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(OCH2 CH2)(2)OCH2. (4(.)), HOCH2CH2OCH2CH2. (5(.)), and H(OCH2CH2)(2)OCH2CH2. (6( .)) are produced in the gas phase by fast atom bombardment ionization and t heir 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 a t distinct centers, thus representing a novel type of distonic radical cati ons. Radical reactions prevail for all [R-. + X](+) species studied. The pr edominant dissociation of metalated 1(.)-4(.) (-O-. or -OCH2. terminus) inv olves cleavage of CH2=O via ion-molecule complexes in which the newly detac hed formaldehyde molecule remains bound to the metal ion. With Li+ cationiz ation, H-. transfer within these intermediate complexes also takes place, l eading to the elimination of OCH.; this reaction is particularly competitiv e at low internal energy. In sharp contrast to 1(.)-4(.), metalated 5(.) an d 6(.) (-OCH2CH2. terminus) primarily decompose by 1,4- and 1,5-H-. rearran gements, followed by cleavage of (CH3)-C-. and (C2H5)-C-. radicals, and wit h 6(.), also HOCH2. and HOCH2CH2. radicals; at higher internal energies, th e direct cleavage of CH2=CH2 becomes a further significant dissociation cha nnel. Although the metal ion does not directly participate in the observed reactions, it plays an important role in either promoting or impeding speci fic radical-induced bond cleavages and H-. rearrangements by (1) preventing bond rotations in R-. (through coordination), (2) allowing for the formati on of intermediary metal ion-bound heterodimer complexes, and (3) influenci ng the energetics of the radical site decompositions.