Methylcyclopentadiene is any of three

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

ic cyclic di

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

s with the formula C₅MeH₅ (Me = CH₃). These isomers are the organic precursor to the methylcyclopentadienyl

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

(C₅H₄Me, often denoted as Cp′), commonly found in

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

. As with

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−. This colorless liquid has a strong and unpleasant odor. At room temperature, ...

, methylcyclopentadiene is prepared by

thermal cracking In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking ...

of its Diels–Alder dimer, followed by distillation for removal of cyclopentadiene, a common impurity.

Methylcyclopentadienyl anion

Deprotonation of methylcyclopentadiene gives the

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

methylcyclopentadienyl

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

. This ion is useful as a

for

organometallic complex Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

es. Relative to the corresponding cyclopentadienyl (Cp) complexes, complexes of Cp′ exhibit enhanced solubility in

organic solvent A solvent (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

s. Cp′ can be used to probe the structure of organometallic complexes. For example, Cp′Fe(PPh₃)(CO)I has four different signals in the ¹H NMR spectrum for the ring hydrogens and five different signals in the ¹³C NMR spectrum for the ring carbons. There is therefore no symmetry within the ring even accounting for rotation around the ring–metal axis, but instead there is a

diastereotopic In stereochemistry, topicity is the stereochemical relationship between substituents and the structure to which they are attached. Depending on the relationship, such groups can be ''heterotopic'', ''homotopic'', ''enantiotopic'', or ''diastereotopi ...

relationship as a result of being part of a

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

complex. The achiral precursor complex Cp′Fe(CO)₂I has only two signals for those hydrogens and three for those carbons, indicating a symmetric structure.

Methylcyclopentadienyl anion

References

See also