Absolute configuration assignment of ortho, meta, or para isomers by mass spectrometry

• Published in: Journal of the American Society for Mass Spectrometry Vol. 16; no. 4; pp. 431 - 436
• Main Authors: Moraes, Luis Alberto B., Sabino, Adão A., Meurer, Eduardo C., Eberlin, Marcos N.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.04.2005; Elsevier Science; Springer Nature B.V
• Subjects: Cations; Chemistry; Configuration management; Configurations; Derivatives; Diagnostic systems; Exact sciences and technology; Ions; Isomers; Mass spectra; Mass spectrometry; Nitrobenzene; Organic chemistry; Reactivity and mechanisms; Structural analysis; Nitro compound; Collisional activation; Position isomer; Separation; Mass spectrometry MS/MS; Benzene derivatives; Absolute configuration; Ketone; Mass spectrometry; Structural analysis
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/j.jasms.2004.12.001

A general method based solely on mass spectrometric techniques for the absolute configuration assignment of ortho, meta, or para isomers of acyl nitrobenzenes and derivatives is described. Instead of comparing the mass spectra of the three intact molecules of each positional isomer and investigating each one of the many sets of positional isomers, the method generalizes the effort by performing structural analysis on configurationally diagnostic fragment ions that are common for a given class of compounds. These ions must therefore retain the positional information of the parent molecules and be unequivocally distinguished. Nitrobenzoyl cations are common and stable fragment ions of most acyl nitrobenzenes and derivatives retaining the respective ortho, meta, or para configuration of the precursor molecules. The different NO 2 and CO + ring alignments profoundly influence their collision-induced dissociation and bimolecular reactivity, and the isomeric 2-, 3-, and 4-nitrobenzoyl cations are found to be unequivocally distinguished using both approaches. Absolute ortho, meta, or para positional assignment by tandem MS of every isomeric molecule of the acyl nitrobenzene class and derivatives forming detectable amounts of any of those diagnostic nitrobenzoyl cations is, therefore, possible. The ability to perform absolute (non-comparative) configuration assignment using such diagnostic ions is exemplified for a single test molecule of (2R)-(−)-2-methylglycidyl 4-nitrobenzoate. The general application of this absolute MS-only method for other classes of positional isomers is discussed.