CHEM10050 : Gilheany Lecture 7 - Alkyl Halides

What is the general structure of haloalkanes?

a) R‒H

b) R‒O‒R

c) R‒X

d) R‒OH

c) R‒X

Which of the following is not a halogen atom that can be present in a haloalkane?

a) F

b) Cl

c) Br

d) O

d) O

What is a reagent in a chemical reaction?

a) The starting material

b) The liquid medium

c) The product

d) The chemical that does the conversion

d) The chemical that does the conversion

What is a solvent in a chemical reaction?

a) The starting material

b) The liquid medium

c) The product

d) The chemical that does the conversion

b) The liquid medium

Which of the following is a common solvent for chemical reactions involving haloalkanes?

a) Water

b) Alcohol

c) Alkane

d) Ether

d) Ether

What is the role of the solvent in a chemical reaction?

a) It moderates the reaction and dissipates heat

b) It dissolves the product

c) It reacts with the starting material

d) It does not play any role in the reaction

a) It moderates the reaction and dissipates heat

Which of the following is a rare solvent for chemical reactions involving haloalkanes?

a) Water

b) Alcohol

c) Alkane

d) Ether

b) Alcohol

Which of the following is an example of a substitution reaction involving haloalkanes?

a) Esterification

b) Saponification

c) Hydrolysis

d) Nucleophilic substitution

d) Nucleophilic substitution

What is the reactivity of fluoroalkanes compared to other haloalkanes?

a) More reactive

b) Less reactive

c) Equally reactive

d) None of the above

a) More reactive

Which of the following is not a learning objective related to haloalkanes?

a) Distinguish between enantiomers and diastereomers

b) Draw and describe a diagram of a polarimeter

c) Identify chiral centres in complex structures

d) Explain the importance of chirality in biological systems

b) Draw and describe a diagram of a polarimeter

What is the main difference between a by-product and a side product in a chemical reaction?

a) By-products are avoidable while side products are inevitable.

b) By-products are a different reaction while side products are a result of the main reaction.

c) By-products are the desired product while side products are not.

b) By-products are a different reaction while side products are a result of the main reaction.

How does temperature affect the rate of a chemical reaction?

a) Every 20 ̊C raised doubles the rate.

b) Every 5 ̊C raised approx. doubles the rate.

c) Every 10 ̊C raised approx. doubles the rate.

c) Every 10 ̊C raised approx. doubles the rate.

How can we determine when a chemical reaction is over?

a) Watch the substrate disappear.

b) Watch the product appear.

c) Both a) and b).

c) Both a) and b).

What is yield in a chemical reaction?

a) The number of grams of product.

b) The number of grams of starting material.

c) The number of grams of solvent.

a) The number of grams of product.

What is % yield in a chemical reaction?

a) The number of grams of product.

b) The number of grams of starting material.

c) The number of grams of product divided by the maximum possible grams of product.

c) The number of grams of product divided by the maximum possible grams of product.

How can we determine the purity of a product in a chemical reaction?

a) Quick check using melting or boiling point.

b) By performing chromatography or spectroscopy.

c) Both a) and b).

c) Both a) and b).

Which of the following is true about haloalkanes?

a) They are highly soluble in water.

b) The halogens have two bonds and two lone pairs.

c) Their chemical reactivity varies dramatically depending on the halogen.

d) Their chemical reactivity is the same for all halogens.

c) Their chemical reactivity varies dramatically depending on the halogen.

What is the hybridization of a halogen in a haloalkane?

a) sp

b) sp2

c) sp3

c) sp3

What is the nomenclature for a haloalkane?

a) Same as for alkanes, with halogens listed as substituents.

b) Same as for alcohols, with halogens listed as substituents.

c) Same as for alkenes, with halogens listed as substituents.

a) Same as for alkanes, with halogens listed as substituents.

What is the primary sub-class of a haloalkane?

a) The C bearing halogen is attached to only one other carbon.

b) The C bearing halogen is attached to two other carbons.

c) The C bearing halogen is attached to three other carbons.

a) The C bearing halogen is attached to only one other carbon.

What is halothane?

a) A common refrigerant.

b) A super greenhouse gas.

c) An excellent general anesthetic.

c) An excellent general anesthetic.

What is 1,1,1,2-tetrafluoroethane?

a) A common refrigerant.

b) A super greenhouse gas.

c) An excellent general anesthetic.

a) A common refrigerant.

Which of the following statements is true regarding haloalkanes?

a) They are highly soluble in water

b) Their reactivity is independent of the halogen present

c) Their boiling points increase with increasing size of the halogen atom

d) They always have the same physical properties as their corresponding alkanes

c) Their boiling points increase with increasing size of the halogen atom.

