In organic chemistry, an orthoester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula RC(OR′)₃. Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name 'ortho ester' is derived. An example is ethyl orthoacetate, CH₃C(OCH₂CH₃)₃, more correctly known as 1,1,1-triethoxyethane. Orthoesters are used in organic synthesis as protecting groups for esters.