Gas-phase Conformational Landscape and Ring-puckered Structure of 1-aminoindane.

Indane-based molecules are effective scaffolds for different pharmaceutical products, so it is relevant to analyze the relation between structure and functionality in indane derivatives. Here, we have characterized the conformational landscape and molecular structure of 1-aminoindane in the gas phase using chirped-excitation Fourier-transform microwave spectroscopy and computational methods. The rotational spectrum confirmed the presence of two conformers, which were identified based on their rotational constants and ¹⁴N nuclear quadrupole coupling tensor elements. The observed conformers share the cyclopentane puckering and amino equatorial configuration but differ in the orientation of the amino group hydrogens. The spectral analysis further allowed the observation of all monosubstituted ¹³C and ¹⁵ N isotopologues in natural abundance for the most stable isomer, allowing a precise structural determination for this species. Structural information was derived using the substitution ( $r_s$ ) and effective vibrational ground state ( $r_0$ ) methods, revealing that the structure of 1-aminoindane is very similar to that of indane. A calculation of the potential energy surface along the pathway for the conversion between the most stable equatorial species permitted to rationalize the non-observation of additional conformers via molecular relaxation during the adiabatic expansion. The computational results include ab initio (MP2) and DFT methods (B3LYP, ωB97X-D and M06-2X).