Rotational spectrum and quantum chemical calculations of methyl cyanoacetate: A compound of potential astrochemical interest

Abstract

The rotational spectrum of methyl cyanoacetate (H3CO(CO)CH2CN) was investigated for the first time using Fourier transform microwave spectroscopy in the 6–19 GHz range. The observed spectral pattern is that of a single, dominant conformer and reveals both 14N quadrupole hyperfine structure and characteristic A/E splittings due to the methyl internal rotor. The rotational constants determined from analysis of the complex spectral pattern confirm that the observed spectrum is that of the lowest energy conformer of methyl cyanoacetate predicted at the B3LYP-D3(BJ) and MP2 levels of theory using the aug-cc-pVTZ basis set. This global minimum corresponds to a geometry which orients the COCO and CCCO dihedral angles in syn and near anti arrangements, respectively and is governed by a balance of stabilizing orbital interactions and destabilizing steric effects identified using non-covalent interaction and natural bond orbital analyses.