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.
Highlights
Xylene is an aromatic compound that has methyl groups substituted on benzene ring
Xylene is found to be predominant in the carbonization of coal producing coke fuel. It is the major precursor in terephthalic acid and dimethyl terephthalate which are being utilized in polyethylene terephthalate (PET) production and related derivatives of which p-xylene is the building block of PET. [4, 5] Scientific studies on p-xylene have been reported by many researchers
We observed an interesting trend in chemical reactivity and stability of the studied compounds 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
Summary
Xylene is an aromatic compound that has methyl groups substituted on benzene ring. Depending on the positions of methyl groups in the benzene ring, xylene could be classified into ortho xylene (o-xylene), meta xylene (m-xylene) and para xylene (p-xylene) [1, 2, 3]. M. studied chemical properties and anticancer activity of tetra bromo-p-xylene [6]. They have been no report on in silico study on halogen effect of. P-xylene in terms of quantum chemical descriptors, natural bond orbital (NBO) and spectroscopic study using DFT. We are inquisitive to know how halogen affect p-xylene, we looked at quantum chemical descriptors, NBO and spectroscopic properties of p-xylene as well as 3,6-di-(flouro, chloro and bromo) p-xylene. The DFT method using the hybrid exchange correlation functional B3LYP have been employed in this research due to its effectiveness and accuracy in the investigation of conjugated systems or lone pair containing species and vast application in various researches reported in literature
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