One hypothesis for the formation of the observed species is depicted in Scheme 1 and features intramolecular nucleophilic attack of a protonated adipic acid rotamer (AAH + rotamer) This presumably reflects a reduction of steric hindrance for the longer chains. As we show in the Supplementary Information, these species also undergo similar sequential loss of two water molecules and loss of CO upon CID, consistent with our observations of protonation adipic acid.