Experimental and computational evidence for appreciable p-bonding in [CH2OH]+ and homologous CnH2n+1O+ oxonium ions

ANYL 57

Richard D. Bowen, r.d.bowen@bradford.ac.uk1, Thanasis Karapanayiotis, tk306@cam.ac.uk2, Charles E. Hudson3, and David J. McAdoo3. (1) University of Bradford, Chemical and Forensic Sciences, Bradford, BD7 1DP, United Kingdom, (2) Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge, CB2 1EW, United Kingdom, (3) The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555
The question of whether [CH2OH]+ should be described as the hydroxymethyl cation, +CH2OH, or protonated formaldehyde, CH2=OH+, is reconsidered. Arguments that the charge distribution in [CH2OH]+ reflects the incremental stabilization of [CH2OH]+ induced by homologation on carbon (to give [CH3CHOH]+) or oxygen (to produce [CH2OCH3]+) are shown to be superficial. Preferential protonation of enol derivatives at the b-position is evidence for additional stabilization of oxonium ions by p-bonding. Computational information, including charges on the carbon and oxygen atoms in [CH2OH]+ and homologous species, is examined critically. Attention is focused on the calculated bond lengths and barriers towards rotation about the C-O bond(s) in [CH2OH]+, [CH3CHOH]+, [(CH3)2COH]+, CH3OH, and [CH2OCH3]+. Trends in these data are consistent with appreciable p-bonding only in the C-O connections that correspond to the C=O bond in the parent aldehyde or ketone from which CnH2n+1O+ oxonium ion may be derived by protonation or alkyl cationation.

 

General Papers
7:00 PM-9:00 PM, Sunday, 10 September 2006 Moscone Center -- Hall D, Poster

Division of Analytical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006