Unimolecular Fragmentation of CH₃NH₂: Towards a Mechanistic Description of HCN Formation

Abstract

Keywords: Density functional calculations / Dehydrogenation / Mass spectrometry / MethylamineThe mechanism of the consecutive fragmentation of methylamine, CH 3 NH 2 , is studied by means of neutralization-reionization mass spectrometry (NRMS), labeling experiments, and calculations employing density functional theory. It is shown that under the conditions of NRMS the fragmentations proceed by a radical mechanism that involves four distinct X-H bond cleavages (X = C, N). In the first step, a hydrogen atom is eliminated from the methyl group; next, homolytic cleavage of an N-H bond occurs. The so-formed CH 2 NH intermediate then, in competition, releases a hydrogen atom

Fragmentation of the (Cyclam‐acetato)iron Azide Cation in the Gas Phase

“…[c] The CID spectrum is corrected for interfering isotopes of [ [20] although a definitive assignment of the neutral fragment cannot be made; (iii) even though other options cannot be rigorously excluded, the labeling patterns as well as the known structure of [1][PF 6 ] imply that ∆m = -44 corresponds to decarboxylation, which is further supported by the fragment with ∆m = -61, whose genesis can be explained by combined losses of CO 2 and ammonia; (iv) ∆m = -99 and ∆m = -142 are assigned to fragmentations of the ligand backbone after initial decarboxylation, with only limited participation of the amino protons. It is noteworthy that the azido N-atom is incorporated in the neutral fragment lost; (v) investigation of the 54 Fe isotope demonstrates that iron is not contained in any of the neutral fragments lost.…”

Dynamics of Formation of Products D2CN+, DCN+, and CD3+ in the Reaction of N+ with CD4: A Crossed-Beam and Theoretical Study

“…However, an even more probable process seems to be the subsequent loss of two H atoms shown to be a prevailing mechanism in the dissociation of internally excited small amines. 32 Therefore, most likely, both intermediates (i.e., 3 (CH 3 -NH + ) and 3 (CH 2 -NH 2 + )) are likely to lose sequentially two hydrogen atoms and form 1 (CHNH + ) (∆E rel,0K ) -4.28 eV, pathway A′). Another fragmentation of the intermediate 3 (CH 3 NH + ) is the C-N bond cleavage to form CH 3 + + 3 (NH) (∆E rel,0K ) -3.91 eV, pathway C).…”

“…First, both of these intermediates can lose a H 2 molecule and form products 3 (CHNH + ) + H 2 (Δ E rel,0K = −4.10 eV, pathway A). However, an even more probable process seems to be the subsequent loss of two H atoms shown to be a prevailing mechanism in the dissociation of internally excited small amines . Therefore, most likely, both intermediates (i.e., 3 (CH 3 −NH + ) and 3 (CH 2 −NH 2 + )) are likely to lose sequentially two hydrogen atoms and form 1 (CHNH + ) (Δ E rel,0K = −4.28 eV, pathway A′).…”

Ab Initio Classical Trajectory Study of the Dissociation of Neutral and Positively Charged Methanimine (CH2NHn+ n = 0−2)

“…[16][17][18][19][21][22][23][24][25] Dissociation of H 2 CNH has been studied experimentally and computationally. [17][18][19][20]24,27 It can occur by loss of hydrogen atom from either the carbon or the nitrogen with barriers of 85-95 kcal/mol to form HCNH and H 2 CN, which can lose another hydrogen atom with barriers of 30-35 kcal/mol to produce HCN. 18,[28][29][30] Alternatively, H 2 CNH, HC-NH 2 , and CH 3 N can dissociate by 1,1-or 1,2-H 2 eliminations with barriers of 85-100 kcal/mol above H 2 CNH.…”