Nature of Organic Compounds and Reactions
SYLLABUS
Theme 1: Nature of Organic Compounds and Reactions
Course: Organic Chemistry IIA (OCA216X)
Prescribed Book: Organic Chemistry by Janice Gorzynski Smith, 6th edition
NATURE OF ORGANIC COMPOUNDS AND REACTIONS
Study Unit 1.1: Classification of Organic Compounds
Study Unit Theme 1.1.1: Functional Groups
Specific Outcomes:
Understand organic compounds
Define the term "functional group"
Correctly identify and group organic compounds into functional group families
ORGANIC COMPOUNDS
Definition of Organic Compound:
An organic compound is a compound containing carbon bonded to other atoms, particularly through Carbon-Carbon (C-C) and Carbon-Hydrogen (C-H) σ bonds.
Features of Organic Compounds:
May contain heteroatoms (atoms other than carbon and hydrogen).
May contain π bonds; the most common occur in C-C and C-O double bonds.
Can be categorized into a small number of categories based on functional groups.
FUNCTIONAL GROUPS
Definition:
A functional group is an atom or group of atoms within a larger molecule that imparts characteristic chemical behavior.
Chemical Reactions:
Molecules with the same functional group will undergo similar chemical reactions regardless of their size.
Categories of Functional Groups:
Groups such as alkenes, alkynes, and aromatics contain C-C multiple bonds and display structural and chemical similarities.
FUNCTIONAL GROUPS WITH CARBON SINGLY BONDED TO AN ELECTRONEGATIVE ATOM
Examples include:
Alkyl halides, alcohols, ethers, alkyl phosphates, amines, thiols, sulfides.
Electronegative Atoms:
Halogen, oxygen, nitrogen, sulfur.
FUNCTIONAL GROUPS WITH A CARBON-OXYGEN DOUBLE BOND (CARBONYL GROUPS)
Characteristics:
Carbonyl groups are commonly found in many organic compounds and biological molecules.
The carbonyl carbon carries a partial positive charge (δ+) while the oxygen carries a partial negative charge (δ-).
STUDY UNIT 1.2: TYPES OF ORGANIC REACTIONS
Study Unit 1.2.1: General Organic Reactions
Specific Outcomes:
Addition reactions
Elimination reactions
Substitution reactions
Rearrangement reactions
Oxidation reactions
Reduction reactions
ADDITION REACTION
Definition:
An addition reaction occurs when two reactants combine to form a single new product.
Example:
Ethylene (an alkene) combines with Chloroethane (an alkyl halide) to illustrate an addition reaction.
ELIMINATION REACTION
Definition:
An elimination reaction is the reverse of an addition reaction where a single organic compound splits into two products, often releasing a small molecule such as H2O or HCl.
Example of Reaction:
Acid-catalyzed reaction.
SUBSTITUTION REACTIONS
Definition:
A substitution reaction takes place when two reactants exchange parts to yield two new products.
Example:
A –Cl group substitutes the –H group of an alkane to form two new products.
REARRANGEMENT REACTIONS
Definition:
Rearrangement reactions occur when a single organic reactant reorganizes its bonds and atoms to produce a single isomeric product.
REACTION OF ETHYLENE AND MENTHENE
Illustrates chemical reactivity concerning functional groups found in peppermint oil and in plants that cause fruit ripening.
OXIDATION REACTION
Definition:
Oxidation reactions involve the addition of oxygen in the form of carbonyl or hydroxyl groups, depending on the conditions.
Example:
Hydroxylation and oxidative cleavage of an alkene using KMnO4 and H3O+.
REDUCTION REACTION
Definition:
A reduction reaction is characterized by the addition of hydrogen, described as either the addition of hydrogen or the removal of oxygen from a molecule.
Nature of Reaction:
The double bond undergoes hydrogenation, i.e., it is reduced.
STUDY UNIT 1.3: MECHANISM OF ORGANIC REACTIONS
Study Unit Theme 1.3.1: Radical and Polar Reactions
Specific Outcomes:
Identify and explain different ways of bond formation and breaking
Predict reactivity of bonds based on the nature of reactive species present.
MECHANISM OF ORGANIC REACTIONS
Definition:
The mechanism of a reaction relates to the step-by-step process of how the reaction proceeds.
Key Components:
Details which bonds are broken and formed, and in what sequential order.
Relative rates of these steps.
RADICAL AND POLAR REACTIONS
Bond Breaking:
A covalent (two-electron) bond can break in two ways:
Symmetrically (homolytic cleavage): Each fragment receives one electron (produces radicals).
Unsymmetrically (heterolytic cleavage): Both electrons go to one product fragment (produces polarized species).
Definitions:
Radical: A neutral species with an unpaired electron (odd number of electrons).
Polar Reactions: Involves species with an even number of electrons, having paired electrons.