What is the general formula for a haloalkane?

a) R-O-R'

b) R-C≡C-R'

c) R-X

d) R-CO-R'

c) R-X

What is the term used to describe a halogen that has only one bond and three lone pairs?

a) monovalent

b) divalent

c) trivalent

d) tetravalent

a) monovalent

Which of the following haloalkanes is used as a general anaesthetic?

a) 2-chloro-2-methylpropane

b) 1-chloropropane

c) 2-bromo-2-chloro-1,1,1-trifluoroethane

d) 1-iodobutane

c) 2-bromo-2-chloro-1,1,1-trifluoroethane

Which subclass of haloalkanes depends on how many other carbons are attached to the carbon bearing the halogen?

a) primary

b) secondary

c) tertiary

d) all of the above

d) all of the above

Why are fluorine atoms in fluoroalkanes unreactive?

A) The lone pairs are in high energy orbitals

B) Fluorine is less electronegative than oxygen and nitrogen

C) The C-F bond is very strong

D) The C-F bond is very weak

C) The C-F bond is very strong

What is the approximate mean bond dissociation energy (BDE) for a C-F bond?

A) 350 kJ mol-1

B) 450 kJ mol-1

C) 550 kJ mol-1

D) 650 kJ mol-1

B) 450 kJ mol-1

Why are fluoroalkanes chemically unreactive?

A) The C-F bond is polarised

B) Fluorine atoms are very nucleophilic

C) Fluorine atoms are very electrophilic

D) The C-F bond is very strong and nucleophiles do not react at the δ+

D) The C-F bond is very strong and nucleophiles do not react at the δ+

Which of the following is an example of a fluoropolymer?

A) Polyethylene

B) Polypropylene

C) Teflon

D) Nylon

C) Teflon

What is the chemical resistance of fluoropolymers?

A) They are very reactive

B) They are very unreactive

C) They are very nucleophilic

D) They are very electrophilic

B) They are very unreactive

What is the main use of Teflon?

A) As a fuel

B) As a non-stick coating on cookware

C) As a cleaning agent

D) As a refrigerant

B) As a non-stick coating on cookware

Why are C-F bonds often used in drugs?

A) They are less stable than C-H bonds

B) They are more polarised than C-H bonds

C) They are more reactive than C-H bonds

D) They are more stable than C-H bonds and less vulnerable to oxidation

D) They are more stable than C-H bonds and less vulnerable to oxidation

What is the main advantage of using fluorinated analogues of drugs?

A) They are less stable than non-fluorinated analogues

B) They have a shorter duration of action

C) They are less effective

D) They are more stable and have a longer duration of action

D) They are more stable and have a longer duration of action

What is the difference between a by-product and a side product?

A) There is no difference

B) By-products are avoidable, while side products are inevitable

C) By-products are inevitable, while side products are avoidable

D) By-products and side products are the same thing

D) By-products and side products are the same thing

What is the % yield of a product?

A) The number of grams of product

B) The maximum number of grams of product possible

C) The percentage of the maximum number of grams of product possible

D) The percentage of the starting material that is converted to product

C) The percentage of the maximum number of grams of product possible

What is the central reaction in organic chemistry that involves halogenated alkanes?

a) Oxidation

b) Reduction

c) Nucleophilic Substitution (SN)

d) Electrophilic Addition

c) Nucleophilic Substitution (SN)

Which of the following acts as an electrophile in nucleophilic substitution reactions?

a) Nucleophile

b) Halide ion

c) Carbon bonded to the halogen

d) Leaving group

c) Carbon bonded to the halogen

Which of the following happens when a neutral nucleophile becomes bonded to the carbon with the halogen during nucleophilic substitution?

a) The carbon-halogen bond is broken, and the halogen leaves as a halide ion

b) The carbon-halogen bond is broken, and the nucleophile becomes positive

c) The carbon-halogen bond is broken, and the nucleophile becomes neutral

d) The carbon-halogen bond is strengthened, and the halogen leaves as a halide ion

a) The carbon-halogen bond is broken, and the halogen leaves as a halide ion

What is alkylated in nucleophilic substitution reactions?

a) Halide ion

b) Nucleophile

c) Leaving group

d) Carbon bonded to the halogen

b) Nucleophile

Why are halogenated alkanes reactive?

a) Because they have strong C-F bonds

b) Because the halide ions are unstable species

c) Because the halogens have high electronegativity

d) Because they are large molecules

b) Because the halide ions are unstable species

Which of the following halogens results in the most reactive halogenated alkane?

