Definition
Cyclopentene is an unsaturated hydrocarbon belonging to the class of cycloalkenes. Its molecular formula is C₅H₈, and it consists of a five‑membered carbon ring containing one carbon–carbon double bond.
Overview
Cyclopentene is a colorless liquid at room temperature with a characteristic hydrocarbon odor. It is a volatile, flammable compound that is miscible with many organic solvents such as ethanol and ether but exhibits limited solubility in water. The compound is commonly employed as an intermediate in organic synthesis, particularly in the preparation of polymers, pharmaceuticals, and fine chemicals. Industrially, cyclopentene can be derived from the catalytic dehydrogenation of cyclopentane or via the hydrogenation of cyclopentadiene under controlled conditions.
Etymology / Origin
The name combines “cyclo‑,” indicating a cyclic (ring) structure, with “pent‑,” denoting five carbon atoms, and the suffix “‑ene,” which specifies the presence of a carbon–carbon double bond. The systematic IUPAC name is simply cyclopentene, reflecting its straightforward structure.
Characteristics
| Property | Value / Description |
|---|---|
| Molecular formula | C₅H₈ |
| Molar mass | 68.11 g·mol⁻¹ |
| Structural formula | A five‑membered ring with one C=C double bond |
| Physical state | Liquid (20 °C) |
| Density | ≈0.78 g·cm⁻³ at 20 °C |
| Boiling point | 63–64 °C |
| Melting point | –108 °C |
| Refractive index | ~1.460 (20 °C) |
| Flammability | Highly flammable; flash point ≈ –20 °C |
| Solubility | Insoluble in water; soluble in most organic solvents |
| Spectroscopic data | ^1H NMR: signals for vinyl and allylic protons; ^13C NMR: characteristic signals for sp² and sp³ carbons; IR: C=C stretch near 1640 cm⁻¹ |
Reactivity: As an alkene, cyclopentene undergoes typical addition reactions such as hydrogenation, halogenation, hydrohalogenation, and hydroboration–oxidation. The double bond is confined to the ring, which influences both its steric and electronic properties compared with acyclic alkenes. Under catalytic conditions, cyclopentene can be polymerized to form poly(cyclopentene), though such polymers are less common than those derived from larger cycloalkenes.
Related Topics
- Cyclopentane – the fully saturated analogue (C₅H₁₀).
- Cyclopentadiene – a conjugated diene (C₅H₆) used as a precursor to many organometallic complexes.
- Alkene – a broader class of hydrocarbons containing carbon–carbon double bonds.
- Cycloalkene – cyclic alkenes such as cyclohexene, cyclooctene, etc.
- Catalytic hydrogenation – a key method for converting cyclopentene to cyclopentane.
- Polymerization of cyclic olefins – processes generating polymers from cyclic monomers.
Note: The information presented reflects current scientific consensus and publicly available chemical data as of the knowledge cutoff date.