Abstract
Most H2 eliminations from cations in the gas phase are formally 1,1- or 1,2- processes. Larger ring size H2 eliminations are rare and little studied. Thus, whether the 6-center, 1,4- elimination CH3CH=N+HCH3→CH2=CHN+H=CH2+H2 is concerted and synchronous, as indicated by isotope effects and predicted by conservation of orbital symmetry, is a significant question. This reaction is characterized here by application of QCI and B3LYP theories. CH bond-breaking and H-H bond-making in this reaction are found by theory to be highly synchronized, consistent with previously established isotope effects and in contrast to “forbidden” 1,2-eliminations from organic cations in the gas phase. This reaction is made feasible by its conservation of orbital symmetry, the energy supplied by formation of the H-H bond, and a favorable geometry of the ion for eliminating H2.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Uggerud, E. Translational Energy Release: Experiment and Theory: H2-Elimination Reactions of Small Gas Phase Ions and Correspondence to H-H Bond Activation. Mass Spectrom. Rev 1999, 18, 285–308.
Woodward, R. B.; Hoffmann, R. The conservation of orbital symmetry. Angew. Chem. Int. Ed 1969, 8, 781–932.
Wendelboe, J. F.; Bowen, R. D.; Williams, D. H. Unimolecular Reactions of Ionized Alkanes. J. Am. Chem. Soc 1981, 103, 2333–2339.
McAdoo, D. J.; Bowen, R. D. Alkane Eliminations from Ions in the Gas Phase. Eur. Mass Spectrom 1999, 5, 389–400.
Williams, D. H.; Hvistendahl, G. Kinetic Energy Release in Relation to Symmetry—Forbidden Reactions. J. Am. Chem. Soc 1974, 96, 6753–6757.
Williams, D. H.; Hvistendahl, G. Kinetic Energy Release as a Mechanistic Probe: The Role of Orbital Symmetry. J. Am. Chem. Soc 1974, 96, 6755–6757.
Øiestad, Å. M. L.; Uggerud, E. Loss of H2 from CH2NH +2 and NHNH +2 : Reaction Mechanisms and Dynamics from Observation of Metastable Ion Fragmentation and ab Initio Calculations. Int. J. Mass Spectrom. Ion Processes 1997, 167/168, 117–126.
Uccella, N. A.; Howe, I.; Williams, D. H. Structure and Isomerization of Gaseous C3H8N+ Metastable Ions. J. Chem. Soc. B 1971, 1933–1939.
Bowen, R. D. The Chemistry of CnH2n+2N+ ions. Mass Spectrom. Rev 1991, 10, 225–279.
Dewar, M. J. S. Multibond Reactions Cannot Normally be Synchronous. J. Am. Chem. Soc 1984, 106, 209–219.
McKee, M. L.; Shevlin, P. B.; Rzepa, H. S. Concerted Dihydrogen Exchange Between Methanol and Formaldehyde: A Theoretical Study. J. Am. Chem. Soc 1986, 108, 5793–5798.
Olivella, S.; Solé, A.; McAdoo, D. J.; Griffin, L. L. Unimolecular Reactions of Ionized Alkanes: Theoretical Study of the Potential Energy Surface for CH3· and CH4 Losses from Ionized Butane and Isobutane. J. Am. Chem. Soc 1994, 116, 11078–11088.
Olivella, S.; Solé, A.; McAdoo, D. J. Methane Elimination from Ionized Propane Through an Ion-Neutral Complex: An Ab Initio Study. J. Am. Chem. Soc 1996, 118, 9368–9376.
Hudson, C. E.; McAdoo, D. J. Characterization by Theory of H-Transfers and Onium Reactions of CH3CH2CH2N+H=CH2. J. Am. Soc. Mass Spectrom 2007, 18, 270–278.
Hudson, C. E.; McAdoo, D. J. Ethene-Elimination from CH3CH2NH=CH +2 : Reaction Pathways at the Boundary Between Stepwise and Concerted Processes. J. Am. Soc. Mass Spectrom 1998, 9, 138–148.
Hudson, C. E.; McAdoo, D. J. Methane Loss from (CH3)3O+: An Asynchronous, Concerted 1,2-Alkane Elimination. Int. J. Mass Spectrom 2006, 248, 103–107.
Traeger, J. C.; Hudson, C. E.; McAdoo, D. J. A Photoionization Study of the Ion-Neutral Complexes [CH3CH+CH3· CH2CH3] and [CH3CH2CH +CH3· CH3] in the Gas Phase: Formation, H-transfer, and C-C Bond Formation Between Partners, and Channeling of Energy into Dissociation. J. Am. Soc. Mass Spectrom 1996, 7, 73–81.
Tramontini, M. Advances in the Chemistry of Mannich Bases. Synthesis 1973, 12, 703–775.
Dyke, S. F. The Chemistry of Enamines; Cambridge University Press: London, 1973.
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Revision B04, Gaussian Inc: Pittsburgh, PA, 2003.
Scott, A. P.; Radom, L. Harmonic Vibrational Frequencies: An Evaluation of Hartree-Fock, Møller-Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors. J. Phys. Chem 1996, 100, 16502–16513.
Gonzalez, C.; Schlegel, H. B. An Improved Algorithm for Reaction Path Following. J. Chem. Phys 1989, 90, 2154–2161.
Gonzalez, C.; Schlegel, H. B. Reaction Path Following in Mass-Weighted Internal Coordinates. J. Phys. Chem 1990, 94, 5523–5527.
Kao, J. A Molecular Orbital Based Molecular Mechanics Approach to Study Conjugated Hydrocarbons. J. Am. Chem. Soc 1987, 109, 3817–3829.
Anslyn, E. V.; Dougherty, D. A. Modern Physical Organic Chemistry; University Science Books: Sausalito, CA, 2004; p 115
Author information
Authors and Affiliations
Corresponding author
Additional information
Published online October 22, 2007
Rights and permissions
About this article
Cite this article
Hudson, C.E., Bowen, R.D. & McAdoo, D.J. Elimination of H2 from CH3CH=N+HCH3: A synchronous, concerted 1,4-H2 elimination. J. Am. Soc. Spectrom. 19, 27–32 (2008). https://doi.org/10.1016/j.jasms.2007.10.005
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1016/j.jasms.2007.10.005