Abstract
The mechanism of the collision‐induced fragmentation of peracetylated methyl‐α‐D‐glucopyranoside was investigated using deuterium‐labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C~14~H~19~O~9~]^+^. This ion further dissociates via two pathways, the first including m/z 271, [C~12~H~15~O~7~]^+^, 169, [C~8~H~9~O~4~]^+^ and 109, [C~6~H~5~O~2~]^+^, and the second including m/z 211, [C~10~H~11~O~5~]^+^, 169, [C~8~H~9~O~4~]^+^ and 127 [C~6~H~7~O~3~]^+^. The first path proceeds via loss of acetate at C(3), followed by a single‐step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)‐acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill‐defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single‐step concerted loss of acetates from C(2) and C(4).