Reactions in organic chemistry Flashcards
(102 cards)
1
Q
What are substitution reactions
A
reactions in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms
2
Q
describe the balanced equation for the reaction of methane with clorine in a substitution reaction
A
CH4 + Cl2 → CH3Cl + HCl
methane + chlorine → clorormethane + hydrogen cloride
3
Q
Write the balanced equation for the reaction of ethane with chlorine in the presence of UV light in a substitution reaction
A
C2H6 + CL2 → C2H5Cl + HCl
ethane + chlorine → chloroethane + Hydrogen chloride
4
Q
Give a use of halogenated alkane
A
Used as flame retardants
5
Q
What name is given to the mechanism by which methane/ ethane and chlorine undergo a substitute reaction
A
Free radical substitution mechanism
6
Q
what is a free radical
A
an atom or group of atoms with an unpaired electron which are highly reactive
7
Q
the free radical substution mechanism involves homolytic fission. what is homolytic fission
A
homolytic fission is the splitting of a covalent bond where each atom takes one electron, forming free radicals
8
Q
What causes homolytic fission in the free radical substitution mechanism
A
the presense of ultra- violet light
9
Q
Describe free radical subtitution mechanism for Methane and chlorine
A
- Initiation
* Homolytic fission occours - A chlorine molecule is split into two chlorine free radicals in the presence of UV light - Propagation 1: A Chlorine free radical reacts with a methane molecule forming hydrogen chloride and a methyl free radical CH3
- Propergation 2 : a methy free radical reacts with a separate chlorine molecule forming chloromethane and a chlorine free radical. This sets up a chain reaction until one reactant is used up. It causes constant formation of chloromethane and hydrogen chloride
step 3: termination : The chain reaction ends when the free radicals combine to form chlorine, chloromethane and ethane
10
Q
Describe the evidece that the free radical subtitution for Methane and chlorine is photochemical
A
Uv light is required to cause homolytic fission and split Cl2 into Cl free radical
11
Q
Describe the evidence that in radical subtitution for Methane and chlorine that free radicals are forming causing a chain reaction/ propagation stage is occouring
A
a) adding tetramethyl lead. It decomposes to form CH3 free radicals.
It causes an increase in rate of reaction, they promote the chain reaction.
b) for every photon of light absorbed, thousands of molecues of chloromethane are formed.
12
Q
describe the evidence that in radical subtitution for Methane and chlorine, the radicals combine at the termination stage
A
The formation of the hydrocarbon ethane in trace amounts must have come from the combination of CH3 radicals
13
Q
why in radical subtitution for Methane and chlorine is only a trance quantity of ethane formed
A
the probability of CH3 radicals combining with other CH3 radicals is small due to the small concentration of CH3 radicals. There is a much higher probability of CH3 radicals combining eith Cl2 due to the large conc of Cl2
14
Q
Describe free radical subtitution mechanism for ethane and chlorine
A
- Initiation
* Homolytic fission occours - A chlorine molecule is split into two chlorine free radicals in the presence of UV light - Propagation 1: A Chlorine free radical reacts with a ethane molecule forming hydrogen chloride and a ethyl free radical C2H5
- Propergation 2 : a ethyl free radical reacts with a separate chlorine molecule forming chloroethane and a chlorine free radical. This sets up a chain reaction until one reactant is used up. It causes constant formation of chloroethane and hydrogen chloride
step 3: termination : The chain reaction ends when the free radicals combine to form chlorine, chloroethane and butane
15
Q
Describe the evidece that the free radical subtitution for ethane and chlorine is photochemical
A
Uv light is required to cause homolytic fission and split Cl2 into Cl free radical
16
Q
Describe the evidence that in radical subtitution for ethane and chlorine that free radicals are forming causing a chain reaction/ propagation stage is occouring
A
a) adding tetraethyl lead. It decomposes to form C2H5 free radicals.
It causes an increase in rate of reaction, the C2H5 radicals promote the chain reaction.
b) for every photon of light absorbed, thousands of molecues of chloroethane are formed.
