A-level Chemistry > Mechanisms > Flashcards

Mechanisms Flashcards

(48 cards)

Study These Flashcards
1
Q

What are free radicals?

A

Atoms / a group of atoms which have a single unpaired electron which are formed when a bond is broken by homolytic fission

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What kind of reaction does free radical substitution cause?

A

Causes a chain reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is free radical substitution ?

A

A reaction between alkanes and halogens in the presence of UV light.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the stages in free radical substitution?

A
  1. Initiation
  2. Propagation
  3. Termination
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the steps in the free radical substitution of chlorine and methane?

A

Initiation:

Cl-Cl ——> 2•Cl

Propagation:

  • Cl + CH4 ——> HCL + •CH3
  • CH3 + Cl2 ——> CH3Cl + •Cl

Termination:

  • Cl + •Cl ——> Cl2
  • CH3 + •CH3 ——> C2H6
  • Cl + •CH3 ——> CH3Cl
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Show how the ozone is broke. Down by free radical substitution.

A
  • Cl + O3 ——> •ClO + O2
  • ClO + O3 ——> 2O2 + •Cl

The chlorine free radical acts as a catalyst in the breakdown of ozone

Overall:

2O3 ——> 3O2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the reaction conditions for free radical substitution?

A

Halogen into free radicals

Uv light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What kind of mechanism is the nitration of benzene?

A

Electrophilic substitution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the electrophile used in the nitration of benzene and how is it generated?

A

Nitronium ion (NO2^+)

Generating the electrophile:

H2SO4 + HNO3 ——> NO2^+ + HSO4^- + H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the reaction conditions for the nitration of benzene?

A

Conc H2SO4

Conc HNO3

Below 55

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the mechanism for the nitration of benzene?

A
  1. Curly arrow from the delocalised ring of electrons of benzene to the nitronium ion
  2. Draw benzene with an H atom and nitro group on the benzene molecule. With the delocalised ring not completed and having a + charge
  3. Curly arrow from the hydrogen bond to the delocalised ring
  4. Draw nitrobenzene + H^+
  5. Show that the H+ would react with HSO4^- to reform H2SO4 as a catalyst
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does the H+ ions reform the H2SO4 catalyst?

A

H+ would recombine with HSO4^- to reform H2SO4 showing it is a catalyst

H+ + HSO4^- ——> H2SO4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the reaction conditions for the reduction of nitrobenzene?

A

Room temperature

Sn/HCL as a reducing agent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Write out equations for the reduction of nitrobenzene

A

C6H5NO2 + 6[H] ——> C6H5NH2 + 2H2O

C6H5NH2 + HCL ——> CH5NH3^+ +Cl^-

Amine reacts with acid to form an ionic salt, so add NaOH to liberate the amine

C6H5NH3^+ + NaOH ——> C6H5NH2 + Na^+ +Cl^- + H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the reaction conditions used in the acylation of benzene to form phenylketone?

Fiedel crafts reaction

A

ROCl

AlCl3 catalyst

Reflux

Non aqueous environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Show the equations for the AlCl3 catalyst in an acylation reaction

A

ROCl + AlCl3 ——> RCO^+ + AlCl4^-

This has generated the RCO^+ electrophile

H+ coming off during the substitution reaction is used to regenerate the AlCl3 catalyst

AlCl4^- + H^+ ——> AlCl3 + HCL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the electrophilic substitution mechanism for the acylation of benzene

Friedel crafts reaction

A
  1. Electrophile generated from acyl group and AlCl3
  2. Curly arrow from the delocalised electron ring of benzene to the electrophile carbocation
  3. Draw benzene with H atom and electrophile coming off it and delocalised ring not completed with a + charge
  4. Curly arrow from H atom to delocalised ring
  5. Draw phenylketone and H+
  6. Show how H+ is used to regenerate AlCl3 catalyst
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is a nucleophile?

A

An electron pair donor

A species which is attracted to electron deficient regions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why are acyl chlorides susceptible to attack from nucleophiles?

A

Due to the polarity of the molecule and the carbon having two highly electronegative groups bonded to it drawing electrons away from the carbon so it is slightly positive and electron deficient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What kind of reaction occurs with acyl chlorides an nucleophiles?

Study These Flashcards
A

Nucleophilic addition elimination reactions

Acylation reactions

21
Q

What are the possible nucleophiles used in addition elimination reactions / acylation reactions?

What products are formed when reacting with an acyl chloride?

Study These Flashcards
A

Water forms carboxylic acids

Alcohol forms esters

Ammonia forms amides

Amines forms N-substituted amides

22
Q

What are the reaction conditions for acylation reactions?

Nucleophilic addition elimination

Study These Flashcards
A 
Nucleophile:
Water
Alcohols 
Ammonia
Amines

Room temperature

23
Q

Describe the generic mechanism for a nucleophilic addition elimination reaction (acylation reaction)

Study These Flashcards
A
  1. Slightly positive carbon and slightly negative chlorine and oxygen atoms in the acyl chloride
  2. Lone pair of nucleophile curly arrow towards the carbon atom of acyl chloride. Curly arrow from the double bond of oxygen to oxygen atom in acyl chloride.
  3. Curly arrow from oxygen lone pair to reform double bond as a curly arrow comes from carbon to chlorine bond to the chlorine atom. Negative charge on oxygen and positive charge on nucleophile
  4. Curly arrow from the lone pair on the chlorine to the hydrogen atom of nucleophile as another curly arrow goes from the nucleophile to hydrogen bond to the nucleophile
  5. Draw product and HCL as a by product
24
Q

What are the reaction conditions for the nucleophilic addition of cyanide to an aldehyde or ketone?

