Haloalkanes

Question 1

What is the general formula for haloalkanes?

Answer 1

CnH2n+1X

X represents a halogen (F, Cl, Br, or I)

Question 2

How are haloalkanes classified?

Answer 2

Primary, Secondary, Tertiary

Classification is based on the number of carbon atoms bonded to the carbon holding the halogen

Question 3

What is a primary haloalkane?

Answer 3

A haloalkane where the halogen is bonded to a carbon that is bonded to 1 other carbon

Example structure: C - C - X

Question 4

What is a secondary haloalkane?

Answer 4

A haloalkane where the halogen is bonded to a carbon that is bonded to 2 other carbons

Example structure: C - C - C
|
X

Question 5

What is a tertiary haloalkane?

Answer 5

A haloalkane where the halogen is bonded to a carbon that is bonded to 3 other carbons

Question 6

How are haloalkanes named?

Answer 6

As substituted alkanes with fluoro, chloro, bromo, or iodo as prefixes

Example: Bromomethane for CH3Br

Question 7

Fill in the blank: The prefix for a haloalkane with a fluorine atom is _______.

Answer 7

fluoro

Question 8

Fill in the blank: The prefix for a haloalkane with a bromine atom is _______.

Answer 8

bromo

Question 9

Fill in the blank: The prefix for a haloalkane with an iodine atom is _______.

Answer 9

iodo

Question 10

True or False: Haloalkanes can only contain chlorine as the halogen.

Answer 10

False

Question 11

How can haloalkanes be synthesized from alkanes?

Answer 11

By reaction with halogens in free radical substitution reactions

This process involves the substitution of hydrogen atoms in alkanes with halogen atoms.

Question 12

What type of reactions can synthesize haloalkanes from alkenes?

Answer 12

Electrophilic addition reactions with hydrogen halides and halogens

This includes the formation of dihaloalkenes.

Question 13

What is the general equation for synthesizing haloalkanes from alcohols?

Answer 13

ROH + HX → RX + H2O

In this equation, the OH group of the alcohol is substituted for a halide ion.

Question 14

What reagents are used to synthesize chloroalkanes?

Answer 14

NaCl and H2SO4

An example reaction is CH3CH2CH2OH + NaCl → CH3CH2CH2Cl + NaOH.

Question 15

What is the ionic equation for synthesizing chloroalkanes?

Answer 15

CH3CH2CH2OH + Cl⁻ → CH3CH2CH2Cl + OH⁻

This reaction substitutes the OH group for a Cl ion.

Question 16

Which reagents are used to synthesize bromoalkanes?

Answer 16

Sodium bromide in the presence of concentrated sulfuric acid (NaBr/H2SO4)

An example reaction is CH3CH(OH)CH3 + NaBr → CH3CHBrCH3 + NaOH.

Question 17

What is the ionic equation for synthesizing bromoalkanes?

Answer 17

CH3CH(OH)CH3 + Br⁻ → CH3CHBrCH3 + OH⁻

This shows the substitution of the OH group with a Br ion.

Question 18

What reagents are used to synthesize iodoalkanes?

Answer 18

Sodium iodide and phosphoric acid (NaI/H3PO4)

An example reaction is CH3CH2OH + NaI → CH3CH2I + NaOH.

Question 19

What is the ionic equation for synthesizing iodoalkanes?

Answer 19

CH3CH2OH + I⁻ → CH3CH2I + OH⁻

The reaction substitutes the OH group for an I ion.

Question 20

What role do sulfuric acid and phosphoric acid play in the synthesis of bromoalkanes and iodoalkanes?

Answer 20

They act as catalysts

Catalysts speed up the reaction without being consumed in the process.

Question 21

What is a mechanism in chemistry?

Answer 21

A mechanism is a pictorial representation of the movement of a pair of electrons during a chemical reaction

Mechanisms illustrate how bonds are formed and broken between atoms.

Question 22

What do curly arrows represent in a mechanism?

Answer 22

Curly arrows show the movement of a pair of electrons in a mechanism

They indicate where electrons are moving when bonds are broken or formed.

Question 23

As what can pairs of electrons be present in a molecule?

Answer 23

• As a shared pair in a covalent bond
• As a lone pair on an atom

These locations determine how curly arrows are drawn in mechanisms.

Question 24

What is heterolytic fission?

Answer 24

Heterolytic fission is when the pair of electrons in the bond move to one atom, forming ions

This is represented by a double-headed curly arrow.

Question 25

What is homolytic fission?

Answer 25

Homolytic fission is when each electron in the bond moves to a different atom, forming radicals ## Footnote This is represented by two half-headed curly arrows, which are not required in A level chemistry.

Question 26

Fill in the blank: Heterolytic bond cleavage results in _______.

Answer 26

ions ## Footnote This occurs when the electron pair moves to one atom.

Question 27

Fill in the blank: Homolytic bond cleavage results in _______.

Answer 27

radicals ## Footnote This occurs when each electron moves to a different atom.