17
Q
describe the evidence that in radical subtitution for ethane and chlorine, the radicals combine at the termination stage
A
The formation of the hydrocarbon butane in trace amounts must have come from the combination of C2H5 radicals
18
Q
why in radical subtitution for ethane and chlorine is only a trance quantity of butane formed
A
the probability of C2H5 radicals combining with other C2H5 radicals is small due to the small concentration of C2H5 radicals. There is a much higher probability of C2H5 radicals combining eith Cl2 due to the large conc of Cl2
19
Q
What is an addition reaction
A
An addition reaction is a chemical reaction in which two or more molecules react to form a single molecule
20
Q
Using a balanced equation describe the addition reaction between ethene with chlorine.
A
C2H4 + Cl2 → C2H4Cl2
21
Q
Using a balanced equation describe the addition reaction between ethene with bromine
A
C2H4 + Br2→ C2H4Br2
22
Q
would you expect benzene to readily undergo an addition reaction?
A
No, benzene is neither saturated nor unsaturated. Its bonds are an identical intermediate between a single and a double bond
23
Q
Using a balanced equation describe the addition reaction between ethene with hydrogen chloride
A
C2H4 + HCl→ C2H4Cl
24
Q
Using a balanced equation describe the addition reaction between ethene with water / Hydration of ethene
A
C2H4 + H2O→ C2H5OH
25
Using a balanced equation describe the addition reaction between ethene with hydrogen/ Hydrogenation of ethene
C2H4 + H2→ C2H6
26
what transition metal catalyst is used for hydrogenation/ addition of hydrogen to a molecule (NB)
name its importance
Nickel.
Hydrogenation of vegtable oils produces soild fats used in ,margarines
27
what name is given to the mechanism by which an addition reaction takes place
the ionic addition mechanism - involves ions
28
the ionic addition mechanism involves heterolytic fission. What is heterolytic fission
the splitting of a covalent bond, where one atom takes BOTH electrons from the covalent bond forming a potive ion and a negative ion
29
what causes heterolytic fission in the ionic addition mechanism
the high electron density present in the alkene's double bond
30
Describe the Ionic addition mechanism for the ionic addition mechanism for the reaction between ethene and bromine
1. Polaristaion.
* The Br2 molecule approaches the double bond of the ethene molecule
* It becomes polarised by the high electron density in the alkenes carbon- carbon double bond
2. Heterolytic fission
* The polarisation becomes so great that heterolytic fission occours and the Br2 molecule splits up into Br+ and Br- ions
3. Carbonium ion formation:
* The Br+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond
* Leaves the formation of an INTERMEDISTE carbonium ion
4.Ionic addition:
* The intermediate carbonium ion is sttacked by the Br- ion, this results in the formation of 1,2-dibromoethane
31
Describe the Ionic addition mechanism for the ionic addition mechanism for the reaction between ethene and chlorine
1. Polaristaion.
* The Cl2 molecule approaches the double bond of the ethene molecule
* It becomes polarised by the high electron density in the alkenes carbon- carbon double bond
2. Heterolytic fission
* The polarisation becomes so great that heterolytic fission occours and the 2 molecule splits up into Cl+ and Cl- ions
3. Carbonium ion formation:
* The Cl+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond
* Leaves the formation of an INTERMEDIATE carbonium ion
4.Ionic addition:
* The intermediate carbonium ion is sttacked by the Cl- ion, this results in the formation of 1,2-dichloroethane
32
Describe the Ionic addition mechanism for the ionic addition mechanism for the reaction between ethene and Hydrogen chloride
1. Polaristaion.
* The Hδ+ in the polar HCl molecule approaches the double bond of the ethene molecule
* It becomes increasingly polarised by the high electron density in the alkenes carbon- carbon double bond
2. Heterolytic fission
* The polarisation becomes so great that heterolytic fission occours and the HCl molecule splits up into H+ and Cl- ions
3. Carbonium ion formation:
* The H+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond
* Leaves the formation of an INTERMEDISTE carbonium ion
4.Ionic addition:
* The intermediate carbonium ion is sttacked by the Cl- ion, this results in the formation of chloroethane
33
State the evidence that the ionic addition mechanism is not a free radical substitution mechanism
This reaction can occour during the dark
34
State the evidence that the addition reactions have an ionic addition mechanism
(That a negative ion attacks a carbonium ion in step 4)
If only Bromine is added to ethene, the only product that can be formed is 1,2 dibromoethane.
