Collision-induced dissociation mass spectra of positive ions derived from tetrahydropyranyl (THP) ethers of primary alcohols

✍ Scribed by Josef Ruzicka; Carl Weisbecker; Athula B. Attygalle

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 560 KB
• Volume: 46
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1849

✦ Synopsis

Abstract

Peaks for [M + H]^+^ are not observed when electrospray ionization mass spectra of tetrahydropyranyl (THP) ethers are recorded under acidic conditions. However, gaseous [M + H]^+^ ions can be generated from ammonium adducts of THP ethers of primary alcohols by in‐source fragmentation. The product ion spectra of these proton adducts show two significant peaks at m/z 85 and 103. Tandem mass spectrometric data obtained from appropriately deuteriated derivatives and ab initio calculations indicate that the m/z 85 ion originates from more than one mechanism and represents two structurally different species. A charge‐directed E1‐elimination mechanism or an inductive cleavage mechanism can produce the 3,4,5,6‐tetrahydropyrylium ion as one of the structures for the m/z 85 ion, whereas a charge‐remote process with ring contraction can generate the 5‐methyl‐3,4‐dihydro‐2__H__‐furylium ion as the other structure. A comparison of the relative abundances of product ions from different isotopologues showed that the charge‐remote process is the preferred mechanism. This is congruent with the ab initio calculations, which showed that the dihydrofurylium ion bears the lowest energy structure. The less abundant m/z 103 ion, which represents a protonated tetrahydropyran‐2‐ol, is formed by a charge‐remote process via a proton transfer from the alkyl substituent. This process involves the formation and rearrangement of a carbenium ion in close association with a hydroxypentanal molecule. A proton transfer from the carbenium ion to the aldehyde is followed by elimination of an alkene. Copyright © 2010 John Wiley & Sons, Ltd.