Types and Mechanisms of Chemical Reactions

Questions and Answers

A reaction in which elements are added to a starting material is classified as a(n) _____ reaction.

addition

For this type of reaction to occur, the starting material must have a _____ bond to which elements can be added.

A reaction in which an atom or group of atoms is replaced by another atom or group of atoms is classified as a(n) _____ reaction.

substitution

A detailed description of the steps in a reaction is called a reaction _____.

mechanism Signup and view all the answers

In a(n) ___ elements of the starting material are 'lost' and a new bond is formed.

elimination, pi Signup and view all the answers

Which of the following statements correctly describe the conventions used when writing equations for organic reactions? (Select all that apply)

Reagents are often shown above the reaction arrow. Signup and view all the answers

Select all the statements that correctly describe the changes occurring in addition reactions.

Compounds with double bonds can undergo addition reactions. Signup and view all the answers

Which of the following options correctly describe the characteristics of an elimination reaction? (Select all that apply)

Hydrogen is often one of the atoms eliminated in this reaction type. Signup and view all the answers

Which of the following statements are correct about a reaction mechanism? (Select all that apply)

In a stepwise reaction, a reactive intermediate is formed in the conversion of starting material to product. Signup and view all the answers

What is heterolytic bond cleavage?

Both bonding electrons go to the same atom. Signup and view all the answers

What is homolytic bond cleavage?

Electrons are evenly divided between bonding atoms. Signup and view all the answers

_ generates charged reactive intermediates, whereas generates uncharged reactive intermediates.

Heterolysis, Homolysis Signup and view all the answers

Since bonds are broken and formed in the same step, the reaction is said to be _____.

concerted Signup and view all the answers

A stepwise reaction involves the formation of at least one reactive _____, which then goes on to form the product(s).

intermediate Signup and view all the answers

A half-headed (fishhook) curved arrow is used to show the movement of a electron(s), whereas a full-headed arrow shows the movement of a electron(s).

single, pair of Signup and view all the answers

Heterolytic bond cleavage _____. (Select all the options that complete the sentence correctly.)

is a process that requires energy. Signup and view all the answers

If a bond C-Z undergoes heterolytic cleavage and both bonding electrons move to the carbon atom, the intermediate formed will have a charge on the carbon atom and will be called a .

negative, carbanion Signup and view all the answers

A reaction intermediate that has a lone pair and a negative charge on a carbon atom is called a(n) , whereas an intermediate with a positive charge on a carbon atom is called a(n) .

carbanion, carbocation Signup and view all the answers

Which of the following options correctly describe the reactivity of the different reaction intermediates formed by bond cleavage? (Select all that apply)

A carbocation is electron deficient and therefore acts as an electrophile. Signup and view all the answers

What is a polar reaction?

A reaction between a nucleophile and an electrophile. Signup and view all the answers

A carbocation or a carbon radical will act as a(n)

electrophile. Signup and view all the answers

A carbanion will act as a(n)

nucleophile. Signup and view all the answers

An electron-deficient carbon atom is present in

carbocations and carbon radicals. Signup and view all the answers

A lone pair of electrons on a carbon atom is present in

a carbanion. Signup and view all the answers

Which of the following options correctly describe bond formation? (Select all that apply)

Bond formation always releases energy. Signup and view all the answers

The bond dissociation energy is the energy needed to _ cleave a(n) _ bond.

homolytically, covalent Signup and view all the answers

When two radicals bond,

each bonding atom contributes one bonding electron. Signup and view all the answers

When two oppositely charged ions bond,

both bonding electrons are contributed by one atom. Signup and view all the answers

Which of the following options correctly describe ΔHo for a reaction? (Select all that apply)

If ΔHº is positive, the reaction absorbs heat energy from its surroundings. Signup and view all the answers

If ΔHo for a particular reaction is positive, which statements correctly describe the reaction? (Select all that apply)

More energy is needed to break bonds than is released by forming bonds. Signup and view all the answers

Which of the following options correctly interpret the bond dissociation energy for the H-F bond, which is 569 kJ/mol? (Select all that apply)