Question 28

What are the characteristics of the C-X bond in haloalkanes?

Answer 28

The halogen atoms are more electronegative than carbon, making the C-X bond polar and creating a slight positive charge on the carbon atom. ## Footnote This polarity results in an electron deficient carbon atom.

Question 29

What type of species attacks the electron deficient carbon atom in nucleophilic substitution?

Answer 29

A nucleophile ## Footnote A nucleophile is a species that contains a lone pair of electrons.

Question 30

In nucleophilic substitution, what does the nucleophile do?

Answer 30

The nucleophile donates its lone pair of electrons to the carbon atom, forming a bond. ## Footnote This process leads to the breaking of the carbon-halogen bond.

Question 31

What happens to the carbon-halogen bond during nucleophilic substitution?

Answer 31

The bond breaks by heterolytic fission, releasing a halide ion. ## Footnote Heterolytic fission involves the breaking of a bond where both electrons go to one atom.

Question 32

What is one thing to remember about the nucleophile's lone pair during the reaction?

Answer 32

The lone pair on the nucleophile forms a covalent bond with the electron deficient carbon atom. ## Footnote This is typically illustrated using a curly arrow.

Question 33

How do the electrons in the C-X bond behave during the nucleophilic substitution process?

Answer 33

The two electrons in the C-X bond move onto the halogen atom, breaking the C-X bond. ## Footnote This movement is also represented using a curly arrow.

Question 34

What does the halogen atom form after gaining electrons from the C-X bond?

Answer 34

A halide ion ## Footnote This occurs as a result of the halogen atom receiving the electrons from the bond.

Question 35

What is a nucleophile?

Answer 35

A lone pair donor ## Footnote Nucleophiles are species that have a pair of electrons available for donation to form a chemical bond.

Question 36

What reagent is used in the hydrolysis reaction of haloalkanes to form alcohols?

Answer 36

NaOH(aq) or KOH(aq) ## Footnote These reagents provide hydroxide ions (OH-) which act as nucleophiles.

Question 37

What are the conditions required for the hydrolysis reaction with hydroxide ions?

Answer 37

Warm, aqueous ## Footnote Heating the reaction mixture increases the rate of nucleophilic substitution.

Question 38

What is the overall reaction when CH3CH2Br is reacted with NaOH?

Answer 38

CH3CH2Br + NaOH → CH3CH2OH + NaBr ## Footnote This reaction results in the formation of ethanol and sodium bromide.

Question 39

What type of mechanism occurs during the hydrolysis of haloalkanes with hydroxide ions?

Answer 39

Nucleophilic substitution ## Footnote This mechanism involves the replacement of the leaving group (Br) with the nucleophile (OH).

Question 40

Fill in the blank: When CH3CH(Br)CH3 is reacted with NaOH, it produces _______ and NaBr.

Answer 40

CH3CH(OH)CH3 ## Footnote This reaction converts the haloalkane into an alcohol.

Question 41

What is the first step in the experiment to show the rate of hydrolysis of haloalkanes?

Answer 41

Gently warm separate samples of 1-chloropropane, 1-bromopropane, and 1-iodopropane in a water bath with a little added ethanol.

Question 42

What is added to each test tube after warming the haloalkanes?

Answer 42

Equal amounts of aqueous silver nitrate.

Question 43

What is measured in the experiment to determine the rate of hydrolysis?

Answer 43

Time taken for a precipitate to form.

Question 44

What color of precipitate is formed from 1-chloropropane?

Answer 44

White.

Question 45

What is the ionic equation for the precipitation reaction?

Answer 45

Ag(aq) + I⁻(aq) → AgI(s)

Question 46

How does bond strength of C-X change as you go down the group?

Answer 46

The bond C-X gets weaker.

Question 47

Why is the C-F bond stronger than other C-X bonds?

Answer 47

The shared electrons in the C-F bond are strongly attracted to the fluorine nucleus.

Question 48

What trend is observed in the rate of hydrolysis as we go down the group?

Answer 48

Rate of hydrolysis increases.

Question 49

Which type of compounds are predicted to be the most reactive based on bond enthalpies?

Answer 49

Iodo-compounds.

Question 50

What type of compounds are predicted to be the least reactive based on bond enthalpies?

Answer 50

Fluoro-compounds.

Question 51

True or False: The shared electrons in the C-X bond get closer to the halogen nucleus as you go down the group.

Answer 51

False.

Question 52

What is the formula for the cyanide ion?

Answer 52

CN-

Question 53

What reagent is used to form nitriles from haloalkanes?

Answer 53

KCN dissolved in ethanol

Question 54

What type of reaction occurs when haloalkanes are warmed with ethanolic KCN?

Answer 54

Nucleophilic substitution

Question 55

Fill in the blank: The reaction of CH2CH2Br with :CN results in __________.

Answer 55

CH3CH2CN + :Br

Question 56

In the reaction mechanism, what is the role of the cyanide ion?

