Steric Hindrance


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steric hindrance

[′ster·ik ′hin·drəns]
(organic chemistry)
The prevention or retardation of chemical reaction because of neighboring groups on the same molecule; for example, ortho-substituted aromatic acids are more difficult to esterify than are the meta and para substitutions.

Steric Hindrance

 

a lowering of the rate of a chemical reaction caused by the blocking of the reactive site of a molecule by adjacent atoms or groups of atoms. For example, the esterification of di-ortho-substituted benzoic acids (I,a) is quite difficult, as is the hydrolysis of their esters (I,b):

For di-ortho-substituted phenylacetic acids (II), where the COOH group is somewhat removed from the blocking substituents (X and Y), both esterification and hydrolysis of their esters proceed without hindrance.

References in periodicals archive ?
This kind of observation from the objective measurement of pH comes to strengthen the model of the colloid particle protection shield, which is acting through the mechanism of steric hindrance rather than ionic colloid protection, although it is obviously necessary to do additional work and provide more details in its support.
As shown in the tridimensional structural model of FVIII, the cysteine residue may cause a steric hindrance effect (Fig.
To maintain minimum steric hindrance between two hydrazides in the complex and hence greater stability, the configuration of hydrazides in complexes is proposed to be trans [58].
A primary finding of the molecular simulation results is that the steric hindrance and neighboring molecule effects of reactive moieties on monomers can cause heats of reaction to change up to 17% for urethane-forming reactions.
The limited steric hindrance of the methyl groups favors the ductility of the resin, especially if compared with the cumbersome epoxy derivatives, allowing the deposition of thick layers.
The high stability is due to the electrostatic repulsive force and steric hindrance of the PEI polymers against aggregation, and the high hydrophilicity of MPEG may also contribute to the stability.
In homogeneous medium, both acids give terminal double bond hydrogenation, producing the [alfa] and [beta] methyl position stereoisomers, favoring the [beta] isomer, probably due to less steric hindrance during the Ru metal [pi] complex formation.
This critical value was consistently explained from the steric hindrance effect of hIgG molecules.
It has also been shown from earlier studies that the steric hindrance and anchimeric effect can play key roles in hydrolysis reaction.
The ionic form of the resin contributes to selectivity by virtue of its charge co-ordination stability, steric hindrance with the pores of the resin, or through a combination of these factors.
This shows that complex has greater steric hindrance involving free rotation of molecules.
Molecular recognition--and especially chiral recognition--is a central concept in molecular biology and many fields of organic chemistry, and is frequently thought to be dominated by steric hindrance (perhaps taking Fischer's metaphor a little too literally).