Isotope effects play a pivotal role in chemistry and biology. Protein stability strongly depends on deuteration of the protein-backbone or deuteration of the solvent water. The change from protonated to deuterated water increases the strength of the solvent-solvent as well as the solvent-protein hydrogen bonds and thus significantly influences the protein-folding process. Isotope effects are also crucial in atmospheric chemistry, where isotopic compositions change as a function of temperature and pressure, strongly affecting chemical reactions. D-bonds are assumed to be stronger than H-bonds due to quantum effects, mainly the lowering of the zero point vibrational energy. Since H and D are electronically identical, the total energies of the related complexes are equal, and differences are associated with the masses and mass distributions, primarily governed by vibrational energies. What is well established for hydrogen-bonded molecular liquids such as water and methanol is still unclear for hydrogen bonded cations and anions in ionic liquids (ILs). These liquid materials attract increasing interest in science and technology due to their unique properties, which result from the delicate balance of Coulomb interactions, hydrogen bonding and dispersion forces between the charged entities. Specific strength, locality and directionality of the different types of interactions govern the structure, dynamics, and phase behavior of ILs. For structure determination of molecular as well as ionic liquids, isotopic labeling is used in neutron diffraction experiments assuming that the structure is similar for the differently labelled species, regardless where and to which extend they are deuterated. However, there are some scattering studies indicating that this prerequisite is not always justified. The importance of high conductivity electrolytes for devices such as fuel cells, batteries, and solar cells is a compelling motivation for studying deuterium isotope effects in ILs. It is the purpose of our work to study the influences of isotopic substitution on hydrogen bonding and structural ordering of the model protic ionic liquid (PIL) triethylammonium methanesulfonate [TEA][OMs] by means of deuterium solid-state NMR spectroscopy. We use the N-D deuterons of the triethylammonium cations for probing structural rearrangements, equilibria between static and mobile states and hydrogen bonding depending on selective deuteration of the three ethyl groups. We show that structural changes and interactions vary characteristically with temperature and that the equilibria between static and mobile fractions in the PIL are highly sensitive to deuteration of the alkane chains with respect to both, the transition temperature and the cooperativity of the transition. We demonstrate that solid-state NMR spectroscopy is a suitable method for understanding the origin of changes in thermodynamic, structural and dynamical properties in complex materials caused by isotopic substitution.