Alkenes and Reaction Mechanisms

Organic Chemistry

What do reaction progress diagrams show in the context of energy changes during a reaction?

They show how energy changes throughout the reaction, identifying reactants, transition states, intermediates, and products.

What is activation energy (Ea)?

The energy barrier that must be overcome for a reaction to proceed.

What characterizes an exergonic reaction?

Products have lower energy than reactants, resulting in a negative Gibbs free energy change (∆G < 0).

What does a positive Gibbs free energy change (∆G > 0) signify?

It indicates a non-spontaneous endergonic reaction where products have higher energy than reactants.

What equation relates Gibbs Free Energy (ΔG) to enthalpy (ΔH) and entropy (ΔS)?

ΔG = ΔH - TΔS.

What does ΔG < 0 indicate about a chemical reaction?

The reaction is spontaneous in the forward direction.

What is the significance of the equilibrium constant K in relation to Gibbs Free Energy?

ΔG° = -RT ln K, linking standard free energy change to equilibrium.

What is a transition state in a chemical reaction?

A high-energy, fleeting configuration where bonds are breaking/forming during the reaction.

What are reactive intermediates?

Unstable species like carbocations, carbanions, radicals, or silicates that form during multi-step reactions.

What does the Hammond Postulate state?

The structure of the transition state resembles the species (reactants or products) to which it is closer in energy.

Define a nucleophile.

An electron-rich species that donates a pair of electrons to form a new bond (e.g., OH⁻, NH₃).

What is an electrophile?

An electron-deficient species that accepts a pair of electrons to form a new bond (e.g., H⁺, CH₃⁺).

What does curved arrow notation represent in organic chemistry?

The movement of electron pairs during chemical reactions.

In curved arrow notation, what does the arrow tail indicate?

The source of electrons (e.g., lone pair or bond).

What does the E/Z nomenclature refer to in alkenes?

A system to denote the configuration of substituents based on priority; Z indicates higher-priority groups on the same side, E indicates them on opposite sides.

How do cis and trans isomers differ in alkenes?

Cis has substituents on the same side of the double bond, trans has them on opposite sides.

What rule determines where H adds in electrophilic addition reactions of alkenes?

Markovnikov's Rule states that H adds to the carbon with more hydrogen substituents.

What is the order of carbocation stability?

Tertiary > Secondary > Primary.

What happens during carbocation rearrangements?

Methyl or hydride shifts occur to form a more stable carbocation.

What characterizes the addition of X₂ in halogenation?

Anti-addition of halogens across the double bond, forming a halonium ion intermediate.

How do halohydrins form from alkenes?

Through the reaction of an alkene with a halogen in the presence of water, where OH adds preferentially to the more substituted carbon.

What is the purpose of oxymercuration-demercuration in hydration reactions?

It adds mercuric acetate to the alkene and then water to yield alcohol at the more substituted carbon.

What is the key step in hydroboration-oxidation hydration reactions?

BH₃ adds to the alkene, followed by oxidation to transform BH₂ into OH on the less substituted carbon.

What is the result of hydrogenation of alkenes?

The catalytic addition of H₂ across the double bond produces an alkane.

What is epoxidation?

The reaction of alkenes with peracids to form a three-membered epoxide ring.

What does ozonolysis accomplish?

It breaks the double bond in alkenes to form ketones or aldehydes.

How can one identify repeat units in alkene polymers?

By drawing the structure of the polymer and identifying repeating segments.

What is the reverse polymerization process used for?

To deduce the monomer units from polymer structures.