Vibrational properties of diterpene rel-(1S, 4aS, 7S,8aS)-7-(vinyl)-tetradecahydro-1,4a-dimethylphenanthrene-7,8a-carbolactone-1-carboxylic acid studied by Raman and infrared spectroscopy together with ab initio calculations

In this work results on vibrational properties of an organic substance that is used in popular medicine, the diterpene kaurane rel-(1S, 4aS, 7S,8aS)-7-(vinyl)-tetradecahydro-1,4a-dimethylphenanthrene-7,8a-carbolactone-1-carboxylic acid (C20H28O4), extracted from Croton argyrophylloides, is presented. This plant is considered endemic in the Northeast of Brazil, and the diterpene is only one among several substances with potential pharmaceutical application. Fourier Transform Raman spectroscopy and Fourier Transform infrared spectroscopy were utilized in order to obtain the vibrational normal modes of the substance. Additionally, ab initio calculations by density functional theory with the B3LYP functional and calculations of potential energy distribution, performed to assign the bands observed by both spectroscopies, are shown. Finally, studies performed with Raman spectroscopy at low temperatures between 20 and 300 K, in order to investigate evidence of a possible phase transition, are presented.