Vibrational, electronic, spectroscopic properties, and NBO analysis of p-xylene, 3,6-difluoro-p-xylene, 3,6-dichloro-p-xylene and 3,6-dibromo-pxylene: DFT study

Emmanuel A Bisong; Hitler Louis; Tomsmith O Unimuke; Joseph O Odey; Emmanuel I Ubana; Moses M Edim; Fidelis Timothy Tizhe; John A Agwupuye; Patrick M Utsu

doi:10.1016/j.heliyon.2020.e05783

Vibrational, electronic, spectroscopic properties, and NBO analysis of p-xylene, 3,6-difluoro-p-xylene, 3,6-dichloro-p-xylene and 3,6-dibromo-pxylene: DFT study

Heliyon. 2020 Dec 23;6(12):e05783. doi: 10.1016/j.heliyon.2020.e05783. eCollection 2020 Dec.

Authors

Affiliations

¹ Department of Pure and Applied Chemistry, Faculty of Physical Sciences, University of Calabar, Calabar, Cross River State, Nigeria.
² Computational Quantum Chemistry Research Group, Department of Pure and Applied Chemistry, Faculty of Physical Sciences, University of Calabar, Calabar, Cross River State, Nigeria.
³ Department of Textile and Polymer Engineering, Ahmadu Bello University, Zaria, Nigeria.
⁴ Department of Chemistry, Cross River University of Technology, Calabar, Calabar, Cross River State, Nigeria.
⁵ Institute of Chemistry, Chinese Academy of Sciences, 10900 Beijing, China.

Abstract

This study explains the vibration and interaction of p-xylene and effect of three elements (fluorine, chlorine and bromine) of the halogen family substitution on it. Basic chemistry of four, compounds p-xylene (PX); 3,6-diflouro-p-xylene (DFPX); 3,6-dichloro-p-xylene (DCPX) and 3,6-dibromo-p-xylene (DBPX) has been explained extensively using theoretical approach. Vibrational energy distribution analysis (VEDA) software was used to study the potential energy distribution (PED) analysis, bond length, bond angles and dihedral angles of PX, DFPX, DCPX, DBPX after optimization with GAUSSIAN 09 software. The trend in chemical reactivity and stability of the studied compounds was observed to show increasing stability and decreasing reactivity moving from DBPX, DCPX, DFPX to PX and this was obtained from the calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) values. Our results show that PX is the best electron donor (best nucleophile) while DBPX is the best electron acceptor (the best electrophile). We also observed that the substituted halogen increases the value of the bond angles but the effect is reduced as the size of the halogen increases. The maximum intensity and the frequency value for the maximum intensity of the different compounds was determined using the VEDA 04 software. From our natural bond orbital (NBO) 7.0 program analysis, the studied compounds are said to show biological activities as well as the intramolecular hyperconjugative interactions responsible for stabilizing the compounds. The NBO results also revealed that the non-bonding interaction existing between the lone pair electron on the halogen atoms and the aromatic ring increases the stability of the halogen substituted para-xylene molecules. Multiwfn: A Multifunctional Wavefunction Analyzer was used for the spectroscopic plots.

Keywords: DBPX; DCPX; DFPX; DFT; Frequency; NBO; PX; Spectroscopy.