**However - If bromine water containing sodium chloride (Sources of Br-, OH-, and Cl-) are added to ethene, three separate products form**
**1,2-dibromoethane
2-bromoethanol
1-bromo2-chloroethane**
**These three different products suggest a postive intermediate carbonium ion is always formed that is subject to addition from different negative**
35
What is an elimation reaction?
A Chemical reaction in which a small molecule is removed from a larger molecule leaving a double bond in the larger molecule
36
describe the reaction of removing water from ethanol. What is this reaction also called?
C2H5OH -(Al2O3)→ H2O + C2H4
This is also called a dehydration reaction.
37
What dehydrating agent is always used
Al2O3
38
Identify the bonds broken and formed in the elimation/dehydration of water from ethanol
Bonds broken:Carbon to oxygen sigma bond broken,
Carbon to Hydrogen sigma bond broken.
Bonds Formed: Carbon to carbon Pi bonf
Oxygen to hydrogen sigma bonf
39
When the no of atoms on either side of the equation are equal, the reaction is....
Describe its mechanism
a subsution reaction.
Alkane uses chorine.
free radical mechanism
40
when the atoms of the left hand side are less than the atoms of the right hand side... the reaction is
Addition reaction.
Alkene + Br2/Cl2/(H2 nickel catalyst.
Mechanism is Ionic addition
41
When the molecules on the right hand side are less than the atoms on the left hand side .... the reaction is
elimation reaction
(molecule with no double bonds)→(Alkene + chloroalkene)
42
Describe a oxidation reaction (NB) for a primary alcohol
A Primary Alcohol -(Oxidised)→ Aldehyde-(Oxidised)→Carboxylic acid
43
Describe the Oxidation for a secondary Alcohol
secondart alcohol -(oxidised)→ Ketone
44
Name four Oxidising agents used to carry out the oxidation above
Strong oxidising agents:Acidified sodium dichromate
Acidified potassium manganate(VII)
weak oxidising agents : Fehlings reagent
ammoniacal silver nitrate
45
Describe the full reduction of a carboxylic acid
Primary alcohol←Aldehyde ←Carboxylic acid
46
Describe the reduction of a Ketone
secondary alcohol ← Ketone
47
How are carboxylic acids reduced to aldehydes and ketones . ketones to alchohols
In the Presence of a hydrogen and a nickel catalyst
48
describe the procedure and result for showing the oxidation of aldehydes using acidified potassium manganate VII
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Acidified potassium manganate (VII)
* the aldehyde is placed in a test tube in a warm water bath.
* using a dropper, acidified dilute potassium manganate VII is added to the aldehyde
* **Result: the purple colour of the potassium manganate turns colourless**
49
Write the half reactions that occour when acidified potassium manganate VII is added to ethanal
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Acidified potassium manganate (VII)
MnO4- + 8H+ +5e- → Mn2+ +4H20
50
Explain the colour change that occurs when when acidified potassium manganate VII is reacted with ethanal
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Acidified potassium manganate (VII)
MnO4- contain Mn7+ ions causing a purple colour.
when reacted with a colourless aldehyde in an acidic enviorment, Mn 7+ ions and reduced to Mn2+ ions. Mn2+ ions are colourless
51
What is Fehling's reagent and why does it have a blue colour
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Fehling's reagent
Fehling's reagent is an equal mixture of fehling's A and Fehling's B
it is blue to the presence of copper Cu2+ ions
52
Describe the prodedure and result for tesing for aldehydes using fehling's reagent
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Fehling's reagent
* the aldehyde is placed in a test tube in a warm water bath
* using a dropper, equal amounts of Fehlings A and Fehling's B are added to the aldehyde.
