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Core Practicals > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

0
Q

How are alkenes obtained ?

A

Cracking and catalytic reforming of crude oil

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1
Q

How is polymerisation represented?

A 
Double bond broken
Square brackets around
N
H   CH3
 |      |
C = C
 |      |
H    COOCH3
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2
Q

What is the general formula of an alkene?

A

CnH2n

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3
Q

What is the single bond represented by?

A

Sigma o

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4
Q

Do double bonds make a molecule saturated or unsaturated?

A

Unsaturated

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5
Q

What is the second bond represented by and where is electron density concentrated in this?

A

Pi
In two regions on either side of the axis of the bond
Does not allow rotation around the axis

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6
Q

Why is a double bond less than twice as strong as a single bond?

A

Electron density further from nuclei

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7
Q

What does the arrangement of electron density explain?

A

Reactive because of attraction of positively polarised groups
So geometric isomerism as rotation is not possible around pi bond
125

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8
Q

How do alkenes compare equivalent alkanes ?

A

Physically similar properties

Melting point little lower

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9
Q

What is a geometric isomer?

A

When components of the molecule are arranged on different sides of the double bond

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10
Q

What is meant by a cis isomer?

A 
Both methyl groups on one side of bond
H      H
 |        |
C  =  C
 |        |
H3C  CH3
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11
Q

What is the shape of a molecule governed by?

A

Valence shell electron pair repulsion theory
Bonding pairs and lone pairs are vitally important
Double bond counts same as single bond

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12
Q

What is meant by a trans isomer?

A

Two methyl groups are on opposite side of double bond

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13
Q

What different properties do geometric isomers show?

A

Melting/boiling point
Densities
Occasionally reactions

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14
Q

What limitations does the cis-trans system have?

A

Doesn’t work with all geometric isomers

So E-Z isomerisation

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15
Q

What makes a Z-isomer?

A

2 higher priority on the same side

Z-but-2-ene

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16
Q

What makes an E-isomer?

A

Higher priority on opposite side

E-but-2-ene

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17
Q

What are the two main effects of double bonds?

A

Geometric isomerism as no rotation around C=
C
Addition reactions where two substances react to form a single product

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18
Q

Why are all keen is more reactive than corresponding alkanes?

A

Less energy required to break C=C

129

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19
Q

Why is C=C attacked when a sigma positive atom approaches?

A

High electron density

Species is electrophilic

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20
Q

What is an electrophile?

A

An electron deficient species that can form a new covalent bond, using an electron pair provided by the carbon compound (H+)

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21
Q

What is Markovnikov’s rule?

A

When HX adds across asymmetric double bond, the major product formed is the molecule in which hydrogen adds to the carbon atom in the double bond with the greater number of hydrogen already attached to it

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22
Q

What are reaction mechanisms?

A

How organic reactions happen

Predict outcome of similar reactions

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23
Q

What does a half curly arrow represent?

A

Movement of 1 electron

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24
Q

What does a full curly arrow represent?

A

Movement of a pair of electrons

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25
Q

What happens when ?

A

Pair of elections in pi bond form a new bond with positively polarised attacking group (electrophile)
Electrophorus attack on electron rich pi bond
Carbocation formed from attack
Positive ion attacked by nucleophiles

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26
Q

Where is bromine most likely to go when it reacts with propene?

A

Middle

2 methyl groups donate electron density to stabilise positive charge

27
Q

Define polymer

A

A very large molecule made up of long chains of smaller monomers units joined together

28
Q

What happens when ethene is polymerised?

A

Repeating units link together to form long chain

Double bond in ethene breaks to form poly(ethene)

29
Q

What did Karl Ziegler produce polythene?

A

Using catalyst
60°C
Atmospheric pressure
Produces HDPE

30
Q

How was polythene first made?

A

Polymerisation of ethene with oxygen traces
200°C
1200 atm
Produces LDPE

31
Q

What is the general formula for alkanes?

A

CnH2n+2

32
Q

How are alkanes obtained?

A

From crude oil and petroleum
Primary distillation changes crude oil into useful chemicals
Fractional distillation

33
Q

What happens during fractional distillation?

A

Crude oil boiled
Gases pass up through tower through bubble caps
Gas condenses at particular temperature on cap

34
Q

What does cracking produce?

A

Short chained alkane and alkene

35
Q

What is used to reduce cost when cracking catalysts? What is this known as?

