Alkenes Lecture Notes Flashcards

Vocabulary terms and definitions related to the structure, naming, reactivity, and polymerization of alkenes based on the lecture material.

Alkenes

Unsaturated hydrocarbons made of carbon and hydrogen only, containing one or more carbon-carbon double bonds.

General formula of Alkenes

The formula for the homologous series of alkenes with one double bond is $C_n H_{2n}$.

Shape of Ethene

A planar (flat) molecule where the bond angles between each bond are roughly $120^\text{o}$.

$\pi$-orbital

An orbital formed by the overlap of two p-orbitals, creating a cloud of electron density above and below the single bond that prevents rotation.

$\sigma$-orbital

The orbital formed by the overlap of two p-orbitals along the line joining two carbon atoms to form a single bond.

Position Isomers

Isomers that have the double bond in different positions between adjacent carbon atoms in a carbon chain.

Geometrical Isomerism

A form of stereoisomerism where molecules have the same structural formula but different spatial arrangements around a $C=C$ bond.

E-Z Isomerism

A notation system for geometrical isomers based on atomic numbers; Z (zusammen) means together (same side) and E (entgegen) means opposite.

Cahn-Ingold-Prelog (CIP) notation

A system used to determine E-Z notation by assigning priority to substituents based on the atomic numbers of the atoms attached to the double bond.

Electrophile

An electron pair acceptor that is attracted to electron-rich areas, such as the area of high electron density in a C=C bond.

Bond Enthalpy of $C=C$

The energy required to break the double bond is $612\,kJ\,mol^{-1}$, compared to $347\,kJ\,mol^{-1}$ for a $C-C$ single bond.

Electrophilic Addition

The typical reaction of alkenes where the double bond opens up as it is attacked by an electrophile to form a saturated product.

Carbocation

A reactive intermediate involving a carbon atom with a positive charge.

Heterolytic Bond Breaking

The breaking of a covalent bond where both electrons go to one of the atoms, resulting in the formation of a negative ion and a positive ion.

Markovnikov's Rule

A rule stating that when hydrogen halides add to alkenes, the hydrogen adds to the carbon atom which already has the most hydrogen atoms.

Positive Inductive Effect

The electron-releasing effect of alkyl groups (like $-CH_3$ or $-C_2H_5$) that helps stabilize the positive charge of a carbocation.

Carbocation Stability Order

Tertiary carbocations are more stable than secondary, which are more stable than primary carbocations.

Bromine Water Test

A test for a carbon-carbon double bond where reddish-brown bromine solution is decolourised upon reaction with an alkene.

Plasticisers

Small molecules added to polymers to get between chains, allowing them to slide more easily and making the plastic more flexible.

Addition Polymers

Large molecules made from monomers with carbon-carbon double bonds (alkenes) that open up to form a continuous carbon backbone.

Biodegradability of Polyalkenes

Polyalkenes are non-biodegradable because they have a backbone of strong, non-polar $C-C$ and $C-H$ bonds that are not attacked by biological agents.

Mechanical Recycling

The process of separating, washing, grinding into pellets, melting, and remoulding plastics.

Feedstock Recycling

The process of heating plastics to break polymer bonds and produce monomers that can be used to make new plastics.