TuP-13


THE STRUCTURE OF THE STABLE C2H4O+· ION FROM ETHYLENE CARBONATE REVISITED

John K MacLeod and Carl Braybrook

Research School of Chemistry, Australian National University, Canberra, ACT 0200


In 1981, we published an ICR study of the ion-molecule reaction of the C2H4O+· ion from doubly-labelled ethylene carbonate (1) with d5-pyridine,1 the results of which could only be interpreted as showing that the CH2CH2O+· ion, if formed initially, must undergo rearrangement to CH2OCH2+· (m/z 44) prior to reaction with neutral pyridine (Scheme 1). This conclusion gained support from CA and metastable ion studies by Holmes et al.2 and by Cooks et al.3 using surface-induced dissociation of the C2H4O+· ion from ethylene carbonate. In addition, high level ab initio molecular orbital calculations4 showed that the CH2CH2O+· ion lies in a shallow potential well 182 kJ/mol higher than the energy minimum of the CH2OCH2+· ion, with a barrier of only 22 kJ/mol to rearrangement via the cyclic oxirane ion. It was therefore surprising to us when in 1990 Wesdemiotis et al.5 using a four-sector (EB-EB) mass spectrometer, claimed that the results of their CAD and NRMS experiments showed that the m/z 44 ion from ethylene carbonate had the CH2CH2O+· structure.

Scheme 1


We have now repeated our ion-molecule reaction study with (1), this time using a ZAB-2SEQ hybrid (BEqQ) mass spectrometer with the neutral reactant gas (pyridine, acetonitrile) in the rf-only quadrupole. The results, which we will present, confirm our previous conclusion that the stable C2H4O+· ion from ethylene carbonate has the CH2OCH2+· structure.

  1. B.C.Baumann and J.K.MacLeod, J.Am.Chem.Soc. 1981, 103, 6623-6624.
  2. J.M.Buschek, J.L.Holmes and J.K.Terlouw, J.Am.Chem.Soc. 1987, 109, 7321-7325.
  3. Md.A.Mabud, T.Ast, S.Verma, Y.-X.Jiang and R.G.Cooks, J.Am.Chem.Soc. 1987, 109, 7597-7602.
  4. R.H.Nobes, W.J.Bouma, J.K.MacLeod and L.Radom, Chem.Phys.Lett. 1987, 135, 78-83.
  5. C.Wesdemiotis, B.Leyh, A.Fura and F.W.McLafferty, J.Am.Chem.Soc. 1990, 112, 8655-8660.