Theoretical Insights into Alanine Maleate and Alanine Fumarate: NLO‐Active Single Crystals Stabilized by N─H Intramolecular Hydrogen Bonding

ABSTRACT The DFT study of Alanine Maleate and Alanine Fumarate NLO crystals assisted by B3LYP/6‐31+G * in the gas phase investigates the optimized geometry, Mulliken charges, Frontier Molecular Orbitals (FMO), Hyperpolarizability, and Vibrational spectra of the molecules. The Natural Bond Orbital analysis of Alanine Maleate and Alanine Fumarate sheds light on the hyperconjugative interactions of LP N3 → σ* H5─O25 and LP N3 → σ * O23─H24, suggesting the existence of the hydrogen bond between N3─H5 and N3─H24, respectively. The analysis of Quantum Theory of Atoms in Molecules (QTAIM) with the help of Multiwfn revealed the type of hydrogen bonding on the basis of topological parameters at the Bond Critical Points. The Reduced Density Gradient study has facilitated a pictorial depiction of the strong hydrogen bonding of N─H and other Non‐Covalent Interactions (NCI) present within the molecules. The kinetic stability of the material has been sufficiently indicated by the HOMO‐LUMO energy gap. The UV spectra obtained from TD‐DFT highlighted the transparency of Alanine Maleate and Alanine Fumarate above 300nm in the UV region, with a cut‐off wavelength around 250nm. The Molecular Electrostatic Potential Surface displayed the electrophilic sites of Alanine Maleate and Alanine Fumarate. The theoretically predicted IR and Raman spectra demonstrated the characteristic vibrations of the functional groups, including the N─H hydrogen bonds. The computed first‐order Hyperpolarizability value of Alanine Maleate and Alanine Fumarate is 3.9 and 1.64 times that of Urea, quoting its prominent NLO efficiency.