Cryptochirality

Cryptochirality in stereochemistry is a special case of chirality where due to the electronic properties of the chiral molecule its specific rotation is non-measurable. The term was introduced by K. Mislow in 1977.

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For example the alkane 5-ethyl-5-propylundecane or (n-butyl)ethyl(n-hexyl)(n-propyl)methane found in certain species of Phaseolus vulgaris has two enantiomeric forms without any observable optical rotation^[1]

It is still possible to distinguish between the two enantiomers by asymmetric synthesis with the (S)-alkane 3 in an autocatalytic system of the achiral aldehyde 1^[2] and achiral Diisopropylzinc 2 to the chiral (R)-alcohol 4 with enantiomeric excess 94%:

For chiral induction to be possible C-H bonds in the alkane are believed to interact with the pi electrons of the aldehyde.

Cryptochirality also occurs in polymeric systems growing from chiral initiators for example in dendrimers with lobes of different size attached to a central core.^[3]

See also

• More on diisopropylzinc autocatalysis see: homochirality

References

1. ^ Chiral Discrimination of Cryptochiral Saturated Quaternary and Tertiary Hydrocarbons by Asymmetric Autocatalysis Kawasaki, T.; Tanaka, H.; Tsutsumi, T.; Kasahara, T.; Sato, I.; Soai, K. J. Am. Chem. Soc.; (Communication); 2006; 128(18); 6032-6033. Abstract
2. ^ 2-(3,3-dimethylbut-1-ynyl)pyrimidine-5-carbaldehyde
3. ^ Cryptochirality and dendrimers Struijk, MP Peerlings, HWI Meijer, EW Polymer Preprints 37(2), 497-498 (1996) Article