4.1.3 - Alkenes Flashcards
What is the general formula for alkenes?
The general formula for alkenes is CₙH₂ₙ.
What functional group defines alkenes?
The functional group that defines alkenes is the carbon-carbon double bond (C=C).
How does the bonding in alkenes differ from alkanes?
Alkenes have a double bond between two carbon atoms, which consists of one sigma bond (σ-bond) and one pi bond (π-bond), while alkanes only have single sigma bonds.
Why are alkenes more reactive than alkanes?
Alkenes are more reactive than alkanes because the double bond in alkenes can easily be broken, allowing them to undergo reactions such as electrophilic addition.
What is an electrophilic addition reaction?
An electrophilic addition reaction is a type of reaction in which an electrophile adds to a double bond, breaking it and forming a new product.
What is the product of the electrophilic addition of hydrogen (H₂) to an alkene?
The product is an alkane, formed by the addition of hydrogen atoms across the double bond.
What is the product when an alkene reacts with a halogen, like chlorine (Cl₂)?
The product is a dihaloalkane, where two halogen atoms are added across the double bond.
What is the product when an alkene reacts with hydrogen halide (e.g., HCl)?
The product is a haloalkane, with the halogen atom added to the carbon that originally had the most hydrogen atoms (Markovnikov’s rule).
What is the mechanism of electrophilic addition to an alkene?
The mechanism involves the formation of a carbocation intermediate after the alkene’s double bond reacts with the electrophile, followed by the nucleophile attacking the carbocation.
What is the Markovnikov rule?
The Markovnikov rule states that in an electrophilic addition reaction, the hydrogen atom will add to the carbon of the double bond with the most hydrogen atoms, and the halide will add to the other carbon.
What is polymerization in the context of alkenes?
Polymerization is a process in which many alkene molecules (monomers) react to form a large molecule called a polymer, often using heat or a catalyst.
What is the most common polymer produced from alkenes?
The most common polymer produced from alkenes is polyethylene, made from ethene (C₂H₄).
What is an addition polymer?
An addition polymer is a polymer formed by the repeated addition of monomers, typically alkenes, through breaking their double bonds.
What is the effect of the double bond on the shape of alkenes?
The double bond in alkenes creates a planar structure with restricted rotation around the bond, making the molecules rigid.
What is cis-trans isomerism in alkenes?
Cis-trans isomerism occurs in alkenes when two identical groups are attached to each carbon of the double bond, leading to different spatial arrangements (cis = same side, trans = opposite sides).
What is the result of the hydration of an alkene?
The hydration of an alkene, in the presence of a catalyst like sulfuric acid (H₂SO₄), results in the formation of an alcohol.
What type of bond is present in the double bond of alkenes?
The double bond consists of one sigma (σ) bond and one pi (π) bond, with the pi bond formed by the sideways overlap of p-orbitals.
What is the electrophilic addition of bromine (Br₂) to an alkene?
The electrophilic addition of bromine to an alkene results in the formation of a vicinal dibromide, where bromine atoms are added to the two carbons of the double bond.
What is the difference between alkene and alkane reactivity?
Alkenes are more reactive than alkanes because of the presence of the double bond, which is more easily broken than the single bonds in alkanes.
What is a polymer?
A polymer is a large molecule made up of repeating structural units (monomers) that are covalently bonded, commonly produced through polymerization reactions.
What are the products of the addition of hydrogen chloride (HCl) to ethene (C₂H₄)?
The product is chloroethane (C₂H₅Cl), where a chlorine atom and a hydrogen atom are added across the double bond.
What is the reaction between an alkene and a peracid called?
The reaction is called an epoxidation, where an alkene reacts with a peracid to form an epoxide (a three-membered ring with an oxygen atom).
What is the role of a catalyst in alkene reactions?
A catalyst speeds up the rate of a reaction without being consumed, often used in processes like hydrogenation, polymerization, and hydration.
What is the effect of branching on alkene boiling points?
Branched alkenes have lower boiling points compared to straight-chain alkenes due to weaker van der Waals forces between branched molecules.
What are the environmental impacts of alkenes?
Alkenes can contribute to air pollution and smog formation. For example, alkenes like ethene and propene can participate in reactions that produce ozone in the atmosphere.
