Journal of the American Chemical Society p. 4810 - 4818 (1987)
Update date:2022-08-12
Topics:
Drewello, Thomas
Heinrich, Nikolaus
Maas, Wilfried P. M.
Nibbering, Nico M. M.
Weiske, Thomas
Schwarz, Helmut
The combined application of Fourier-transform ion cyclotron resonance and tandem mass spectrometries, complemented by ab initio MO calculations, provides a relatively detailed description of crucial aspects of the potential energy surface of ionized acetamide (CH3CONH2.+, 6) and the complexes formed in ion/molecule reactions of ionized ketene (CH2CO.+, 5) with ammonia.Both the unimolecular decarbonylation of 6 and the bimolecular substitution of 5 generate the distonic ion CH2NH3.+, which is fully characterized by proton-transfer reactions and collision-induced dissociations.Although the two fundamentally different reactions are linked by common intermediates, which are suggested to be hydrogen-bridged complexes, there are some distinct differences.The reaction of ammonia with CH2CO.+ to generate CH2NH3.+ and CO occurs in a region of the potential energy surface which does not result in the formation of hydrogen-scrambled product ions.In contrast, starting from CH3CONH2.+ the isomerization steps involve intermediates which, prior to the formation of CH2NH3.+ and CO, permit hydrogen-exchange processes to occur.The enol of ionized acetamide (CH2=C(OH)NH2.+, 8) is separated by a significant barrier from CH3CONH2.+.If 8 is internally excited it also dissociates to CH2NH3.+ and CO, presumably via CH3CONH2.+.Recent suggestion that nucleophilic substitutions involving radical cations are "forbidden" processes and should therefore have an inherent, low reactivity are not confirmed.The substitution reaction NH3 + CH2=C=O.+ -> CO + CH2NH2.+ is relatively facile.
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