In:
The Journal of Chemical Physics, AIP Publishing, Vol. 120, No. 22 ( 2004-06-08), p. 10470-10482
Abstract:
Infrared photodissociation (IRPD) spectra of clusters composed of protonated phenol (C6H7O+) and several ligands L are recorded in the O–H and C–H stretch ranges using a tandem mass spectrometer coupled to a cluster ion source. The C6H7O+–Ln complexes (L=Ar/N2, n=1–6) are generated by chemical ionization of a supersonic expansion. The IRPD spectra of mass selected C6H7O+–Ln clusters obtained in various C6H7O+–Lm fragment channels (m & lt;n) display the unambiguous fingerprints of at least two different C6H7O+ nucleation centers: the oxonium ion (5) and the carbenium ion(s) corresponding to protonation of phenol in ortho and/or para position (1/3). These two classes of C6H7O+–Ln isomers show very different fragmentation behavior upon IR excitation, facilitating the assignment of the observed vibrational transitions. The vibrational frequency shifts as a function of cluster size reveal that the microsolvation of 1/3 and 5 in Ar and N2 begins with the formation of intermolecular hydrogen bond(s) to the acidic OH group(s) and proceeds by the formation of intermolecular π-bonds to the respective six-membered rings. The analysis of photofragmentation branching ratios yields estimated ligand binding energies of the intermolecular OH- and π-bonds for solvation of the different C6H7O+ isomers. The effects of microsolvation on the properties of 1/3 as reactive intermediates in electrophilic aromatic substitution reactions are discussed. Comparison of clusters of protonated phenol with those of neutral phenol reveals the drastic protonation-induced changes in the topology of the intermolecular potential of aromatic molecules interacting with a nonpolar solvent. Moreover, the results show that the IRPD process can be used to selectively generate a spectroscopically clean ion beam of either 1/3 or 5 with some control over their internal energies.
Type of Medium:
Online Resource
ISSN:
0021-9606
,
1089-7690
Language:
English
Publisher:
AIP Publishing
Publication Date:
2004
detail.hit.zdb_id:
3113-6
detail.hit.zdb_id:
1473050-9
