Polarized Raman and Infrared Spectroscopy and ab Initio Calculation of Palmitic and Stearic Acids in the Bm and C Forms

L F L da Silva; T Andrade-Filho; P T C Freire; J Mendes Filho; J G da Silva Filho; G D Saraiva; S G C Moreira; F F de Sousa

doi:10.1021/acs.jpca.7b04117

Polarized Raman and Infrared Spectroscopy and ab Initio Calculation of Palmitic and Stearic Acids in the B_m and C Forms

J Phys Chem A. 2017 Jun 29;121(25):4830-4842. doi: 10.1021/acs.jpca.7b04117. Epub 2017 Jun 15.

Authors

L F L da Silva¹, T Andrade-Filho², P T C Freire³, J Mendes Filho³, J G da Silva Filho³, G D Saraiva⁴, S G C Moreira¹, F F de Sousa²

Affiliations

¹ Faculdade de Física, Universidade Federal do Pará , CEP 66075-110, Belém, PA, Brazil.
² Instituto de Ciências Exatas, Universidade Federal do Sul e Sudeste do Pará , CEP 68505-080, Marabá, PA, Brazil.
³ Departamento de Física, Universidade Federal do Ceará , CEP 60455-970, Fortaleza, CE, Brazil.
⁴ Faculdade de Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará , CEP 63900-000, Quixadá, CE, Brazil.

PMID: 28585821
DOI: 10.1021/acs.jpca.7b04117

Abstract

A complete experimental study on the vibrational properties of palmitic and stearic acids crystallized in the B_m and C forms, both belonging to the monoclinic system with the P2₁/a (C_2h⁵) space group, through polarized Raman and infrared spectroscopy, is reported in this paper. Density functional theory calculations were also performed to assign the normal modes and to help in the interpretation of the experimental data. The different polarizations were compared and their influence on the spectral profiles, in both the lattice and the internal mode regions, was discussed. In general, the Raman and infrared spectra exhibit accentuated differences among the polymorphic forms, which are associated with the different molecular modifications, defined as gauche and all-trans conformations. Insights about interaction among different groups are also furnished.