Study These Flashcards
A

KCN or HCN

Dilute H2SO4

Room temperature

25
Describe the nucleophilic addition mechanism of a ketone with cyanide ion.
1. Formation of cyanide ion 2. Curly arrow from the lone pair on the cyanide to the slightly positive carbon. Curly arrow from the double bond to the oxygen 3. Curly arrow from the negative oxygen atom lone pair to the H+ ion from solvent 4. Product formed is a hydroxynitrile
26
Why does addition reactions of KCN with dilute acid from a mixture of enantiomers?
Produced a racemic mixture since the cyanide ion can add onto the aldehyde or ketone from above or below the double bond.
27
Why is HCN not commonly used to addition reactions?
Toxic gas which needs to be prevent from escaping so instead KCN is used followed by dilute acid as a source of H+ ions
28
What kind of reaction occurs when changing an aldehyde or ketone to an alcohol?
Reduction reaction | Nucleophilic addition mechanism
29
What is the nucleophile used in reducing aldehydes and ketones and what is the source of this nucleophile?
:H^- hydride ions | Sourced from NaBH4 Sodium tetrahydridoborate III
30
What are the conditions for the reduction of aldehydes and ketones?
NaBH4 dissolved in alcohol or water Refluxed
31
Describe the reduction of aldehydes or ketones reaction | Nucleophilic addition mechanism
1. Curly arrow from lone pair of hydride ions towards the carbon and curly arrow from double bond to the oxygen atom 2. Curly arrow from lone pair of negative oxygen atom to positive H+ atom fro dilute acid or water 3. Forms an alcohol
32
What are the reaction conditions for nucleophilic substitution reactions between a haloalkane and potassium/sodium hydroxide?
Haloalkane Nucleophile: :OH^- from KOH or NaOH aqueous Room temperature Solvent of ethanol
33
Describe the nucleophilic substitution reaction between a haloalkane and NaOH
1. Curly arrow from lone pair on hydroxide ion to the carbon. Curly arrow from the C-X bond to the halogen 2. Forms an alcohol with the halide ion coming off
34
What are the reaction conditions for nucleophilic substitution reactions between a haloalkane and potassium cyanide?
KCN source of :CN^- ions Aqueous alcoholic solution
35
Describe the nucleophilic substitution reaction between haloalkane and potassium cyanide
1. Curly arrow from lone pair on cyanide ion to the carbon. Curly arrow from the C-X bond to the halogen 2. Forms an nitrile with the halide ion coming off
36
What are the reaction conditions for nucleophilic substitution reactions between a haloalkane and ammonia
Excess conc ammonia In ethanol Under pressure
37
Describe the nucleophilic substitution reaction between haloalkane and ammonia
1. Curly arrow from lone pair on the ammonia to the carbon. Curly arrow from the C-X bond to the halogen. 2. Curly arrow from the lone pair on the excess ammonia to a hydrogen atom on the bonded ammonia molecule. Curly arrow from N-H bond towards the positive N+ atom 3. Forms an amine with the halide ion coming off and an ammonium ion
38
What is an electrophile?
An electron pair acceptor An electron deficient atom attracted to an electron dense region
39
What kind of reaction takes place between an alkene and an electrophile?
Electrophilic addition reaction
40
What are the possible electrophiles for electrophilic addition of an alkene?
HBr H2SO4 Br2
41
Describe the electrophilic addition reaction between an alkene and HBr
1. Curly arrow from double bond to the hydrogen atom of H-Br and a curly arrow from the H-Br bond to the Br atom. 2. Curly arrow from the lone pair of the :Br ion to the carbocation 3. Forms a haloalkane
42
What are the reaction conditions for electrophilic addition reactions?
Alkene / presence of a double bond Electrophile Room temperature Solvent conditions
43
Describe the electrophilic addition reaction between an alkene and bromine (Br2)
1. Curly arrow from the double bond to a bromine atom as well as a curly arrow from the Br-Br bond to the other bromine atom 2. Curly arrow from the bromine atom to the carbocation 3. Forms a dibromoalkane
44
Describe the electrophilic addition reaction between an alkene and H2SO4
1. Curly arrow from double bond to hydrogen atom of H2SO4. Curly arrow from H-O bond to Oxygen atom of H2SO4 2. Curly arrow from lone pair of oxygen atom of H2SO4 to the carbocation 3. Product formed
45
What are the conditions for nucleophilic substitution using hydroxide ions?
NaOH or KOH dissolved in ethanol Room temperature Aqueous (dissolved in water)
46
What are the reaction conditions for elimination using hydroxide ions?
NaOH or KOH dissolved in ethanol High temperature (refluxed) Dissolved in ethanol
47
What is the role of the hydroxide ions during an elimination reaction?
Acts as a base by accepting a hydrogen atom and forming water
48
Describe the elimination reaction between a haloalkane and NaOH?
1. Curly arrow from the lone pair of the hydroxide ion to the hydrogen atom of the haloalkane. 2. Curly arrow from the C-H bond to the C-C bond 3. Curly arrow from the C-X bond to the halogen 4. Forms an alkene, water molecule and halide ion. (May form a mixture of geometric isomers
A-level Chemistry
flashcards
Decks in class (33)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions