Origin of the [C4H9O]+ ions in the mass spectrum of n‐butyl ethyl ether

Abstract

AbstractThe mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C4H9O]+ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α‐ and β‐hydrogens and a γ‐hydrogen from the butyl group. The minor route involves the loss of ethylene from the [MH]+ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α‐ and β‐methylenes and a γ‐hydrogen, while the methyl is the δ‐methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec‐butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n‐ and sec‐butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n‐pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3‐pentyl and 2‐pentyl ether ions. Di n‐butyl and n‐butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.