Infrared Spectra of the Bromocyclohexadienyl Radicals (C6H6Br∙) and Iodocyclohexadienyl Radicals (C6H6I∙) Isolated in Solid para-Hydrogen
| Autor: | Tsai, Huei-Ru, 蔡蕙如 |
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| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 108 In organic synthesis, the selectivity of the reaction between halogen atoms and hydrocarbons is affected by the presence of aromatic hydrocarbons solvent, which indicates that the interaction between halogen atoms and aromatic hydrocarbons affects the reaction of halogen atoms. The reaction of X (X = Cl, Br, or I) with benzene (C6H6) are benchmark examples. The structure of ClC6H6 is σ1, σ-bonded to one carbon atom, but those of BrC6H6 and IC6H6 are still uncertain, both theoretically and experimentally. Taking advantage of the diminished cage effect, we produced BrC6H6 or IC6H6 in p-H2 via bimolecular reaction of Br or I with C6H6 in photo-irradiated Br2 (or I2)/C6H6/p-H2 matrices. In the reaction of Br + C6H6, the newly appeared lines upon 405-nm irradiation were divided into three groups (B, C, and D) according to their correlated behaviors at various stages of experiment, such as annealing and secondary photolysis. The assignments were achieved by comparing the observed wavenumbers and relative intensities of lines in each group with the anharmonic vibrational wavenumbers and IR intensities of possible structures predicted with the B3LYP/aug-cc-pVTZ method. The lines in group B, C, and D are assigned to the π-bonded η1-BrC6H6, trans-5,6-dibromocyclohexa-1,3-diene, and trans-3,6-dibromocyclohexa-1,4-diene. Besides, we observed absorption lines of the Br2-C6H6 complex (group A) and assigned them to the v-Br2-C6H6 structure with Br2 nearly perpendicular to the benzene ring. In the reaction of I + C6H6, the newly appeared lines upon 560 nm irradiation were divided into two groups (B and C). The lines in group B and C are assigned to the η1-IC6H6, and trans-5,6-diiodocyclohexa-1,3-diene, respectively. Besides, we observed absorption lines of the I2-C6H6 complex (A) and assigned them to the v-I2-C6H6 structure with I2 nearly perpendicular to the benzene ring. In the assignments of η1-BrC6H6, the experimental results are consistent with quantum-chemical calculations except for the line at 697.3 cm^(-1). This line is similar to that predicted for the transition-state structure η2. Similarly, for η1-IC6H6, the line at 679.3 cm^(-1) is similar to that predicted for the transition-state structure η2. It is likely that the Br or I atom can move freely from one carbon atom to the neighboring carbon atom. This observation agrees with the predicted small barrier for moving Br or I from one C to the neighboring C, which is less than 1.0 or 0.1 kJ mol^(-1), respectively. In the reaction of C6H6 with two Br, trans-5,6-dibromocyclohexa-1,3-diene and trans-3,6-dibromocyclohexa-1,4-diene, which have the smallest relative energy, were produced. In the reaction of C6H6 with two I, the least-energy trans-5,6-diiodocyclohexa-1,3-diene was produced. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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