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Questions and Answers
Which type of alkyl halide generally exhibits higher boiling points due to increased surface area?
Which type of alkyl halide generally exhibits higher boiling points due to increased surface area?
What is the boiling point of tert-butyl bromide compared to n-butyl bromide?
What is the boiling point of tert-butyl bromide compared to n-butyl bromide?
Which factor has a smaller impact on the boiling points of alkyl halides?
Which factor has a smaller impact on the boiling points of alkyl halides?
Which alkyl halides are generally denser than water?
Which alkyl halides are generally denser than water?
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When water is shaken with hexane, which compound is found in the top phase?
When water is shaken with hexane, which compound is found in the top phase?
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Why is free-radical halogenation not generally an effective method for synthesizing alkyl halides?
Why is free-radical halogenation not generally an effective method for synthesizing alkyl halides?
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What is a benefit of using free-radical halogenation in industrial synthesis of alkyl halides?
What is a benefit of using free-radical halogenation in industrial synthesis of alkyl halides?
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Which of the following will occur when water is shaken with chloroform?
Which of the following will occur when water is shaken with chloroform?
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What is the primary reason chloroform was abandoned as an anesthetic?
What is the primary reason chloroform was abandoned as an anesthetic?
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Which anesthetic is often used topically for minor procedures due to its cooling effect?
Which anesthetic is often used topically for minor procedures due to its cooling effect?
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What environmental concern is associated with the release of freons into the atmosphere?
What environmental concern is associated with the release of freons into the atmosphere?
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What was Freon-12 primarily replaced with in aerosol cans?
What was Freon-12 primarily replaced with in aerosol cans?
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Which halogenated anesthetic is less toxic than chloroform and goes by the trade name halothane?
Which halogenated anesthetic is less toxic than chloroform and goes by the trade name halothane?
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Which of the following substances is considered an HCFC?
Which of the following substances is considered an HCFC?
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What impact did alkyl halides have on human health historically?
What impact did alkyl halides have on human health historically?
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What historical event caused a significant population decline in Europe due to insect-borne diseases?
What historical event caused a significant population decline in Europe due to insect-borne diseases?
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In free-radical halogenation of cyclohexane, what is controlled by using a small amount of chlorine and an excess of cyclohexane?
In free-radical halogenation of cyclohexane, what is controlled by using a small amount of chlorine and an excess of cyclohexane?
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What makes free-radical bromination highly selective?
What makes free-radical bromination highly selective?
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Which hydrogen atoms are preferentially abstracted in the free-radical bromination of isobutane?
Which hydrogen atoms are preferentially abstracted in the free-radical bromination of isobutane?
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What type of radical is formed when a bromine radical abstracts an allylic hydrogen atom?
What type of radical is formed when a bromine radical abstracts an allylic hydrogen atom?
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What occurs after the formation of a resonance-stabilized allylic radical in the mechanism of bromination?
What occurs after the formation of a resonance-stabilized allylic radical in the mechanism of bromination?
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Which characteristic of the allylic radical contributes to its stability compared to typical radicals?
Which characteristic of the allylic radical contributes to its stability compared to typical radicals?
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What is the result of the second resonance form of the allylic radical reacting with bromine?
What is the result of the second resonance form of the allylic radical reacting with bromine?
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During the free-radical bromination of cyclohexene, where does the bromine atom usually substitute?
During the free-radical bromination of cyclohexene, where does the bromine atom usually substitute?
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Why are small anions more strongly solvated than large anions in a protic solvent?
Why are small anions more strongly solvated than large anions in a protic solvent?
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What effect does enhanced solvation have on the nucleophilicity of small anions?
What effect does enhanced solvation have on the nucleophilicity of small anions?
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How does the polarizability of anion species vary in relation to atomic number?
How does the polarizability of anion species vary in relation to atomic number?
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In what type of solvent do anions typically exhibit increased reactivity?
In what type of solvent do anions typically exhibit increased reactivity?
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What is one disadvantage of using aprotic solvents in reactions?
What is one disadvantage of using aprotic solvents in reactions?
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What role do crown ethers play in reactions involving cations and anions?
What role do crown ethers play in reactions involving cations and anions?
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Which condition is necessary for a molecule to be a suitable substrate for SN2 reactions?
Which condition is necessary for a molecule to be a suitable substrate for SN2 reactions?
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What happens to fluoride ion's nucleophilicity in aprotic solvent compared to protic solvent?
What happens to fluoride ion's nucleophilicity in aprotic solvent compared to protic solvent?
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What is the process called when an asymmetric carbon atom's configuration is inverted?
What is the process called when an asymmetric carbon atom's configuration is inverted?
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In the reaction of cis-1-bromo-3-methylcyclopentane with hydroxide ion, what type of product is formed?
In the reaction of cis-1-bromo-3-methylcyclopentane with hydroxide ion, what type of product is formed?
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What characterizes a stereospecific reaction?
What characterizes a stereospecific reaction?
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In the SN1 reaction of tert-butyl bromide in boiling methanol, what acts as the nucleophile?
In the SN1 reaction of tert-butyl bromide in boiling methanol, what acts as the nucleophile?
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Which statement is true regarding the rate of the SN1 reaction involving tert-butyl bromide?
Which statement is true regarding the rate of the SN1 reaction involving tert-butyl bromide?
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Why does the nucleophile not impact the rate of the SN1 reaction?
Why does the nucleophile not impact the rate of the SN1 reaction?
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What type of reaction is characterized by the nucleophile replacing a leaving group in an alkyl halide without involving the nucleophile during the slow step?
What type of reaction is characterized by the nucleophile replacing a leaving group in an alkyl halide without involving the nucleophile during the slow step?
