The enol of glycine, H 2 N-CH C(OH) 2 , is generated in the gas phase by neutralization of the corresponding radical cation, which is available by dissociative electron ionization of isoleucine. Reionization ∼0.6 µs later shows that the isolated enol (2) exists and does not isomerize to the significantly more stable glycine molecule, H 2 N-CH 2 -COOH (1); hence the intramolecular tautomerization 2 → 1 must be associated with high barriers. The neutralization-reionization reactivity of 1 Yž further confirms that neutral glycine has a canonical structure (1) and is not a zwitterion. The unimolecular chemistry of 1 Yž is dominated by C-C bond cleavage to the immonium ion Y H 2 NCH 2 ; in sharp contrast, 2 Yž primarily loses H 2 O. The ylide ion Y H 3 N-CH ž -COOH, an intermediate in the water loss from 2 Yž , is found to readily equilibrate to 2 Yž prior to dissociation. Tautomers 1 Yž and 2 Yž differ in their charge-stripping behavior, with only 2 Yž forming a stable dication. The radical anions 1 -ž and 2 -ž , formed by charge reversal of 1 Yž and 2 Yž , respectively, dissociate extensively to (mainly) different closed-shell fragment anions. An important channel is H ž loss; 1 -ž yields the carboxylate ion H 2 N-CH 2 -COO -whereas 2 -ž yields the enolate ion H 2 N-CH C(OH)O -.