The complex [Fe(H2C=C=CH2)(CO)3] is an organometallic compound that contains an iron atom bonded to three carbonyl (CO) ligands and one allyl (H2C=C=CH2) ligand. At low temperatures, the structure of the complex can be drawn as a tetrahedral arrangement around the iron atom, with the allyl ligand occupying one vertex and the carbonyl ligands occupying the other three vertices.
In the 1H NMR spectrum at low temperatures, we should observe two types of signals. One signal corresponds to the protons in the allyl ligand, which are chemically equivalent and therefore give rise to a single signal. The other signal corresponds to the protons in the solvent or any other proton-containing species in the sample.
At higher temperatures, the complex may undergo structural changes that affect the chemical equivalence of the protons in the allyl ligand. This could result in additional signals appearing in the 1H NMR spectrum. A possible mechanism for this structural change could involve the rotation of the allyl ligand around its bond to the iron atom, leading to different conformations of the complex.
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