Zigzags, planar

The repeat distance along the chain axis (0.468 nm) is significantly less than that calculated for a planar zigzag stmcture. Therefore, the polymer must be in some other conformation (65—67). Based on k and Raman studies of PVDC single crystals and normal vibration analysis, the best conformation appears to be where the skeletal angle, is 120°, and the torsional of opposite sign) is 32.5°. This conformation is in... 

The conformation adopted by a molecule in the crystalline structure will also affect the density. Whereas polyethylene adopts a planar zigzag conformation, because of steric factors a polypropylene molecule adopts a helical conformation in the crystalline zone. This requires somewhat more space and isotactic polypropylene has a lower density than polyethylene. 

M(0H)2SOi, H2O where M=Zr (8), Hf (12) also have been determined and reveal the presence of almost planar zigzag chains of metal atoms joined by double hydroxide bridges. The single exception to this trend toward formation of double hydroxy-bridged metal dimers or chains is the compound which is best described as CeOSOif,H20 (17). However, even in this structure the cerium ions form chains which are linked by bridging oxide ions. 

Like the polymethylene hydrocarbons, acyclic carbohydrates and alditols tend to adopt the planar, zigzag conformation wherein all of the carbon atoms lie in the same plane. " However, non-bonded interactions between parallel hydroxyl groups in the 1,3 positions (sy/i-axial interaction) are the most highly destabilizing, and, in xylitol and ribitol, this... 

Among the hexitols, n.m.r. and X-ray crystallographic data " showed that galactitol and D-mannitol exist as planar zigzag conformers. Solutions of the others contain appreciable proportions of sickle and other bent carbon-carbon chain conformers. The low sweetness of the hexitols could possibly be due to increased hydrogen-bonding due to increased chain-length. 

If the chain is fully extended so that all of the chain atoms lie in a plane (planar zigzag form) as in formula X... 

Fig. 81.—Potential energy associated with bond rotation as a function of angle, (a) Symmetrical potential according to Eq. (23) (b) and (c) potential energy functions with lowest minimum at 0=0 corresponding to the planar zigzag form of a polymethylene chain. These curves were calculated by Taylor. 0...

P2X Z = 2 Dx = 1.59 R = 0.11 for 881 intensities. The acyclic molecule has the planar, zigzag conformation. The terminal OH and N-OH groups are +syn and ap, respectively. There is an interesting system of O-H N hydrogen-bonds which forms a spiral along the screw-axis. Only seven of the hydrogen atoms were located. 

According to conformational energy calculations, the POx chain can assume conformations other than planar zigzag, such as T3G and T2G2, and, according X-ray and IR studies, these two conformations are stable. The POx assuming them is thicker than the planar zigzag one, so that it may be included in / -CD as well as a-CD. 

The complex formation of a-CD with POx was found to obey the same stoichiometry as that for PEG. In fact, the X-ray powder pattern of the complex does not differ from that of the a-CD-PEG complex. Fig. 17(a) illustrates the POx chain in the complex with a-CD when its conformation is planar zigzag, and Fig. 17(b) sketches the POx chain in the / -CD cavity where it favors the T3G conformation thanks to the wider cavity of this CD. 

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