**1**3c nmr in solution has been employed to make a comparative study of the distribution of the substituents in carboxymethyl ethers of amylose, dextran and cellulose. the resonance signals of the **1**3c nuclei in the spectra of the compounds studied is fully interpreted providing quantitative information on the position of the carboxymethyl groups in the d-glucopyranose unit of the macromolecules of the above mentioned polysaccharides. the reactivity of the oh groups in the reaction of carboxymethylation of amylose drops in the series c//6 $greater than$ c//2 $greater than$ c//3 while for cellulose c//2 $greater than$ c//6 $greater than$ c//3 and for dextran c//3 $greater than$ c//2 $greater than$ c//4. the influence of the structural factors on the difference in the reactivity of the oh group for certain positions of the carbon atoms of the pyranose cycle of the macromolecules of the polysaccharides of similar structure but differing in the details of the structure is discussed. (author abstract) 28 refs