Free-jet absorption millimeter-wave spectrum of 2’-aminoacetophenone

The rotational spectrum of 2’-aminoacetophenone has been recorded and assigned using a Stark-modulated Free-Jet Absorption Millimeter-Wave (FJ-AMMW) spectrometer in the 59.6-74.4 GHz frequency range. Some transition lines show a hyperfine structure due to the internal rotation of the methyl group. A global fitting including previous measurements performed in the microwave region allowed the determination of the D J and D K quartic centrifugal distortion constants and methyl internal rotation barrier V 3 =644(3) cm −1 value. The A-E tunnelling splitting is estimated to be Δ 0 =23 MHz. Calculations at the MP2/aug-cc-pVTZ level underestimate the height of the V 3 barrier by about 23 cm −1 . This value increases to 150 cm −1 with B3LYP-D3(BJ)/Def2-TZVP. • Rotational spectrum of 2’-aminoacetophenone extended in the 60-74 GHz region. • The methyl internal rotation barrier is 7.70(4) kJ/mol. • V3 barrier higher than those of meta and para isomers and acetophenone.