The mechanism of the recently discovered, unusual tetrabutylammonium fluoride (TBAF) deacylation of cellulose esters has been investigated by methods including kinetic isotope effect (KIE) studies. The secondary KIE (k(H)/k(D) = 1.26 +/- 0.04) measured for deacylation at C-2/3 suggests a mechanism involving a ketene intermediate for those positions. An inverse KIE (k(H)/k(D) = 0.87 +/- 0.03) for the deacylation at C-6 indicates the involvement of a tetrahedral intermediate in the mechanism. Additional studies suggest the possibility that TBAF chelation by neighboring acyl groups may account for the unexpected regioselectivity at the secondary alcohol esters that is observed in the TBAF deacylation of cellulose esters.