title: Mass spectrometry of analytical derivatives. 2. "Ortho" and "Para" effects in electron ionization mass spectra of derivatives of hydroxy, mercapto and amino benzoic acids.
abstract: Derivatives requiring either anhydrous or aqueous reaction conditions were prepared for robust and reliable gas chromatography/mass spectrometry (GC/MS) characterization of hydroxyl, mercapto, and amino benzoic acids Methylation and trialkylsilytation are employed for blocking the acidic function. Alkyl, trimethylsilyl, acetyl, perfluoroacyl and alkoxycarbonyl derivatization groups are introduced to hydroxyl, mercapto and amino functions. The electron ionization induced fragmentation characteristics of corresponding derivatives are explained by comparing the MS1spectra of unlabeled compounds to their2H and13C labeled analogs, and analysis of collision-induced dissociation data from MS2spectra. Competing fragmentation alternatives are identified and specific decomposition processes are detailed that characterize (a)orthoisomers due to interaction or vicinal functional substituents and (b)paraisomers prone to formingparaquinoid type structures. Skeletal and hydrogen rearrangements typical for methyl benzoates and the blocking groups are considered when discussing diagnostically important ions. Characteristic ions produced as a result of rearrangements inorthoisomers are classified, and skeletal rearrangements required to produceparaquinoid type ions specific for para isomers are noted. Key ions for structure elucidation and differentiation of isomers for derivatives of substituted benzoic acids by GC/MS are suggested.
authors.affiliation: National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8362, USA.
authors.forename: Nino G
authors.initials: NG
authors.lastname: Todua
authors.affiliation: National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8362, USA.
authors.forename: Anzor I
authors.initials: AI
authors.lastname: Mikaia
keywords: alkoxycarbonyl derivatives; alkylation; anthranilic acid; derivatization; gas chromatography/mass spectrometry (GC/MS); perfluoroacylation; salicylic acid; silylation; thiosalicylic acid; “ortho effect”; “para effect”