a) Chlorine

b) Bromine

c) Iodine

d) Fluorine

c) Iodine

What is the order of reactivity of halogenated alkanes from most to least reactive?

a) C-Br > C-I > C-Cl > C-F

b) C-I > C-Br > C-Cl > C-F

c) C-Cl > C-Br > C-I > C-F

d) C-F > C-Cl > C-Br > C-I

b) C-I > C-Br > C-Cl > C-F

Which of the following is a leaving group in nucleophilic substitution reactions?

a) Nucleophile

b) Carbon bonded to the halogen

c) Halide ion

d) Neutral Y:

c) Halide ion

What is the main cause of increasing reactivity in halogenated alkanes going down the group from C-F to C-I?

a) The halogens have higher electronegativity

b) The halogens get smaller

c) The halogens get larger, resulting in progressively longer and weaker bonds

d) The halogens form weaker leaving groups

c) The halogens get larger, resulting in progressively longer and weaker bonds

Why are C-F bonds unreactive compared to C-Cl, C-Br, and C-I bonds?

a) F is more electronegative than Cl, Br, and I

b) C-F bonds are longer than C-Cl, C-Br, and C-I bonds

c) F is a larger atom than Cl, Br, and I

d) F does not form stable halide ions

a) F is more electronegative than Cl, Br, and I

Which of the following functional groups do not undergo nucleophilic substitution?

a) Amines

b) Alcohols

c) Halogens

d) Both a and b

d) Both amines and alcohols do not undergo nucleophilic substitution.

Why don't amines and alcohols act as electrophiles in nucleophilic substitution reactions?

a) The C-N and C-O bonds are too weak.

b) Amines and alcohols are too large to undergo substitution reactions.

c) The leaving groups NH2 and OH are too stable.

d) Both a and c

d) Both the C-N and C-O bonds are strong and the leaving groups NH2 and OH are not stable enough to leave easily.

Why is hydroxide a bad leaving group in nucleophilic substitution reactions?

a) It is not electronegative enough.

b) It is too large.

c) It is too unstable.

d) It is too reactive.

c) Hydroxide is not stable enough to leave easily.

Under what conditions can tertiary alcohols undergo nucleophilic substitution?

a) Under acidic conditions

b) Under basic conditions

c) Under neutral conditions

d) They cannot undergo nucleophilic substitution

a) Tertiary alcohols can undergo nucleophilic substitution under acidic conditions.

What is the leaving group in the reaction between HCl and a tertiary alcohol?

a) Cl-

b) OH2

c) H+

d) None of the above

b) The leaving group is neutral OH2.

What is the intermediate species formed when a tertiary alcohol is reacted with HCl?

a) A carbocation

b) An alkoxide ion

c) A haloalkane

d) A trialkylammonium ion

a) The intermediate species is a carbocation.

Why are carbocations relatively stable when they are tertiary?

a) Because they are large

b) Because they have a high charge density

c) Because they have three alkyl substituents attached

d) Because they are resonance stabilized

c) Carbocations are relatively stable when they are tertiary because they have three alkyl substituents attached.

What is the nucleophile in the second step of the reaction between HCl and a tertiary alcohol?

a) Cl-

b) OH2

c) H+

d) None of the above

a) The nucleophile is Cl-.

Which of the following has the highest reactivity in a nucleophilic substitution reaction?

a) C-Cl

b) C-Br

c) C-I

d) C-F

c) C-I has the highest reactivity in a nucleophilic substitution reaction.

Why does the reactivity of halogens in nucleophilic substitution reactions increase as you go down the periodic table?

a) Because the halogens get larger, resulting in progressively longer and weaker bonds

b) Because the halogens get smaller, resulting in stronger bonds

c) Because the electronegativity of the halogens decreases as you go down the periodic table

d) Because the halogens become more electronegative as you go down the periodic table

a) The reactivity of halogens in nucleophilic substitution reactions increases as you go down the periodic table because the halogens get larger, resulting in progressively longer and weaker bonds.