Answer 56

Nucleophile

Question 57

True or False: Nitriles can be formed by the reaction of haloalkanes with water.

Answer 57

False

Question 58

What is the general type of compound formed from haloalkanes when reacted with cyanide ions?

Answer 58

Nitriles

Question 59

What is the reagent used to form primary amines from haloalkanes?

Answer 59

NH3 dissolved in ethanol (ethanolic ammonia) ## Footnote Excess ammonia is necessary for the reaction to proceed effectively.

Question 60

What is the condition required for the formation of primary amines?

Answer 60

Excess NH3 ## Footnote This ensures complete reaction with haloalkanes.

Question 61

What type of reaction occurs when haloalkanes react with ammonia?

Answer 61

Nucleophilic substitution ## Footnote The nitrogen atom in ammonia acts as a nucleophile.

Question 62

What is formed alongside primary amines during the reaction with haloalkanes?

Answer 62

HX ## Footnote Hydrogen halogen is an acid that reacts with excess ammonia.

Question 63

What is the overall equation for the reaction of haloalkanes with ammonia?

Answer 63

CH3CH2Br + 2NH3 → CH3CH2NH2 + NH4Br ## Footnote This equation is essential for exam purposes.

Question 64

In the nucleophilic substitution mechanism, what does the nitrogen atom in ammonia provide?

Answer 64

One lone pair of electrons ## Footnote This lone pair is crucial for forming a bond with the carbon atom in the haloalkane.

Question 65

Fill in the blank: When haloalkanes are warmed with excess NH3, they form _______.

Answer 65

Primary amines ## Footnote This process involves the substitution of the halogen atom.

Question 66

True or False: The reaction of haloalkanes with ammonia requires heat.

Answer 66

True ## Footnote Heating facilitates the reaction process.

Question 67

What is the product formed from the reaction of CH3CHBrCH3 with ammonia?

Answer 67

CH3CH(NH2)CH3 + NH4Br ## Footnote This demonstrates the formation of a primary amine from a secondary haloalkane.

Question 68

What are the primary amines formed in reactions also referred as?

Answer 68

Nucleophiles

Question 69

When a primary amine reacts with another haloalkane what is produced ?

Answer 69

Secondary amine + HX X= halogen

Question 70

When a secondary amine reacts with another haloalkane what is produced ?

Answer 70

Tertiary amine + HX

Question 71

What is the product of the reaction between a haloalkane and a tertiary amine?

Answer 71

Quaternary ammonium salt ## Footnote Example: CH3Br + (CH3)3N → [(CH3)4N]* Br

Question 72

What type of ammonium salts are usually obtained from reactions involving haloalkanes?

Answer 72

Mixtures of primary, secondary, tertiary, and quaternary ammonium salts

Question 73

What effect does a large excess of haloalkane have on the yield of quaternary ammonium salt?

Answer 73

Leads to a high yield of quaternary ammonium salt

Question 74

What effect does a large excess of ammonia have on the yield of amines?

Answer 74

Leads to a better yield of primary amine

Question 75

What is notable about the nitrogen in a quaternary ammonium salt?

Answer 75

Contains NO lone pair on the nitrogen

Question 76

True or False: Further substitution can occur on the nitrogen of a quaternary ammonium salt.

Answer 76

False

Question 77

What are chlorofluorocarbons (CFCs)?

Answer 77

Haloalkanes containing both chlorine and fluorine but no hydrogen

Question 78

What is an example of a short chain CFC?

Answer 78

CCIF: trichlorofluoromethane

Question 79

What were short chain CFCs used for?

Answer 79

Refrigerators

Question 80

What are longer chain CFCs used for?

Answer 80

Dry cleaning and as de-greasing solvents

Question 81

What happens to CFC gases in the atmosphere?

Answer 81

They are decomposed to give chlorine free radicals

Question 82

Why is the ozone layer important?

Answer 82

It absorbs harmful UV radiation from the Sun that causes skin cancer

Question 83

What is the molecular formula for ozone?

Answer 83

O3

Question 84

What is the equilibrium reaction involving ozone?

Answer 84

O2 + O = O3

Question 85

How do chlorine radicals affect ozone in the stratosphere?

Answer 85

They decompose ozone, causing a hole in the Earth's ozone layer

Question 86

What initiates the breakdown of C-CI bond in CFCs?

Answer 86

UV radiation

Question 87

What is produced when the C-CI bond breaks?

Answer 87

Cl• (chlorine radical)

Question 88

What do chlorine radicals do to ozone?

Answer 88

They attack ozone molecules, leading to its decomposition

Question 89

What is the overall equation for ozone breakdown?

Answer 89

2 O3 → 3 O2

Question 90

Fill in the blank: Chlorine acts as a ________ in the breakdown of ozone.

Answer 90

catalyst

Question 91

True or False: Chlorine radicals are destroyed in the process of decomposing ozone.

Answer 91

False

Question 92

What is the result of chlorine radicals attacking ozone?

Answer 92

Breakdown of ozone to oxygen