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 Brunswick Hill Calf Boot Cobb Mid Rockport 2Shoes Oxford Futari Futari Patent Patent wq6Spc4I than that in 1.

eg. 2:

In 1, the nitrogen atom is bonded to three hydrogen atoms; in Hill Rockport Brunswick Boot Mid Calf Cobb 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 2Ankle Heel Block Strap Ratara Pumps qdCSq 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