Electron Movement Notation:
One electron in symmetrical processes is indicated by a half-headed or “fishhook” arrow.
Two electrons in unsymmetrical processes are indicated by a full-headed curved arrow.
BOND POLARITY
Characteristics of Polar Reactions:
Reactions occur between electron-rich sites and electron-poor sites.
Bond Formation and Breaking:
Bonds are formed by sharing electrons between a rich atom and a poor atom.
Bonds break when one atom claims both electrons from a bond.
Terminology:
Nucleophile:
A species that is "nucleus loving", attracted to positive charges. Typically has negatively polarized, electron-rich atoms, is neutral or negatively charged, and can form bonds by donating electrons.
Electrophile:
A positively polarized, electron-poor species.
NEUTRAL COMPOUNDS AS NUCLEOPHILE OR ELECTROPHILE
Neutral compounds can act as nucleophiles or electrophiles based on the presence of electron-rich or electron-poor sites.
REACTION ENERGY
STUDY UNIT THEME 1.3.2: REACTION ENERGY DIAGRAMS
Specific Outcomes:
Identify different structures on a reaction energy diagram
Identify different events on a reaction energy diagram
Derive enthalpy information from a reaction energy diagram.
REACTION ENERGY DIAGRAM
Overview:
Reactions occur when reactant molecules collide, leading to the reorganization of atoms and bonds.
Example Process:
In the addition reaction of HCl with ethylene:
Two reactants approach, C=C π bond, and H-Cl bond breaks; a new C-H bond forms.
A new C-Cl bond is formed.
ACTIVATION ENERGY DIAGRAM
Purpose:
Chemists utilize energy diagrams to visually represent the energy changes during a reaction.
Axes in Diagram:
Vertical axis denotes total energy of reactants.
Horizontal axis (reaction coordinate) indicates the progression of the reaction from beginning to end.
Steps in Diagrams:
A: At the reaction's start, reactants' energy level is at point A.
B: Interaction causes an increase in energy due to electron cloud repulsion until a transition state (maximum energy) is reached.
Transition State: Represents the highest energy required in this step.
C: Following the transition state, the energy drops to the carbocation (intermediate) at minimum energy level C.
D: The carbocation reacts with Cl- to produce chloroethane; this stage has its own activation energy and transition state.
E: Finally, the curve declines as the C-Cl bond completes, indicating the final product.
F: The overall energy difference between initial reactants and final products is illustrated.
ACTIVATION ENERGY DETAILS
Activation Energy (Eact):
Reactions with Eact < 80 kJ/mol typically occur at or below 25°C.
Reactions with a higher Eact may require heating to provide sufficient energy to overcome the activation barrier.
Favorable Reactions:
Favourable when final product energy is lower than that of reactants, indicated by released energy.
Unfavorable Reactions:
Unfavorable reactions occur when the energy of the final product is greater than that of the reactants, resulting in absorbed energy.
SYLLABUS
Theme 1: Nature of Organic Compounds and Reactions. Course: Organic Chemistry IIA (OCA216X). Prescribed Book: Organic Chemistry by Janice Gorzynski Smith, 6th edition.
NATURE OF ORGANIC COMPOUNDS AND REACTIONS
Study Unit 1.1: Classification of Organic Compounds
The first theme covers the functional groups of organic compounds, with specific outcomes to understand organic compounds, define the term "functional group," and correctly identify and group organic compounds into functional group families.
ORGANIC COMPOUNDS
An organic compound is defined as a compound containing carbon bonded to other atoms, particularly through Carbon-Carbon (C-C) and Carbon-Hydrogen (C-H) σ bonds. These compounds may also contain heteroatoms, which are atoms other than carbon and hydrogen, and can have π bonds, most commonly found in C-C and C-O double bonds. Organic compounds can be categorized into a small number of categories based on their functional groups.
FUNCTIONAL GROUPS
A functional group is defined as an atom or group of atoms within a larger molecule that imparts characteristic chemical behavior. Molecules with the same functional group will undergo similar chemical reactions regardless of their size. Functional groups are categorized into groups such as alkenes, alkynes, and aromatics, which contain C-C multiple bonds and exhibit structural and chemical similarities.
FUNCTIONAL GROUPS WITH CARBON SINGLY BONDED TO AN ELECTRONEGATIVE ATOM
Examples include alkyl halides, alcohols, ethers, alkyl phosphates, amines, and thiols, with electronegative atoms being halogen, oxygen, nitrogen, and sulfur.
FUNCTIONAL GROUPS WITH A CARBON-OXYGEN DOUBLE BOND (CARBONYL GROUPS)
Carbonyl groups are commonly found in many organic compounds and biological molecules; the carbonyl carbon carries a partial positive charge (δ+), while the oxygen carries a partial negative charge (δ-).
