Optical rotation of petroleums

Abstract

Abstract Although oils and oil distillates are usually dextrorotatory, some levorotations can be measured in lower boiling distillates. Fractional distillation of a Colombia crude oil of Eocene age showed that optical rotation is maximal at an average molecular weight of 464. The rotatory power of petroleum reflects the extent to which its composition has been transformed during geochemical maturation. Optical rotations thus can be correlated with the degree of maturity in much the same way as can such other compositional features as aromatic character or content of steroid‐like substances, which are demonstrable in petroleums. The optical activity of petroleum is gradually degraded by maturational influences, and a decreasing trend in rotatory power is recognized in a comparison of oils produced from rocks of progressively greater geologic age. The optical rotation of dark crude oils can be measured in a polarimeter of suitable photometric sensitivity. The measurements extend geochemical application of oil polarimetry, which was restricted formerly to oil distillates and decolorized oils.