The (Dimethylamino)methyl Radical. A Neutralization-Reionization and ab Initio Study

Scott A. Shaffer, František Tureček, Ronald Cerny

Research output: Contribution to journalArticle

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Abstract

The (dimethylamino)methyl radical (1) is generated in the gas phase by collisional neutralization of (CH3)2N+=CH2(1+) with Xe, (CH3)3N, and CH3SSCH3 and by collisionally activated dissociation of ionized 1,2- bis(dimethylamino)ethane (2) at 8 keV and characterized by neutralization-reionization mass spectrometry. Vertical neutralization of 1+ involves large Franck-Condon effects and produces 1 with ≥76 kJ mol−1 excess internal energy. Neutral 1 dissociates by loss of methyl to give CH3N==CH2 which undergoes further dissociation upon reionization. In contrast to vacuum pyrolysis, a significant fraction of 1 survives for 3.6 μs to yield 0.6–2.5% 1+ after collisional reionization with O2, ICl, NO2, and TiCl4, whereas >25% of 1 survives after collisionally activated dissociation of 2•+. Equilibrium geometries of 1 and 1+ from ab initio calculations with the 6-31G* basis set substantially differ in the C-N bond lengths and pyramidization at N and CH2. Calculations using the Møller-Plesset theory at the MP4- (SDTQ)/6-31G* and MP4(SDQ)/6-311G** levels with zero-point vibrational energy corrections are used to estimate the relative stabilities of 1, 1+, and their ionic and neutral dissociation products. The vertical ionization energies of 1 and C2H5N isomers are calculated and evaluated at the MP2 and MP4/6-311G** levels of theory. Large Franck- Condon effects are predicted by theory and found by experiment in the vertical neutralization of CH3N==CH2•+ and aziridine•+. Stable H2CNHCH2 biradical is prepared by neutralization of +CH2NHCH2 and predicted to be the (1A1) singlet electronic state.

Original languageEnglish (US)
Pages (from-to)12117-12124
Number of pages8
JournalJournal of the American Chemical Society
Volume115
Issue number25
DOIs
StatePublished - Dec 1 1993

Fingerprint

Ethane
Vacuum
Mass Spectrometry
Gases
Ionization potential
Bond length
Electronic states
Isomers
Mass spectrometry
Pyrolysis
Geometry
aziridine
methyl radical
titanium tetrachloride
Experiments

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

The (Dimethylamino)methyl Radical. A Neutralization-Reionization and ab Initio Study. / Shaffer, Scott A.; Tureček, František; Cerny, Ronald.

In: Journal of the American Chemical Society, Vol. 115, No. 25, 01.12.1993, p. 12117-12124.

Research output: Contribution to journalArticle

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abstract = "The (dimethylamino)methyl radical (1) is generated in the gas phase by collisional neutralization of (CH3)2N+=CH2(1+) with Xe, (CH3)3N, and CH3SSCH3 and by collisionally activated dissociation of ionized 1,2- bis(dimethylamino)ethane (2) at 8 keV and characterized by neutralization-reionization mass spectrometry. Vertical neutralization of 1+ involves large Franck-Condon effects and produces 1 with ≥76 kJ mol−1 excess internal energy. Neutral 1 dissociates by loss of methyl to give CH3N==CH2 which undergoes further dissociation upon reionization. In contrast to vacuum pyrolysis, a significant fraction of 1 survives for 3.6 μs to yield 0.6–2.5{\%} 1+ after collisional reionization with O2, ICl, NO2, and TiCl4, whereas >25{\%} of 1 survives after collisionally activated dissociation of 2•+. Equilibrium geometries of 1 and 1+ from ab initio calculations with the 6-31G* basis set substantially differ in the C-N bond lengths and pyramidization at N and CH2. Calculations using the M{\o}ller-Plesset theory at the MP4- (SDTQ)/6-31G* and MP4(SDQ)/6-311G** levels with zero-point vibrational energy corrections are used to estimate the relative stabilities of 1, 1+, and their ionic and neutral dissociation products. The vertical ionization energies of 1 and C2H5N isomers are calculated and evaluated at the MP2 and MP4/6-311G** levels of theory. Large Franck- Condon effects are predicted by theory and found by experiment in the vertical neutralization of CH3N==CH2•+ and aziridine•+. Stable •H2CNHCH2• biradical is prepared by neutralization of +CH2NHCH2• and predicted to be the (1A1) singlet electronic state.",
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