Key D-substitution patterns for the energetically favored pathways leading to methanimine and methylamine from HNC and ¹[HC:NH₂]. Single deuterium substitutions are shown as color-coded H atoms. Bare values correspond to ZPE-corrected activation energies (in kJ mol⁻¹ ; when present), and values in parentheses indicate the transition-state imaginary frequencies (|v^‡|; in cm⁻¹). Reaction steps without any activation energy value are barrier-less.