Syntheses and crystal structures of 2,2,5-trimethyl-1,3-dioxane-5-carb-oxy-lic acid and 2,2,5-trimethyl-1,3-dioxane-5-carb-oxy-lic anhydride

In 2,2,5-trimethyl-1,3-dioxane-5-carb-oxy-lic acid, C H O , the carboxyl group occupies an equatorial position on the 1,3-dioxane ring. In the crystal, O-H⋯O hydrogen bonds form chains of mol-ecules, which are linked into a three-dimensional network by C-H⋯O hydrogen bonds. The asymmetric unit of 2,2,5-trimethyl-1,3-dioxane-5-carb-oxy-lic anhydride, C H O , consists of two independent mol-ecules, which are linked by C-H⋯O hydrogen bonds. In the crystal, these units are connected into corrugated layers two mol-ecules thick and parallel to the plane by additional C-H⋯O hydrogen bonds.