Conformations and Structures of 3-Oxopentanenitrile and 4-Methyl-3-oxopentanenitrile Revealed by Rotational Spectroscopy.

The conformations and molecular structures of two cyano-substituted ketones, namely 4-methyl-3-oxopentanenitrile (MPN) and 3-oxopentanenitrile (PN), have been investigated by using supersonic jet Fourier transform microwave (FTMW) spectroscopy. The rotational spectrum of a single conformation was measured and assigned for 4-methyl-3-oxopentanenitrile (MPN-I) and 3-oxopentanenitrile (PN-I), respectively. Additional measurements were conducted for 13C and 15N singly substituted isotopologues of conformer PN-I in natural abundance. The comprehensive rotational spectroscopic investigations yield accurate values for the rotational constants and 14N quadrupole coupling constants, which facilitate the structural elucidations of the observed conformers. For conformer PN-I, the near constancy of the Pcc values upon isotopic substitution indicates that the heavy atoms of this conformation are closely located to the ab-plane. Quantum chemical calculations, noncovalent interaction analysis, and molecular electrostatic surface potentials provide further insight into the energetics and structures of the two molecules.