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What is the result of the reaction between (S)-1-bromo-1-fluoroethane and sodium methoxide?
What is the result of the reaction between (S)-1-bromo-1-fluoroethane and sodium methoxide?
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What type of mechanism do tertiary alkyl halides typically undergo?
What type of mechanism do tertiary alkyl halides typically undergo?
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Which type of nucleophile is required for the SN2 reaction?
Which type of nucleophile is required for the SN2 reaction?
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In what type of solvent does the SN1 reaction typically occur most effectively?
In what type of solvent does the SN1 reaction typically occur most effectively?
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How does the rate of an SN1 reaction relate to its reactants?
How does the rate of an SN1 reaction relate to its reactants?
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Which substrates are unlikely to undergo SN1 substitutions?
Which substrates are unlikely to undergo SN1 substitutions?
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What is the relationship between substrate structure and the mechanism used in nucleophilic substitution?
What is the relationship between substrate structure and the mechanism used in nucleophilic substitution?
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Why might polar aprotic solvents enhance the strength of weak nucleophiles in the SN2 reaction?
Why might polar aprotic solvents enhance the strength of weak nucleophiles in the SN2 reaction?
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What effect does the strength of a nucleophile have on the rate of an SN2 reaction?
What effect does the strength of a nucleophile have on the rate of an SN2 reaction?
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Study Notes
Chapter 6: Alkyl Halides
- Alkyl halides are a class of halogenated organic compounds
- Three major classes: alkyl, vinyl, and aryl halides
- Alkyl halides: halogen bonded to sp³ carbon
- Vinyl halides: halogen bonded to sp² carbon
- Aryl halides: halogen bonded to sp² carbon
- Physical properties and common uses of each vary
Learning Outcomes
- Name alkyl halides, explain their physical properties, and describe their common uses.
- Predict the products of substitution and elimination reactions, and explain what factors favor each type of reaction.
- Identify the differences between first-order and second-order substitution and elimination reactions, and explain what factors determine the order of the reaction.
- Given a set of reaction conditions, identify the possible mechanisms, and predict which mechanism(s) and product(s) are most likely.
Reactivity of Alkyl Halides
- The carbon-halogen bond is polar, making the carbon atom electrophilic.
- A nucleophile can attack the electrophilic carbon.
- The halogen atom can leave as a halide ion.
- Alkyl halides can be substituted or eliminated by various reactions.
Nomenclature of Alkyl Halides
- IUPAC nomenclature: names are based on the longest carbon chain & substituents (fluoro-, chloro-, bromo-, iodo-).
- Common names are used for simpler alkyl halides (e.g., isopropyl bromide).
Classification of Alkyl Halides
- Primary (1°): halogen bonded to one carbon
- Secondary (2°): halogen bonded to two carbons
- Tertiary (3°): halogen bonded to three carbons
- Methyl halide: halogen bonded to a methyl group
Dihalides (with examples)
- Geminal: two halogens on the same carbon
- Vicinal: two halogens on adjacent carbons
Common Uses of Alkyl Halides
- Solvents: carbon tetrachloride (dry cleaning), chloroform, methylene chloride
- Refrigerants: Freons (CFCs)
- Anaesthetics: chloroform, halothane
- Pesticides: DDT, other chlorinated insecticides
- Many synthetic uses as starting materials
Densities of Alkyl Halides
- Alkyl fluorides and chlorides are less dense than water.
- Alkyl bromides and iodides are denser than water.
Free-Radical Halogenation
- Not an effective method for alkyl halide synthesis.
- Usually produces many different products due to different reactivity levels of hydrogen atoms.
SN2 Reaction
- Nucleophile replaces the halogen.
- The halogen leaves with its electrons as a halide ion.
- The reaction takes place in one step.
- The rate depends on both the alkyl halide concentration and nucleophile concentration.
- Inverted configuration, with the nucleophile attacking from the backside of the carbon.
SN1 Reaction
- Ionization forms a carbocation prior to the nucleophile attack.
- Rate depends on the carbocation stability and substrate concentration.
- The carbocation is planar.
- There's a mixture of possible products: retention and inversion of configuration
E1 Reaction
- The reaction forms a carbocation intermediate, leading to an eventual alkene product.
- The reaction rate is slower for secondary and primary alkyl halides.
- A weak base often serves as the attacking reagent during the second step.
- A possible method to determine if the reaction will result in an E1 product or a SN1 product if there's a difference in leaving groups or if the base for the reaction is strong enough
E2 Reaction
- A strong base removes a proton.
- The base and the substrate are in a transition state.
- Formation of a new double bond during this reaction.
- The reaction rate is faster than SN1 and E1
- A concerted reaction: bonds break and form simultaneously.
Factors Affecting SN1/SN2/E1/E2 Reactions
- Substrate: Methyl > Primary > Secondary > Tertiary.
- Nucleophile: Strong nucleophiles favor SN2; weak nucleophiles favor SN1.
- Base: Strong bases favor E2; weak bases favor E1.
- Solvent: Polar protic solvents favor SN1 and E1; polar aprotic solvents favor SN2 and E2.
- Stereochemistry: SN2 results in inversion, while SN1 and El produce a racemic mixture.
Summary
- The reactions of alkyl halides (substitution and elimination) are important in organic chemistry
- The rate, mechanism, stereochemistry, and product types depend on different factors which this chapter details.
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Description
Test your knowledge on alkyl halides, including their boiling points, density characteristics, and uses in anesthesia. This quiz covers factors affecting boiling points, free-radical halogenation, and environmental concerns related to halogenated compounds. Perfect for students studying organic chemistry concepts.
