(A2) Alkenes and Alkanes Flashcards
1
Q
What is an alkene?
A
A series of unsaturated hydrocarbons
2
Q
What is an alkane?
A
A series of saturated hydrocarbons
3
Q
Formula of Alkene
A
Cn H(2n)
4
Q
Formula of Alkane
A
Cn H(2n+2)
5
Q
What are saturated hydrocarbons?
A
Hydrocarbons that only contain single bonds between carbon atoms
6
Q
What are unsaturated hydrocarbons?
A
Hydrocarbons that contain at least one carbon-carbon double bond
7
Q
Type of Alkenes
A
- Straight Chain
- Branched Chain
- Cyclic Alkenes
8
Q
Nomenclature for 1
A
Meth
9
Q
Nomenclature for 2
A
Eth
10
Q
Nomenclature for 3
A
Prop
11
Q
Nomenclature for 4
A
But
12
Q
What is cracking?
A
The breaking down of long chain hydrocarbons to smaller hydrocarbons
13
Q
Types of Cracking
A
- Thermal Cracking
- Catalytic Cracking
14
Q
What is catalytic cracking?
A
Using a catalyst to cause cracking
15
Q
What is thermal cracking?
A
High temperature is used to cause cracking
16
Q
Product of Cracking
A
1) Long Chain –> alkene + alkene
2) Long Chain –> alkene + alkene + H₂
17
Q
What is combustion?
A
The burning of oxygen and fuel (alkane)
18
Q
Types of Combustion
A
- Complete Combustion
- Incomplete Combustion
19
Q
What is complete combustion?
A
There is large supply of oxygen
20
Q
Formula of Complete Combustion
A
Alkane + Oxygen –> Carbon Dioxide + Water
CH₄ + O₂ –> CO₂ + 2H₂O
21
Q
What is formed in complete combustion?
A
- Carbon Dioxide
- Water
22
Q
What color is the flame in complete combustion?
A
Blue
23
Q
What is incomplete combustion?
A
There is a limited supply of oxygen
24
Q
Formula of Incomplete Combustion
A
Alkane + Oxygen –> Carbon Monoxide + Water
2CH₄ + 3O₂ –> 2CO + 4H₂O
25
What is formed in incomplete combustion?
* Carbon Monoxide
* Soot
* Water
* Carbon
26
What color is the flame in incomplete combustion?
Orange
27
Why is incomplete combustion undesirable?
It releases less energy and produces carbon monoxide(poisonous) unlike complete combustion which releases the maximum amount of energy from the fuel being reacted
28
What is Benzene?
A planar molecule where all the atoms lie in one plane which contains a ring of six carbon atoms that form a perfectly regular hexagon
29
What is the formula for Benzene?
C₆H₆
30
Which type of bond is shorter, double or single?
Double Bond
31
What bond angle is Benzene?
120°
32
Order of Bond Strength (alkenes, alkanes and benzene)
Strongest I
I Alkenes
I Benzene
I Alkanes
Weakest I
33
What is the bond length in Benzene?
All the bonds in benzene are the same length (0.14 nm)
34
What is the bond length of single and double bonds?
0.147 nm for single
0.135 nm for double
35
What is hybridisation?
When two orbitals fuse together
36
What are sigma bonds?
A covalent bond that occurs from the end to end overlap between orbitals
37
Symbol for Sigma Bonds
σ
38
What are pi Bonds?
A covalent bond that occurs from the side to side overlap between orbitals
39
Symbol for pi Bonds
𝛑
40
What orbital overlaps does a sigma bond have?
P-P (end to end)
S-P (end to end)
S-S (end to end)
41
What orbital overlaps does a pi bond have?
P-P (side by side)
42
How many σ and 𝛑 does a single bond have?
1 σ bond and 0 𝛑 bonds
43
How many σ and 𝛑 does a double bond have?
1 σ bond and 1 𝛑 bonds
44
How many σ and 𝛑 does a triple bond have?
1 σ bond and 2 𝛑 bonds
45
What is an alkyne?
A triple bond
46
What is stronger a sigma or a pi bond?
A sigma bond
47
Differences between sigma and pi bond
* A sigma bond has lower bond enthalpy than a pi bond
* A sigma bind has electron density between bonding atoms whilst a pi bond has electron density above and below bonding atoms
48
What is the bond angle for sp¹?
180°
49
What is the bond angle for sp²?
120°
50
What is the bond angle for sp³?
109.5°
51
What is a free radical?
A species with an unpaired electron
52
What is fission?
Splitting
53
What is fusion?
Combining
54
Types of free radical fission
* Heterolytic Fission
* Homolytic Fission
55
What is heterolytic fission?
One bonding atom receives both electrons from the bonding pair, ions are formed
56
What is homolytic fission?
Each bonding atom receives one electron from the bonding pair forming two radicals
57
What are the reagents in free radical substitution?
A halogen and an alkane
58
What is condition is needed for free radical substitution?
UV light
59
Stages of Free Radical Substitution (FRS)
1. Initiation
2. Propagation
3. Termination
60
What happens during the initiation step?
Radicals are formed
61
How many equations does the initiation step have?
One
62
How many equations does the propagation step have?
Two
63
What happens during the termination step?
Radicals join to form products
64
How many equations does the termination step have?
At least one (Usually three)
65
Why is FRS not a good method?
Because biproducts are formed
66
Why are free radicals reactive?
Because they are trying to pair up their unpaired electron
67
What does inter mean?
In between the molecules
68
What does intra mean?
Inside the molecules
69
What are the types of isomers
* Structural Isomers
* Stereoisomers
70
What are structural isomers?
Compounds that have the same molecular formula but different structural arrangement
71
What are stereoisomers?
Compounds that have the same structural formula but different arrangement in space
72
What is a cis isomer?
Atoms that are on the same side of the double bond
73
What is the alternative name for the cis isomer?
Z isomer
74
What is a trans isomer?
Atoms that are on the opposite sides of the double bond
75
What is the alternative name for the trans isomer?
E isomer
76
What determines the priority of the isomers
The higher the atomic number of the atom attached to the carbon the higher its priority
e.g. Br>Cl>H
77
What is a carbocation?
A carbon with only three bonds and a positive charge
78
What is a "R" Group?
A chain of carbon atoms (CH₃)
79
What is a primary carbocation?
One of the three groups is an "R" group
H
H C CH₃
+
80
What is a secondary carbocation?
Two of the three groups is an "R" group
CH₃
H C CH₃
+
81
What is a tertiary carbocation?
All of the three groups is an "R" group
CH₃
H₃C C CH₃
+
82
Order of Stability of Carbocations
Highest I
I Tertiary
I Secondary
I Primary
Lowest I
83
Why is tertiary the most stable out of all the carbocations?
Because there are more "R" groups which adds more electrons
84
What are most reactions of alkenes?
Additional reaction
85
What are electrophiles?
A species that can accept a pair of electrons
They are either positive ions or polar molecules with partial charges
86
What are electrophiles attracted to?
high electron density carbon double bonds
87
What happens in electrophilic addition if the alkene is symmetrical?
The two carbocation are identical which leads to one product
88
What happens in electrophilic addition if the alkene is asymmetrical?
There are two different carbocations which leads to two possible products
89
What is the major product?
The more stable carbocation during electrophilic addition
90
What is the minor product?
The less stable carbocation during electrophilic addition
91
What needs to be added in an electrophilic addition diagram?
* Direction Arrow
* Dipole
* Charges
* Lone Pair
