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Cyclopentadiene is a highly reactive diene in the Diels–Alder reaction because minimal distortion of the diene is required to achieve the envelope geometry of the transition state compared to other dienes. [11] Famously, cyclopentadiene dimerizes. The conversion occurs in hours at room temperature, but the monomer can be stored for days at ...
At temperatures above about 125 °C in the vapor phase, dissociation to cyclopentadiene monomer starts to become thermodynamically favored (the dissociation constant K d = [cyclopentadiene] 2 / [dicyclopentadiene] > 1). For instance, the values of K d at 149 °C and 195 °C were found to be 277 and 2200, respectively. [10]
Melting point: −135 °C (−211 °F; 138 K) Boiling point: ... It can also be produced by the catalytic hydrogenation of cyclopentadiene. [6] Reactions
2 Na + 2 C 5 H 6 → 2 NaC 5 H 5 + H 2. The conversion can be conducted by heating a suspension of molten sodium in dicyclopentadiene. [2] In former times, the sodium was provided in the form of "sodium wire" or "sodium sand", a fine dispersion of sodium prepared by melting sodium in refluxing xylene and rapidly stirring.
C 5 H 6 + LiC 4 H 9 → LiC 5 H 5 + C 4 H 10. Because lithium cyclopentadienide is usually handled as a solution, the solvent-free solid is rarely encountered. According to X-ray crystallography, LiCp is a "polydecker" sandwich complex, consisting of an infinite chain of alternating Li + centers sandwiched between μ-η 5:η 5-C 5 H 5 ligands. [2]
Magnesocene is a white solid at room temperature. [1] It has a melting point of 176 °C, though at atmospheric pressures it sublimes at 100 °C. [1] Unlike ferrocene, magnesocene displays slight dissociation and subsequent ion association in polar, electron-donating solvents (such as ether and THF).
The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
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