Ethylene

Definition

Ethylene is a colorless, flammable gas with the chemical formula C₂H₄. It is the simplest alkene and is widely used in the chemical industry for the production of various organic compounds and polymers. Ethylene is a key term that connects to several important topics in organic chemistry, including the structure of alkenes, chemical bonding, and industrial applications.

5 Must Know Facts For Your Next Test

1. Ethylene is the simplest alkene, with a carbon-carbon double bond and the molecular formula C₂H₄.
2. The carbon atoms in ethylene form sp² hybrid orbitals, which allow for the formation of a σ bond and a π bond between the carbon atoms.
3. Ethylene is a key industrial chemical used in the production of various organic compounds, including polymers like polyethylene.
4. The Hammond Postulate is used to predict the structure of the transition state in the addition of HBr to ethylene, a polar reaction.
5. Ethylene can undergo radical addition reactions, leading to the formation of chain-growth polymers like polyethylene.

Review Questions

• Explain the sp² hybridization of the carbon atoms in ethylene and how this contributes to the structure and stability of the molecule.
  • The carbon atoms in ethylene form sp² hybrid orbitals, where the s orbital and two of the p orbitals combine to create three equivalent sp² hybrid orbitals. This allows the carbon atoms to form a σ bond and a π bond between them, resulting in a planar, trigonal planar structure for the ethylene molecule. The sp² hybridization and the presence of the π bond contribute to the stability of ethylene by delocalizing the electrons and making the molecule more resistant to breaking apart.
• Describe how molecular orbital theory can be used to explain the bonding in ethylene and the reactivity of the carbon-carbon double bond.
  • Molecular orbital theory considers the interactions between the atomic orbitals of the atoms in a molecule to form molecular orbitals. In the case of ethylene, the carbon-carbon double bond is formed by the overlap of the sp² hybrid orbitals to create a σ bond, and the overlap of the p orbitals to create a π bond. The resulting molecular orbitals, including the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), can be used to predict the reactivity of the carbon-carbon double bond in ethylene. For example, the HOMO of ethylene is relatively high in energy, making the molecule susceptible to electrophilic addition reactions, such as the addition of hydrogen bromide (HBr).
• Explain how the Hammond Postulate can be used to predict the structure of the transition state in the addition of HBr to ethylene, and discuss the implications of this for the overall reaction mechanism.
  • The Hammond Postulate states that if two transition states are close in energy, the one more closely resembling the reactants will be favored. In the case of the addition of HBr to ethylene, the transition state will resemble the reactants more closely, with the bromine atom and the hydrogen atom still somewhat separated. This indicates that the reaction proceeds through a polar mechanism, where the bromine atom acts as an electrophile and attacks the carbon-carbon double bond, while the hydrogen atom is then added to the other carbon atom. The Hammond Postulate helps explain the regioselectivity of this reaction, where the hydrogen atom is added to the carbon atom that can best stabilize the resulting carbocation intermediate.

Related terms

sp² Hybridization: The process in which an atom's s orbital and two of its p orbitals combine to form three equivalent sp² hybrid orbitals, which are used to form σ bonds in planar molecules like ethylene.

Molecular Orbital Theory: A model that describes the behavior of electrons in molecules by considering the interactions between atomic orbitals to form molecular orbitals, which can be used to explain the stability and reactivity of molecules like ethylene.

Electrophilic Addition: A type of reaction where an electrophile adds to the carbon-carbon double bond of an alkene, such as the addition of hydrogen bromide (HBr) to ethylene.