Glide operation

The glide operations are indicated by a,c, or n, depending on the direction of the translation component. 

The stereocenters in all three stereoregular polymers are achirotopic. The polymers are achiral and do not possess optical activity. The diisotactic polymers contain mirror planes perpendicular to the polymer chain axis. The disyndiotactic polymer has a mirror glide plane of symmetry. The latter refers to superposition of the disyndiotactic structure with its mirror image after one performs a glide operation. A glide operation involves movement of one structure relative to the other by sliding one polymer chain axis parallel to the other chain axis. 

This table is essentially self-explanatory. Each plane that is perpendicular to the page is shown by a line drawn where it intersects the page. The type of line shows the type of plane. When the plane is in or parallel to the page it is shown by a pair of lines, without arrowheads for a simple mirror and with one or more arrowheads (or an additional arrow ) to indicate the direction of a glide operation. To show the height of a plane above the base of the cell, its fractional distance will be given. 

The projections shown are on the at plane. The screw axes are seen running parallel to the b axis, and it is indicated that they lie at z = J. The c-glide planes, which are perpendicular to the diagram, are represented by dotted lines at b = i and. As a consequence of the presence of these defining symmetry elements there is also a set of inversion centers, as also shown. Those shown in the ab plane are, of course replicated in the plane at z = % by the screw and glide operations. 

Y screw or glide operations do give H.Jone pair overlap lor relatively thin substituents... 

Figure 8.55 Ways of packing monoalcohols with variable thickness of substituent (a) thin substituents pack by translation or by 2, screw or glide operations, (b) with thicker substituents rings are favoured, (c) thicker substituents may also pack with more than one molecule in the asymmetric unit and (d) very thick substituents result in packing about higher order screw or improper rotation axes.84...

New research (Mumme, private communication) may have expanded the family of category (iii), cannizzarite-related, Pb-Bi(-Cu) sulphosalts (Table 7). Another member, wittite, is a disordered structure probably closely related to cannizzarite. The others are CC structures, apparently composed of either cannizzarite-like portions displaced by glide operations perpendicular to the layers (weibullite), or of periodically-stepped layers of the junoite type (nordstrdmite). 

Glide Operation that is a product of a mirror and a translation that is a fraction of the lattice vector in the plane of the mirror. There are axial glides, double glides, diagonal glides, and diamond glides. 

Figure 3.9 The glide operation (a) reflection across a mirror line (b) translation parallel to the mirror plane by a vector t, which is constrained to be equal to T/2, where T is the lattice repeat vector parallel to the glide line. The lattice unit cell is shaded...

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