In
stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoi ...
, cryptochirality is a special case of
chirality
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from ...
in which a molecule is chiral but its
specific rotation
In chemistry, specific rotation ( �'') is a property of a chiral chemical compound. It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a sampl ...
is non-measurable. The underlying reason for the lack of rotation is the specific electronic properties of the molecule. The term was introduced by
Kurt Mislow
Kurt Martin Mislow (June 5, 1923 – October 5, 2017) was a German-born American organic chemist who specialized in stereochemistry.
Born in Berlin on June 5, 1923, Mislow had moved to London by 1938, after some time in Milan. With the help of h ...
in 1977.
For example, the
alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in wh ...
5-ethyl-5-propylundecane found in certain species of ''
Phaseolus vulgaris
''Phaseolus vulgaris'', the common bean, is a herbaceous annual plant grown worldwide for its edible dry seeds or green, unripe pods. Its leaf is also occasionally used as a vegetable and the straw as fodder. Its botanical classification, ...
'' is chiral at its central
quaternary carbon
A quaternary carbon is a carbon atom bound to four other carbon atoms. For this reason, quaternary carbon atoms are found only in hydrocarbons having at least five carbon atoms. Quaternary carbon atoms can occur in branched alkanes, but not in li ...
, but neither enantiomeric form has any observable optical rotation:
It is still possible to distinguish between the two enantiomers by using them in
asymmetric synthesis
Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecul ...
of another chemical whose stereochemical nature can be measured. For example, the
Soai reaction In organic chemistry, the Soai reaction is the alkylation of pyrimidine-5-carbaldehyde with diisopropylzinc. The reaction is autocatalytic and leads to rapidly increasing amounts of the same enantiomer of the product. The product pyrimidyl alcohol ...
of 2-(3,3-dimethylbut-1-ynyl)pyrimidine-5-carbaldehyde with
diisopropylzinc performed in the presence of 5-ethyl-5-propylundecane forms a secondary alcohol with a high
enantiomeric excess based on the major enantiomer of the alkane that was used.
Even a slight enantiomeric excess of the alkane is rapidly amplified due to the
autocatalytic nature of this reaction.
Cryptochirality also occurs in
polymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
ic systems growing from chiral
initiators, for example in
dendrimer
Dendrimers are highly ordered, branched polymeric molecules. Synonymous terms for dendrimer include arborols and cascade molecules. Typically, dendrimers are symmetric about the core, and often adopt a spherical three-dimensional morphology. The ...
s having lobes of different sizes attached to a central core.
The term is also used to describe a situation where an enantiomeric excess lies far below the observational horizon, but is still relevant, e.g. in highly enantiosensitive, self-amplifying reactions.
[''Absolute Asymmetric Synthesis: A Commentary'', Kurt Mislow, Collect. Czech. Chem. Commun. 2003, 68, 849-864, https://doi.org/10.1135/cccc20030849 ]
References
Stereochemistry