Podcast
Questions and Answers
What is the bond angle around a positively charged carbon in a carbocation?
What is the bond angle around a positively charged carbon in a carbocation?
- 120° (correct)
- 180°
- 90°
- 105°
Which type of carbocation is the most stable?
Which type of carbocation is the most stable?
- Methyl carbocation
- 2° carbocation
- 1° carbocation
- 3° carbocation (correct)
What phenomenon explains the polarization of electron density toward a positively charged carbon?
What phenomenon explains the polarization of electron density toward a positively charged carbon?
- Resonance effect
- Hybridization effect
- Inductive effect (correct)
- Electrostatic effect
Which statement about methyl and 1° carbocations is true?
Which statement about methyl and 1° carbocations is true?
How does the stability of carbocations relate to the area of charge delocalization?
How does the stability of carbocations relate to the area of charge delocalization?
What characteristic makes a carbocation an electrophile?
What characteristic makes a carbocation an electrophile?
Which of the following carbocations requires the lowest activation energy for formation?
Which of the following carbocations requires the lowest activation energy for formation?
In terms of hybridization, which type of orbitals are used by carbon in a carbocation?
In terms of hybridization, which type of orbitals are used by carbon in a carbocation?
What type of rearrangement occurs when a 2° carbocation shifts to form a 3° carbocation?
What type of rearrangement occurs when a 2° carbocation shifts to form a 3° carbocation?
What is the primary product when 2-methylpropene reacts with methanol in the presence of an acid catalyst?
What is the primary product when 2-methylpropene reacts with methanol in the presence of an acid catalyst?
Which of the following correctly describes a stereoselective reaction?
Which of the following correctly describes a stereoselective reaction?
What type of ion is formed as a key intermediate during the addition of bromine to an alkene?
What type of ion is formed as a key intermediate during the addition of bromine to an alkene?
In the mechanism of electrophilic addition of bromine to alkenes, what is the first step?
In the mechanism of electrophilic addition of bromine to alkenes, what is the first step?
Which statement correctly describes carbocation stability?
Which statement correctly describes carbocation stability?
What is a characteristic of the addition of Cl2 and Br2 to alkenes?
What is a characteristic of the addition of Cl2 and Br2 to alkenes?
When a positively charged intermediate forms during a carbocation reaction, which step usually follows?
When a positively charged intermediate forms during a carbocation reaction, which step usually follows?
What is a key feature of the first step in the acid-catalyzed hydration of alkenes?
What is a key feature of the first step in the acid-catalyzed hydration of alkenes?
Which statement best describes Markovnikov's Rule in relation to hydration reactions?
Which statement best describes Markovnikov's Rule in relation to hydration reactions?
What factor primarily determines the stability of a carbocation?
What factor primarily determines the stability of a carbocation?
What is formed after the reaction of the carbocation intermediate with water during hydration?
What is formed after the reaction of the carbocation intermediate with water during hydration?
In the acid-catalyzed hydration process, what happens in the final step?
In the acid-catalyzed hydration process, what happens in the final step?
Why can acid-catalyzed hydration not readily produce 1° alcohols?
Why can acid-catalyzed hydration not readily produce 1° alcohols?
During the acid-catalyzed hydration, what does the positively charged carbon in a carbocation exhibit?
During the acid-catalyzed hydration, what does the positively charged carbon in a carbocation exhibit?
Which of the following statements about carbocations is incorrect?
Which of the following statements about carbocations is incorrect?
What does a larger activation energy (Ea) imply about the rate of a reaction?
What does a larger activation energy (Ea) imply about the rate of a reaction?
Which characteristic defines an exothermic reaction according to energy diagrams?
Which characteristic defines an exothermic reaction according to energy diagrams?
In an energy diagram, what does the transition state represent?
In an energy diagram, what does the transition state represent?
Which statement accurately describes the heat of reaction ($ riangle H$)?
Which statement accurately describes the heat of reaction ($ riangle H$)?
What role does a reaction intermediate play in an energy diagram for a two-step reaction?
What role does a reaction intermediate play in an energy diagram for a two-step reaction?
What characteristic of a carbocation affects its role as a Lewis acid?
What characteristic of a carbocation affects its role as a Lewis acid?
In terms of stability, which statement about carbocations is accurate?
In terms of stability, which statement about carbocations is accurate?
What effect does the electronegativity of a carbon atom with a positive charge exert?
What effect does the electronegativity of a carbon atom with a positive charge exert?
What is the relationship between carbocation stability and charge delocalization?
What is the relationship between carbocation stability and charge delocalization?
Why are methyl and 1° carbocations rarely observed in reactions?
Why are methyl and 1° carbocations rarely observed in reactions?
In a polar covalent bond, what is the charge characteristic of the more electronegative atom?
