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Hydrogen Abstractions from Arylmethanes

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Hydrogen Abstractions from Arylmethanes AN ABSTRACT OF THE THESIS OF JERRY DEAN UNRUH for the DOCTOR OF PHILOSOPHY (Name) (Degree) in ORGANIC CHEMISTRY presented on ttr:e-( /9 2 O (Major) Title: HYDROGEN ABSTP ArTTnNs FROM ARV! ,TviWTHANES Redacted for Privacy Abstract approved: Dr. 'Gerald Jay Gleicher The relative rates of hydrogen abstraction from a series of 13 arylmethanes by the trichloromethyl radical were determined at 700. The attacking radical was generated from bromotrichloromethane us ing benzoyl peroxide as the initiator.The solvent was benzene- bromotrichloromethane. An excellent correlation, with a coefficient of 0.977, was obtained when the logs of the relative rates of hydrogen abstraction were plotted against the change in pi-binding energy be- tween the incipient radicals and the arylmethanes, if the pi-binding energy were calculated by the SCF approach. When the logs of the kinetic data were correlated with the change in pi-binding energy as calculated by the HMO approach, the correlation was poor, with a co- efficient of 0.855. A possible explanation for this difference might be the HZIckel method's complete neglect of electron interactions. The kinetic data were also plotted against the values of a param- eter,Z1E-3,which are indicative of the ground state electronic environment of the methyl group. A correlation was essentially non- existent.This, coupled with the excellent correlation with the changes in pi-binding energies, indicates that the transition state for hydrogen abstraction by the trichloromethyl radical must certainly lie near the intermediate radical with carbon-hydrogen bond breaking well advanced. The relative rates of hydrogen abstraction from a series of nine arylmethanes by the t-butoxy radical were also determined at 70o. t-Butoxy radical was generated from t-butyl hypochlorite using benzoyl peroxide as the initiator.The solvent was benzene. Best agreement was obtained when the data was correlated with a four parameter equation which included both the change in pi-binding ener- gy and E IR3.This is tentatively taken to mean that the transition state is at a point intermediate between the reactants and the inter- mediate radicals. Hydrogen Abstractions from Arylmethanes by Jerry Dean Unruh A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1971 APPROVED: Redacted for Privacy Associate Professor of Organic Chemistry in charge of major Redacted for Privacy Chairman of Chemistryiiepartment Redacted for Privacy Dean of Graduate School Date thesis is presented aelI 3, /97d Typed by Donna L. Olson for Jerry Dean Unruh TABLE OF CONTENTS Page INTRODUCTION 1 Free Radical Hydrogen Abstraction 1 Molecular Orbital Correlations of Reactivity 21 DISCUSSION OF THE PROBLEM 23 RESULTS 30 Synthesis of Unsubstituted Arylmethanes 30 Products of the Reaction of 1 - Methylnaphthalene and Bromotrichloromethane with Light Initiation 30 Products of the Reaction of 9-Methylanthracene and Bromotrichloromethane with Light Initiation 31 Products of the Reaction of 1 - Methylnaphthalene and Bromotrichloromethane; Benzoyl Peroxide Initiation 31 Reaction of. Chloroform with Benzoyl Peroxide 32 Reaction of Anthracene and 9-Methylanthracene with Sulfuryl Chloride 32 Products of the Reaction of 9-Methylanthracene and t-butyl Hypochlorite; Benzoyl Peroxide Initiation 33 Reaction of 1-Methylpyrene with t-Butyl Hypochlorite 33 Products of the Reaction of 1 -Methylnaphthalene and t-Butyl Hypochlorite; Benzoyl Peroxide Initiation 34 Products of the Reaction of 6-Methylchrysene and t- Butyl Hypochlorite; Benzoyl Peroxide Initiation 34 Reaction of 9, 10- Dimethylanthracene with t-Butyl Hypochlorite 35 Relative Rates of Hydrogen Abstraction from a Series of Arylmethanes by Trichloromethyl Radical; Peroxide Initiation 35 Relative Rates of Hydrogen Abstraction from a Series of Arylmethanes by t-Butoxy Radical; Peroxide Initiation 36 DISCUSSION 40 Kinetic Studies Using Trichloromethyl Radical 40 Kinetic Studies Using t-Butoxy Radical 55 Page EXPERIMENTAL 61 Procedures 61 Purification of Reagents 61 Purificationof o-Dichlorobenzene 61 Purificationof Bromotrichloromethane 62 Purificationof Benzene 62 Purificationof Benzoyl Peroxide 62 Purificationof Trichloroethylene 62 Purificationof Sulfuryl Chloride 62 Purificationof Toluene 62 Purificationof 1 -Methylnaphthalene 63 Pur ificationof 2 -Methylnaphthalene 63 Purificationof 9 -Methylanthrac ene 63 Purificationof Naphthalene 63 Purificationof Anthracene 63 Purificationof Phenanthrene 63 Purificationof Pyrene 63 Purificationof Chrysene 64 Purificationof Triphenylene 64 Preparation of Compounds 64 Preparationof 2 -Methylanthracene 64 Preparationof 1-Methylanthracene 64 Preparationof 1 - Methylphenanthrene 65 Preparationof 3 -Methylphenanthrene 66 Preparationof 1-Methylpyrene 67 Preparationof 9 -Methylphenanthr ene 68 Preparationof 6 -Methylchrys ene 68 Preparationof 1 - Methyltriphenylene 69 Preparationof 2 -Methyltriphenylene 70 Preparationof t-Butyl Hypochlorite 71 Preparationof 7, 10-Dimethylanthracene 71 Product Studies 72 Procedure for the Product Study of the Reaction of 1-Methylnaphthalene and Bromotrichloro- methane; Light Initiation 72 Procedure for the Product Study of the Reaction of 9 -Methylanthracene and Bromotrichloro- methane; Light Initiation. 