CHAP 4: The Study of Chemical Reactions

Free Radical Chain Reaction

The free radical chain reaction is a fundamental mechanism in organic chemistry, especially in halogenation processes. It involves the generation and propagation of free radicals through a series of steps.

• Initiation: Formation of free radicals, often by homolytic cleavage induced by heat or light.

• Propagation: Radicals react with stable molecules to form new radicals, continuing the chain.

• Termination: Two radicals combine to form a stable molecule, ending the chain reaction.

• Example: Chlorination of methane: via a radical mechanism.

Free Energy

Free energy determines the spontaneity of chemical reactions. The change in free energy () is crucial for predicting reaction feasibility.

• Gibbs Free Energy Equation:

• Spontaneous reactions: Occur when .

Enthalpy and Entropy Definitions

Enthalpy () and entropy () are thermodynamic quantities that influence reaction energetics.

• Enthalpy (): Heat absorbed or released at constant pressure.

• Entropy (): Measure of disorder or randomness in a system.

Transition State, Activation Energy, Reaction Kinetics

The transition state is a high-energy, unstable arrangement of atoms during a reaction. Activation energy () is the minimum energy required to reach the transition state.

• Activation Energy Equation:

• Reaction kinetics: Study of reaction rates and mechanisms.

Radical Inhibitors

Radical inhibitors are substances that slow or stop radical chain reactions by reacting with free radicals to form stable products.

• Example: Antioxidants like BHT (butylated hydroxytoluene).

Reactive Intermediate

Reactive intermediates are short-lived species formed during chemical reactions, such as free radicals, carbocations, and carbanions.

• Example: Methyl radical () in halogenation.

CHAP 5: Stereochemistry

Chirality: Conditions, Mesocompound (Definition)

Chirality is a property of a molecule that makes it non-superimposable on its mirror image. Mesocompounds are achiral despite having stereocenters due to an internal plane of symmetry.

• Chiral center: Typically a carbon atom bonded to four different groups.

• Mesocompound: Compound with multiple stereocenters but is achiral due to symmetry.

• Example: Tartaric acid (meso form).

R and S Nomenclature

The R/S system assigns absolute configuration to chiral centers using the Cahn-Ingold-Prelog priority rules.

• R (rectus): Clockwise arrangement of priorities.

• S (sinister): Counterclockwise arrangement.

• Steps: Assign priorities, orient lowest priority away, determine direction.

Plane Polarized Light (Equation, Rotation)

Chiral molecules rotate plane-polarized light, a property measured as optical activity.

• Specific rotation equation:

• Where: = observed rotation, = path length (dm), = concentration (g/mL).

CHAP 6: Halides; Nucleophile Substitution

Alkyl Halides (Nomenclature, Uses, Structure)

Alkyl halides are organic compounds containing halogen atoms bonded to an alkyl group. They are named by identifying the parent alkane and the halogen substituent.

• General formula: , where R = alkyl group, X = halogen.

• Uses: Solvents, intermediates in synthesis, pharmaceuticals.

• Structure: Polar C–X bond due to electronegativity difference.

Free Radical Halogenation

Free radical halogenation introduces halogen atoms into alkanes via a radical mechanism, often used for alkyl halide synthesis.

• Example: Bromination of propane.

Unimolecular and Bimolecular Nucleophilic Substitution

Nucleophilic substitution reactions are classified as unimolecular (SN1) or bimolecular (SN2) based on their mechanisms.

• Example: SN2:

• Example: SN1: Hydrolysis of tert-butyl bromide.

*Additional info: Academic context and examples have been added to expand upon the brief points in the original notes.*