General Organic Chemistry for JEE

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Questions and Answers

How does the presence of fluorine affect the stability of a carbocation compared to chlorine?

  • Fluorine decreases stability more than chlorine because it is less electronegative.
  • Fluorine has no effect on the stability of carbocations compared to chlorine.
  • Fluorine decreases stability less than chlorine due to its electron-donating effect.
  • Fluorine decreases stability more than chlorine because it is more electronegative. (correct)

What characterizes the +I effect in a carbon chain?

  • Transmission of a negative charge through the chain (correct)
  • Induction of a dipole moment by electronegativity differences
  • Transmission of a positive charge through the chain
  • Introduction of an electron-withdrawing group to the chain

Which factor influences the magnitude of the inductive effect the most?

  • The distance between the atoms in the chain (correct)
  • The size of the alkyl groups present in the molecule
  • The type of hybridization of the carbon atom
  • The electronegativity of the carbon atom only

Which of the following statements about the -I effect is true?

<p>It induces a transmission of a positive charge through the chain (D)</p> Signup and view all the answers

How does the inductive effect impact the stability of carbocations?

<p>Electron-donating groups enhance the stability of carbocations (B)</p> Signup and view all the answers

What is the result of introducing a halogen, such as chlorine, into a carbon chain?

<p>Induction of a permanent dipole resulting in a partial positive charge on carbon (A)</p> Signup and view all the answers

Which of the following correctly describes the roles of electrophiles and nucleophiles in organic reactions?

<p>Electrophiles are electron-deficient and attack regions of high electron density. (A)</p> Signup and view all the answers

What is the main difference between homolytic fission and heterolytic fission?

<p>In homolytic fission, each atom retains one electron, while in heterolytic fission, one atom retains both. (C)</p> Signup and view all the answers

Which statement about inductive effects is true?

<p>The inductive effect results in a permanent dipole due to the presence of electron-rich or electron-deficient species. (B)</p> Signup and view all the answers

In an organic reaction, what is the correct sequence of steps from reactants to products?

<p>Reactants + Catalyst → Intermediate → Products (C)</p> Signup and view all the answers

Which of the following correctly characterizes resonance in organic compounds?

<p>Only the most stable resonance structure contributes to the resonance hybrid. (B)</p> Signup and view all the answers

Flashcards

Electrophiles

Species that are electron-deficient and seek to gain electrons by attacking regions of high electron density in the substrate.

Nucleophiles

Species that are electron-rich and donate their electrons to regions of low electron density in the substrate.

Homolytic Fission

The cleavage of a covalent bond where each atom retains one electron, resulting in the formation of highly reactive free radicals.

Heterolytic Fission

The cleavage of a covalent bond where one atom takes both electrons, resulting in the formation of a positively charged cation and a negatively charged anion.

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Inductive Effect

A permanent dipole formed in a carbon chain due to the presence of an electron-rich or electron-deficient group that influences the distribution of electron density.

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Positive Inductive Effect (+I)

Electron-donating group influences electron density, increasing the electron availability in the chain.

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Negative Inductive Effect (-I)

Electron-withdrawing group influences electron density, decreasing the electron availability in the chain.

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Inductive Effect Strength

Inductive effect's strength decreases as the distance between atoms increases, diminishing its influence.

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Inductive Effect Transmission

Inductive effect transmits through single bonds (sigma bonds) in a molecule, affecting electron distribution in the chain.

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Inductive Effect (-I effect)

The tendency of a group to withdraw electron density from a carbon chain due to its electronegativity, leading to a permanent dipole.

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Electromeric Effect

A temporary effect where pi electrons in an organic compound shift completely to one of the bonded atoms due to an attacking reagent.

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Carbocation

A positively charged carbon atom, often formed by the loss of a leaving group.

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Carbanion

A negatively charged carbon atom, often formed by the gain of an electron.

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Electron-donating groups (+I Effect)

Groups that increase the stability of carbocations and decrease the stability of carbanions due to their electron-donating nature.

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Study Notes

General Organic Chemistry (GOC) for JEE

  • Key topics in general organic chemistry include electrophiles, nucleophiles, inductive effect (+I, -I), electromeric effect (+E, -E), hyperconjugation, mesomeric effect, resonance, structural isomerism, and stereoisomerism.

GOC Basics

  • Organic Reactions: A typical reaction follows this sequence: Reactants + Catalyst/Energy → Intermediate (Transition State) → Product. Reaction conditions form intermediates which quickly react to yield a product.
  • Reagents & Substrates: Reagents are reactive species triggering a reaction by attacking another species (the substrate).
    • Electrophiles: Electron-deficient species attack regions of high electron density.
    • Nucleophiles: Electron-rich species attack regions of low electron density.
  • Cleavage of Bonds: Covalent bonds break in two ways:
    • Homolytic Fission: Each atom gains one unpaired electron, forming free radicals.
    • Heterolytic Fission: One atom retains both electrons forming a cation and an anion.

Inductive Effect

  • Inductive effect is a permanent dipole induced by electronegativity differences within a molecule.
  • The magnitude of the partial charge decreases as distance from the affecting atom increases.
  • The effect decreases significantly after the fourth carbon atom.
  • Salient features:
    • A permanent effect.
    • Depends on the distance between atoms.
    • Transmitted through sigma bonds.
  • +I effect: Electron-donating group (e.g., alkyl group) transmits negative charge.
  • -I effect: Electron-withdrawing groups (e.g., halogens) transmit positive charge.

Gauging Stability of Molecules

  • Electronegative atoms increase the stability of carbocations.
  • Electron-donating groups decrease carbocation stability.

Electromeric Effect

  • Complete transfer of pi electrons to an atom in a molecule when an attacking reagent (electrophile or nucleophile) is present.
  • Temporary effect disappearing when the attacking reagent is removed.
  • +E: Pi electrons shift towards the electrophile causing negative charge to the atom with the bond pair.
    • Example: Protonation of alkenes
  • -E: Pi electrons shift away from the nucleophile causing a positive charge to the atom losing the pi electrons.

Hyperconjugation

  • Adjacent sigma bonds donate electrons to stabilize carbocations.
  • Stability is proportional to the number of alpha hydrogens.

Mesomeric Effect

  • Delocalization of pi electrons over a network of pi bonds.
  • Creates polarity in the molecule.
  • +M effect: Electrons shift away from the +M group
    • Example: Methoxy ether
  • -M effect: Electrons shift towards the -M group.
    • Example: CHO and NO2 groups

Resonance Effect

  • Delocalization of pi electrons and lone pairs across a molecule.
  • Results in multiple hypothetical resonance structures.
  • +R Effect: Release of lone pair of electrons into a molecule, transmitting a negative charge, the electron-donating species becomes positively charged.
  • -R Effect: Transmission of a positive charge, electron-withdrawing species

Isomerism

  • Molecules with the same chemical formula but different chemical structures.
  • Types:
    • Structural isomerism (constitutional isomerism): Different arrangement of atoms.
    • Stereoisomerism: Different three-dimensional arrangement of atoms.
      • Chain
      • Positional
      • Functional
      • Metamerism
      • Tautomerism
      • Ring-chain
      • Geometric
      • Optical

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