Field ionization kinetics. Unimolecular decomposition of the hexanal radical cation over the time range from 10 ps to 10 .mu.s

Abstract

Rates of formation of the major product ions from decomposition of hexanal, [3,3-2H2]hexanal, [4,4-2H2]hexanal, and [5,5-2H2]hexanal following field ionization have been determined over the time range 10 ps to several microseconds. These ions can be attributed to decomposition processes initiated by ß-, -, -, or e-hydrogen transfer to the oxygen via five-, six-, seven-, or eight-membered cyclic transition states. It is suggested that the McLafferty rearrangement at short times (<10-10 s) forms a vinyl alcohol ion and but-l-ene, and at longer times (10-10 to 10-6 s) a but-2-ene ion and vinyl alcohol. The observations at times <1 ns of m/e 57, m/e 73, and m/e 82 with [3,3-2H2]hexanal and m/e 73 with [4,4-2H2]hexanal are explained by decompositions initiated by /3-hydrogen transfer. The intermediate so formed rearranges by a 1,2-hydrogen shift to (CH= 0+,iHCH2C,sH1'HCTHCH2CH3), which then decomposes along its usual pathways (i.e., as if it were formed directly by -hydrogen transfer).

Ion-molecule complexes in unimolecular fragmentations of gaseous cations. Alkyl phenyl ether molecular ions

“…Neopentyl phenyl ether: m/e (rel intensity) 164 (24), 149 (6.0), 110 (5.0) , 108 (3.0), 107 (8.0), 94 (100), 77 (12), 72 (4.5), 71 (7.5), 70 (16), 66 (6.0), 65 (6.0), 57 (6.0), 55 (20), 51 (8.5), 43 (37), 42 (5.0), 41 (19), 39 (14). Neopentyl-dg phenyl ether (6): m/e (rel intensity) 173 (23), 172 (2), 155 (5.5), 110(1.5), 109 (5.0), 108 (3.5), 107 (1.5), 95 (100), 94 (90), 80 (10), 79 (22), 78 (3.0), 77 (16), 67 (8.0), 66 (9.0) , 65 (9.0), 61 (16), 60 (10), 51 (13), 50 (10), 49 (25), 48 (24), 47 (8), 46 (19), 45 (11), 44 (8), 43 (5), 42 (9), 41 (9), 40 (5), 39 (16). Neopentyl-d2 phenyl ether (7): m/e (rel intensity) 166 (18), 165 (0.3), 151 (4.5), 110(2.0) 109(3.0), 108 (3.0), 107 (1.5), 95 (52), 94 (100), 78 (2.0), 77 (19), 73 (9.0), 71 (18), 67 (2.5), 66 (8.0), 65 (9.0), 57 (20), 56 (13), 55 (5.5), 51 (18), 45 (19), 44 (27), 43 (20), 42 (11),41 (16), 40 (7.5), 39 (19).…”

“…Previous investigators have discussed nonspecific hydrogen transfer in terms of mechanism A, with close competition among transition states of different sizes. [8][9][10][11] Alkyl phenyl ethers (X = -OPh) have been widely studied as an example where the major decomposition pathway involves hydrogen transfer from every position of the alkyl chain. Under 12-70-eV electron impact, the phenol molecular ion constitutes the base peak.9-12 Borchers, Levsen, and Beckey11 and Nib-bering12 have demonstrated that the hydrogen transferred from the chain remains distinct, consistent with the formula C6H5OH4"•.…”