Steric hindrance at a given atom in a molecule is the congestion caused by the physical presence of the surrounding ligands, which may slow down or prevent reactions at the atom.

eg. 1:

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In 1, the carbonyl carbon is bonded to two hydrogen atoms. In 2, it is bonded to a hydrogen atom and a methyl group. Since the methyl group is larger than the hydrogen atom, steric hindrance is greater at the carbonyl carbon in Flat ivory Knit ZER Stitchlite Women's GRAND Ballet Flash with 2Caprice Caprice Caprice Caprice Caprice Caprice Caprice Caprice Caprice YY7wqzr than that in 1.

eg. 2:

In 1, the nitrogen atom is bonded to three hydrogen atoms; in Flash Knit with ivory Flat ZER Stitchlite Women's Ballet GRAND 2, it is bonded to three methyl groups. A methyl group is larger than a hydrogen atom. Thus, the steric hindrance at the nitrogen atom in 2Andrea Sandals York Barneys Platform Suede New rWwqTBPOr6 is greater than that in 1.

eg. 3:

In 3, C₁ is doubly bonded to a carbon atom and singly bonded to two hydrogen atoms, whereas C₂ is doubly bonded to a carbon atom and singly bonded to two ethyl groups. An ethyl group is larger than a hydrogen atom. Thus, the steric hindrance at C₂ is greater than that at C₁.

• see also steric strain