An Electron Diffraction Investigation of the Molecular Structure of trans-2-Butenedial (Fumaraldehyde) in the Vapour Phase.

Structure and Properties of Fumaryl Fluoride

“…[ 16,17 ] In acrolein e.g., the configuration of the lowest energy is the trans ‐position [ 17,18 ] with an energy difference to the cis conformer of 6.99 kJ · mol –1 . [ 19 ] This is consistent with fumaraldehyde [ 11,20 ] existing only as its trans‐trans rotational isomer revealing an energy difference to the cis‐cis species of 13.50 kJ · mol –1 . [ 20 ] The energy differences between the cis and the trans species for some molecules of the general formula RHC=CHC(O) X are summarized in Table 4.…”

“…A comparison of the bond lengths and angles of fumaryl fluoride with fumaryl chloride [ 10 ] and fumaraldehyde [ 11 ] is summarized in Table S3 (Supporting Information). Drawing comparisons of fumaryl fluoride with these two derivatives is very interesting, based on the atomic size of fluorine, lying in‐between hydrogen and chlorine.…”

“…The C=O bond lengths [1.190(2) Å (C2–O1)] of fumaryl fluoride agree well with formal C=O double bonds (1.19 Å) [ 12 ] and the C=O bond in fumaryl chloride. [ 10 ] However, this bond is significantly shorter than in fumaraldehyde [1.207(2) Å], [ 11 ] which is attributed to the strong electron‐withdrawing effect of fluorine. The C–F bond lengths are with 1.334(2) Å slightly shorter than formal C–F bonds (1.36 Å).…”

“…In contrast to fumaraldehyde, for which only one conformer ( trans‐trans ) was found, [ 11 ] in fumaryl fluoride and fumaryl chloride, a mixture of different rotational isomers was observed, respectively. [ 6,8 ] Using the values in Figure 6, we find that the cis‐trans conformer of fumaryl fluoride has an energy 1.12 kJ · mol –1 higher than the trans‐trans conformer.…”

“…Comparing the three discrete rotational isomers, their energy differences were calculated at the CCSD‐FC/aug‐cc‐pVTZ level of theory. Comparison to related molecules like fumaryl chloride [ 8 ] and fumaraldehyde [ 11 ] showed that the substitution of a halogen atom for an aldehyde proton has a considerable effect on the energy of the conformation. The same impact is observed, when comparing the conformation of acrolein [ 19 ] with that of acrylyl chloride [ 23 ] and acrylyl fluoride.…”