Functional Groups 3
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Questions and Answers

What is the result of heterolysis in a covalent bond?

  • Both electrons go to one fragment, forming ions. (correct)
  • The bond weakens, but no fragments are formed.
  • Both fragments retain their electrons.
  • A bond is formed between the two fragments.

Which characteristic defines a carbanion?

  • It contains exclusively σ bonds.
  • It has a positive charge.
  • It is a strong acid.
  • It possesses a lone pair of electrons. (correct)

How does a Bronsted-Lowry acid behave in a chemical reaction?

  • It accepts a proton.
  • It donates an electron pair.
  • It donates a proton. (correct)
  • It remains neutral without participating.

Which of these is a characteristic of electrophiles?

<p>They are electron pair acceptors. (A)</p> Signup and view all the answers

What type of bond-breaking process results in the formation of carbocations?

<p>Heterolysis of a polar bond. (A)</p> Signup and view all the answers

Which factor does NOT affect the strength of acids?

<p>The number of hydrogen atoms present in the molecule. (B)</p> Signup and view all the answers

What type of reaction occurs when bromine reacts with ethene?

<p>Addition reaction. (D)</p> Signup and view all the answers

Which type of bond-breaking generates free radicals?

<p>Homolysis. (B)</p> Signup and view all the answers

Which of the following statements about pKa values is true?

<p>A lower pKa emphasizes a stronger acid. (B)</p> Signup and view all the answers

What primarily influences the strength of an acid?

<p>The ability of the anion to delocalize the negative charge. (D)</p> Signup and view all the answers

Which of the following correctly describes a Bronsted-Lowry acid?

<p>A substance that donates a proton. (A)</p> Signup and view all the answers

Which factor contributes to ammonia acting as a base in water?

<p>It has an unbonded electron pair that can bond with a proton. (A)</p> Signup and view all the answers

What is the approximate ionization for a compound when pH is equal to pKa + 2?

<p>99% ionized. (C)</p> Signup and view all the answers

Which of the following statements is true about carboxylic acids?

<p>They can dissociate to donate a proton due to their acidic hydrogen. (D)</p> Signup and view all the answers

Which compound is likely to be a stronger base based on conjugate acid pKa?

<p>A compound with a conjugate acid pKa of 15. (B)</p> Signup and view all the answers

What characteristic of a carbanion contributes to its stability?

<p>The ability to resonance stabilize the negative charge. (A)</p> Signup and view all the answers

What term describes a species that seeks an electron pair due to having a positive charge?

<p>Electrophile (C)</p> Signup and view all the answers

Which of the following best describes a carbanion?

<p>A species with six electrons in its valence shell (A), A species with an unbonded pair of electrons (D)</p> Signup and view all the answers

In the Bronsted-Lowry definition, how is an acid defined?

<p>A substance that donates a proton (C)</p> Signup and view all the answers

What is the relationship between the equilibrium constant Ka and the strength of an acid?

<p>A lower Ka indicates a weaker acid (A)</p> Signup and view all the answers

Which term is used to refer to a species that donates an electron pair in a reaction?

<p>Nucleophile (B)</p> Signup and view all the answers

What happens to a strong acid in an aqueous solution in terms of ionization?

<p>It ionizes completely (A)</p> Signup and view all the answers

What is produced as a result of homolytic cleavage of a bond?

<p>Free radicals (C)</p> Signup and view all the answers

Which of the following statements about carbocations is true?

<p>They seek electron pairs to achieve stability (D)</p> Signup and view all the answers

What type of reaction is exemplified when the OH group replaces a Cl atom in an organic molecule?

<p>This reaction is a substitution reaction.</p> Signup and view all the answers

Identify the key feature of addition reactions in organic chemistry.

<p>Addition reactions involve the combination of two molecules to form a single product.</p> Signup and view all the answers

What process occurs during an elimination reaction?

<p>In an elimination reaction, elements from a molecule are removed, often resulting in the formation of a double bond.</p> Signup and view all the answers

Describe the difference between heterolytic and homolytic cleavage.

<p>Heterolytic cleavage involves both electrons going to one fragment, while homolytic cleavage results in each fragment receiving one electron.</p> Signup and view all the answers

What type of ion is formed as a result of heterolysis?

<p>Heterolysis produces ions, specifically a carbocation or a carbanion.</p> Signup and view all the answers

What type of bond breaking produces free radicals?

<p>Homolytic cleavage generates free radicals.</p> Signup and view all the answers

What do you understand by the term 'substitutions' in organic reactions?

