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Wednesday, April 22 • 9:20am - 9:40am
Computational Study of Substituent Effect on the Threshold Energy for the 1,2-Interchange of Halogens, Pseudohalogens, and Various R Groups

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The possibility of gaseous halocarbons undergoing a 1,2-interchange reaction in competition with typical 1,2-HF or HCl eliminations offers an interesting explanation for their reactivity in the atmosphere. In order to determine the most energetically feasible interchanges, the threshold energies for the interchange of various halogens (F, Cl, Br), pseudohalogens (SH, CH3, NH2, CN, OH, OCH3), and other groups (OCF3, OCH3, CH=CH2, CH2CH3, CH3, CH2OH, C≡CH, CH2CF3, CCl3, CF3) were calculated using computational methods. Ground state and transition state geometries were optimized with the B3PW91 level of theory and 6-311+G(2d,p) basis set. The Br-Br interchange had the lowest E0 (33.8 kcal/mol), and CH3-CH3 had the highest (134.8 kcal/mol). In general, larger atoms/groups with lone pairs of electrons such as halogens, SH, OH, OCH3, and NH2 tend to lower the E0 barrier for interchange, making them the most likely to undergo rearrangement, as their E0 barriers were under 70 kcal/mol. Those groups can be considered for further experimental observation, but CH3 is unlikely to interchange due to its high E0 barriers. C-C≡N bond lengths were considered too long to represent accurate transition states for CN interchange.


Wednesday April 22, 2015 9:20am - 9:40am PDT
123 Zeis Hall