Deuterium magic angle spinning (MAS) NMR is used to study the dynamics of an organic molecule, N-[triethoxysilylpropyl]acetamide-d₃, grafted at the inner surface of the mesoporous silica material, MCM-41. The grafted molecule has a deuterated methyl group at its free terminus to monitor its local mobility through changes in its dynamic ²H-MAS NMR spectrum. Different spectra were recorded as a function of temperature from two different water containing samples. Observation shows that a major part of the grafted molecule remains static, irrespective of the temperature and hydration state of the sample, whereas the rest shows spectral changes indicative of a two-site jump motion of the methyl groups. Experimental observations were substantiated using molecular dynamic (MD) simulations of the grafted molecule. Subsequently, the MD results corroborate a model for the grafted molecules experiencing an exchange between two conformations consistent with the analysis of the ²H-MAS NMR spectra.