A DFT investigation exploring the influence of lone electron pair on hyperfine structures of N-centered radicals

Highlights: • One basis set could not get accurate AN value for NLP and LP radicals simultaneously. • Accurate A_N value of NLP radicals could be acquired by simple DFT method. • The SOP effect could be induced by the high spatial symmetry of system. -- Abstract: The accurate calculation of nitrogen hyperfine coupling constants ($A_{\text{N}}$ value) for different N-centred radicals is still a challenge. Since the different rehybridization of hybrid orbitals could be regarded as the main discrepancy between nitrogen centered radicals with the presence (LP) and absence (NLP) of lone pair of electrons, the spin polarization contribution to$A_{\text{N}}$ value arising from valence orbitals (SOP effect) are more important than spin polarization effect (SP) for NLP radicals. Considering this effect, 159 nitrogen centered radicals have been calculated using the B3LYP density functional with different Pople basis sets. Compared with current methods using same basis set, for 52 nitrogen radicals with lone electron pair (such as Aniline, C₄H₈N, etc.) and dominant SP effect, comparable results to literature was got by B3LYP level with 6-31++G(3d,3p) basis set, however, for 122 nitrogen radicals without lone electron pair (such as DMPO/OH, C₄H₈NH⁺, etc.), better computational accuracy (RMS = 0.118) was achieved by B3LYP level with 6-31++G basis set and IEFPCM solvent model which can reflect the significant SOP effect in this kind of radicals.