isomorphous structures

in polymers
Also contains definition of: enantiomorphous structures in polymers
https://doi.org/10.1351/goldbook.I03299
In the crystalline state, polymer chains are generally parallel to one another but neighbouring chains of equivalent @[email protected] may differ in @[email protected] and/or orientation. Chains of identical @[email protected] and @[email protected] are isomorphous. Chains of opposite @[email protected] but equivalent @[email protected] are enantiomorphous. For example, two ...TG+TG+TG+... helices of isotactic poly(propylene) are isomorphous. Isotactic poly(propylene) chains of the ...TG+TG+TG+... and ...GTGTGT... types are mutually enantiomorphous. With regard to orientation, consider a repeating @[email protected] originating at atom \(A_{1}^{i}\), the first atom of the @[email protected] being \(B_{\alpha }^{i}\). For certain chain symmetries (helical, for instance) the bond vectors \(\overset{\rightarrow }{\mathbf{b}}(A_{1}^{i},B_{\alpha }^{i})\) have the same components (positive or negative) \(\frac{\overset{\rightarrow }{\mathbf{b}}\cdot \overset{\rightarrow }{\mathbf{c}}}{|\overset{\rightarrow }{\mathbf{c}}|}\) along the c axis for every \(i\).
I03299.png
Two equivalent (isomorphous or enantiomorphous) chains in the crystal lattice, having identical components of the bond vectors along c, both positive or both negative, are designated isoclined; two equivalent chains having bond vectors along c of the same magnitude but opposite sign are designated anticlined.
Source:
Purple Book, 1st ed., p. 43 [Terms] [Book]