Introduction of GOC and Intermediates

• Organic reactions inherently involve the breaking or formation of covalent bonds.

Bond Fission

• Two types of bond breaking:
  1. Homolytic Bond Breaking:
  • Bonding electrons are equally distributed between the bonding atoms, resulting in the formation of electrically neutral intermediates (free radicals).
  1. Heterolytic Bond Breaking:
  • Bonding electrons are transferred to one of the atoms, leading to the formation of charged intermediates (ions).
• Key notes about bond breaking:
  • Any covalent bond can break in both homolytic and heterolytic manners.
  • Heterolytic bond breaking primarily occurs in polar solvents, while homolytic bond breaking occurs in gas phases or in non-polar solvents.
  • Bond Energy: Minimum energy required to break a bond during homolytic cleavage.

Example Reactions:

• Radicals and ions form under prolonged heating:
  • $A—B <br /> ightarrow A + B ext{ (free radical)}$
  • $A—B <br /> ightarrow A^+ + B^-$
  • $Cl + ext{h}<br /> u <br /> ightarrow Cl• + Cl•$ (Proceeds in $H_2O$)
  • $Cl + ext{h}<br /> u <br /> ightarrow Cl + Cl$

Intermediates

• Definition: Species generated between reactants and products during a reaction.
  • Types of intermediates include:
  • Carbocation:
    • Characteristics:
    • Highly unstable
    • Incomplete octet (only 6 electrons)
    • Lewis Acid (accepts electrons)
    • Hybridization: $sp^2$
    • Bond angle: $120^ ext{°}$
  • Carbanion:
    • Characteristics:
    • Highly unstable
    • Complete octet (8 electrons)
    • Lewis Base (donates electrons)
    • Hybridization: $sp^3$
    • Bond angle: $107^ ext{°}$
  • Carbon free radical:
    • Characteristics:
    • Highly unstable
    • Incomplete octet (only 7 electrons)
    • Neither Lewis Acid nor Lewis Base
    • Hybridization: $sp^2$
    • Bond angle: $108^ ext{°}$

Electronic Displacement Effects

• Inductive Effect (I-effect):
  • Diagrams of electron displacement effects and stability comparisons are presented, with relationships and stability orders illustrated.
• Effects:
  1. Permanent Effects:
  • Inductive effect and its types (I and I effect).
  • Reaction attributes align with consequences of electron positioning in the compound.

Types of Inductive Effect

• -I Effect: Permanent displacement of sigma electrons by electron-withdrawing groups (EWG).
  • Examples in order of decreasing electron-withdrawing ability:
  • -NO_2 > -CN > -SO_3H > -CHO > -COOH > -F > -Cl > -Br > -I > -OH > -NH_2
• +I Effect: Permanent displacement of sigma electrons by electron-donating groups (EDGs).
  • Examples in order of increasing electron-donating ability:
  • -CH_2-CH_3 > -C_2H_5 > -CD_3 > -CH_3 > -T > -D > -H

Application of Inductive Effects on Stability

• For carbocation stability:
  • More +I groups increases stability, whereas more -I groups increases stability of carbanions.

Acidic and Basic Strength

• Acidic Strength:
  • Increases with more -I groups, decreases with more +I groups.
  • Examples and strength orders showcase how variations impact stability.

Basic Strength

• Basic Strength:
  • Increases with more +I groups, decreases with more -I groups.
  • Comparative analysis emphasizes changes in hybridization and resulting basicities.

Resonance and Stability

• Resonance Effect: More than one structure describes a molecule's attributes, mainly effects from hybrid structures.
  • Conditions for Resonance:
  1. Planarity
  2. Conjugation is required for effective resonance with factors influencing stability and properties.

Solvent Effects

• Classification of solvents affecting reactions and intermediates, emphasizing polar protic and aprotic solvents. Examples include:
  • Polar Protic: Can donate H+ (e.g., H2O, CH3OH)
  • Polar Aprotic: Cannot donate H+ (e.g., DMSO, DMF)

Electrophiles and Nucleophiles

• Electrophiles: Molecules that accept electron pairs, which can be positively charged or neutral with an incomplete octet.
• Nucleophiles: Electron-rich species that donate electron pairs, primarily categorized into negatively charged and neutral kinds. Ambident nucleophiles exhibit dual reactivity.

Conclusion

• Overall Dynamics: The interactions, charge distributions, solvent effects, and resultant stability form the basis for understanding organic reactions, the nature of intermediates, and the general reactivity patterns observed within organic chemistry. Each reaction characteristic enhances prediction and comprehension in practical organic synthesis scenarios.