Conformational properties of structurally rigid polyamides. II. Effect of strong acids on the circular dichroism spectra of asymmetric polyamides with varying degree of structural rigidity

We have investigated the effect of methanesulfonic acid (MSA) on the circular dichroism (CD) spectra of some stereoregular polyamides derived from three cyclic 1,2‐dicarboxylic acids (I–III) and piperazine (PIP), trans‐2,5‐dimethylpiperazine (DMPIP), or N,N′‐dimethylethylenediamine (DMED). On the basis of a detailed knowledge of the conformational properties of these polymers, we have attempted an essentially empirical interpretation of the CD spectra and of their relative changes. A striking dependence of the optical properties from the conformational properties and/or transitions in the polymers has been found. Although far from suggesting a 1:1 correspondence between CD spectra and conformational changes, we wish to stress their general correspondence.