Isotope labeling and infrared multiple-photon photodissociation investigation of product ions generated by dissociation of [ZnNO 3 (CH 3 OH) 2 ] + : Conversion of methanol to formaldehyde.

Electrospray ionization was used to generate species such as [ZnNO3 (CH3 OH)2 ]+ from Zn(NO3 )2 •XH2 O dissolved in a mixture of CH3 OH and H2 O. Collision-induced dissociation of [ZnNO3 (CH3 OH)2 ]+ causes elimination of CH3 OH to form [ZnNO3 (CH3 OH)]+ . Subsequent collision-induced dissociation of [ZnNO3 (CH3 OH)]+ causes elimination of 47 mass units (u), consistent with ejection of HNO2 . The neutral loss shifts to 48 u for collision-induced dissociation of [ZnNO3 (CD3 OH)]+ , demonstrating the ejection of HNO2 involves intra-complex transfer of H from the methyl group methanol ligand. Subsequent collision-induced dissociation causes the elimination of 30 u (32 u for the complex with CD3 OH), suggesting the elimination of formaldehyde (CH2  = O). The product ion is [ZnOH]+ . Collision-induced dissociation of a precursor complex created using CH3 -18 OH shows the isotope label is retained in CH2  = O. Density functional theory calculations suggested that the "rearranged" product, ZnOH with bound HNO2 and formaldehyde is significantly lower in energy than ZnNO3 with bound methanol. We therefore used infrared multiple-photon photodissociation spectroscopy to determine the structures of both [ZnNO3 (CH3 OH)2 ]+ and [ZnNO3 (CH3 OH)]+ . The infrared spectra clearly show that both ions contain intact nitrate and methanol ligands, which suggests that rearrangement occurs during collision-induced dissociation of [ZnNO3 (CH3 OH)]+ . Based on the density functional theory calculations, we propose that transfer of H, from the methyl group of the CH3 OH ligand to nitrate, occurs in concert with the formation of a Zn-C bond. After dissociation to release HNO2 , the product rearranges with the insertion of the remaining O atom into the Zn-C bond. Subsequent C-O bond cleavage, with H transfer, produces an ion-molecule complex composed of [ZnOH]+ and O = CH2 .