Substituent effect on fragmentations and ion-molecule reactions of ionized alkyn alcohols

The fragmentation patterns and ion-molecule reactions of two alkyn alcohols, 2-propyn-1-ol (HC≡CCH₂OH) and 2-methyl-3-butyn-2-ol (HC≡CC(CH₃)₂OH), were investigated using Fourier transform mass spectrometry (FTMS). The most abundant fragment ions formed from the molecular ions were [M-H]⁺ for 2-propyn-1-ol and [M-CH ₃]⁺ for 2-methyl-3-butyn-2-ol. The dehydrated ion, [M-H₂O]⁺ was formed only from 2-propyn-1-ol in which α-hydrogen atoms were available for α,α-elimination reaction. The protonated molecules were dissociated into [M+H-H₂O]⁺ and [M+H-C₂H₂]⁺ through dehydration and deacetylenylation processes. The formations of [M+H-H₂O]⁺ and [M+H-C₂H₂]⁺ from 2-methyl-3-butyn-2-ol were more favorable than those from 2-propyn-1-ol due to stabilization by two methyl groups at α-carbon. Ion-neutral complexes formed at long ion trapping time gave dehydrated and/or deacetylenylated ion products by further dissociation.