A covalent bond in which overlap between two atomic orbitals (e.g., of sp, sp2, or sp3 hybridization) produces a single bonding orbital in which the distribution of shared electrons has a roughly cylindrical symmetry about the axis linking the two atoms; see pi bond, single bond, double bond, triple bond. By themselves, sigma bonds present little barrier to rotation of one substructure with respect to another, although steric effects and cyclic structures may hinder or block rotation.

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