In a polar covalent bond, what is the charge characteristic of the more electronegative atom?
When drawing a Lewis structure, which statement about the arrangement of electrons is true?
When drawing a Lewis structure, which statement about the arrangement of electrons is true?
Which statement correctly describes the bonding requirements for carbon in neutral molecules?
Which statement correctly describes the bonding requirements for carbon in neutral molecules?
What indicates a formal charge is positive on an atom in a molecule?
What indicates a formal charge is positive on an atom in a molecule?
In an electron density model of a polar covalent bond, what does red signify?
In an electron density model of a polar covalent bond, what does red signify?
Which statement correctly describes a property of polar molecules?
Which statement correctly describes a property of polar molecules?
What must be true for two Lewis structures to be considered acceptable contributing structures?
What must be true for two Lewis structures to be considered acceptable contributing structures?
Which of the following correctly describes the role of curved arrows in resonance structures?
Which of the following correctly describes the role of curved arrows in resonance structures?
In what way do resonance structures contribute to the understanding of a molecule's properties?
In what way do resonance structures contribute to the understanding of a molecule's properties?
Which of the following statements concerning nonpolar molecules is correct?
Which of the following statements concerning nonpolar molecules is correct?
Which scenario defines a realistic representation of resonance?
Which scenario defines a realistic representation of resonance?
What is the primary criterion for validating a resonance structure?
What is the primary criterion for validating a resonance structure?
What is the predicted bond angle in a methane molecule according to VSEPR theory?
What is the predicted bond angle in a methane molecule according to VSEPR theory?
Which shape is predicted for a molecule with a trigonal planar distribution of electron density?
Which shape is predicted for a molecule with a trigonal planar distribution of electron density?
In terms of polarity, how does a water molecule behave due to its geometry?
In terms of polarity, how does a water molecule behave due to its geometry?
What characteristic defines carbon dioxide as a nonpolar molecule despite having polar covalent bonds?
What characteristic defines carbon dioxide as a nonpolar molecule despite having polar covalent bonds?
Regarding resonance structures, which option correctly describes the nature of these structures?
Regarding resonance structures, which option correctly describes the nature of these structures?
In a molecule exhibiting tetrahedral geometry, what is the influence of lone pairs on bond angles?
In a molecule exhibiting tetrahedral geometry, what is the influence of lone pairs on bond angles?
What is a distinguishing feature of the bond angles in benzene, C6H6?
What is a distinguishing feature of the bond angles in benzene, C6H6?
Which of the following accurately describes the electron density in acetylene?
Which of the following accurately describes the electron density in acetylene?
How does VSEPR theory predict the shape of molecules formed from two single bonded atoms and a lone pair?
How does VSEPR theory predict the shape of molecules formed from two single bonded atoms and a lone pair?
How many valence electrons are present in the nitrous oxide molecule, N2O?
How many valence electrons are present in the nitrous oxide molecule, N2O?
Which statement accurately describes the shape of a p orbital?
Which statement accurately describes the shape of a p orbital?
Which is a consequence of hybridization in atomic orbitals?
Which is a consequence of hybridization in atomic orbitals?
When drawing contributing structures for a resonance hybrid, what is an essential aspect to include?
When drawing contributing structures for a resonance hybrid, what is an essential aspect to include?
What occurs during the overlap of atomic orbitals to form a covalent bond?
What occurs during the overlap of atomic orbitals to form a covalent bond?
In the context of hybrid atomic orbitals, what does sp3 hybridization involve?
In the context of hybrid atomic orbitals, what does sp3 hybridization involve?
What validates a contributing structure as unacceptably resonant in a molecule like N2O?
What validates a contributing structure as unacceptably resonant in a molecule like N2O?
What defines the size relationship between 1s, 2s, and 3s orbitals?
What defines the size relationship between 1s, 2s, and 3s orbitals?
How do sp2 hybrid orbitals differ from sp3 hybrid orbitals?
How do sp2 hybrid orbitals differ from sp3 hybrid orbitals?
What is the characteristic feature of resonance structures in a molecule?
What is the characteristic feature of resonance structures in a molecule?
What factor has the greatest impact on the relative acidity of an organic acid?
What factor has the greatest impact on the relative acidity of an organic acid?
Why are carboxylic acids stronger acids than alcohols?
Why are carboxylic acids stronger acids than alcohols?
How does inductive polarization influence acidity?
How does inductive polarization influence acidity?
Which option is NOT a factor in determining the stability of an anion?
Which option is NOT a factor in determining the stability of an anion?
In terms of resonance structures, what is the primary reason for the greater acidity of carboxylic acids compared to alcohols?
In terms of resonance structures, what is the primary reason for the greater acidity of carboxylic acids compared to alcohols?
