Unimolecular chemistry of Li+- and Na+-coordinated polyglycol radicals, a new class of distonic radical cations

The lithium and sodium ion complexes of the polyglycol-derived radicals (R-.) HOCH2CH2O. (1(.)), H(OCH2CH2)(2)O-. (2(.)), HOCH2CH2OCH2. (3(.)), H(OCH2CH2)(2)OCH2. (4(.)), HOCH2CH2OCH2CH2. (5(.)), and H(OCH2CH2)(2)OCH2CH2. (6(.)) are produced in the gas phase by fast atom bombardment ionization and their structures and unimolecular chemistry are investigated by tandem mass spectrometry. Parallel ab initio MO calculations show that the [R-. + X](+) (X = Li, Na) complexes carry their positive charge and unpaired electron at distinct centers, thus representing a novel type of distonic radical cations. Radical reactions prevail for all [R-. + X](+) species studied. The predominant dissociation of metalated 1(.)-4(.) (-O-. or -OCH2. terminus) involves cleavage of CH2=O via ion-molecule complexes in which the newly detached formaldehyde molecule remains bound to the metal ion. With Li+ cationization, H-. transfer within these intermediate complexes also takes place, leading to the elimination of OCH.; this reaction is particularly competitive at low internal energy. In sharp contrast to 1(.)-4(.), metalated 5(.) and 6(.) (-OCH2CH2. terminus) primarily decompose by 1,4- and 1,5-H-. rearrangements, followed by cleavage of (CH3)-C-. and (C2H5)-C-. radicals, and with 6(.), also HOCH2. and HOCH2CH2. radicals; at higher internal energies, the direct cleavage of CH2=CH2 becomes a further significant dissociation channel. Although the metal ion does not directly participate in the observed reactions, it plays an important role in either promoting or impeding specific radical-induced bond cleavages and H-. rearrangements by (1) preventing bond rotations in R-. (through coordination), (2) allowing for the formation of intermediary metal ion-bound heterodimer complexes, and (3) influencing the energetics of the radical site decompositions.