Developing a S ystem to Study the Dynamics of the Heterolysis of PSubstituted Radicals in terms of Magnetic Field Effects by Elaine K. Adams Submitted in partial fulfiiIlment of the requirements for the degree of Master of Science Dalhousie University Halifax, Nova Scotia September, 1998 @ Copyright by Elaine K. Adams, 1998 National hirary Bibliothèque nationale du Canada Acquisitions and Acquisiins et Biliograpfii Services seMces bibliographiques The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seli reproduire, prêter, distriiuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de micro fi ch el^ de reproduction sur papier ou sur fonnat électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la thése ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Table of Contents List of Figures ........................................................................................ vi ... List of Tables ........................................................................................ xm 1.1 General Introduction ........................................................................ -1 1.2 Introduction to the Radical Pair Model .....................................................2 1.2.1 GeneraI MiceUar Characteristics....................................................... 4 1.3 Observation of Magnetic Field Effects ..................................................... 6 1-4 Magne tic Field Effec ts on PHeterolysis Reac tions .................................... 12 1-5 Scope of Thesis................ ... .......................................... .. ......... 15 Chapter 2 Heterolytic Cleavage for p-Substituted Radicals ................. 16 2.1 General Introduction ....................................................................... 16 2.2 Laser Photolysis of 2-Chloro- 1-(4-methoxyphenyl)ethyl acetate..................... 18 2.3 Laser Photolysis of 2-Chloro- 1-(4-methoxypheny1)propyl acetate.................. -21 2.4 Laser Photolysis of 2-Bromo- 1-(4-methoxypheny1)ethyl acetate.................... -23 2.5 Laser Photolysis of 2-Bromo- 1-(4-methoxypheny1)propyl acetate ................... 25 2.6 Discussion ...................................................................................27 Chapter 3 Reactivity of Radical Cations with Radicals ...................... 33 3- 1 GeneraI Introduction ....................................................................... 33 3.2 Laser Photolysis of Anethole in Acetonitrile ............................................ 35 3.2.1 Laser Photolysis with Benzyl bromide ............................................. 36 3.2.2 Laser Photolysis with 3-Cyanobenzyl brornide ................................... 42 3.2.3 Laser Photolysis with Diphenylmethyl chloride................................... 46 3.2.4 Identification of the Transient at 345 nm ........................................... 49 3.3 Laser Photolysis of Anethole in SDS .................................................... 56 3.3.1 Laser Photolysis with Benzyl bromide ............................................. 57 3.3.2 Laser Photolysis with 3-Cyanobenzyl bromide ................................... 61 3.3.3 Laser Photolysis with Toluene and 3-Cyanotoluene.............................. 64 3.4 Laser Photolysis of Anethole in CTAB .................................................. 69 3.4.1 Laser Photolysis with Benzyl bromide ............................................ -70 3.5 Laser Photolysis of p-Methoxystyrene in Acetonibile ................................. 72 3.5.1 Laser Photolysis with Benzyl bromide ............................................. 74 3.5.2 Laser Photolysis with 3-Cyanobenzyl bromide ................................... 78 3.5.3 2-Bromo- 1-(4-meth0xyphenyl)ethyl Radical Formation ......................... 80 3.6 Irradiation of ~Methoxystyrenein SDS................................................. 83 3.6.1 Laser Photolysis with Benzyl bromide ............................................. 84 3.6.2 Laser Photolysis with 3-Cyanobenzyl bromide ................................... 88 3.6.3 Laser Photolysis with Toluene and 3-Cyanotoluene .............................. 91 3.7 Irradiation of p-Methoxystyrene in CTAB .............................................. 94 3.8 Discussion................................................................................. 97 3.8.1 Homogeneous media: Acetonitrile .................................................. 97 3.8.2 Heterogeneous medi a.. .............................................................. IO1 Chapter 4 Preliminary Work in Radical Pair Generation .................. 