Which statement regarding the stability of anions is accurate?
Which statement regarding the stability of anions is accurate?
Which aspect does NOT contribute to the charge delocalization in an anion?
Which aspect does NOT contribute to the charge delocalization in an anion?
How does the inductive effect differ from resonance stabilization?
How does the inductive effect differ from resonance stabilization?
What combination of characteristics can make an acid less acidic?
What combination of characteristics can make an acid less acidic?
Which property does NOT enhance the stability of an anion directly?
Which property does NOT enhance the stability of an anion directly?
Flashcards
Carbocation stability
Carbocation stability
3° carbocations are more stable than 2° and 1° carbocations.
Carbocation Structure
Carbocation Structure
A carbocation has a positively charged carbon that's sp2 hybridized, with bond angles of 120°.
Alkene Hydration
Alkene Hydration
Adding water to an alkene, using an acid catalyst, to create an alcohol.
Alkene Hydration Limitation
Alkene Hydration Limitation
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Carbocation Rearrangement
Carbocation Rearrangement
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1° Carbocation
1° Carbocation
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2° Carbocation
2° Carbocation
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3° Carbocation
3° Carbocation
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Carbocation Definition
Carbocation Definition
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Carbocation Electrophility
Carbocation Electrophility
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Carbocation Bond Angles
Carbocation Bond Angles
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Carbocation Hybridisation
Carbocation Hybridisation
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Inductive Effect in Carbocation
Inductive Effect in Carbocation
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Delocalization and Stability
Delocalization and Stability
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Carbocation as Lewis Acid
Carbocation as Lewis Acid
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1,2-shift
1,2-shift
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Nucleophile
Nucleophile
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Electrophile
Electrophile
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Stereoselective reaction
Stereoselective reaction
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Anti stereoselectivity
Anti stereoselectivity
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Energy Diagram
Energy Diagram
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Transition State
Transition State
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Activation Energy (Ea)
Activation Energy (Ea)
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Exothermic Reaction
Exothermic Reaction
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Endothermic Reaction
Endothermic Reaction
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Carbocation as an Electrophile
Carbocation as an Electrophile
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What is a Lewis Acid?
What is a Lewis Acid?
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Polar Molecule
Polar Molecule
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Nonpolar Molecule
Nonpolar Molecule
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Resonance
Resonance
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Contributing Structures
Contributing Structures
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Resonance Hybrid
Resonance Hybrid
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Curved Arrow
Curved Arrow
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Allowed Electron Redistribution
Allowed Electron Redistribution
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Rules for Acceptable Contributing Structures
Rules for Acceptable Contributing Structures
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Resonance Structures
Resonance Structures
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Formal Charge
Formal Charge
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s Orbital
s Orbital
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p Orbital
p Orbital
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Orbital Overlap
Orbital Overlap
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Covalent Bond
Covalent Bond
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Hybridization
Hybridization
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sp3 Hybridization
sp3 Hybridization
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Acidity and Anion Stability
Acidity and Anion Stability
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Electronegativity and Acidity
Electronegativity and Acidity
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Resonance and Acidity
Resonance and Acidity
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Inductive Effect and Acidity
Inductive Effect and Acidity
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Size and Delocalization of Charge
Size and Delocalization of Charge
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Carboxylic Acid Acidity
Carboxylic Acid Acidity
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pKa and Acidity
pKa and Acidity
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Alkoxide Anions and Acidity
Alkoxide Anions and Acidity
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Inductive Effect on Acidity
Inductive Effect on Acidity
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Comparing Carboxylic Acids and Alcohols
Comparing Carboxylic Acids and Alcohols
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Polar Covalent Bond
Polar Covalent Bond
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Lewis Structure
Lewis Structure
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Valence Electrons
Valence Electrons
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What is a Lewis Structure?
What is a Lewis Structure?
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VSEPR Theory
VSEPR Theory
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Electron Density
Electron Density
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Bond Angle
Bond Angle
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Tetrahedral Geometry
Tetrahedral Geometry
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Trigonal Planar Geometry
Trigonal Planar Geometry
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Linear Geometry
Linear Geometry
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Study Notes
Introduction to Organic Chemistry Chapter 5: Reactions of Alkenes and Alkynes
- The chapter focuses on reactions of alkenes and alkynes
- Table 5.1 details characteristic reactions of alkenes.
