C„ axis of symmetry

A C point group contains a C axis of symmetry and n a planes of symmetry, all of which contain the C axis. It also contains other elements which may be generated from these. 

The z axis is a twofold proper axis of symmetry, designated C2. A molecule possesses a C axis of symmetry if the operation of rotation by... 

Cone-Roof Tanks. Cone-roof tanks are cylindrical shells having a vertical axis of symmetry. The bottom is usually flat and the top made ia the form of a shallow cone. These are the most widely used tanks for storage of relatively large quantities of fluid because they are economic to build and the market supports a number of contractors capable of building them. They can be shop-fabricated ia small sizes but are most often field-erected. Cone-roof tanks typically have roof rafters and support columns except ia very small-diameter tanks when they are self-supporting (see Fig. 4b and c Table 3). 

The carbides of the lanthanoids and actinoids can be prepared by heating M2O3 with C in an electric furnace or by arc-melting compressed pellets of the elements in an inert atmosphere. They contain the C2 unit and have a stoichiometry MC2 or M4(C2)3. MC2 have the CaC2 structure or a related one of lower symmetry in which the C2 units lie at right-angles to the c-axis of an orthogonal NaCl-type cell. They are more reactive than the alkaline-earth metal... 

SnMe4 Snl4-like structure. Tetrahedral molecule with 3-fold axis of symmetry along a slightly shorter Sn—C bond. The different Sn—C bond lengths are in accord with NMR, INS and Mossbauer data (see Table 2). 131, 204... 

Figure 4. Plot of the full-field solution for the normalized hydrostatic stress

Fig. 3.3. Structure of MPT synthase. (A) Overall structure of the heterotetramer. MoaD subunits are shown in yellow, MoaE subunits in cyan and magenta. The view is along the two-fold axis of symmetry. N- and C-termini and residues adjacent to a disordered loop...

Other molecules in which the presence of a C2 axis of symmetry also simplifies the syntheses are squalene (5) rmd P-carotene (6). Notice that in such cases the simplification derives from the fact that the syntheses are convergent and reflexive i.e., syntheses which start from identical precursors [5]. In practice, the synthesis of these two substances may be carried out not only by dimerisation of two identical moieties [10] [11] -which may lead to a mixture of isomers-, but preferentially by addition of two identical fragments to a central bifunctional unit according to the scheme -1- + C. = Cjj (squalene Cji -t-Cg + Cj] = 30 [12] p-carotene ... 

Fig. 2.17 Schematic representation of the structure of the zeolite natrolite [Na2Al2Si30io 2H2OI. (A) The (Si04, AIO4) chains, viewed parallel to c (along the chain length) and down c. The striped tetrahedra are AIO4. (B) The structure of natrolite and dehydrated natrolite. Solid circles are Na" , open circles are H2O, = axis of symmetry a/2 and b/2 indicate vector direction in the crystal structures. Note the rotation of tetrahedra and shift of the Na" positions in the dehydrated structure. Dehydration changes the configuration of the open areas between chains.

The C2-symmetric ansa metallocenes possess a C2 axis of symmetry, are chiral, and their two active sites are both chiral. The two sites are equivalent (homotopic) and enantioselective for the same monomer enantioface. The result is isoselective polymerization. C2 ansa metallocenes are one of two classes of initiators that produce highly isotactic polymer, the other class being the C ansa metallocenes (Sec. 8-5e). C2 ansa metallocenes generally produce the most isoselective polymerizations. 

---