## 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 @C01258@ may differ in @C01058@ and/or orientation. Chains of identical @C01058@ and @C01258@ are isomorphous. Chains of opposite @C01058@ but equivalent @C01258@ 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 @P04472@ originating at atom $$A_{1}^{i}$$, the first atom of the @P04472@ 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]