Which of the following functional groups does not undergo substitution reactions?

a) Alcohols

b) Amines

c) Carboxylic acids

d) Aldehydes

a) Alcohols

Why do amines and alcohols not act as electrophiles in substitution reactions?

a) The C-N and C-O bonds are too weak

b) The C-N and C-O bonds are too strong

c) The N and O atoms are too small

d) The N and O atoms are too electronegative

b) The C-N and C-O bonds are too strong

What makes amide a poor leaving group in substitution reactions?

a) The nitrogen atom is too electronegative

b) The nitrogen atom is too small

c) The amide ion is too stable

d) The amide ion is too reactive

b) The nitrogen atom is too small

Why is hydroxide a bad leaving group in substitution reactions?

a) The oxygen atom is too small

b) The hydroxide ion is too stable

c) The oxygen atom is too electronegative

d) The hydroxide ion is too reactive

b) The hydroxide ion is too stable

Which of the following can turn into a good electrophile in substitution reactions?

a) Primary alcohols

b) Secondary alcohols

c) Tertiary alcohols

d) All of the above

c) Tertiary alcohols

What is the first step in the preparation of ethers from alcohols via substitution reactions?

a) The reaction of alkoxides with alkyl halides

b) The deprotonation of the alcohol using a strong base

c) The formation of a carbenium ion

d) The attack of the nucleophile on the carbocation

b) The deprotonation of the alcohol using a strong base

Why must alcohols be converted into alkoxides for the preparation of ethers via substitution reactions?

a) Alcohols are too reactive

b) Alcohols are too stable

c) Alcohols are too weak nucleophiles

d) Alcohols are too strong nucleophiles

c) Alcohols are too weak nucleophiles

Which of the following is the most common pathway for methylation of biomolecules?

a) Reaction with NaH

b) Reaction with S-adenosyl methionine

c) Reaction with alkyl halides

d) Reaction with alkoxides

b) Reaction with S-adenosyl methionine

What type of leaving group is involved in the enzyme-catalysed methylation of biomolecules with S-adenosyl methionine?

a) Neutral sulfide species

b) Halide ions

c) Alkoxide ions

d) Hydroxide ions

a) Neutral sulfide species

Which atom in norepinephrine is most nucleophilic in the enzyme-catalysed methylation to produce epinephrine?

a) Nitrogen

b) Oxygen

c) Carbon

d) Sulfur

a) Nitrogen

Which functional groups do not act as electrophiles in substitution reactions?

a) Amines and alcohols

b) Carboxylic acids and esters

c) Aldehydes and ketones

d) Alkanes and alkenes

a) Amines and alcohols

Why are amides and hydroxide bad leaving groups in substitution reactions?

a) They are not nucleophilic enough

b) They are not electrophilic enough

c) They are not stable enough

d) They are too stable

c) They are not stable enough

Which type of alcohol can turn into a good electrophile in substitution reactions?

a) Primary alcohols

b) Secondary alcohols

c) Tertiary alcohols

d) All types of alcohols

c) Tertiary alcohols

What is the first step in the preparation of ethers from alcohols?

a) Reaction with alkyl halides

b) Formation of alkoxides

c) Deprotonation using a strong base

d) Formation of a C-Br bond

c) Deprotonation using a strong base

What type of leaving group is common in biological chemistry?

a) Sulfur anion

b) Nitrogen anion

c) Oxygen cation

d) Oxygen anion

d) Oxygen anion

Why are triphosphate and diphosphate good leaving groups in biochemistry?

a) They are highly nucleophilic

b) They are highly electrophilic

c) They are electron-withdrawing and stabilize the negative charge on the leaving group

d) They are electron-donating and destabilize the negative charge on the leaving group

c) They are electron-withdrawing and stabilize the negative charge on the leaving group

What is a substituent electronic effect?

a) The ability of a leaving group to accept/donate electrons

b) The ability of a nucleophile to accept/donate electrons

c) The ability of a functional group to change its properties based on its position in a molecule

d) The ability of a molecule to undergo substitution reactions

c) The ability of a functional group to change its properties based on its position in a molecule

Why are haloaromatic compounds different from haloalkanes?

a) They are more nucleophilic

b) They are more electrophilic

c) They are less reactive

d) They are more reactive

d) They are more reactive

Which leaving group is commonly used to convert OH into better leaving groups?

a) Halide

b) Sulfate

c) Nitrate

d) Phosphate

b) Sulfate

What is the most nucleophilic atom in norepinephrine in the methylation reaction to form epinephrine?

a) Carbon

b) Nitrogen

c) Oxygen

d) Sulfur

b) Nitrogen

What is an elimination reaction?

a) The loss of two groups to form a double bond.

b) The addition of two groups to form a double bond.

c) The substitution of two groups to form a double bond.

a) The loss of two groups to form a double bond.

What is the role of a strong base in an elimination reaction?

a) To add two groups to form a double bond.

b) To remove a hydrogen ion from the carbon next to the halide.

c) To substitute two groups to form a double bond.

b) To remove a hydrogen ion from the carbon next to the halide.

What is the leaving group in an elimination reaction?

a) The strong base.

b) The carbon next to the halide.

c) The halide anion.

c) The halide anion.

