Hemicarcerands, and

D. J. Cram, J. M. Cram, Hemicarcerands and Constrictive Binding , In Container Molecules and Their Guests (Ed. J. F. Stoddart), The Royal Society of Chemistiy, Cambridge, 1994, pp. 149-169, and references cited therein. 

Development of ditopic receptors 58 for both an anion and a cation is a logical extension [19b]. It should be stressed that the recognition by cyclodextrins, calixarenes, hemicarcerands, and many other systems does not involve specific recognition sites, whereas tetrahedral recognition by 53 and 54, the adenine 56 selective binding, and multiple recognition like the one shown in formula 59 [20] require the presence of specific sites in receptor capable of directional interactions. 

The Complexes Involving Induced Fit and Without It Endohedral Fullerene, Hemicarcerand and Soft Rebek s Tennis Ball-Like Hosts... 

Carcerands, Hemicarcerands and Novel Molecular Flasks Enabling Preparation and Stabilization of Shortlived Species [1]... 

It should be stressed that calixarenes, hemispherands and spherands, carcerands and hemicarcerands, and some other molecules discussed elsewhere in this book, belong to the cyclophane group of compounds. 

Carbenes can be highly reactive but modification of their chemistry through supra-molecular encapsulation by cyclodextrins, hemicarcerands, and zeolites has been discussed in a microreview.10... 

Cram [49a] elaborated further on this concept by enclosing space in his carcerands and hemicarcerands (See Scheme 1) to form a new inner phase which he has referred to as a new phase of matter . In contrast to the hollow space found inside clathrates and zeolites for instance, the cages of these molecules are independent of the form and physical state. For example, hemicarcerands and related supramolecular systems (i.e. hemicarceplexes) prevail in the solid, liquid, or gas phase. This characteristic-hollow space, the inside surface — is maintained across all phase transitions. The inner surfaces and spaces of these systems are not manifested as bulk properties. An extensive review on the synthesis of these materials has been published recently [205]. 

How many different carcerands, hemicarcerands, and quests have you studied, and what are the extremes in the pfuest sizes ... 

About eight different carcerand systems, fifteen different hemicarcerands, and more than seventy different guests have led to several hundred fully characterized complexes. Guests have been as small as water, oxygen and nitrogen, and as large as [3.3]paracyclophane (18-carbon atoms) and 1,3,5-trisisopropylbenzene. 

The synthesis of hemicarcerands and carceplexes is a templated reaction and the proper choice of template molecule, which complements the shape and size of the inner cavity... 

Also interesting is the autoxidation of incarcerated CHTE in aerated solution. Under these conditions, oxygen diffuses into the hemicarcerand and adds to the central aUene C to produce a spirocychc dioxirane 86. The latter 86 rapidly decarboxylates to benzene at room temperature. 

We have defined the terms carcerand, carceplex, hemicarcerand, and hemicarceplex The formation of carcer-ands an carceplexes has led to some important information regarding templation by neutral molecules Similarly, the properties of hemicarcerands and hemicarceplexes has led to some interesting host-guest properties, including the storage of highly reactive species such as cyclobutadiene or benzyne... 

In this chapter, we discuss aspects of the assembly of carcerands and hemicarcerands, which is a templated process, and discuss their molecular recognition properties. Hemicarcerands show high size and shape selectivity in equilibrium binding experiments as well as with respect to rates of complexation/decomplexation. Finally, we highlight some of the dynamic aspects of hemicarcerands and their guests and give examples of their use as molecular reactions flasks. 

The efficiency of these hemicarcerand and polycavitand nanocapsule syntheses approaches those of self-assembly processes using hydrogen bonding or metal-ligand coordination and results from selection of the least strained capsule through the thermodynamic control and reversibility of the system. 

The idea behind through-shell PET and ET is to generate a triplet excited state inside a hemicarcerand and to measure rate constants and efficiencies of quenching the excited state by bulk-phase quenchers that are not covalently connected and are prevented from coming closer than... 

Hemicarceplex A host-guest complex of a hemicarcerand and a suitable guest. These complexes are conceptually and structurally related to carceplexes, differing only in the rate at which guest molecular entities can (slowly) dissociate. Guest dissociation from a hemicarceplex is possible without covalent bond rupture. See mechanical bond. 

Reversible photochemical transformations by Scheme 5.107 between the hemicarcerand 834 and its closed carcerand derivative 835 are reported in [106]. A photoswitchable cycle between the open (hemicarcerand) and closed (carcerand) states of this host has been controlled by using different wavelengths of radiation, and the controlled encapsulation and release of the guest molecules such as 1,4-dimethoxybenzene have been also observed in this work. 

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