Reactions of Alkenes
- Hydrohalogenation: Addition of HX (e.g., HCl, HBr, HI) across the double bond
- Hydration: Addition of water (Hâ‚‚O/Hâ‚‚SOâ‚„)
- Bromination: Addition of Xâ‚‚ (e.g., Clâ‚‚, Brâ‚‚) across the double bond
- Hydroboration: Addition of BH₃ followed by oxidation
Energy Diagrams
- Energy diagrams graph energy changes during a chemical reaction
- Energy is plotted on the y-axis and reaction progress on the x-axis
- Figure 5.1 illustrates a one-step exothermic reaction of C and A-B to give C-A and B
- Transition state is a maximum on the energy diagram, representing an unstable species during a reaction
- Activation energy (Ea) is the difference in energy between reactants and the transition state. It determines the reaction rate. A large Ea indicates a slow reaction.
Energy Diagram (Continued)
- Heat of reaction (ΔH) is the difference in energy between reactants and products, determining if the reaction is exothermic or endothermic -Exothermic: Products have lower energy than reactants; heat is released -Endothermic: Products have higher energy than reactants; heat is absorbed
Energy Diagram (Continued 2)
- Figure 5.2 displays a two-step exothermic reaction involving intermediate formation
- The reaction has distinct transition states and an intermediate
- The rate-determining step is the step with the highest activation energy barrier, that is the slowest step
Mechanism Patterns
- Pattern 1: Adding a Proton
- Adds a proton across the pi bond of a C=C double bond to form a new C-H bond.
- Typical of acid-catalyzed reactions
- Pattern 2: Taking a Proton Away
- Reverses the process of adding a proton, with focus on the compound that loses the proton
- Pattern 3: Reaction of an Electrophile and a Nucleophile
- Reaction of an electron-poor species (electrophile) and an electron-rich species (nucleophile) to form a new covalent bond
- Electrophiles are electron-poor species(Lewis acid). Nucleophiles are electron-rich species (Lewis base).
- Pattern 4: Rearrangement of a bond
- Rearrangements occur when bonding electrons from a sigma bond move to an adjacent atom.
- Form a new covalent bond.
- Pattern 5: Breaking a bond to form a stable molecule/ion
- A carbocation can be formed when a bond breaks
- The breaking of the bond releases the leaving group (e.g. bromide ion)
Electrophilic Additions to Alkenes
- Addition of hydrogen halides (HCl, HBr, HI)
- Addition of water (Hâ‚‚O/Hâ‚‚SOâ‚„)
- Addition of halogens (Clâ‚‚, Brâ‚‚).
- Regioselectivity, Markovnikov's rule in addition of HX to a double bond, H adds to the carbon with the greater number of hydrogen atoms.
Regioselectivity
- Markovnikov's rule is one example of regioselectivity
Carbocation
- Figure 5.3 depicts the structure of a tert-butyl cation
- A carbocation is a species with a positively-charged carbon atom, attached to three other atoms
- Carbocations are highly unstable, and are often intermediates in chemical reactions.
- Stable carbocations are most commonly 3* carbocations.
Carbocation (Continued)
- Carbocation stability: 3° > 2° > 1° > methyl. -A 3º carbocation is more stable than a 2° carbocation; requires lower activation energy for formation
-A 2° carbocation is more stable than a 1° carbocation and requires lower activation energy for formation
-Methyl and 1° carbocations are highly unstable. -Inductive effect -delocalization of charge over nearby atoms in a molecule leads to greater stability.
Carbocation Rearrangements
- Carbocation rearrangements happen in organic reactions
- 1,2-shifts: alkyl or hydrogen migrations with bonding electrons to an adjacent electron-deficient atom, leading to a more stable carbocation.
Addition of Hâ‚‚O to an Alkene
- Acid-catalyzed hydration of an alkene gives a protonated intermediate (e.g. oxonium ion)
- Hydronium ion adds to the less substituted carbon.
Reduction of Alkenes
- Reaction with Hâ‚‚ in the presence of a metal catalyst
- Catalytic reduction or catalytic hydrogenation converts alkenes to alkanes.
- Syn addition: Both H atoms add to the same face of the double bond. Hydrogenation of alkenes often involves syn stereoselectivity
Reduction of Alkynes
- Treatment of alkyne with H2 in the presence of a transition metal catalyst
- Two moles of H2 add to the triple bond converting it to alkane.
Addition of Chlorine and Bromine
- A reaction of alkenes with halogens, carried out with either the pure reagents or an inert solvent.
- A stereoselective reaction wherein one stereoisomer is preferentially formed or destroyed, and one stereoisomer is given preference over other products.
- Syn-addition happens at three membered ring, the transition metal catalyst.
Additional Notes
- Problems are provided in the slides for students practice.
- Mechanisms are illustrated for various addition reactions of alkenes, alkynes and carbocations.
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Description
Explore the reactions of alkenes and alkynes in this comprehensive quiz based on Chapter 5 of Organic Chemistry. Understand the mechanisms behind hydrohalogenation, hydration, bromination, and hydroboration, as well as the significance of energy diagrams in chemical reactions.
