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 ?
It is found that DPI-T shows a higher photocurrent than BPI-T due to the excellent conjugation system with relatively better electron-donating ability and smaller steric hindrance, which produces a broader absorption spectrum and a higher extinction coefficient.
Due to electrostatic repulsion and steric hindrance of the CTBA barrier, the agglomeration and growth of Ti[O.sub.2] grain was inhibited, the particle size of Ti[O.sub.2] was significantly reduced, and the specific surface area increased.
Compounds 2a-d provide low cytotoxicity due to the occurrence of steric hindrance which prevent them from reaching the receptor of enzymes.
As shown in the tridimensional structural model of FVIII, the cysteine residue may cause a steric hindrance effect (Fig.
The absence of substituent on phenyl ring and the presence of CH2 or NH groups attached to ring in complexes could contribute in decreasing steric hindrance near the metal centre.
For the emulsion polymerization with A3, the low conversion rate could be due to steric hindrance caused by the longer EO chain of A3.
In the small intestine, the macromolecules cannot permeate through tight junctions of the intestinal cell wall because of multiple factors, including molecular size and steric hindrance effects, and are vulnerable to further enzymatic and hydrolytic degradation.
Strong steric hindrance is expected for the [pi] Ru complex with the internal double bond in the grandiflorenic substrate, leading to no hydrogenation of this internal double bond.
The structure of such haptens makes interaction with 2 binding proteins (e.g., antibodies) very unlikely because of steric hindrance that occurs following binding of a hapten to one binding protein.
Chitosan contributed the steric hindrance to stabilize the nanoparticles as shown in Figure 1.
Furthermore, the steric hindrance in the transition-state also affects the selectivities of Michael adducts.
This movement could be due to less steric hindrance with Ala 44, Met 67, and Ala 74-75 and aiding the ligand to be in the hydrophobic pocket and the remaining part of the ligand to be in the polar region of the protein.