Podcast
Questions and Answers
What is the name of the chemical reaction where elements of the starting material are "lost" and a pi bond is formed?
What is the name of the chemical reaction where elements of the starting material are "lost" and a pi bond is formed?
Elimination reaction
What is the name given to a reaction where an atom or group of atoms is replaced by another atom or group of atoms?
What is the name given to a reaction where an atom or group of atoms is replaced by another atom or group of atoms?
Substitution reaction
What are the three general types of reactions discussed in the text?
What are the three general types of reactions discussed in the text?
Substitution, Elimination, Addition
What do the arrows in chemical reactions convey?
What do the arrows in chemical reactions convey?
Signup and view all the answers
Organic reactions may not show by-products.
Organic reactions may not show by-products.
Signup and view all the answers
Organic reactions may not be balanced.
Organic reactions may not be balanced.
Signup and view all the answers
Where are the parameters of a chemical reaction often shown?
Where are the parameters of a chemical reaction often shown?
Signup and view all the answers
What are two ways that bonds can be broken?
What are two ways that bonds can be broken?
Signup and view all the answers
What is the name given to an intermediate that results from the homolytic cleavage of a bond?
What is the name given to an intermediate that results from the homolytic cleavage of a bond?
Signup and view all the answers
What is the name given to an intermediate that results from the heterolytic cleavage of a bond and has a positive charge?
What is the name given to an intermediate that results from the heterolytic cleavage of a bond and has a positive charge?
Signup and view all the answers
Bond breaking is generally an endothermic process.
Bond breaking is generally an endothermic process.
Signup and view all the answers
Bond formation is generally an exothermic process.
Bond formation is generally an exothermic process.
Signup and view all the answers
What is the name given to the energy needed to homolytically cleave a covalent bond?
What is the name given to the energy needed to homolytically cleave a covalent bond?
Signup and view all the answers
What is the enthalpy change?
What is the enthalpy change?
Signup and view all the answers
What is Gibbs Energy?
What is Gibbs Energy?
Signup and view all the answers
What is entropy?
What is entropy?
Signup and view all the answers
Entropy increases when a single starting material forms two products.
Entropy increases when a single starting material forms two products.
Signup and view all the answers
Entropy decreases when an acyclic compound forms a ring.
Entropy decreases when an acyclic compound forms a ring.
Signup and view all the answers
The total energy change in a reaction is due to the change in bonding energy and the change in disorder.
The total energy change in a reaction is due to the change in bonding energy and the change in disorder.
Signup and view all the answers
Study Notes
Organic Chemistry Chapter 6
- Organic reactions involve electron movement
- Look for "reaction sites" on molecules where interactions can occur
- General reaction types: substitution, elimination, addition
- Understand how to write and read chemical reactions
- Reaction parameters (conditions, reactants, solvents) are shown above and below reaction arrows
- Organic reactions may not show all by-products or other products, only the direction of the reaction
- Reactions may not be balanced in the equation; full balancing is done experimentally
- Reactions may show a specific stepwise order
- Look for changes in functional groups between reactants and products.
- Examine the chemicals/reagents above/below the arrows to discover what molecules and conditions cause a chemical change.
Writing Equations for Organic Reactions
- Example:
- CH3CH3 + Br2 → CH3CH2Br + HBr
- H2, Ni is a catalyst
Writing Equations for Sequential Reactions
- Steps are numbered above or below the reaction arrow to show the order
- Example:
- CH3MgBr [1] + O → CH3CH2OH [2]
- Inorganic byproducts are sometimes omitted
Arrows Used in Organic Reactions
- Reaction arrow: drawn between reactants and products
- Double reaction arrows (equilibrium arrows): used between reactants and products in equilibrium equations.
- Double-headed arrow: used between resonance structures
- Full-headed curved arrow: shows movement of an electron pair
- Half-headed curved arrow (fishhook): shows movement of a single electron
Substitution Reactions
- Substitution: an atom or group is replaced by another atom or group
- In a general substitution, Y replaces Z on a carbon atom
- More electronegative elements will substitute for a heteroatom on a carbon
- Substitution can occur on aromatic rings, replacing a hydrogen
- One o-bond breaks, and another forms at the same carbon atom.
Elimination Reactions
- Elimination: elements of the starting material are lost, and a pi bond is formed
- Two sigma bonds are broken, and a pi bond is formed between adjacent atoms
- Common examples occur when X = H and Y is a heteroatom more electronegative than carbon.
