Desymmetrization
Encyclopedia
Desymmetrization in stereochemistry
is the modification of a molecule
that results in the loss of one or more symmetry elements. An important application involves the introduction of chirality
. Formally, such conversion require the loss of an improper axis of rotation (mirror plane, center of inversion, rotation-reflection axis). In other words, desymmetrizations convert prochiral
precursors into a chiral
products.
.
In another example, transfer hydrogenation
converts benzil
(PhC(O)C(O)Ph) into one enantiomer of hydrobenzoin
:
The precursor benzil has C2v symmetry
, and the product has C2 symmetry.
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms within molecules. An important branch of stereochemistry is the study of chiral molecules....
is the modification of a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
that results in the loss of one or more symmetry elements. An important application involves the introduction of chirality
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
. Formally, such conversion require the loss of an improper axis of rotation (mirror plane, center of inversion, rotation-reflection axis). In other words, desymmetrizations convert prochiral
Prochiral
In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step.If two identical substituents are attached to a sp3-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two...
precursors into a chiral
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
products.
Examples
One example is the conversion of cis-3,5-diacetoxycyclopentene to its the monoacetate. In this transformation, the plane of symmetry in the precursor is lost, and the product is asymmetric. The desymmetrization itself is not usually considered useful. The enantioselective desymmetrization however delivers a useful product. This particular conversion utilizes the enzyme cholinesteraseCholinesterase
In biochemistry, cholinesterase is a family of enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation.-Types:...
.
In another example, transfer hydrogenation
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...
converts benzil
Benzil
Benzil is the organic compound with the formula 2, generally abbreviated 2. This yellow solid is one of the most common diketones...
(PhC(O)C(O)Ph) into one enantiomer of hydrobenzoin
Benzoin
Benzoin is an organic compound with the formula PhCHCPh. It is a hydroxy ketone attached to two phenyl groups. It appears as off-white crystals, with a light camphor-like odor. Benzoin is synthesized from benzaldehyde in the benzoin condensation...
:
- PhC(O)C(O)Ph + 2 H2 → PhCH(OH)CH(OH)Ph
The precursor benzil has C2v symmetry
Symmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...
, and the product has C2 symmetry.