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The term "chiral" in general is used to describe the object that is non-superposable on its mirror image. [18] In chemistry, chirality usually refers to molecules. Two mirror images of a chiral molecule are called enantiomers or optical isomers. Pairs of enantiomers are often designated as "right-", "left-handed" or, if they have no bias ...
Molecular symmetry and chirality Rotational axis (C n) Improper rotational elements (S n) Chiral no S n: Achiral mirror plane S 1 = σ: Achiral inversion center S 2 = i: C 1: C 1: C s: C i: C 2: C 2 (Note: This molecule has only one C 2 axis: perpendicular to line of three C, but not in the plane of the figure.) C 2v: C 2h Note: This also has a ...
A crystal may have zero, one, or multiple axes of symmetry but, by the crystallographic restriction theorem, the order of rotation may only be 2-fold, 3-fold, 4-fold, or 6-fold for each axis. An exception is made for quasicrystals which may have other orders of rotation, for example 5-fold. An axis of symmetry is also known as a proper rotation.
In chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain many of a molecule's chemical properties , such as whether or not it has a dipole moment , as well ...
Any planar pattern that does not have a line of mirror symmetry is 2d-chiral, and examples include flat spirals and letters such as S, G, P. In contrast to 3d-chiral objects, the perceived sense of twist of 2d-chiral patterns is reversed for opposite directions of observation.
However, compounds that contain an even number of asymmetric atoms sometimes lack chirality because they are arranged in mirror-symmetric pairs, and are known as meso compounds. For instance, meso tartaric acid (shown on the right) has two asymmetric carbon atoms, but it does not exhibit enantiomerism because there is a mirror symmetry plane.
Homochirality is a uniformity of chirality, or handedness.Objects are chiral when they cannot be superposed on their mirror images. For example, the left and right hands of a human are approximately mirror images of each other but are not their own mirror images, so they are chiral.
In a molecule that also has an axis of symmetry, a mirror plane that includes the axis is called a vertical mirror plane and is labeled σ v, while one perpendicular to the axis is called a horizontal mirror plane and is labeled σ h. A vertical mirror plane that bisects the angle between two C2 axes is called a dihedral mirror plane, σ d. [6]