Addition Reactions
- Addition: elements are added to the starting material
- Addition to a multiple bond to form 2 single bonds
- A pi bond is broken.
- Two sigma bonds are formed.
- X and Y added to the starting material
- A pi bond is broken and two sigma bonds are formed
- Example: water is added to a double bond
Relationship of Addition and Elimination Reactions
- Addition and elimination reactions can complement each other and are reversible.
Reaction Mechanisms
- Mechanisms are used to study how a reaction proceeds, including which bonds are broken and formed, and the components involved.
- This helps predict products in new reactions.
- One-step reactions are called concerted reactions.
- A stepwise reaction involves more than one step, often with unstable reactive intermediates
- Example of a concerted reaction: a starting material is converted directly to a product.
Bonds Cleavage
- Homolysis: electrons are divided equally
- Heterolysis: electrons are divided unequally to the more electronegative atom
- These result in free radicals, carbocations and carbanions
- Carbocation and radicals are electrophiles
- Carbanions are nucleophiles
Bond Formation
- Bond formation occurs in two ways:
- Two radicals can each donate one electron to create a two-electron bond.
- Two ions with opposite charges can come together to create a two-electron bond.
Bond Dissociation Energy
- Bond dissociation energy is the energy needed to break a covalent bond homolytically
- Energy to break a bond equals the energy to form a bond but is opposite in sign
- Bond breaking requires energy (endothermic), bond forming releases energy (exothermic)
Example: Energy Associated with the H₂ Bond
- H-H bond requires +435 kJ/mol to cleave (endothermic)
- Releases -435 kJ/mol when formed (exothermic)
Reaction Mechanisms (concerted & stepwise)
- An example of a concerted reaction: a starting material is converted directly to a product
- Example of a stepwise reaction: involves unstable reactive intermediates (often several steps)
Intermediates Behavior
- Radicals and carbocations are electrophiles because they have an electron-deficient carbon.
- Carbanions are nucleophiles because they contain a carbon with a lone pair.
Energy Diagrams
- Energy diagrams display energy changes as reactants are converted to products.
- Y-axis: energy
- X-axis: reaction coordinate/progress
- Transition state: energy maximum during the reaction
- Activation energy (Ea): energy difference between the transition state and the starting material
- ΔH° (overall): energy difference between reactants and products (overall enthalpy change)
- Shows products lower in energy than starting materials.
What are Transition States
- Transition state is a structure showing bond breaking and forming in a reaction
- Transition states often show partial charges on atoms and contain partial bonds represented by dashed lines.
- Transition states are drawn in brackets, with a superscript double dagger (†).
Different Types of Energy Diagrams
- Different shapes depending on whether it is endo/exothermic (positive/negative enthalpy) and whether it is slow/fast (high/low activation energy).
Kinetics and Energy Diagrams
- Kinetics studies reaction rates.
- Higher reactant concentration = faster rate
- Higher temperature = faster rate
- Energy of activation must be overcome in order for a reaction to occur.
Rate Law
- Rate law shows relationship between reaction rate and reactant concentrations.
- Experimentally determined by measuring decrease in reactant concentrations or product appearance
- Rate = k[reactants]
- k = rate constant
- Fast reactions have large rate constants; slow reactions have small rate constants.
Rate Equations (for Two-Step Reactions)
- Rate equation shows which reactants involved in the rate determining (slowest) step
- For a two step reaction, only the reactants of the rate-determining step appear in the equation
- Rate-determining step is slowest step of a multi-step reaction
- Often at the highest point of the graph.
Order of Reaction
- Order of a reaction depends on number of molecules participating in the rate determining step
- A unimolecular reaction depends on the concentration of one reactant only.
- A bimolecular reaction depends on the concentration of two reactants (second order equation).
Catalysts
- Catalysts speed up reactions, but are unchanged after
- Accelerate reaction rates by lowering the activation energy
- No effect on overall enthalpy change
Summary of Chapter 6
- The homework assignments listed on the last slide are considered review questions.
- The functional group tables from chapter 3 are important to study, and you should be able to recognize functional groups.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Dive into the intricacies of organic reactions in Chapter 6. This quiz will test your understanding of electron movement, different reaction types, and how to write and read chemical equations. Explore the parameters and functional groups involved in organic chemistry.
