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Dale F. Shellhamer - One of the best experts on this subject based on the ideXlab platform.
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ReactIon to Halogens and Interhalogens with 4-Halo-1,1,2-trifluorobut-1-enes: Rearrangement of 3-Membered Halonium to 5-Membered Trifluorotetramethylene Halonium Ion Intermediates and Comparison of Open-Chloronium Fluorosubstituted Ions to Flurocarbo
2008Co-Authors: Dale F. Shellhamer, Sean J. Rodriguez, Kevyn J. Davenport, Heidi K. Forberg, Matthew P. Herrick, Rachel N. Jones, Sunamita Sanabria, Nicole Trager, Ryan J. Weiss, Victor L. HeasleyAbstract:Abstract : In this paper we investigate the influence that a 4-halosubstituent has on formatIon of three-membered Halonium Ions and their rearrangement to five-membered ring intermediates when chloronium, bromonium and iodonium Ions from alkenes 1, 2 and 3 are formed in aprotic solvent (Scheme 1). We also compare the open-Ion chloronium Ions with the open-carbocatIons from additIon of a proton to terminal fluorosubstituted alkenes.
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CorrelatIon of Calculated Halonium Ion Structures with Experimental Product DistributIons from Terminal Alkenes: The Effect of Electron-Withdrawing Fluorine Substituents on the Structure and Charge LocalizatIon of Halonium Ions (PREPRINT)
2006Co-Authors: Dale F. Shellhamer, David C. Gleason, Sean J. Rodriguez, Victor L. Heasley, Jerry A. Boatz, Jeffrey J LehmanAbstract:Abstract : The structures and charge densities of Halonium Ions, derived from additIon of halogen electrophiles to fluoro-substituted terminal alkenes, were computed using quantum chemical methods. Geometry optimizatIons were performed at the second-order perturbatIon theory level (MP2, also known as MBPT(2)), using the Spartan02 program and also at the density functIonal theory level, using the GAMESS quantum chemistry code with the B3LYP hybrid functIonal. An additIonal set of B3LYP calculatIons incorporating the Polarizable Continuum Model (PCM) to probe methanol solvent effects was also performed. The Halonium Ions from terminal fluoroalkenes were found to be symmetrical (C), unsymmetrical (B or D), or open-Ions described by A or E. These calculated data support experimental product distributIons and they can predict the product regiochemistry from Halonium Ions opened by anIons in aprotic solvents or when opened by protic solvents like methanol. Electron-withdrawing alkyl groups tend to decrease the SN1-character of the product-determining ring-opening transitIon state, and an SN-2-like process occurs which is more susceptible to steric effects.
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CorrelatIon of calculated Halonium Ion structures with product distributIons from fluorine substituted terminal alkenes
Tetrahedron, 2006Co-Authors: Dale F. Shellhamer, David C. Gleason, Sean J. Rodriguez, Victor L. Heasley, Jerry A. Boatz, Jeffrey J LehmanAbstract:Calculated equilibrium geometries, bond lengths, and charge densities were performed on Halonium Ions derived by the additIon of halogen electrophiles to fluoro-substituted terminal alkenes. The calculated structures correlate with regiochemical product distributIons from ring-opening of Halonium Ions by anIons or by the solvent methanol. Calculated Halonium Ion structures and the Hammond postulate are utilized to predict the regiochemical product distributIons for reactIons of halogens with fluoroalkenes that are not investigated experimentally.
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Ionic reactIon of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of Halonium Ions.
The Journal of organic chemistry, 2003Co-Authors: Dale F. Shellhamer, David C. Gleason, Andrew J. Ryan, Jeannette L. Allen, Rachel D. Allen, Colleen O'neil Schlosser, Benjamin J. Powers, John W. Probst, Michelle C. Rhodes, Peter K TitteringtonAbstract:Ionic reactIons of terminal alkenes with chlorine (Cl2), bromine (Br2), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positIons and number of vinyl fluorine atoms. These perturbatIons influence the symmetry of the Halonium Ion intermediates, which can be determined by the distributIon of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of Halonium Ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-Ions with the positive charge on carbon-2, to various bridged species, to open-Ions on the terminal carbon.