73 Procedure for the Product Study of the Reaction of 1-Methylnaphthalene and Bromotrichloro- methane; Benzoyl Peroxide Initiation. 74 Page Procedure for the Product Study of the Reaction of 9-Methylanthracene and t-Butyl Hypo- chlorite; Benzoyl Peroxide Initiation 75 Procedure for the Product Study of the Reaction of 1 - Methylnaphthalene and t-Butyl Hypo- chlorite; Benzoyl Peroxide Initiation 76 Procedure for the Product Study of the Reaction of 6-Methylchrysene and t-Butyl Hypochlorite; Benzoyl Peroxide Initiation 77 Determination of Relative Rates of Hydrogen Abstraction 78 Procedure for the Determination of the Relative Rates of Hydrogen Abstraction by Bromotri- chloromethane 78 Procedure for the Determination of the Relative Rates of Hydrogen Abstraction by t-Butyl Hypochlorite 80 BIBLIOGRAPHY 82 APPENDIX I.KINETIC STUDIES USING BROMOTRICHLORO- METHANE; BENZOYL PEROXIDE INITIATION 89 APPENDIX II. KINETIC STUDIES USING t-BUTYL HYPO- CHLORITE; BENZOYL PEROXIDE INITIATION 117 LIST OF FIGURES Figure Page 1. Potential energy diagram for a three body reaction. 2 2. General cases of the Hammond Postulate. 5 3. Transition state for hydrogen abstraction by an electrophilic radical. 7 4. The peri-hydrogen non-bonded interaction. 24 5. Relative rates of hydrogen abstraction from a series of arylmethanes by the trichloromethyl radical correlated with HMO calculations. 46 6. Relative rates of hydrogen abstraction from a series of arylmethanes by the trichloromethyl radical correlated with SCF calculations. 47 7. Occupied orbitals of the allyl radical. 48 8. (kX/1(0)cal vs. (kx/Ic._u )expfor hydrogen ab- straction tf8utoxy radical. 59 LIST OF TABLES Table Page 1. Relative rates of hydrogen abstraction from a series of arylmethanes by trichloromethyl radical at 70o; benzoyl peroxide initiated. 37 2. Relative rates of hydrogen abstraction from a series of arylmethanes by trichloromethyl radical at 70°; light initiated. 38 3. Relative rates of hydrogen abstraction from a series of arylmethanes by t-butoxy radical at 70°; benzoyl peroxide initiated. 39 4. Relative pi-binding energy differences between a series of arylmethyl radicals and the correspond- ing arylmethanes. 44 5. Ring current intensities of several aromatic hydrocarbons. 53 6. Relative values of E IR3for the methyl protons of a series of arylmethanes. 54 7. Summary of the results of the kinetic studies using t-butyl hypochlorite. 57 8. Reaction of chloroform with benzoyl peroxide. 89 9. Relative rates of disappearance of 1 - methyl- naphthalene to naphthalene. 90 10. Relative rates of disappearance of 2-methyl- naphthalene to naphthalene. 91 11. Relative rates of disappearance of 1-methyl- phenanthrene to phenanthrene 92 12. Relative rates of disappearance of 3-methyl- phenanthrene to phenanthrene. 93 Table Page 13. Relative rates of disappearance of 9-methyl- phenanthrene to phenanthrene. 94 14. Relative rates of disappearance of 1-methyl- anthracene to anthracene. 95 15. Relative rates of disappearance of 2-methyl- anthracene to anthracene. 96 16. Relative rates of disappearance of 9-methyl- anthracene to anthracene. 98 17. Relative rates of disappearance of 1-methyl- pyrene to pyrene. 99 18. Relative rates of disappearance of 6-methyl- chrysene to chrysene. 100 19. Relative rates of disappearance of 1-methyl- triphenylene to triphenylene. 101 20. Relative rates of disappearance of 2-methyl- triphenylene to triphenylene. 102 21. Relative rates of disappearance of toluene to 1-methylnaphthalene. 103 22. Relative rates of disappearance of 2-methyl- naphthalene to toluene. 104 23. Relative rates of disappearance of 1-methyl- phenanthrene to 1 - methylnaphthalene. 105 24. Relative rates of disappearance of 3-methyl- phenanthrene to 1 - methylnaphthalene. 106 25. Relative rates of disappearance of 9-methyl- phenanthrene to 1 - methylnaphthalene. 107 26. Relative rates of disappearance of 1-methyl- pyrene to 1 - methylnaphthalene. 108 Table Page 27. Relative rates of disappearance of 1-methyl- anthracene to 1 - methylnaphthalene. 109 28. Relative rates of disappearance of 2-methyl- anthracene to 1 - methylnaphthalene. 110 29. Relative rates of disappearance of 9-methyl- anthracene to 1 - methylpyrene. 112 30. Relative rates of disappearance
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