105 4.1 General Introduction ..................................................................... -105 4.2 Addition of -CH2Br and -CH20COPh to Dibenzylketone.......................... -106 4.3 Addition of Formaldehyde to Dibenzyketone ......................................... 107 4.4 Preparation of 1,3~bis(4.methoxyphenyl)~2~propanone.............................. IO8 4.4.1 Addition of -CH2Br and -CH20COPh ........................................... 109 4.4.2 Addition of Formaldehyde .......................................................... 109 4.5 Laser Expe~hents......................................................................... Il0 4.5.1 Magnetic Field Trial ................................................................. 111 4.6 Future Work ............................................................................... 114 Chapter 5 Experimental ........................... .... ..... ............ 115 5.1 Materials .................................................................................... 115 5.2 General Instmtmention ................................................................... 115 5.3 Laser Flash Photolysis.................................................................... 116 5.3.1 Equipment ........................................................................... -116 5.3.2 Data Processing ...................................................................... 117 5.4 Sample Preparation........................................................................ 117 5.4.1 p-Heterolysis studies ................................................................ 117 5.4.2 Photoionkation studies .............................................................. 118 5.5 Laser Photolysis with an Applied Magnetic Field ..................................... 120 5.5.1 Sample Preparation .................................................................. 120 5.5.2 Apparatus ............................................................................ -121 5.6 Syuthetic Procedures ...................................................................... 121 References .......................................................................................... 126 List of Fimes Figure 2- 1. Transient absorption spectnim of 2-chloro- 1-(4-methoxypheny1)e thyl acetate in nitrogen-saturated 0.1 M SDS recorded 76 (a), 128 (O) 224 (a),and 368 (Ci) ns after the laser pulse. Inset shows the tirne-resolved growth at 370 nrn under nitrogen (a) and oxygen-saturated (O)conditions. ................................................................. 20 Figure 2-2. Transient absorption spectrum of 2chloro- L -(4-methoxypheny1)ethyl acetate in nitrogen-saturated 0.05 M CTAB recorded 2 10 ns (a),540 ns (O), 920 ns (a), and 1.86 ps ((O) after the laser pulse. Inset shows the tirne-resolved growth at 370 nm under nitrogen (8)and oxygen-saturateci (O) conditions.. ........................................... -20 Figure 2-3. Transient absorption spectrum of 2cbioro- 1-(4-methoxypheny1)propyl acetate in nitrogen-saturated 0.1 M SDS recorded 70 (@), 148 (O), 232 (m), and 564 (0)ns afier the laser pulse. Inset shows. the tirne-resolved growth at 390 nrn under nitrogen (a) and oxygen-saturated (O) conditions. ................................................................. 22 Figure 24. Transient absorption spectmm 2chloro- 1-(4-methoxypheny1)propyl acetate in nitrogen-saturated 0.05 M CT'AB recorded 208 ns (a), 552 ns (O), and 1.29 ps (i)after the laser pulse. Inset shows. the the-resolved growth at 390 nrn under nitrogen (a) and oxygen-saturated (O) conditions. ................................................................. 22 Figure 2-5. Transient absorption spectnim of 2-bromo- 1-(4-methoxypheny1)ethyl acetate in nitrogen-saturated 0.1 M SDS recorded 120 (a), 308 (O), and 548 (i)ns after the laser pulse. Inset shows decay trace at 370 nm under N2 (a) and 02(O) conditions.. .........24 Figure 2-6. Transient absorption spectrum of 2-bromo- 1-(4-methoxypheny1)ethyl acetate in nitrogen-saturated 0.05 M CTAB recorded 130 (a),300 (O), and 670 (i) ns after the laser pulse. Inset shows decay trace at 350 nm under N;! (e)and 02 (0)conditions.. ... 24 Figure 2-7. Transient absorption spectrum of 2-bromo- 1-(4-methoxypheny1)propyl acetate in nitrogen-saturated 0.1 M SDS recorded 60 (a), 192 (O), 408 (W), and 640 (0)ns after the laser pulse. Inset shows the decay trace rnonitored at 390 nm under nitrogen (a) and oxygen-saturated