* **result: The blue colour of fehling's reagent turns into a brick red precipitate**
53
write the half equations that occour when fehling's reagent is added to a colourless aldehyde
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Fehling's reagent
Cu2+ ---> Cu+↓
blue to a brick red perciptate
54
Explain the colour change that occours when Fehling's reagent is reacted with a colourless aldehyde
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using Fehling's reagent
Fehling's solutio contains Cu2+ ions causing a blue colour
when reacted with an aldehyde the Cu2+ are reduced to Cu+ ions
Cu+ ions have a red colour and are not soluble so a brick red precipitate forms
55
by what other name is ammonical silver nitrate known and why is it colourless
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
Tollen's reagent
the colourlessness is caused by the Ag+ ions in the solution
56
Why must Tollen's reagent always be freshly made up?
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
If tollens reagent is stored, it is likely explosive products could form
57
Describe the procedure and the result
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
* the aldehyde is placed in a test tube in a warm water bath.
* Using a dropper, ammoniacal silver nitrate is added to the aldehyde
* **Result ; the colourless Ag+ solution reacts and a silver mirrir is formed on the inside of the test tube**
58
Write the half reactions that occour when ammonical silver nitrate is added to ethanal
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
Ethanal→ethanoic acid
Ag+ + 1e- → Ag↓
59
Explain the colour change that occours when ammoniacal silver nitrate is added to ethanal
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
* Tollen's reagent contain Ag+ ion causes a colourless solution.
* when reacted with ethanal Ag+ ions are reduced to forn Ag.
* Ag precipitates out of solution causing a silver mirror.
60
In each test performed, no change is oberved if an aldehyde is replaced with propananone or butanone
## Footnote
Mandatory expeirment: to show the oxidation of alldehydes/ Testing for aldehydes using ammonical silver nitrate
propanone and butanone are ketones. Ketones ar very difficult to oxidise.
no reducation = no colour change
61
To show that aldehydes are eaasily oxidised, a weak oxidising agent such as ..... can be listed
fehling's reagent or ammonical silver nitrate
62
63
What is a hydrolysis reaction
a chemical reaction in which a larger molecule reacts with water causing it ro break up into smaller molecules
64
name the two types of ester hydrolysis
normal hydrolysis (w/ H2O)
Base hydrolysis (NaOH/KOH)
65
Descibe an ester hydrolysis using a word equation
ester + Water → carboxylic acid + Alcohol
66
In Hydrolysis reaction, the alchohol name will come from....
And the carboxylic acid name will come from the ...
side goup of the ester
ester main chain
67
What is base hydrolysis
An ester is reacted with a base to form soap and achohol
68
Describe base hydrolysis using a word equation (NB)
Ester + Base → Soap + Alchohol
69
describe how base hydrolysis/ soponification works
The ester side group bonds with the OH of the base
ester main chain bonds with the 'metal' of the base. (Na or K)
70
Describe the reaction between methyl propanoate and NaOH
Methyl propanoate + NaOH → Methan-1-ol + sodium propanoate
71
what are polymerisation reactions
chemical reaction in which long chain molecules are made by joinin many small molecules
72
where are polymers used (NB)
Plastics
73
What homologous series are the raw material from which all platics are derived
Alkenes
74
describe the polymerisation of ethene to form polyethene
ethnes added together n times
~(C2H4)n~
75
what is polyethnen used in?
Plastic bags
76
draw out the polymerisation of propene to form polypropylene
~(CH2CHCH3)n~
77
what is poly propene used in
straws
78
Draw out the polymerisation of Polychloroethene NB
~(CH2CHCl)n~
79
what is polychloroethene used in NB
Pluming pipes, gutters
80
By what nameis polychororethene also known and where is it used
Polyvinyl chloride (PVC)
81
what s organic synthesis
process of making useful corganic compounds from more simpler starting materials
82
outline the mechanism by which PVC (Polyvinyl choride) is manufactured by organic synthesis
* The reaction between ethene and clorine to form 1,2- dichloroethane(Intermediate compound)
* 1,2 dichloro ethae is cracked in hot conditions removing HCl (Elimatiion reaction) to from chloroethane (Intermediate)
* Polymerisation of chloroethane forms polychloroethane (PVC) ~(CH2CHCl)n~
83
What organic compunds can act as acids and why
Alcohols and carboxylic acids, they have a
-OH group, the h can be donated as a proton
84
when can alcohols act as acids?
