Molecular structure of trans-cinnamaldehyde as determined by gas electron diffraction aided by DFT calculations

Abstract

The molecular structure of trans-cinnamaldehyde (( E)-3-phenyl-2-propenal) was determined by means of gas electron diffraction. The nozzle temperature was 165 °C. The results of B3LYP calculations with the 6-31G ∗∗ basis set were used as Supporting information. It was found that this molecule has two stable conformers, s- cis and s- trans, which differ in the orientation of the CH O group. Their abundances at 165 °C were determined to be 25 ± 19% and 75%, for the s- cis and s- trans, respectively. This conformational composition is consistent with the prediction by the theoretical calculations. The determined structural parameters ( r g and ∠ α) of the more abundant conformer, s- trans, of trans-cinnamaldehyde are as follows: < r(C C) ring> = 1.398(1) Å; r(C C) = 1.348 (←) Å; r(C 1 C) = 1.470(8) Å; r(C C( O)) = 1.473(←) Å; r(C O) = 1.225(6) Å; < r(C H)> = 1.116(6) Å; ∠C 6 C 1 C 2 = 118.6(3)°; ∠C 1 C 2 C = 121.0(←)°; ∠C C 6 C 1 = 121.4(←)°; ∠C 2 C 1 C( C) = 122.0(26)°; ∠C 1 C C = 128.3(26)°; ∠C C CO = 115.3(27)°; ∠C C O = 126.6(19)°. The C 1, C 2 and C 6 atoms are on the ring with the C 1 attached to the CH CH CHO group, and the C 2 and C 6 are on the cis and trans sides to the C C bond, respectively. Angle brackets denote average values; parenthesized values are the estimated limits of error (3 σ) referring to the last significant digit; left arrows in the parentheses mean that the differences to the preceding parameters are fixed.