The rates of exchange of acetate—concurrent with anomerization—between the C1-acetoxy groups of the pentaacetates (0.05 M) ofD-glucose andD-mannose and stannic trichloride acetate (0.05 M) in chloroform containing stannic chloride (0.05 M) were determined at 40 °C. using isotopically labelled acetate. 1,2-trans-α-D-Mannose pentaacetate underwent exchange seven times more rapidly than the β-1,2-cis-anomer but eight times less rapidly than 1,2-trans-β-D-glucose pentaacetate. The latter compound was 450 times more reactive than the α-1,2-cis-anomer. In accordance with these results, theD-mannose pentaacetate underwent mercaptolysis in ethyl mercaptan containing zinc chloride at rates intermediate to those found for theD-glucose pentaacetates. The main product from the mannose pentaacetates was in each case ethyl 1,2-trans-α-D-1-thiomannopyranoside tetraacetate (60–70% yield). Tetra-O-acetyl-β-D-glucopyranosyl chloride with silver acetate gave β-D-glucose pentaacetate when the reaction was carried out in dry acetic acid but gave 2,3,4,6-tetra-O-acetyl-α-D-glucose in 90% aqueous acetic acid. Tetra-O-acetyl-β-D-glucopyranosyl chloride with methanol and silver carbonate gave a sirupy product with the properties expected for methyl 1,2-ortho-O-acetyl-α-D-glucopyranose triacetate. The substance was hydrolyzed by 0.005 Nhydrochloric acid in 95% dioxane 18 times more rapidly than the corresponding derivative of β-D-mannose. The significance of these observations toward an understanding of the effect of configuration on reactivity is discussed.