Molecular dynamics of polycrystalline alpha-L-fucopyranose and methyl alpha-L-fucopyranoside have been investigated using (13)C and (1)H spin relaxation times over a range of temperatures (90-400 K). For methyl alpha-L-fucopyranoside at 300 K, both methoxyl and methyl groups had much shorter (13)C T(1) than the carbons in the pyran ring. (13)C T(1) relaxation measurements (at 74.56 MHz) as a function of temperature enabled characterization of the 3-fold rotations of the methoxyl (E(a) similar to 9 kJ/mol, tau(c) similar to 0.7 x 10(-13) s) and methyl (E(a) similar to 9 kJ/mol, tau(c) similar to 2 x 10(-13) s) groups. Proton T(1) (100 MHz) measurements of methyl alpha-L-fucopyranoside showed that the relaxation processes (E(a) similar to 11 kJ/mol, tau(c) similar to 0.7 x 10(-13) s), Corresponding to rotations of the methoxyl and methyl groups, are not distinguishable and occurred together at about 131 K. For alpha-L-fucopyranose, proton T(1) showed a relaxation rate maximum at 224 K, attributed to the 3-fold rotation of methyl group (E(a) similar to 15 kJ/mol, tau(0) similar to 2.6 x 10(-13) s). The rotation processes of the methyl groups dominated T(1rho) processes for both saccharides and appeared at the low-temperature end (90-150 K) of the temperature range. Contributions of hydroxyl groups to both T(1) and T(1rho) processes were obscured by the overwhelming relaxation efficiency of methyl groups. The proton second moment showed a reduction to a lower value at about 150 K due to the rotation of methyl groups.