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Chemistry LibreTexts

Chiral Molecule

[ "article:topic", "authorname:ggunawardena" ]
  • Page ID
    39305
  • A chiral molecule is a molecule that is not superimposable on its mirror image.

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    Molecule 1 is not superimposable on its mirror image and, therefore, is chiral.

     

    eg. 2:

     

     

    Molecule 2 is not superimposable on its mirror image and, therefore, is chiral.

     

    An achiral molecule is a molecule that is superimposable on its mirror image.

    eg. 1:

     

     

    Molecule 3 is superimposable on its mirror image and, therefore, is achiral.

     

    eg. 2:

     

     

    Molecule 4 is superimposable on its mirror image and, therefore, is achiral.

     

    Alternatively, an achiral molecule is a molecule that has at least one plane of symmetry.

    eg. 1:

     

     

    The vertical plane that bisects the bromine atom and the methyl group, which is the plane of the screen, is a plane of symmetry.  Thus, 3 is achiral.

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    The vertical plane that bisects the molecule perpendicular to the plane of the screen is a plane of symmetry.  Thus, 4 is achiral.

    A chiral molecule has no plane of symmetry.

    eg. 1

     

     

    1 is chiral and has no plane of symmetry.

     

    eg. 2:

     

     

    2 is chiral and has no plane of symmetry.

     

    Although relatively rare, molecules do exist that have no plane of symmetry but is achiral.

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    Thus, presence of a plane of symmetry is not a foolproof method to determine whether a molecule is chiral or achiral.