The generation and energetics of reactive organic intermediates

The thermochemistry of a variety of reactive intermediates generated in a Fourier transform mass spectrometer are presented. N-Diaziridyl anion was prepared by reduction of the nitrogen-nitrogen double bond in diazirine and represents the first simple hydrazyl anion observed in the gas phase. The N-H bond dissociation energy (BDE, 88 ± 4 kcal/mol) of trans-diaziridine was obtained. Dodecahedryl anion, a rare example of a stable alkyl anion, was generated upon reaction of dodecahedrane with amide. Studies of the anion afforded the carbon-hydrogen BDE (92 ± 3 kcal/mol) of the Platonic solid.;The rearrangement of aryl substituted cyclopropenyl anions to indenyl structures was probed. The acidity of 3-(4-methylphenyl)cyclopropene (399 ± 2 kcal/mol) was measured by a kinetic method. Gas-phase studies and ab initio calculations revealed benzocyclobutenone enolate is stable despite possessing a resonance structure with cyclobutadiene character. Conditions were devised to generate and trap the enolate in tetrahydrofuran. The conjugate base of benzocyclobutadiene was generated by loss of a proton and molecular nitrogen from benzocyclobutenyl diazirine. The latter compound was synthesized from benzocyclobutenone and found to be remarkably stable. Studies of benzocyclobutadienyl anion provided the acidity (386 ± 3 kcal/mol) and C-H BDE (114 ± 4 kcal/mol) of its conjugate acid. The radical anion of benzocyclobutadiene was prepared by two novel approaches: collision-induced dissociation of an appropriate dicarboxylate dianion and a β-nitroso carbanion. The proton affinity and electron binding energy of this ion were used in a thermodynamic cycle to obtain the heat of hydrogenation (49 ± 4 kcal/mol) and formation (97 ± 4 kcal/mol) of benzocyclobutadiene.;Acenaphthyne radical anion was generated upon dissociation of the requisite dicarboxylate dianion. Studies of the anion afforded the heat of hydrogenation (98 ± 5 kcal/mol) and formation (160 ± 5 kcal/mol) of acenaphthyne. This highly strained cycloalkyne is predicted to be destabilized relative to cyclopentyne by 8 kcal/mol.;The first evidence that a zwitterionic ion, 1-methylpyridinium-3,5-dicarboxylate, and its corresponding neutral counterpart, the conjugate base of 5-methoxylcarbonyl nicotinic acid, are unique species in the gas phase was obtained. The observed reactivity and thermochemistry revealed the influence of electrostatics in a dipolar species.