Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


osu1204653142.pdf (1024 KB)

ETD Abstract Container

Abstract Header

Reactions of Hydroperoxyl Radical with Benzene Derivatives: A DFT Study

Karalti, Ozan
http://rave.ohiolink.edu/etdc/view?acc_num=osu1204653142

Abstract Details

2008, Master of Science, Ohio State University, Chemistry.
The focus of this thesis is to improve our understanding of radical reactions which are important to combustion, atmospheric and biological chemistry. To achieve this purpose, the reactions for hydroperoxyl radical-addition and hydrogen-atom abstraction with benzene derivatives in both the gaseous and condensed phases were studied. The reactions of hydroperoxyl radical with benzene derivatives were investigated at the B3LYP/6-311+G(d,p)//B3LYP/6-31+G(d,p) and MPW1K/6-31+G(d,p) levels of theory. Calculations showed that the radical-addition pathway is the dominant pathway for the reaction of hydroperoxyl radical with benzene in terms of both the free energy of activation barrier and the reaction enthalpy at 298 K. The free energy of activation barrier for hydroperoxyl radical-addition and hydrogen-atom abstraction reactions are 27.0 (28.6) and 31.9 (35.6) kcal/mol, respectively, at the B3LYP (MPW1K) levels of theory. However, above 1000 K, the hydrogen-atom abstraction pathway becomes the dominant pathway which is important in combustion processes. Upon going from the pre-reactant complex to the transition state, the hydroperoxyl radical moiety becomes more anionic, and concomitantly, the benzene ring becomes more like the corresponding radical cation. Thus, charge transfer appears to be important in terms of stabilization of the transition states. For substituted benzene derivatives, a lowering of the activation barriers is observed upon going from electron-withdrawing to electron-donating groups. These observations are consistent with the view of hydroperoxyl radical being electrophilic when reacting with electron-rich aromatic rings. With a contribution from extra hydrogen bonding, ortho substituted benzenes are found to have the most stable transition states compared to the para and meta-substituted cases. The activation barriers for hydroperoxyl radical-addition to benzene derivatives gave a good correlation with the charge separation between the ring and radical moieties in the transition state and with the structure/reactivity parameter (IP-EA). Comparison of the transition states for the reactions of hydroperoxyl radical, methylperoxyl radical and trifluoromethylperoxyl radical-addition to benzene showed that as you stabilize the developing negative charge on the radical at the transition state, one can lower the activation barrier of the reaction. PCM calculations show that the dielectric field alone does not predict a difference in the activation barrier for two solvents (water and acetonitrile). In the case of one explicit solvent molecule coordinated to the transition state, acetonitrile, acting as a hydrogen-bond acceptor, provides a more stable transition state as compared to all others both for the addition and abstraction reactions. By using one explicit solvent molecule, these results suggest that the hydroperoxyl radical addition in acetonitrile will be 10 times faster than in water. However, the ordering is changed upon including more solvent molecules due to acetonitrile being a poor hydrogen-bond donor whereas water can act both as a good hydrogen-bond acceptor and donor. In the presence of two explicit solvent molecules, the calculations suggest that the hydroperoxyl radical's reaction will be 20 times faster in water than in acetonitrile. As in the gas phase, in the transition states, more of the spin density is transferred to the benzene unit, and the benzene ring resembles the radical cation. Simultaneously, the hydroperoxyl radical unit becomes negatively charged.
Christopher Hadad (Advisor)
James Coe (Committee Member)
Chemistry
hydroperoxyl radical; benzene; dft

Recommended Citations

Citations

  • Karalti, O. (2008). Reactions of Hydroperoxyl Radical with Benzene Derivatives: A DFT Study [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204653142

    APA Style (7th edition)

  • Karalti, Ozan. Reactions of Hydroperoxyl Radical with Benzene Derivatives: A DFT Study. 2008. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1204653142.

    MLA Style (8th edition)

  • Karalti, Ozan. "Reactions of Hydroperoxyl Radical with Benzene Derivatives: A DFT Study." Master's thesis, Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204653142

    Chicago Manual of Style (17th edition)

osu1204653142
648
© 2008, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.