Alcohols can act as acids only ehrn reacted with a very reactibe metals. (eg Li, K)
The -OH group of the alcohols belaves acidic and donates a proton.
85
describe the reaction between Ethanol and Sodium using a balanced equation
C2H5OH + Na → C2H5ONa + 1/2H2
86
Why do carboxyic acids have the ability to act as acids i.e. be proton donors
1) Inductive effect:
the Cδ+ attracts the Oδ- in OH
Oδ- in turn attracts electrons from Hδ+
Hδ+ is now more postive and will readily leave as a H+ ion.
2)stability of the Carboxylate ions
The carboxylate ion formed is very stable due to the delocalised nature of the pi electrons between each C---O bond
87
state the procedure and the results that occour
| Show reactions of ethanoic acid/testing for carboxylic acids with Na2Co3
acid + carbonate --> Salt + water + Co2
procedure : using a spatula, sodium carbonate is added to ethanoic acid using a test tube.
**Results: fizzing produced when bubbled through lime water.. will turn limewater milkey white**
88
What gas is produced when sodium carbonate is added to ethanoic acid
| Show reactions of ethanoic acid/testing for carboxylic acids with Na2Co3
CO2
89
Write a balanced equation for the reaction of ethanoic acid and sodium carbonate
| Show reactions of ethanoic acid/testing for carboxylic acids with Na2Co3
2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2
90
name the organic product produced in this reaction
| Show reactions of ethanoic acid/testing for carboxylic acids with Na2Co3
Sodium Ethanoate
91
would there be an reaction observed if ethanol was added to sodium carbonate?
| Show reactions of ethanoic acid/testing for carboxylic acids with Na2Co3
No reaction, alchohols are very weakly acidic - only doate protons when reacted with group 1 alkali metals
92
describe the procedure and the results obtained
| Show reactions of ethanoic acid/testing for carboxylic acids with Mg
Acid + metal --> salt + H2
Using thongs pick up a piece of Magnesium ribon and added to a test tube with ethanoic acid
**Result : fizzing. Bubbles are ptoduced that will ignite with a pop**
93
What gas is produced when magnesium is added to ethanoic acid is
| Show reactions of ethanoic acid/testing for carboxylic acids with Mg
Hydrogen gas
94
write a balanced equation for the reaction with magnesium and ethanoic acid
| Show reactions of ethanoic acid/testing for carboxylic acids with Mg
2CH3COOH + Mg ---> (CH3COO)2Mg + H2
95
Name the organic compound formed in this reaction
| Show reactions of ethanoic acid/testing for carboxylic acids with Mg
magnesium ethanoate
96
describe the procedure and th results
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
Carboxyic acid + alcohol --> ester + water (esterfication)
add some ethanol to a test tube. Using a dropper, a cm of ethanoic qcid and three drops of sulfuric acid are added and the test tube is placed in a hot water bath for 10 min
**result - a fruity smell is observed, no colour change**
97
write and balanced equation for this reaction
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
CH3COOH + C2H5OH--[H+]-> CH3COOC2H5 + H2O
98
what is the function of concentrated sulfuric acid?
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
acts as a catalyst
99
name the organic product formed
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
Ethylethanoate
100
to what group of compounds does the organic product of this reaction belong and how is it identified
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
esters - esters have dinstinct fruity smell
101
why is there no colour change ovserved in this reaction?
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
all of the reactants ad products are colourless
102
What is this reaction known as
| Show reactions of ethanoic acid/testing for carboxylic acid with ethanol
esterfication
