title: A combined nuclear magnetic resonance and computational study of monohydroxyflavones applied to product ion mass spectra.
abstract: A method is presented for the estimation of 13C-chemical shifts for carbon atoms in protonated and deprotonated molecules; in principle, this method can be applied to ions in general. Experimental 13C-chemical shifts were found to vary linearly with computed atomic charges using the PM3 method. Pseudo-13C-chemical shifts for atoms in protonated and deprotonated molecules can be estimated from computed atomic charges for such atoms using the above linear relationship. The pseudo-13C-chemical shifts obtained were applied to the rationalization of product ion mass spectra of protonated and deprotonated molecules of flavone and 3-, 5-, 6-, 7-, 2'-, 3'-, and 4'-hydroxyflavones, where product ion formation is due to either cross-ring cleavage of the C-ring (retro-Diels-Alder reaction) or to cleavage of a C-ring bond followed by loss of either a small neutral molecule or a radical. The total product ion abundance ratio of C-ring cross cleavage to C-ring bond cleavage, gamma, varied by a factor of 660 for deprotonated monohydroxyflavones, i.e., from 0.014:1 to 9.27:1. The magnitude of gamma, which is dependent on the relative bond orders within the C-ring of the protonated and deprotonated molecules of monohydroxyflavones, can be rationalized on the basis of the magnitudes of the 13C- and 1H-chemical shifts as determined by nuclear magnetic resonance spectroscopy.
authors.affiliation: Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 7B8, Canada.
authors.forename: Darcy C
authors.initials: DC
authors.lastname: Burns
authors.forename: David A
authors.initials: DA
authors.lastname: Ellis
authors.forename: Hongxia
authors.initials: H
authors.lastname: Li
authors.forename: Errol G
authors.initials: EG
authors.lastname: Lewars
authors.forename: Raymond E
authors.initials: RE
authors.lastname: March
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D047309:Flavones / Q000032:analysis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D047309:Flavones