<p>Substitutions refer to reactions where one atom or group is replaced by another in a compound.</p> Signup and view all the answers

What defines a carbocation in terms of structure?

<p>A carbocation is defined as a positively charged carbon atom with only six valence electrons.</p> Signup and view all the answers

What is the role of a carbocation in chemical reactions?

<p>A carbocation acts as an electrophile, seeking electron pairs to stabilize its positive charge.</p> Signup and view all the answers

How does a Lewis acid differ from a Bronsted-Lowry acid?

<p>A Lewis acid is an electron pair acceptor, while a Bronsted-Lowry acid donates a proton (H+).</p> Signup and view all the answers

What distinguishes a nucleophile from an electrophile?

<p>A nucleophile is a species that seeks out positive charges and donates an electron pair, whereas an electrophile accepts electron pairs.</p> Signup and view all the answers

What is the outcome of homolytic cleavage of a bond?

<p>Homolytic cleavage results in the formation of two free radicals, with each atom retaining one of the shared electrons.</p> Signup and view all the answers

Why are carbanions considered reactive species?

<p>Carbanions are reactive because they possess a negative charge and can donate an electron pair to stabilize themselves.</p> Signup and view all the answers

What happens to the equilibrium constant Ka when the equilibrium lies to the left?

<p>When the equilibrium lies to the left, the value of Ka is small, indicating that the acid does not readily ionize.</p> Signup and view all the answers

What characterizes a substance as a Lewis base?

<p>A Lewis base is characterized as an electron pair donor in a chemical reaction.</p> Signup and view all the answers

How does the presence of an electron pair affect the reactivity of a nucleophile?

<p>The presence of an electron pair enhances the nucleophile's ability to interact with electrophiles and stabilize their positive charge.</p> Signup and view all the answers

What does a low pKa value indicate about an acid's strength?

<p>A low pKa value indicates that the acid is stronger.</p> Signup and view all the answers

Why is ethanoic acid a stronger acid than ethanol?

<p>Ethanoic acid is stronger due to the resonance stabilization of its anion after losing a proton.</p> Signup and view all the answers

What is the general formula for carboxylic acids?

<p>The general formula for carboxylic acids is RCOOH or RCO2H.</p> Signup and view all the answers

How does pH relate to pKa in determining ionization of weak acids?

<p>When pH = pKa, the compound is approximately 50% ionized.</p> Signup and view all the answers

What role does the presence of a proton play in acidic functional groups?

<p>The presence of a proton allows the group to donate it, contributing to its acidic properties.</p> Signup and view all the answers

What does it mean for a base if its conjugate acid has a larger pKa?

<p>A larger pKa of the conjugate acid indicates a stronger base.</p> Signup and view all the answers

Explain what characteristics contribute to the strength of weak acids.

<p>The strength of weak acids is influenced by their pKa value and the stability of the resulting anion.</p> Signup and view all the answers

What is a key feature of bases in the context of proton acceptance?

<p>A base must have an unbonded electron pair available to bond with a proton.</p> Signup and view all the answers

Flashcards

Acid Strength and pKa

The strength of an acid is inversely related to its pKa value. A lower pKa indicates a stronger acid.

Resonance Stabilization of Anions

Resonance stabilization of an anion makes it easier to form, thus strengthening the acid.

Carboxylic Acid Structure

Carboxylic acids have the general structure RCOOH or RCO2H, where R represents an alkyl group.

pKa and % Ionization

The pKa value of a weak acid relates to the percentage of the acid that is ionized in a particular pH.

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Acidic Functional Groups

Acidic functional groups are groups that can donate a proton (H+).

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Base Strength and Conjugate Acids

The strength of a base is determined by the pKa of its conjugate acid. Higher pKa values of the conjugate acids correspond to stronger bases.

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pH = pKa

At pH equal to pKa, approximately 50% of the weak acid or base is ionized.

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Substituent Effect on Acidity

Substituents on a molecule can affect the acidity of the molecule. This effect generally has to do with the stability of the negatively charged ion being generated.

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Carbocation

A positively charged carbon atom with only six valence electrons, seeking an electron pair to achieve stability.

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Electrophile

A species that accepts an electron pair.

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Nucleophile

A species that donates an electron pair.

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Homolytic Cleavage

A chemical bond breaks, and each atom takes one electron from the bond.

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Free Radical

A species with an unpaired electron.

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Lewis Acid

An electron pair acceptor.

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Lewis Base

An electron pair donor.

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Acid (Brønsted-Lowry)

A substance that donates a proton (H+).

