Reviriego, FelipeDelgado Martínez, PatriciaTorralba, María del CarmenClaramunt, Rosa M.Alkorta, IbonElguero, José2025-10-092025-10-092025-09-27Felipe Reviriego, Patricia Delgado-Martínez, M. Carmen Torralba, Rosa M. Claramunt, Ibon Alkorta, José Elguero The structure of N-(5-aminopyrimidin-2-yl)-N-methyl-2-methoxymethylaniline in solid state (X-ray crystallography) and in solution (NMR) and determination of its protonation site Journal of Molecular Structure 1351 (2026) 144176. https://doi.org/10.1016/j.molstruc.2025.1441760022-2860 | eISSN 1872-8014https://doi.org/10.1016/j.molstruc.2025.144176https://hdl.handle.net/20.500.14468/30356The registered version of this article, first published in Journal of Molecular Structure 1351 (Part 1) 144176, is available online at the publisher's website: https://doi.org/10.1016/j.molstruc.2025.144176La versión registrada de este artículo, publicado por primera vez en Journal of Molecular Structure 1351 (Part 1) 144176, está disponible en línea en el sitio web del editor: https://doi.org/10.1016/j.molstruc.2025.144176This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021–125207NB-C32). Library and scientific-technical services of the Universidad Nacional de Educación a Distancia (UNED) are greatly acknowledged. Thanks are also given to the CTI (CSIC) for their continued computational supportThe structure of the title compound was determined both in the solid state by crystallography and in solution by NMR, particularly concerning the conformation around the C2–N8 bond. Hirshfeld surface (HS) analysis of this molecule was performed, using Crystal Explorer 25.09, in order to evaluate the zones of potential intermolecular contacts in the crystal as well as to determine the atoms involved. As crystals of the protonated form could not be obtained due to the rapid decomposition of the pyrimidine ring, multinuclear 1H, 13C, and 15N NMR spectroscopy was employed. This revealed that protonation occurs on the ring nitrogens in a 90/10 ratio. Theoretical calculations of geometries and energies have been carried out at the Becke Three-parameter Lee–Yang–Parr (B3LYP)/6–311++G(d,p) level, and the optimized structures used to calculate chemical shifts via the Gauge-Invariant Atomic Orbital (GIAO) method. These calculations were crucial to draw definitive conclusions.eninfo:eu-repo/semantics/openAccess2306 Química orgánica2302 Bioquímicaartículo5-aminopyrimidinesX-ray crystallographyB3LYP/6-311++G(d,p) calculationsProtonation site