s. The first generation carcerands are based on
calixarene hemicarcerands with 4 alkyl substituents on the upper rim and 4 reactive
substituents on the lower rim. The coupling of both hemicarcerands takes place through a spacer group. In the original 1985 publication two different hemicarcerands react, one with chloromethylene reactive groups and one with thiomethylene reactive groups in a
nucleophilic displacement and the resulting spacer group is a dimethylsulfide (CH2SCH2). In this experiment the guests were the molecules already present in the reaction medium such as
argon and
dimethylformamide. In another configuration the 4 lower rim functional groups are
aldehydes which
condense with
O-Phenylenediamine to the corresponding di-imines. The 4 spacer groups connecting the two spheres are now much longer and consequently the internal cavity is much larger. Compounds trapped in the cavity are said to be held there by
constrictive binding. They can be introduced by simply heating in neat solvent like hexachlorobutadiene (a
fungicide). The
half-life of the reverse process is 3.2 hours at 25 °C in CDCl3 by NMR analysis.
Ferrocene can be introduced by heating with the hemicarcerand in a large bulky solvent such as tripiperidylphosphine oxide. The half-life for ferrocene liberation is 19.6 hours at 112 °C. ==Large carcerands==