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Comparison of the electrophilic and free-radical additIon of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene
Journal of Fluorine Chemistry, 2003Co-Authors: Dale F. Shellhamer, David C. Gleason, Victor L. Heasley, G.gawayne Vaughan, Andrew J. Ryan, Peter K Titterington, Jeffrey J LehmanAbstract:Abstract Ionic and photochemical reactIon of chlorine (Cl2), bromine (Br2) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditIons that would provide product distributIons under controlled Ionic or free-radical conditIons. Product distributIons for Ionic reactIon of Cl2 and Br2 with 1 are similar and suggest a weakly-bridged Halonium Ion species. Theoretical calculatIons support weakly-bridged chloronium and bromonium Ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from Ionic halogenatIon of 1 than 2 which correlates with the greater charge density on carbon-4 of Halonium Ions from 1. Ionic and free-radical reactIons of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.
Paul Evans - One of the best experts on this subject based on the ideXlab platform.
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Halonium Ion Triggered Rearrangement of Unsaturated Benzo-Annulated Bi- and Tricyclic Sulfonamides
2016Co-Authors: Kimberly Geoghegan, Shaun Smullen, Paul EvansAbstract:The Halonium Ion mediated 1,2-Wagner–Meerwein-type rearrangement of a series of benzo-fused bi- and tricyclic sulfonamides is reported. During this rearrangement the carbon–carbon bond that migrates was selectively set in the intramolecular Mizoroki–Heck (IHR) synthesis of the starting materials. Consequently, this method constitutes a means to access the regioisomeric series of cyclic sulfonamides not observed during the Mizoroki–Heck reactIon
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Halonium Ion triggered rearrangement of unsaturated benzo-annulated bi- and tricyclic sulfonamides.
The Journal of organic chemistry, 2013Co-Authors: Kimberly Geoghegan, Shaun Smullen, Paul EvansAbstract:The Halonium Ion mediated 1,2-Wagner–Meerwein-type rearrangement of a series of benzo-fused bi- and tricyclic sulfonamides is reported. During this rearrangement the carbon–carbon bond that migrates was selectively set in the intramolecular Mizoroki–Heck (IHR) synthesis of the starting materials. Consequently, this method constitutes a means to access the regioisomeric series of cyclic sulfonamides not observed during the Mizoroki–Heck reactIon.
Kimberly Geoghegan - One of the best experts on this subject based on the ideXlab platform.
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Halonium Ion Triggered Rearrangement of Unsaturated Benzo-Annulated Bi- and Tricyclic Sulfonamides
2016Co-Authors: Kimberly Geoghegan, Shaun Smullen, Paul EvansAbstract:The Halonium Ion mediated 1,2-Wagner–Meerwein-type rearrangement of a series of benzo-fused bi- and tricyclic sulfonamides is reported. During this rearrangement the carbon–carbon bond that migrates was selectively set in the intramolecular Mizoroki–Heck (IHR) synthesis of the starting materials. Consequently, this method constitutes a means to access the regioisomeric series of cyclic sulfonamides not observed during the Mizoroki–Heck reactIon
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Halonium Ion triggered rearrangement of unsaturated benzo-annulated bi- and tricyclic sulfonamides.
The Journal of organic chemistry, 2013Co-Authors: Kimberly Geoghegan, Shaun Smullen, Paul EvansAbstract:The Halonium Ion mediated 1,2-Wagner–Meerwein-type rearrangement of a series of benzo-fused bi- and tricyclic sulfonamides is reported. During this rearrangement the carbon–carbon bond that migrates was selectively set in the intramolecular Mizoroki–Heck (IHR) synthesis of the starting materials. Consequently, this method constitutes a means to access the regioisomeric series of cyclic sulfonamides not observed during the Mizoroki–Heck reactIon.
Thomas Lectka - One of the best experts on this subject based on the ideXlab platform.
