assumed as a minimal ...
Such linear relationships correspond to linear free energy relationships, which strongly imply that the effect of the substituents are exerted through changes of potential energy and that the steric and entropy terms remain almost constant through the series. The linear relationship fit well in the Hammett Equation.