Electron affinity and redox potential of tetrafluoro-p-benzoquinone: A theoretical study Mansoor Namazian a, * , Samira Siahrostami b,1 , Michelle L. Coote a, * a ARC Centre of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia b Department of Chemistry, Yazd University, P.O. Box 89195-741, Yazd, Iran Received 25 October 2007; received in revised form 15 November 2007; accepted 19 November 2007 Available online 23 November 2007 Abstract The electron affinity of tetrafluoro-p-benzoquinone (2.69 eV) and the mono- (2.10 eV), 2,3-di- (2.29 eV), 2,5-di- (2.28 eV), 2,6-di- (2.31 eV) and tri- (2.48 eV) fluoro derivatives of p-benzoquinone have been calculated via standard ab initio molecular orbital theory at the G3(MP2)-RAD level of theory. Comparison of calculated electron affinities with the available experimental values shows excellent agreement between theory and experiment. The reduction potential of tetrafluoro-p-benzoquinone in acetonitrile vs. SCE (0.03 V) has been calculated at the same level of theory and employing a continuum model of solvation (CPCM), and is also in excellent agreement with the experimental value (0.04 V vs. SCE). # 2007 Elsevier B.V. All rights reserved. Keywords: G3(MP2)-RAD; Tetrafluoro-p-benzoquinone; CPCM; Reduction potential 1. Introduction Tetrafluoro-p-benzoquinone (TFBQ), which has many applications in chemical synthesis, has aroused much interest [1–5]. Comparing with p-benzoquinone (BQ), the four fluorine substituents make a substantial difference to its behaviour. In particular, the fluorine atoms in TFBQ render the unsaturated carbon atoms carrying them more electropositive than usual; hence TFBQ is much easier to reduce than BQ, both in both the gas and solution phases. A difference of as much as 500 mV in the reduction potential of TFBQ compared to BQ in the non-aqueous solution of acetonitrile has been reported experimentally [6]. A significant difference has also been observed in electron affinities of TFBQ and BQ in the gas phase [7,8]. The accurate calculation of electron affinities and redox potentials is important both in chemistry and biochemistry and plays an important role in explaining the nature of electron- transfer reactions. Recently, we proposed an accurate method for the calculation of the one-electron reduction potentials in non-aqueous solution in which high-level composite methods for the gas-phase energies are combined with a continuum model of solvation. When assessed for a set of thirteen p- quinones (including the substituents CH 3 , NH 2 , Cl and CN) in the non-aqueous solution of acetonitrile, the mean absolute deviation of calculated reduction potential from the experiment was just 0.07 V [9]. However, since modelling of fluorine- substituted compounds can sometimes be problematic [10], it is of interest to determine whether the same level of accuracy can be achieved for the study of TFBQ. In the present work, we describe the theoretical calculation of the electron affinity and redox potential of tetrafluoro-p- benzoquinone in acetonitrile using a reliable high-level composite method of ab initio calculations as well as a continuum model of solvation. Comparing the theoretical values with available experimental data, we demonstrate excellent agreement between theory and experiment. We also study the effect of fluorine substitution on the electron affinity for various mono-, di- and trisubstituted derivatives of p-benzoquinone. www.elsevier.com/locate/fluor Available online at www.sciencedirect.com Journal of Fluorine Chemistry 129 (2008) 222–225 * Corresponding authors. E-mail addresses: namazian@rsc.anu.edu.au (M. Namazian), mcoote@rsc.anu.edu.au (M.L. Coote). 1 Present address: Shiraz University, Shiraz, Iran. 0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2007.11.007