Computational Studies of Protonated Cyclic Ethers and Benzylic Organolithium Compounds

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dc.contributor.authorDeora, Nipaen
dc.contributor.committeechairCarlier, Paul R.en
dc.contributor.committeememberCrawford, T. Danielen
dc.contributor.committeememberEtzkorn, Felicia A.en
dc.contributor.committeememberTanko, James M.en
dc.contributor.committeememberTroya, Diegoen
dc.contributor.departmentChemistryen
dc.date.accessioned2014-03-14T20:12:17Zen
dc.date.adate2010-06-22en
dc.date.available2014-03-14T20:12:17Zen
dc.date.issued2010-05-10en
dc.date.rdate2010-06-22en
dc.date.sdate2010-05-19en
dc.description.abstractProtonated epoxides feature prominently in organic chemistry as reactive intermediates. Gas-phase calculations studying the structure and ring-opening energetics of protonated ethylene oxide, propylene oxide and 2-methyl-1,2-epoxypropane were performed at the B3LYP and MP2 levels (both with the 6-311++G** basis set). Structural analyses were performed for 10 protonated epoxides using B3LYP, MP2, and CCSD/6-311++G** calculations. Protonated 2-methyl-1,2-epoxypropane was the most problematic species studied, where relative to CCSD, B3LYP consistently overestimates the C2-O bond length. The difficulty for DFT methods in modeling the protonated isobutylene oxide is due to the weakness of this C2-O bond. Protonated epoxides featuring more symmetrical charge distribution and cyclic homologues featuring less ring strain are treated with greater accuracy by B3LYP. Ion-pair separation (IPS) of THF-solvated fluorenyl, diphenylmethyl, and trityl lithium was studied computationally. Minimum-energy equilibrium geometries of explicit mono, bis and tris-solvated contact ion pairs (CIPs) and tetrakis-sovlated solvent separated ion pair (SSIPs) were modeled at B3LYP/6-31G*. Associative transition structures linking the tris-solvated CIPs and tetrakis-solvated SIPs were also located. In vacuum, B3LYP/6-31G* ΔHIPS values are 6-8 kcal/mol less exothermic than the experimentally-determined values in THF solution. Incorporation of secondary solvation in the form of Onsager and PCM single-point calculations showed an increase in exothermicity of IPS. Application of a continuum solvation model (Onsager) during optimization at the B3LYP/6-31G* level of theory produced significant changes in the Cα-Li contact distances in the SSIPs. An increase in of ion pair separation exothermicity was observed upon using both PCM and Onsager solvation models, highlighting the importance of both explicit and implicit solvation in modeling of ion pair separation.en
dc.description.degreePh. D.en
dc.identifier.otheretd-05192010-002946en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05192010-002946/en
dc.identifier.urihttp://hdl.handle.net/10919/27800en
dc.publisherVirginia Techen
dc.relation.haspartDeora_N_2010.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectpotential-energy surfaceen
dc.subjectbasis-seten
dc.subjectepoxideen
dc.subjectligaen
dc.titleComputational Studies of Protonated Cyclic Ethers and Benzylic Organolithium Compoundsen
dc.typeDissertationen
thesis.degree.disciplineChemistryen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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