Syntheses and crystal structures of 2,2,5-trimethyl-1,3-dioxane-5-carboxylic acid and 2,2,5-trimethyl-1,3-dioxane-5-carboxylic anhydride.

In 2,2,5-trimethyl-1,3-dioxane-5-carboxylic acid, C8H14O4, the carboxyl group occupies an equatorial position on the 1,3-dioxane ring. In the crystal, O-- H⋯O hydrogen bonds form chains of molecules, 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-carboxylic anhydride, C16H26O7, consists of two independent molecules, which are linked by C--H⋯O hydrogen bonds. In the crystal, these units are connected into corrugated layers two molecules thick and parallel to the ab plane by additional C--H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]