TY - JOUR
T1 - Collision-induced dissociation mass spectra of positive ions derived from tetrahydropyranyl (THP) ethers of primary alcohols
AU - Ruzicka, Josef
AU - Weisbecker, Carl
AU - Attygalle, Athula B.
PY - 2011/1
Y1 - 2011/1
N2 - 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-2H-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.
AB - 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-2H-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.
KW - CID
KW - THP ethers
KW - alcohols
KW - fragmentation
KW - tetrahydropyranyl
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U2 - 10.1002/jms.1849
DO - 10.1002/jms.1849
M3 - Article
AN - SCOPUS:78651358887
SN - 1076-5174
VL - 46
SP - 12
EP - 23
JO - Journal of Mass Spectrometry
JF - Journal of Mass Spectrometry
IS - 1
ER -