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 stereois ...
, 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 which ...
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, alo ...
'' is chiral at its central
quaternary carbon, 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 of 2-(3,3-dimethylbut-1-ynyl)pyrimidine-5-carbaldehyde with
diisopropylzinc
Diisopropylzinc is an organozinc compound with the chemical formula
ZnC6H14.
It is the key reagent in the Soai reaction, which is both autocatalytic and enantiospecific. This chemical is pyrophoric
A substance is pyrophoric (from grc-gre, � ...
performed in the presence of 5-ethyl-5-propylundecane forms a secondary alcohol with a high
enantiomeric excess
In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a sin ...
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
polymeric systems growing from chiral
initiators, for example in
dendrimers 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