Hexamers

Liu K, Brown M G and Saykally R J 1997 Terahertz laser vibration rotation tunneling spectroscopy and dipole moment of a cage form of the water hexamer J. Phys. Chem. A 101 8995-9010... 

Crown 4 and 18 crown 6 are a cyclic tetramer and hexamer respectively of repeat mg —OCH2CH2— units they are polyethers based on ethylene glycol (HOCH2CH2OH) as the parent alcohol... 

Fig. 1. Stmctures of alkyllithium tetramers and hexamers (a) tetrahedron of lithium alkyl groups (b) arrangement of alkyl groups around octahedron of...

Type AABB Methylene, Ethylene, T rim ethylene T etramethylene. Pen tarn ethyl en e Hexam ethyl en e... 

Fig. 2. Silica ring stmctures, where 0= Si Q — O (a) 12-membered Si02 hexamer, and (b) 16-membered Si02 octamer.

Hydroxides. Thorium (TV) is generally less resistant to hydrolysis than similarly sized lanthanides, and more resistant to hydrolysis than tetravalent ions of other early actinides, eg, U, Np, and Pu. Many of the thorium(IV) hydrolysis studies indicate stepwise hydrolysis to yield monomeric products of formula Th(OH) , where n is integral between 1 and 4, in addition to a number of polymeric species (40—43). More recent potentiometric titration studies indicate that only two of the monomeric species, Th(OH) " and thorium hydroxide [13825-36-0], Th(OH)4, are important in dilute (<10 M Th) solutions (43). However, in a Th02 [1314-20-1] solubiUty study, the best fit to the experimental data required inclusion of the species. Th(OH) 2 (44). In more concentrated (>10 Af) solutions, polynuclear species have been shown to exist. Eor example, a more recent model includes the dimers Th2(OH) " 2 the tetramers Th4(OH) " g and Th4(OH) 2 two hexamers, Th2(OH) " 4 and Th2(OH) " 2 (43). 

The melting temperature, T, of PVDC is independent of molecular weight above DP = 100. However, as shown in Eigure 2, it drops sharply at lower molecular weights. Below the hexamer, the products are noncrystalline Hquids. 

In solutions of n-propyllithium in cyclopropane at 0°C, the hexamer is the main species, but higher aggregates are present at lower temperatures. The reactivity of the organo-... 

Address Hexamer House, Sayani Rd. Bombay Maharashtra 400028 India Phone +91 22 200 6155 Fax +91 22 206 2751... 

Tetrafluoroethene hexamer reacts with ammonia to give a nitrile. The reaction occurs probably by initial formation of a very reactive cyanoolefin [95] (equation 81). 

Insulin is composed of two peptide chains covalently linked by disulfide bonds (Figures 5.17 and 6.35). This monomer of insulin is the active form that binds to receptors in target cells. However, in solution, insulin spontaneously forms dimers, which themselves aggregate to form hexamers. The surface of the insulin molecule that self-associates to form hexamers is also the surface that binds to insulin receptors in target cells. Thus, hexamers of insulin are inactive. 

The ring-stacking concept used in the preceding paragraph to explain the occurrence and structure of lithium imide hexamers can be applied more widely to Li-C, Li-N and Li O rings and... 

A quite different structural motif is found in the curious cyclic hexamer [(BNMc2)6] which can be obtained as orange-red crystals by distilling the initial product formed by dehalogenation of (Me2N)2BCl with Na/K alloy ( >... 

These results, together with infrared and electron diffraction studies, indicate that gaseous HF comprises an equilibrium mixture of monomers and cyclic hexamers, though chain dimers may also occur under some conditions of temperature and pressure ... 

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