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Organic Reactions

Most organic reactions fall into one of three main types: substitution, addition, or elimination.

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Substitution Reactions

Reactions where one group replaces (substitutes) another group in a molecule, often occurring in compounds with single bonds.

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Addition Reactions

Reactions where two or more molecules combine to form a single larger molecule, typically involving compounds with multiple bonds.

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Elimination Reactions

Reactions where a small molecule (often H2O or HX) is removed from a larger molecule, often resulting in a double or triple bond.

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Heterolysis

A bond breaking process where both electrons of the bond pair go to one of the fragments, forming ions.

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Homolysis

A bond breaking process where each fragment gets one electron from the original bond, forming radicals.

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What are the main types of organic reactions?

Most organic reactions fall into one of three main types: substitution, addition, or elimination.

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What is Heterolysis?

A type of bond breaking where both electrons of the bond pair go to one of the fragments, resulting in the formation of ions.

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What is Homolysis?

A type of bond breaking where each fragment receives one electron of the bond pair, resulting in the formation of radicals.

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Brønsted-Lowry Acid

A substance that donates a proton (H+) to another molecule.

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pKa and Acid Strength

The pKa value of an acid indicates its strength. A lower pKa value corresponds to a stronger acid.

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Resonance Stabilization

When an anion formed from an acid can be stabilized by delocalization of electrons through resonance, the acid is stronger.

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What makes ethanoic acid stronger than ethanol?

Ethanoic acid is stronger because the formed anion is resonance stabilized, allowing for delocalization of the negative charge. This stabilization is not possible in ethanol.

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What does NH3 do when added to water?

Ammonia (NH3) acts as a base by accepting a proton from water, forming ammonium (NH4+) and hydroxide (OH-) ions.

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Stabilization and Base Strength

The stability of the conjugate acid (acid formed after the base accepts a proton) influences the base's strength. A stable conjugate acid reflects a stronger base.

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Study Notes

Organic Functional Groups

  • Organic reactions are categorized into substitutions, additions, or eliminations.
  • Substitution reactions involve replacing one atom or group with another. An example shows the OH group substituting the Cl atom in a molecule, producing an alcohol. This type of reaction is common in saturated molecules.

Addition Reactions

  • Addition reactions occur with compounds containing multiple Ï€ bonds.
  • The reaction of ethene with bromine is an example. This results in a single molecule formed from two individual molecules.

Elimination Reactions

  • These are the opposite of addition reactions.
  • In elimination reactions, a molecule loses components of another small molecule, often creating multiple bonded products.
  • To understand these reactions, bond-breaking processes must be understood.

Bond Breaking Processes

  • Heterolysis: Both electrons in the covalent bond move to one fragment, producing ions. This occurs in polar bonds.

    • A-B → A+ + B-

  • Homolysis: Each electron in the covalent bond goes to a different fragment, forming free radicals.

    • A-B → A• + B•

Carbocations and Carbanions

  • When bonds involve carbon, carbocations or carbanions can be formed.
  • Carbocation formation involves moving electrons to create a positive carbon center.
  • Carbanions are created by moving electrons to create a negative carbon center.
  • Carbocations and carbanions are highly reactive.

Electrophiles and Nucleophiles

  • Electrophiles seek electrons to achieve a stable valence shell.
  • Nucleophiles seek out positive centers and have an unbonded electron pair.
  • Acids are electron pair acceptors.
  • Bases are electron pair donors.

Acids

  • Organic acids generally do not readily dissociate to lose H+ ions to water.
  • pKa values are used to determine the strength of an acid.
  • Lowering the pKa value means the acid is stronger.
  • The strength of an acid depends on the stability of the anion formed after losing H+.

Bases

  • Bases accept protons from other molecules.
  • Base strength is measured using the pKa values of the conjugate acids formed.
  • Higher pKa values indicate a stronger base.

Functional Groups

  • These groups determine the properties and reactivity of a molecule.
  • Acidic functional groups can donate or lose a proton.
    • This requires a dissociable hydrogen atom (proton).
    • The remaining atoms must be able to delocalize the resulting negative charge.
  • Basic functional groups can accept a proton.
    • This requires an unbonded electron pair that can bond to and accept the proton.

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Organic Functional Groups Lecture 3 PDF

Description

Test your knowledge on organic functional groups and reactions, including substitution, addition, and elimination processes. This quiz also covers bond-breaking mechanisms such as heterolysis. Challenge yourself to understand the core concepts of organic chemistry!

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