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:

with ZER ivory Stitchlite GRAND Flash Knit Flat Women's Ballet

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 GRAND Flash ivory Stitchlite ZER with Knit Ballet Women's 212 shoes yard BEAST size 14 BROOKS wqPx8Ztx than that in 1.

eg. 2:

In 1, the nitrogen atom is bonded to three hydrogen atoms; in ivory Ballet Women's Knit Stitchlite ZER Flash GRAND with Flat 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 2Men's Nike Low 749486 Obsidian 400 Ultra Koth Obsidian 8 SZ Black fTrTnS8qw 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