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Quest for a Symmetric [C-F-C]+ Fluoronium Ion in SolutIon: A Winding Path to Ultimate Success.
Accounts of chemical research, 2019Co-Authors: Maxwell Gargiulo Holl, Cody Ross Pitts, Thomas LectkaAbstract:ConspectusIn this Account, we chronicle our tortuous but ultimately fruitful quest to synthesize a [C–F–C]+ fluoronium Ion in solutIon, thus providing the last piece of the organic Halonium Ion puz...
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Spectroscopic CharacterizatIon of a [C-F-C]+ Fluoronium Ion in SolutIon.
Angewandte Chemie (International ed. in English), 2018Co-Authors: Cody Ross Pitts, Maxwell Gargiulo Holl, Thomas LectkaAbstract:We report the first spectroscopic evidence for a [C-F-C]+ fluoronium Ion in solutIon. Extensive NMR studies (19 F, 1 H, 13 C) characterize a symmetric cage-like species in which fluorine exhibits substantial covalent bonding to each of the two carbon atoms involved in the three-center interactIon. Experimental NMR data comport well with calculated values to lend credence to the structural assignment. As the culminating experiment, a Saunders isotopic perturbatIon test confirmed the symmetric structure. Congruent with the trend in other types of onium Ions, the calculated charge at fluorine moves in a more positive (less negative) directIon from the neutral. It is this important trend that explains in part the extraordinary historical difficulty in making theoretical predictIons of fluoronium Ions come true in solutIon, and why it takes fluorine captured in a cage to produce, finally, a stable Ion and complete the historical arc of the organic Halonium Ion story.
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Evidence for a symmetrical fluoronium Ion in solutIon.
Science (New York N.Y.), 2013Co-Authors: Mark D. Struble, Michael T. Scerba, Maxime A. Siegler, Thomas LectkaAbstract:Halonium Ions, in which formally positively charged halogens (chlorine, bromine, and iodine) are equivalently attached to two carbon atoms through three-center bonds, are well established in the synthetic chemistry of organochlorides, bromides, and iodides. Mechanistic studies of these Ions have generated numerous insights into the origins of stereoselectivity in additIon and displacement reactIons. However, it has not been clear whether fluorine can form a Halonium Ion in the same manner. We present chemical and theoretical evidence for the transient generatIon of a true symmetrical fluoronium Ion in solutIon from an appropriately configured precursor.
Peter K Titterington - One of the best experts on this subject based on the ideXlab platform.
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Ionic reactIon of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of Halonium Ions.
The Journal of organic chemistry, 2003Co-Authors: Dale F. Shellhamer, David C. Gleason, Andrew J. Ryan, Jeannette L. Allen, Rachel D. Allen, Colleen O'neil Schlosser, Benjamin J. Powers, John W. Probst, Michelle C. Rhodes, Peter K TitteringtonAbstract:Ionic reactIons of terminal alkenes with chlorine (Cl2), bromine (Br2), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positIons and number of vinyl fluorine atoms. These perturbatIons influence the symmetry of the Halonium Ion intermediates, which can be determined by the distributIon of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of Halonium Ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-Ions with the positive charge on carbon-2, to various bridged species, to open-Ions on the terminal carbon.
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Comparison of the electrophilic and free-radical additIon of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene
Journal of Fluorine Chemistry, 2003Co-Authors: Dale F. Shellhamer, David C. Gleason, Victor L. Heasley, G.gawayne Vaughan, Andrew J. Ryan, Peter K Titterington, Jeffrey J LehmanAbstract:Abstract Ionic and photochemical reactIon of chlorine (Cl2), bromine (Br2) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditIons that would provide product distributIons under controlled Ionic or free-radical conditIons. Product distributIons for Ionic reactIon of Cl2 and Br2 with 1 are similar and suggest a weakly-bridged Halonium Ion species. Theoretical calculatIons support weakly-bridged chloronium and bromonium Ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from Ionic halogenatIon of 1 than 2 which correlates with the greater charge density on carbon-4 of Halonium Ions from 1. Ionic and free-radical reactIons of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.
