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

•Rotational spectrum of methyl cyanoacetate recorded in the 6–18 GHz range in a supersonic jet.•Geometry of lowest energy conformer has CH3 and CN groups syn and near anti to CO, respectively.•Orientation of CN group governed by delicate trade-off between repulsive steric and attractive hyperconjugative interactions.•Barriers to large amplitude motions involving the methyl rotor and out-of-plane CN motion described.