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🥼organic chemistry review

Bond Rotation

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Bond rotation refers to the ability of atoms in a molecule to rotate around a single covalent bond, allowing the molecule to adopt different spatial arrangements or conformations. This term is particularly relevant in the context of understanding the structure and behavior of alkanes, such as ethane, as well as the concept of sp3 hybridization.

5 Must Know Facts For Your Next Test

  1. Bond rotation is possible in molecules with single covalent bonds, as these bonds allow for free rotation around the bond axis.
  2. The ability of atoms to rotate around a single bond is a consequence of the sp3 hybridization of carbon atoms, which results in tetrahedral bond angles and increased flexibility.
  3. The rotation around a single bond in ethane leads to the formation of different conformations, such as the staggered and eclipsed conformations, which have different energies and stabilities.
  4. Torsional strain, which is the energy required to twist or rotate a molecule around a single bond, can influence the preferred conformations of a molecule.
  5. Steric hindrance, or the repulsive forces between atoms or groups of atoms, can also restrict the rotation around a bond and affect the stability of different conformations.

Review Questions

  • Explain how the concept of bond rotation is related to the sp3 hybridization of carbon atoms in alkanes.
    • The sp3 hybridization of carbon atoms in alkanes, such as ethane, results in a tetrahedral arrangement of bonds around the carbon atom. This tetrahedral geometry allows for free rotation around the single carbon-carbon bonds, enabling the molecule to adopt different spatial arrangements or conformations. The ability to rotate around these single bonds is a direct consequence of the sp3 hybridization, which provides the necessary flexibility for the molecule to change its shape without breaking any bonds.
  • Describe the relationship between bond rotation and the conformations of ethane.
    • The rotation around the carbon-carbon single bond in ethane leads to the formation of different conformations, such as the staggered and eclipsed conformations. The staggered conformation, where the hydrogen atoms are as far apart as possible, is the most stable due to the minimization of torsional strain and steric hindrance. In contrast, the eclipsed conformation, where the hydrogen atoms are closest together, experiences greater torsional strain and is less stable. The ability to rotate around the carbon-carbon bond allows ethane to interconvert between these different conformations, with the staggered conformation being the preferred and most stable arrangement.
  • Analyze how the concept of bond rotation can be extended to understand the conformations of other alkanes beyond ethane.
    • The principle of bond rotation can be applied to understand the conformations of other alkanes, such as propane and butane. In these larger alkanes, the rotation around the carbon-carbon single bonds allows for the formation of different conformations, each with varying degrees of stability based on factors like torsional strain and steric hindrance. For example, in propane, the rotation around the central carbon-carbon bond can lead to the formation of the anti and gauche conformations, with the anti conformation being the most stable. Similarly, in butane, the rotation around the two carbon-carbon bonds can result in a variety of conformations, including the most stable trans conformation. Understanding bond rotation is crucial for predicting and explaining the preferred conformations of alkanes, which is essential for understanding their physical and chemical properties.