A

Catalysts

Catalytic/cat cracking carried out in cat cracker

36
Q

Why are alkanes good for lubricants?

A

Non corrosive

37
Q

H

A

C-C and C-H involve even sharing electrons since electronegativities very close
Not polar so no charge attract polar/ionic

38
Q

What causes reacts of alkanes?

A

Formation of free radicals so high activation energies

39
Q

What is a free radicals?

A

Unpaired electron

40
Q

What is bond fission?

A

Breaking bonds

41
Q

What is homolytic fission?

A 
Equal sharing of electrons in bond
Each receive 1
Half curly arrow used
Unpaired electron gained by each atom indicated by Cl•
No charge but extremely reactive
42
Q

What is hetrolytic fission?

A

Unequal sharing of electrons in covalent bond
Results in 2 charged particles
Normally when covalent bond already has degree of polarity

43
Q

How do alkanes burn?

A

When in gaseous state so solids and liquids less flammable (vaporised before)

44
Q

Why are alkanes combusted?

A

Generate electricity as it produces heat and light energy

Exothermic process more energy produced by new bonds

45
Q

Why is propane often used as a fuel?

A

Liquified under low pressure and low temperature
Allows larger quantities in small spaces
Safe because don’t burn in gaseous state

46
Q

How do you test the oxidation of alkanes?

A

Add 0.5cm3 of 0.01M potassium maganate and 1M sulphuric acid

Add couple drops of liquid alkane

48
Q

How should alkanes react when testing for oxidation?

A

No change

Stayed purple

51
Q

How do you test the action of bromine on alkanes?

A

Add a few drops of alkane to 0.5cm3 of bromine water

52
Q

How do you test for the reaction of alkanes with alkalis?

A

Add 2cm3 of 20% post assign hydroxide dissolved in water to 0.5cm3 or liquid alkane
Shake tube

54
Q

How should alkanes react with bromine when NOT in sunlight?

A

No change

56
Q

How should alkanes react when mixed with an alkali?

A

No reaction

58
Q

How do you test for the reaction of alkanes with sulphuric acid?

A

Add 0.5cm3 of alkane to 2cm3 of concentrated sulphuric acid

60
Q

How should alkanes react when mixed with concentrated sulphuric acid?

A

No reaction

62
Q

How do you test for the action of bromine in sunlight?

A

Add several drops of 2% bromine in an inert solvent to 10cm3 of hexane/cyclohexane
Loosely cork test tube and leave in sunlight

66
Q

What should be the results of alkanes with bromine in sunlight?

A

One in dark stayed orange
One in light turned colourless as Br2 reacts with hexane to produce HBr
Reacts to form NH4Br

66
Q

How should you crack an alkane?

A

Medicinal paraffin soaked in ceramic fibre in test tube
Aluminium oxide granules
Water bath
Heat aluminium oxide strongly

66
Q

Why should you discard the first tube of gas collected from cracking alkanes?

A

Air will expand and be forced out

66
Q

What should you test cracked alkanes for?

A

Turned colourless in bromine water
Lots of smoke and small flame when lit
3 drops KMnO4 2cm3 sulphuric acid, when shaken turns from purple to colourless

66
Q

What is the procedure for testing combustion of alkenes?

A

Dip a combustion spoon into alkene and set fire to it

66
Q

What observations can be made when testing the combustion of alkenes?

A

Became more orange and smokey than corresponding alkane due to C:H ratio
Longer the chain the less volatile therefore smokier and more orange

66
Q

What is the procedure for testing the action of bromine with alkenes?

A

Add few drops of alkene to 0.5cm of bromine water

66
Q

What observations can be made when Alkenes react with bromine?

A

Rapidly turned from Orange to colourless

Produced 1, 2 -dibropropane

66
Q

What is the procedure for testing the action of with sulphuric acid alkenes?

A

Add 0.5cm of alkene to 2cm of concentrated sulphuric acid

66
Q

What is the procedure for testing the oxidation of alkenes?

A

0.25 cm potassium maganate 0.01M
0.25 cm 1M sulphuric acid
Few drops of alkene

66
Q

What is the procedure for testing the procedure of alkenes?

A

In fume cupboard

66
Q

What observations can be made when testing for oxidation with alkenes?

A

Turns from purple to colourless

No double bonds

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