Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

OCR A level Chemistry Year 1 > Alkenes > Flashcards

Alkenes Flashcards

1
Q

Are alkenes saturated or unsaturated

A

Unsaturated because they contain at least one carbon - carbon double bond

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

What is the general formula for an alkene

A

CnH2n

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

Do alkenes form a homologous series

A

Yes

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

For a carbon of the double bond, how many sigma bonds are formed and between which atoms are they formed

A

3 sigma bonds, 1 between the carbon in which it’s double bonded too and 2 to the other atoms e.g. hydrogen or carbon

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

How is a Pi bond formed

A

Formed by the sideways overlap of 2 p-orbitals, one from each carbon atom of the double bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Where is the Pi- electron density concentrated in a double bond

A

Above and below the line joining the nuclei of the bonding atoms

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

What bond (sigma or Pi) locks the carbon atoms in an alkene in place, preventing them from rotating around the double bond

A

Pi bond

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

How does the geometry differ in alkanes and alkenes

A

Rotation is possible in alkanes since there is no Pi bond whereas rotation cannot happen in alkenes due to the presence of a Pi bond.

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

What is the bond angle and shape around the carbon atoms in the double bond in an alkene

A

Trigonal planar (120)
- There are 3 regions of electron density around each carbon atom

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

What is a stereoisomer

A

A compound with the same structural formula but a different arrangement of atoms in space

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

What type of isomerism occurs in compounds with C=C double bond

A

E/Z isomers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why does stereoisomers arise around a double bond

A

Because rotation around the double bond is restricted so the groups attached to each carbon is fixed

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

Why are the groups attached to each double bonded carbon restricted

A

Due to the position of the Pi bond above and below the C=C double bond

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

What 2 conditions are required for a molecule to have E/Z isomerism

A
  • A C=C double bond
  • Different groups attached to each carbon atom of the double bond
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why can But-1-ene not form E/Z isomers whereas But-2-ene can

A

Because one of the carbons in the double bond in But-1-ene is attached to 2 hydrogens meaning that there isn’t a different group attached to each carbon

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

What is cis-trans isomerism

A

The name commonly used to describe a special case of E/Z isomerism.

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

What extra rule differs E/Z isomerism and cis-trans isomerism

A

In cis-trans isomerism one of the attached groups on each carbon atom of the double bond must be hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Is But-2-ene an example of a molecule with E/Z isomers or cis-trans isomers

A

Both, because there is hydrogen attached to each carbon involved in the double bond

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

In a cis isomer, where are the hydrogens

A

On the same side of the molecule

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

In a trans isomer, where are the hydrogens

A

Diagonally opposite each other in the molecules

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

In an E isomer, are the same atoms/groups opposite each other in the molecule or on the same side of the molecule

A

Opposite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

In a Z isomer, are the same atoms/ groups opposite each other in the molecule or on the same side of the molecule

