Abstract Theoretical studies on the thermolysis in the gas phase of three methyl β‐hydroxycarboxylates RR′C(OH)CH 2 COOCH 3 , methyl 3‐hydroxypropanoate (primary alcohol, I ), methyl 3‐hydroxybutanoate (secondary alcohol, II ) and methyl 3‐hydroxy‐3‐methylbutanoate (tertiary alcohol, III ), were carried out using ab initio theoretical methods at the MP2/6–31G(d) and MP2/6–311+G(d,p) levels of theory. The pathways describe a mechanism via a six‐membered cyclic transition state, with the formation of an aldehyde or a ketone and an enol intermediate, followed by the tautomerization of this intermediate to methyl acetate. The progress of the reactions was followed by means of the Wiberg bond indices. The results indicate that the transition states are late, and the proton transfer is the more advanced process. The kinetic parameters calculated for the reactions studied agree well with the available experimental results. A theoretical study on the kinetic deuterium isotope primary and α‐ and β‐secondary effects was also carried out. Copyright © 2004 John Wiley & Sons, Ltd.