When can elimination occur?

a) When Y- is a weak base.

b) When Y- is a large, strong base.

c) When Y- is a small, weak base.

b) When Y- is a large, strong base.

What is the difference between elimination and substitution reactions?

a) Elimination involves the addition of two groups, while substitution involves the loss of two groups.

b) Elimination and substitution involve the same set of reactions.

c) Elimination involves the loss of two groups to form a double bond, while substitution involves the replacement of a leaving group with a nucleophile.

c) Elimination involves the loss of two groups to form a double bond, while substitution involves the replacement of a leaving group with a nucleophile.

When is a 1° halide more likely to undergo elimination rather than substitution?

a) When the base is a strong nucleophile.

b) When the base is a large, strong base.

c) When the base is not nucleophilic, such as bulky tert-butoxide.

c) When the base is not nucleophilic, such as bulky tert-butoxide.

When is a 3° halide more likely to undergo elimination rather than substitution?

a) When there is no base present.

b) When the base is a strong nucleophile.

c) When the base is a large, strong base.

c) When the base is a large, strong base.

When is a 2° halide more likely to undergo elimination?

a) In cold, polar solvents.

b) In hot, polar solvents.

c) In hot, nonpolar solvents.

b) In hot, polar solvents.

What are the classic eliminating conditions for 2° halides?

a) Cold, nonpolar solvents.

b) Hot, nonpolar solvents.

c) Hot, alcoholic KOH.

c) Hot, alcoholic KOH.

What is the difference between elimination and addition to alkenes?

a) They are the same reaction.

b) Elimination involves the loss of two groups to form a double bond, while addition involves the addition of two groups to an existing double bond.

c) Elimination involves the replacement of a leaving group with a nucleophile, while addition involves the loss of a leaving group.

b) Elimination involves the loss of two groups to form a double bond, while addition involves the addition of two groups to an existing double bond.

What type of compound is an alkene?

a) A compound containing a C-C triple bond.

b) A compound containing a C-C double bond.

c) A compound containing a C-O double bond.

b) A compound containing a C-C double bond

Which of the following is not involved in the mechanism for elimination reactions?

a) Base removes a proton from the carbon next to the halide

b) Pair of electrons from the H-C bond form a C=C double bond

c) Halide anion leaves the molecule

d) Base attacks the carbon next to the halide

d) Base attacks the carbon next to the halide

Which type of halide is most likely to undergo elimination reactions rather than substitution reactions?

a) 1° halides

b) 2° halides

c) 3° halides

d) It depends on the solvent and temperature conditions

c) 3° halides

Which of the following is true regarding elimination and substitution reactions?

a) Elimination and substitution reactions cannot occur simultaneously

b) Elimination reactions are faster than substitution reactions

c) Substitution reactions are faster than elimination reactions

d) Elimination and substitution reactions are competing reactions

d) Elimination and substitution reactions are competing reactions

What is the primary difference between haloalkanes and haloaromatics?

a) Haloalkanes are more reactive than haloaromatics

b) Haloaromatics are more reactive than haloalkanes

c) The properties of haloaromatics can be substantially different from haloalkanes when functional groups are attached to the aromatic ring

d) Haloaromatics have a lower boiling point than haloalkanes

c) The properties of haloaromatics can be substantially different from haloalkanes when functional groups are attached to the aromatic ring.

Which functional group is present in haloalkanes?

a) Hydroxyl group

b) Halide group

c) Carbonyl group

d) Amine group

b) Halide group

Which of the following is not a trend in reactivity of haloalkanes?

a) Reactivity increases with increasing size of the halide.

b) Reactivity increases with increasing electronegativity of the halide.

c) Reactivity increases with increasing branching of the carbon chain.

d) Reactivity increases with decreasing steric hindrance.

c) Reactivity increases with increasing branching of the carbon chain.

What is the general equation for the nucleophilic substitution of haloalkanes?

a) R-Br + NaOH → R-OH + NaBr

b) R-Br + KOH → R-OH + KBr

c) R-Br + NaCN → R-CN + NaBr

d) R-Br + NaCl → R-Cl + NaBr

c) R-Br + NaCN → R-CN + NaBr

Which of the following is an example of nucleophilic substitution?

a) Formation of an ether from an alcohol and an alkyl halide

b) Formation of a haloalkane from an alcohol

c) Formation of an alkene through elimination

d) Formation of a carboxylic acid from a primary alcohol

a) Formation of an ether from an alcohol and an alkyl halide

Which mechanism is involved in the formation of an alkene through elimination?

a) Nucleophilic substitution

b) Electrophilic substitution

c) Addition

d) Elimination

d) Elimination