569 kJ of heat will be released in the formation of 1 mole of H-F bonds. Signup and view all the answers

The energy required to homolytically cleave a covalent bond is called the bond _____ energy.

dissociation Signup and view all the answers

Which of the following options correctly describe bond strength, bond dissociation energy, and their periodic trends? (Select all that apply)

Bond dissociation energy increases from left to right across a period. Signup and view all the answers

If ΔHo for a reaction is negative, the reaction is _____.

exothermic Signup and view all the answers

The energy released in forming bonds is _ than the energy needed to break bonds, and the bonds formed in the product(s) are _ than the bonds broken in the starting material(s).

greater, stronger Signup and view all the answers

Energy is absorbed

when bonds are broken. Signup and view all the answers

Energy is released

when bonds are formed. Signup and view all the answers

Bond breaking

is an endothermic process. Signup and view all the answers

Bond formation

is an exothermic process. Signup and view all the answers

Which of the following options correctly describe how to calculate ΔHo for a reaction using bond dissociation energies? (Select all that apply)

Add bond dissociation energies for all bonds formed and give this sum a (-) value. Signup and view all the answers

The C-O bond in CH3OH has a ___ bond dissociation energy than the C-S bond in CH3SH because C-O bond is _ and ___.

higher, shorter, stronger Signup and view all the answers

Reaction rate

is related to kinetic data. Signup and view all the answers

Reaction energies and position of equilibrium

are related to thermodynamic data. Signup and view all the answers

Study Notes

Reaction Types

Addition Reaction: Involves adding elements to a starting material that has a π bond, resulting in the formation of new bonds.
Substitution Reaction: An atom or a group of atoms is replaced by another atom or group of atoms.
Elimination Reaction: Characterized by the loss of elements from the starting material and formation of a new π bond. Typically involves breaking two σ bonds.

Reaction Mechanisms

Mechanism: A detailed account of the sequence of steps in a reaction, providing insight into bond formation and cleavage.
Concerted Reaction: A one-step process where the starting material directly converts to products.
Stepwise Reaction: Involves multiple steps, often generating reactive intermediates.

Bond Cleavage

Heterolytic Bond Cleavage: Both electrons from the bond move to one atom, often resulting in charged intermediates.
Homolytic Bond Cleavage: Electrons split evenly between the two bonded atoms, forming radical intermediates.

Intermediates and Reactivity

Carbocations: Positively charged carbon intermediates that act as electrophiles due to electron deficiency.
Carbanions: Negatively charged carbon intermediates that act as nucleophiles because of their lone pair of electrons.
Radicals: Unstable species with an incomplete octet, often behave as electrophiles.

Nucleophiles and Electrophiles

Nucleophile: A species that donates an electron pair to an electrophile in a reaction.
Electrophile: A species that accepts an electron pair, often represented by carbocations or carbon radicals.

Bond Formation and Energy

Bond Formation: Always releases energy; when two radicals bond, each contributes one bonding electron.
Bond Dissociation Energy: Energy required to homolytically cleave a bond. Increases across a period and correlates with bond strength.
Exothermic vs. Endothermic: A negative ΔHº indicates an exothermic reaction where energy released in bond formation exceeds the energy required to break bonds.

Thermodynamics of Reactions

ΔHº: Representing heat of reaction; positive values indicate endothermic processes while negative values indicate exothermic processes.
Calculating ΔHº: Involves summing bond dissociation energies for bonds broken (positive) and formed (negative).

Periodic Trends in Bond Strength

Bond strength increases from left to right across the periodic table.
Larger atoms generally exhibit lower bond strength and bond dissociation energy.

Summary of Key Points

Each reaction type has distinct characteristics and implications in organic chemistry.
Understanding mechanisms and intermediates is crucial in predicting reaction outcomes.
Energetics play a significant role in determining whether a reaction is favorable or not.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers various types of chemical reactions, including addition, substitution, and elimination reactions. It also explores the mechanisms behind these reactions, highlighting concerted and stepwise processes, as well as different bond cleavage methods. Test your knowledge of these fundamental concepts in chemistry.