Microwave spectrum, molecular structure and dipole moment of pivalaldehyde

Abstract

The microwave spectra of eight isotopic species of pivalaldehyde [(CH₃)₃CCHO] have been studied in the frequency region 9–40 GHz. The zero-point average skeletal structure has been derived to be: r[C(1)O]= 1.206(6)Å, r[C(1)–H]= 1.130(5)Å, r[C(1)–C(2)]= 1.516(7)Å, r[C(2)–C(3)]=r[C(2)–C(4),(5)]= 1.537(2)Å, ∠ C(1)C(2)C(3)= 110.5(4)°, ∠ C(1)C(2)C(4),(5)= 107.4(3)°, proj.∠ C(4),(5)C(2)C(1)= 120.78(4)°, ∠ CCO = 126.0(5)° and ∠ CCH(1)= 113.0(3)°. The tert-butyl group is found to be tilted 2° away from the CO bond. Accurate Stark effect measurements have been performed on the main species, (CH₃)₃CCDO and (CD₃)₃CCHO. The ground-state dipole moment of (CH₃)₃CCHO was determined as µ_a= 2.618(5) D and µ_b= 0.728(2) D giving µ_total= 2.717(5) D at an angle of 13.6° to the CO bond.