Molecular structure and conformation of diisopropyl ketone studied by gas electron diffraction combined with vibrational spectroscopy and SCF MO calculations

Molecular mechanics calculations on carbonyl compounds. II. Open‐chain ketones

“…Conformers 1 and 5 were found from the MM3 and MM4 stochastic searches. Conformer 1 had C 2 symmetry like conformer 2 , except the methyl groups were rotated about 30° from the eclipsed positions and it was different from the C 2 structure found by Takeuchi et al11 ( 2 ). Both MM3 and MM4, as well as DFT, found conformer 1 to be the most stable and the other C 2 conformer ( 2 ) with the eclipsed methyl groups to be the second most stable.…”

“…Both MM3 and MM4, as well as DFT, found conformer 1 to be the most stable and the other C 2 conformer ( 2 ) with the eclipsed methyl groups to be the second most stable. The second conformer ( 5 ) found had C 1 symmetry, but it was different from the C 1 conformer found by Takeuchi et al11 In this conformer, one of the isopropyl CH bonds was ≈40° with respect to the C′O bond and one of the methyl groups on the other side of the carbonyl was about 20° from the eclipsed position.…”

“…The experimental and calculated structures of acetone, 2‐butanone, methyl isopropyl ketone, and diisopropyl ketone are given in Tables III and IV and Supplementary Material Tables S‐I and S‐II. The MM3 and MM4 r g structures were compared to the structures determined by ED 8–11. In addition, MM3 and MM4 calculated ( r z ) structures were compared to MW structures for acetone and 2‐butanone 12.…”

“…The r g geometries for diisopropyl ketone are listed in Table S‐II of the Supplementary Material. The ED structure was determined by Takeuchi et al11 Due to the complexity of this molecule, they reported only the average CC (1.541 Å) and average CH (1.118 Å) bond lengths. The DFT (B3LYP/6‐31G*), MM3, and MM4 calculations on this molecule showed that the lowest energy conformer had C 2 symmetry.…”

“…A gas‐phase ED study was reported for this molecule by Takeuchi et al11 They also studied the conformations of this molecule at the SCF level with a 4‐21G basis set. They found three conformers with C 2 , C 1 , and C s symmetries (conformers 2 , 3 , and 4 , Fig.…”