A

The same side

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

In cis-trans isomerism, is the cis isomer the E or the Z

A

Z isomer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

In cis-trans isomerism, is the trans isomer the E or the Z

A

E isomer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
When naming isomers, how do you assigns priority
Upon their atomic number
25
If the groups of higher priority are on the same side of the double bond, what isomer is the compound
Z isomer
26
If groups of higher priority are diagonally placed across the double bond, what isomer is the compound
E isomer
27
If the 2 atoms attached to a carbon atom in the double bond are the same, what do you do when trying to identity the isomerism
Find the first point of difference
28
Why are alkenes much more reactive than alkanes
Because of the presence of the Pi bond
29
Why do Pi bonds readily break
Because they're on the outside of the double bond, so they are more exposed than the electrons in the sigma bond
30
What are the 4 addition reactions of alkenes
- Hydrogen in the presence of a nickel catalyst - Halogens - Hydrogen halides - Steam in the presence of an acid catalyst
31
What bond breaks when alkenes undergo addition reactions
The Pi bond
32
What are the 2 conditions required for the hydrogenation of alkenes
- Heat - Nickel catalyst
33
What is the conditions required for the halogenation of alkenes
Room temperature
34
What element is used when testing for unsaturation
Bromine
35
What happens to the bromine water when it is added to an organic compound
The orange colour disappears and becomes colourless
36
If bromine is added to any C=C bond what will happen
It will be decolourised
37
What is the name of product when an alkene reacts with a hydrogen halide
Haloalkane
38
How many products are there when an unsymmetrical alkene reacts with an unsymmetrical molecule e.g. HCl
2 possible products
39
When alkenes react with steam what is the name of the group formed
Alcohols
40
What catalyst is required when alkenes react with steam
Phosphoric acid (H3PO4)
41
How many products can be produced when alkenes react with steam
2 products
42
What is an electrophile
An atom or group of atoms that is attracted to an electron-rich centre and accepts an electron pair
43
What is the name of the mechanism, where alkenes take part in addition reactions to form saturated compounds
Electrophilic addition
44
Does the double bond in alkenes, with the presence of a Pi bond, represent a region of high or low electron density
High electron density
45
In an electrophilic addition reaction, what does the high electron density of the Pi bond attract
It attracts electrophiles
46
Is an electrophile, usually an positive or negative ion or a molecule with a slightly positive or negative charge
Positive ion or a molecule with a slightly positive charge
47
What are the 6 steps in an electrophilic addition reaction of But-2-ene and HBr
1. Br is more electronegative than hydrogen, so HBr is polar and contains dipoles 2. The electron pair in the Pi bond is attracted to the slightly positive hydrogen atom, breaking the double bond 3. A bond is now formed between the H and the C which had the initial double bond 4. H-Br bond breaks by heterolytic fission, the electron pair goes to the bromine 5. Leaving a Br- ion and a carbocation 6. Br- ion reacts with the carbocation
48
What is a carbocation
A positively charged carbon atom
49
When a non-polar molecule wants to react in a elecrophilic addition reaction how are the dipoles decided
When one of the atoms in the non-polar molecule approaches the Pi bond, the electrons in the non-polar molecule bond are repelled, so polarity has been induced
50
What are the 3 types of carbocations
- Primary - Secondary - Tertiary
51
How many carbons is a primary carbocation bonded to
1 carbon
52
How many carbons is a secondary carbocation bonded to
2 carbons
53
How many carbons is a teritary carbocation bonded to
3 carbons
54
What is the order of stability of carbocations
Primary < Secondary < Tertiary
55
When drawing the electrophilic addition reaction mechanism what do the curly arrow represent
The bonds breaking
56
What is Markownikoff's rule
The major product of the addition reaction will be the one formed via the more stable carbocation intermediate and the stability is in the order primary
57
What is a polymer
Extremely large molecules formed from many thousands of repeat units of smaller molecules known as monomers
58
What type of polymerisation do unsaturated alkenes undergo to produce long, saturated chains containing no double bonds
Addition polymerisation
59
What 3 conditions are required in industrial polymerisation
- High pressure - High temperature - Using a catalyst
60
Do addition polymers have a high or low molecular mass
High molecular mass
61
When writing out an addition polymerisation equation, what types of brackets is the repeat unit always written in
Square brackets
62
What is the common prefix of addition polymers
Poly(alkene)
63
What is Poly(chloroethene) more commonly known as
PVC
64
Are the major of alkene-based products biodegradable
No, so they tend to grow in landfills
65
Why is recycling polymers good
It conserves finite fossil fuels and decreases the amount of waste going into landfill
66
What is the disposal of PVC so toxic
Due to the high chlorine content
67
What is released when PVC is burnt
HCl, which is a corrosive gas, and other pollutants like toxic dioxins
68
How do we use waste polymers as fuel
Waste polymers can be incinerated to produce heat, which generates steam to drive a turbine producing electricity
69
What is feedstock recycling
Describes the chemical and thermal processes that can reclaim monomers, gases, or oil from waste polymers
70
The products from feedstock recycling resemble products similar to what
Products produced from crude oil refineries
71
What is an advantage of feedstock recycling
It is able to handle unsorted and unwashed polymers
72
What are biodegradable polymers usually made from
- Starch - Cellulose - Additives that alter the structure
73
What does photodegradable mean
Can be broken down by light-driven chemical processes

OCR A level Chemistry Year 1 (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions