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Organic Chemistry > Unit 3: Section 3- Alkenes and Alcohols + RP5 > Flashcards

Unit 3: Section 3- Alkenes and Alcohols + RP5 Flashcards

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1
Q

What is the general formula of alkenes?

A

CnH2n

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2
Q

How can you use one word to describe alkenes?

A

unsaturated

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3
Q

What shape is the arrangement of bonds around the C=C bond?

A

planar

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4
Q

What is the bond angle in alkenes around the C=C bond?

A

120

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5
Q

Explain why alkenes are vulnerable to attack by other species

A

Because the pi bonds are exposed which have high electron density.

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6
Q

What does a C=C double covalent bond consist of?

A

one sigma bond
one pi bond

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7
Q

What type of isomerism can alkenes exhibit?

A

E-Z stereoisomerism

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8
Q

Define electrophile

A

an electron pair acceptor

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9
Q

What is an addition reaction?

A

where two reactants form one product

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10
Q

Describe each step in the electrophilic addition reaction between bromine and alkenes

A
  1. the C=C bond repels the electrons in Br2, polarising Br-Br
  2. the double bond then attracts the Br slightly +, and forms a bond with it. this repels electrons in the Br-Br bond further, until it breaks
  3. you get a positively charged carbocation intermediate, the Br slightly - bonds to the C
  4. one product is formed
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11
Q

What is a carbocation?

A

a positively charged carbon atom

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12
Q

What do alkenes form when they react with hydrogen halides?

A

halogenoalkanes

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13
Q

Give three examples of electrophiles

A

H+
NO2+
Br slightly +

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14
Q

Draw the mechanism for the electrophilic addition reaction between ethene and hydrogen bromide

A
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15
Q

Why is HBr a polar molecule?

A

Br is more electronegative than H

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16
Q

What happens if you add a hydrogen halide to an unsymmetrical alkene?

A

two isomeric products- 1 major product, 1 minor product

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17
Q

What does the amount of product formed in electrophilic addition of alkenes and hydrogen halides depend upon?

A

how stable the carbocation intermediate is

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18
Q

What is the order for stability of carbocations?

A

tertiary (most)
primary (least)

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19
Q

Draw the mechanism for hydrogen bromide reacting with propene

A
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20
Q

What is the chemical formula for sulphuric acid?

A

H2SO4

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21
Q

What are the two changes in functional groups in electrophilic reactions with alkenes and H2SO4?

A
  1. change in functional group from alkene to alkyl hydrogen sulphate
  2. change in functional group from alkyl hydrogen sulphate to alcohol
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22
Q

Describe the reaction between sulphuric acid and alkenes

A
  1. cold concentrated sulphuric acid reacts with an alkene in an electrophilic addition reaction
  2. if you then add cold water, and warm the product, it hydrolyses to form an alcohol
  3. the sulphuric acid isn’t used up- it acts as a catalyst
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23
Q

How can the bromine water test be used quantitively?

A

to show the presence of multiple bonds in compounds like polyunsaturated oils

24
Q

What is addition polymerisation?

A

when addition polymers are formed from alkenes

25
Q

What is a polymer?

A

lots of monomers joined together

26
Q

What is one word to describe polyalkene chains?

A

saturated

27
Q

What does saturated mean?

A

they only contain single carbon bonds in the carbon chain

28
Q

How does increasing length of polyalkenes effect Van der Waals forces?

A

the longer the polymer chains are, the closer together they can get, so the stronger the Van der Waals forces between the chains will be

29
Q

Describe the differences in physical properties of short chain and long chain polyalkenes

A

short, branched chains- weaker and more flexible
long, straight chains- strong and rigid

30
Q

How can you make PVC more flexible?

A

adding a plasticiser

31
Q

What is rigid PVC used for?

A

drainpipes and window frames

32
Q

What can plasticised PVC be used for?

A

electric cable insulation, clothing, flooring tiles

33
Q

What is the general formula of alcohols?

A

CnH2n+1OH

34
Q

What is the H-C-H and C-C-O bond angle and the shape?

A

109.5
tetrahedral

35
Q

Explain the H-C-H and C-C-O bond angle

A

109.5
because there are 4
bonding pairs of electrons
repelling to a position of
minimum repulsion

36
Q

What is the H-O-C bond angle and the shape?

A

104.5
bent line shape

37
Q

Explain the H-O-C bond angle?

A

104.5
there are 2 bonding
pairs of electrons and 2 lone pairs
repelling to a position of minimum
repulsion. Lone pairs repel more than
bonding pairs so the bond angle is
reduced.

38
Q

Explain the boiling points of alcohols

A

the alcohols have relatively high boiling points due to their ability to form hydrogen bond between alcohol molecules

39
Q

Describe what happens when smaller alcohols react in water

A

the can dissolve in water because they can form hydrogen bonds to water molecules

40
Q

Describe a primary alcohol

A

1 carbon is attached to the carbon adjoining the oxygen

41
Q

Describe a secondary alcohol

A

2 carbons are attached to the carbon adjoining the oxygen

42
Q

Describe a tertiary alcohol

A

3 carbon are attached to
the carbon adjoining the oxygen

43
Q

What is potassium dichromate?

A

oxidising agent

44
Q

What reaction occurs when primary alcohols are partially oxized?

A

the primary alcohol forms an aldehyde and water

45
Q

What is an aldehyde?

A

contains the functional group with the structure R-CH=O

46
Q

What are the reagents in the partial oxidation of a primary alcohol?

A

potassium dichromate (VI) solution and dilute sulfuric acid

47
Q
A
48
Q

Describe the conditions needed for the partial oxidation of primary alcohols

A

(use a limited amount of dichromate) warm
gently and distil out the aldehyde

49
Q

Why should you use the approximate boiling point of the desired aldehyde and not higher when distilling?

A

in order to maximise the yield collected

50
Q

Where does the water go in and out in a condenser?

A

water goes in at the bottom to go against gravity, so prevents backflow

51
Q

Give a reason why some organic chemicals are heated with an electric heater

A

organic chemicals are normally highly flammable and could set on fire with a naked flame

52
Q

Describe the reaction of the full oxidation of primary alcohols

A

Reaction: primary alcohol -> carboxylic acid
Reagent: potassium dichromate(VI) solution and dilute
sulfuric acid
Conditions: use an excess of dichromate, and heat
under reflux: (distil off product after the reaction has finished)

observation- the orange dichromate ion reduces to the green Cr3+ ion

53
Q

When is reflux used?

A

when heating organic reaction mixtures for long periods

54
Q

Why are anti-bumping granules used?

A

to prevent vigorous/ uneven boiling

55
Q

What is a ketone?

A

has two alkyl groups attached to the carbonyl carbon atom

56
Q
A

Organic Chemistry (9 decks)

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