Low energy methyl glycolate radical cations , 1, abundantly lose HCO , yielding protonated methyl formate H-C(OH)OCH + 3 . Tandem mass spectrometry based experiments on 2 H, 1 3 C and 1 8 O labelled isotopologues show that this loss is largely (about 75%) atom specific. Analysis of the atom connectivity in the product ions indicates that the reaction proceeds analogously to the loss of HCO and CH 3 CO from ionized acetol and acetoin , respectively. The mechanism, it is proposed, involves isomerization of 1 to the key intermediate , an H-bridged ion-dipole complex of neutral formaldehyde and ionized methyl formate. Next, charge transfer takes place to produce an H-bridged ion-dipole complex of ionized formaldehyde and neutral methyl formate, followed by proton transfer to generate the products.Preliminary ab initio calculations executed at the UMP3/6-31G * //6-31G * +ZPVE level of theory are presented in support of this proposal. The non-specific loss of HCO from 1 (about 25%) is rationalized to occur via the same mechanism, but after communication with isomeric dimethyl carbonate ions 2, via the O H O bonded intermediate . The latter pathway is even more important in pathway is even more important in the formation of CH 2 OH + ions from 1 which, it is shown, is not a simple bond cleavage reaction, but may involve consecutive or concerted losses of CH 3 and CO 2 from the above O H O bonded species.Ionized methyl lactate , the higher homologue of 1, shows a unimolecular chemistry which is akin to that of 1.