Chemical ionization mass spectra of the stereoisomeric 1,5‐anhydropentofuranoses, 1,6‐anhydrohexofuranoses and 1,6 : 3,5‐dianhydrohexofuranoses

The isobutane and methane direct chemical ionization (DCI) mass spectra of mono‐ and dianhydrosugars are substantially influenced by their stereochemistry at temperatures of 150–250°C. The best results are obtained under isobutane CI at 200 or 250°C. l,6:3,5‐Dianhydrogulofuranose gives proton‐bridge stabilized MH + ions and fewer fragment ions compared with its ido epimer. The four diastereomeric 1,5‐anhydropentofuranoses show increased MH + and M 2 H + abundances for the lyxo and ribo isomers with cis ‐1,2‐diol sites capable of proton bridging. The xylo isomer gives a dominant [M OH] + ion. All isomers, but especially xylo and ribo , give abundant [C 3 H 5 O 2 ] + skeleton cleavage ions. They are attributed to an RDA fragmentation of pyranoglycosyl‐type MH + ions. The eight diastereomeric 1,6‐anhydrohexofuranoses with endo / exo configured triol structures show very characteristic MH + abundances (4–41% Σ). They parallel the amount of proton solvation in cis ‐diol sites of the isomers ( gluco ⩽ ido ⩽ altro < gulo < galacto < talo < allo < manno ). The [M OH] + ion abundances (15–47% Σ) are also very characteristic ( galacto ⩽ talo < manno < altro ≪ atto < gluco ⩽ ido ≪ gulo ). They reflect the possible H 2 O or C 4 H,OH loss from the MH + and (M · C 4 H 9 ] + ions, respectively, with formation of protonated 1,6:3,5‐and 1,6: 23‐dianhydrehexofuranose species; the slightly flattened C(5) site of M might favour the departure of the 5‐OH group. In addition, there are especially high abundances of skeleton fragment ions, 15% Σ [MH HCOOH] + , 10% Σ [M OH H 3 O CH 3 O] + and 42% Σ [M OH C 2 H 4 O 2 ) + , for the ido , galacto and gluco isomers, respectively.