2-butene

Definition

2-butene is an unsaturated hydrocarbon with the molecular formula C4H8. It is an alkene with a carbon-carbon double bond located at the second carbon position of the four-carbon chain. This structural feature of 2-butene is central to understanding its behavior and properties in the context of various organic chemistry topics.

5 Must Know Facts For Your Next Test

1. The presence of the carbon-carbon double bond in 2-butene gives rise to cis-trans isomerism, where the two hydrogen atoms attached to the double-bonded carbons can be oriented on the same side (cis) or on opposite sides (trans).
2. The stability of 2-butene is greater than that of 1-butene due to the increased substitution of the double bond, which stabilizes the alkene through hyperconjugation.
3. During the oxidation of 2-butene, the carbon-carbon double bond can be cleaved to form two carbonyl compounds, such as acetaldehyde and formaldehyde.
4. The allylic radical formed from 2-butene is stabilized through resonance delocalization, making it more stable compared to non-allylic radicals.
5. The E2 elimination reaction of 2-butene can be used to study the deuterium isotope effect, where the rate of the reaction is influenced by the mass of the hydrogen atoms involved.

Review Questions

• Explain how the presence of the carbon-carbon double bond in 2-butene leads to cis-trans isomerism and discuss the implications of this phenomenon.
  • The carbon-carbon double bond in 2-butene has two hydrogen atoms attached to the double-bonded carbons. These hydrogen atoms can be oriented in either the same direction (cis) or opposite directions (trans), resulting in two distinct spatial arrangements of the molecule. This cis-trans isomerism affects the physical and chemical properties of 2-butene, such as boiling point, melting point, and reactivity. The cis and trans isomers of 2-butene have different steric interactions and dipole moments, which can influence their stability and behavior in various organic chemistry reactions.
• Describe the stability of 2-butene compared to 1-butene and explain the factors that contribute to this difference in stability.
  • The stability of 2-butene is greater than that of 1-butene due to the increased substitution of the carbon-carbon double bond. In 2-butene, the double bond is flanked by two alkyl groups (methyl groups), whereas in 1-butene, the double bond is flanked by a methyl group and a hydrogen atom. The increased substitution in 2-butene allows for greater stabilization through hyperconjugation, where the sigma bonds of the alkyl groups can interact with the pi bond of the double bond, delocalizing the electrons and stabilizing the overall structure. This enhanced stability of 2-butene compared to 1-butene is an important factor in understanding its reactivity and behavior in various organic chemistry reactions.
• Analyze the role of the allylic radical formed from 2-butene in the context of resonance stabilization and its implications for the reactivity and stability of the radical species.
  • The allylic radical formed from the homolytic cleavage of the carbon-carbon double bond in 2-butene is stabilized through resonance delocalization. The unpaired electron in the allylic radical can be delocalized over three carbon atoms, including the double-bonded carbons. This resonance stabilization makes the allylic radical more stable compared to non-allylic radicals, where the unpaired electron is localized on a single carbon atom. The increased stability of the allylic radical from 2-butene affects its reactivity, making it more likely to participate in radical-based reactions and influencing the overall reaction kinetics and thermodynamics. Understanding the stability of the allylic radical is crucial in predicting the behavior of 2-butene in various organic chemistry processes, such as oxidation, radical additions, and elimination reactions.

Related terms

Cis-trans isomerism: The phenomenon where molecules with the same molecular formula can have different spatial arrangements of their atoms, leading to distinct physical and chemical properties.

Allylic radical: A type of resonance-stabilized radical where the unpaired electron is delocalized over three carbon atoms, including the carbon-carbon double bond.

E2 reaction: A bimolecular elimination reaction where a base removes a proton and an adjacent leaving group is expelled, resulting in the formation of a carbon-carbon double bond.