Conformations and optical rotatory properties of poly‐ O ‐acetylthreonine and poly‐ O ‐acetylallothreonine

Optically active poly‐ O ‐acetylthreonine and poly‐ O ‐acetyl‐allothreonine exist in the β form in pyridine, in 2‐chloruethanol–dichloromethane mixed solvent., and in the solid state. The optical rotatory dispersion of the β form of poly‐ O ‐acetyl‐ L ‐threonine in a 2‐ehloroethanol–dichlomethane mixture showed a Cotton effect in the 230 mμ region. The ORD data in the visible spectral region fit, the Moffitt. equation. The absolute values of b 0 , as measured in pyridine for polypeptides with a molecular weight above 17000, varied in the range 100–200°, the sign depending on the absolute configuration of the side chain.