STUDY UNIT 1.2: TYPES OF ORGANIC REACTIONS
Study Unit 1.2.1: General Organic Reactions
The focus of this unit is on various types of organic reactions, including addition reactions, elimination reactions, substitution reactions, rearrangement reactions, oxidation reactions, and reduction reactions.
ADDITION REACTION
An addition reaction occurs when two reactants combine to form a single new product. For instance, ethylene (an alkene) combines with chloroethane (an alkyl halide) to illustrate an addition reaction.
ELIMINATION REACTION
In contrast, an elimination reaction is the reverse of an addition reaction where a single organic compound splits into two products, often releasing a small molecule such as H2O or HCl, as exemplified by an acid-catalyzed reaction.
SUBSTITUTION REACTIONS
A substitution reaction occurs when two reactants exchange parts to yield two new products. An example is when a –Cl group substitutes the –H group of an alkane, resulting in two new products.
REARRANGEMENT REACTIONS
Rearrangement reactions take place when a single organic reactant reorganizes its bonds and atoms to produce one isomeric product.
REACTION OF ETHYLENE AND MENTHENE
This section illustrates chemical reactivity concerning functional groups found in peppermint oil and in plants that promote fruit ripening.
OXIDATION REACTION
Oxidation reactions involve adding oxygen in the form of carbonyl or hydroxyl groups, varying depending on the conditions. An example includes the hydroxylation and oxidative cleavage of an alkene using KMnO4 and H3O+.
REDUCTION REACTION
A reduction reaction is characterized by the addition of hydrogen, defined as either the addition of hydrogen or the removal of oxygen from a molecule. During this reaction, the double bond undergoes hydrogenation, indicating it is reduced.
STUDY UNIT 1.3: MECHANISM OF ORGANIC REACTIONS
Study Unit Theme 1.3.1: Radical and Polar Reactions
This unit aims to identify and explain different ways of bond formation and breaking, and to predict the reactivity of bonds based on the nature of reactive species present.
MECHANISM OF ORGANIC REACTIONS
The mechanism of a reaction pertains to the step-by-step process through which the reaction proceeds, detailing which bonds are broken and formed and in what sequential order, alongside the relative rates of these steps.
RADICAL AND POLAR REACTIONS
Covalent (two-electron) bonds can break in two ways: symmetrically (homolytic cleavage), where each fragment receives one electron, producing radicals; or unsymmetrically (heterolytic cleavage), where both electrons go to one fragment, leading to polarized species. Definitions include radicals as neutral species with an unpaired electron and polar reactions involving species with an even number of electrons.
Electron Movement Notation
In symmetrical processes, one electron is represented with a half-headed or "fishhook" arrow, while two electrons in unsymmetrical processes are indicated by a full-headed curved arrow.
BOND POLARITY
Reactions typically occur between electron-rich and electron-poor sites, with bonds being formed through electron sharing between rich and poor atoms, and breaking occurs when one atom claims both electrons. Key terminology includes nucleophiles, which are species attracted to positive charges and typically have negatively polarized, electron-rich atoms; and electrophiles, which are positively polarized, electron-poor species.
NEUTRAL COMPOUNDS AS NUCLEOPHILE OR ELECTROPHILE
Neutral compounds can act as either nucleophiles or electrophiles depending on the presence of electron-rich or electron-poor sites.
REACTION ENERGY
STUDY UNIT THEME 1.3.2: REACTION ENERGY DIAGRAMS
This study unit focuses on identifying different structures and events on a reaction energy diagram, and deriving enthalpy information from such diagrams.
REACTION ENERGY DIAGRAM
Reactions occur when reactant molecules collide, leading to the reorganization of atoms and bonds. For example, in the addition reaction of HCl with ethylene, the reactants approach, the C=C π bond and H-Cl bond break, leading to the formation of new C-H and C-Cl bonds.
ACTIVATION ENERGY DIAGRAM
Chemists utilize energy diagrams to visually represent energy changes during reactions. The vertical axis indicates the total energy of reactants, while the horizontal axis represents the reaction progression from start to finish.
Steps in Diagrams
At the start of the reaction, the energy level of the reactants is at point A. As the interaction occurs, energy increases owing to electron cloud repulsion until the transition state is reached (maximum energy). Following this, energy decreases to the carbocation (intermediate), marking minimum energy, and concludes when the C-Cl bond completes, yielding the final product. The overall energy difference between initial reactants and final products is depicted in this model.
ACTIVATION ENERGY DETAILS
Reactions with activation energy (Eact) less than 80 kJ/mol generally occur at or below 25°C. Reactions with higher Eact may necessitate heating to overcome activation barriers. Favorable reactions occur when the final product energy is lower than that of the reactants, reflected by released energy, whereas unfavorable reactions transpire when the energy of the final product surpasses that of the reactants, resulting in absorbed energy.