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alkenes Flashcards

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1
Q

general formula of an alkene

A

CnH2n

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2
Q

functional group alkene

A

c=c

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3
Q

what is the double covalent bond a centre of

A

high electron density

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4
Q

unsaturated

A

contain one or more carbon-carbon double bonds

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5
Q

what is the shape around each carbon in the c=c double bond

A

triganol planar

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6
Q

what is the bond angle around each carbon in the c=c double bond

A

120

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7
Q

what forms when the p orbitals overlap in the c=c group

A

a pi bond

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8
Q

what does the presence of a pi bond create

A

restricted rotation about the planar c=c bond

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9
Q

how are alkenes named

A

like alkanes based on longest unbranched carbon chain with suffix ‘ene’

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10
Q

what must be indicated in alkenes with 4 or more carbon atoms in the longest chain

A

the position of the c=c bond

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11
Q

diene

A

2 c=c bonds

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12
Q

triene

A

three c=c bonds

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13
Q

what is the difference between open chain alkenes and cycloalkenes

A

cycloalkenes have 2 less hydrogen atoms than open chain alkenes

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14
Q

how are cycloalkenes named

A

according to the largest ring containing the c=c bond

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15
Q

structural isomers

A

compound with same molecular formula but different structural formula

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16
Q

stereoisomers

A

compounds with the same structural formula but different arrangement of atoms in space

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17
Q

what type of stereoisomerism is exhibited by alkenes

A

E/Z isomerism

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18
Q

z

A

together

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19
Q

e

A

opposite

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20
Q

why does E/Z isomerism occur

A

as a result of restricted rotation about the c=c double bond

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21
Q

what must both carbon atoms of the c=c double bond be for an alkene to exhibit E/Z isomerism

A

both carbon atoms must be bonded to different groups

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22
Q

what are cycloalkanes

A

functional group isomers of alkenes

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23
Q

how to determine whether an alkene is the E or Z isomer

A

identify the highest priority group on each C atom of the c=c double bond

if both highest priority groups are on same side- z isomer

if both highest priority groups are on opposite sides of C=c bond- E isomer

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24
Q

which atom has the highest priority

A

the atom with the highest atomic NUMBER

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25
what happens if two atoms have the same atomic number
next atom n chain should be compared (first point of difference used to assign priority)
26
why are alkenes reactive
high electron density of c=c double bond
27
what type of reactions do alkenes undergo
addition reactions in which a small molecule is added across C=C group
28
what does the addition reaction of an alkene form
a saturated molecule (pi bond breaks)
29
electrophile
electron pair acceptor
30
why do alkenes react with electrophiles
electrophile are attracted to high electron density of C=C bond
31
what occurs during the reaction between alkenes and electrophiiles
covalent bonds broken and formed
32
what is produced as a result of the reaction between an electrophile and an alkene
a reactive positively charged intermediate called a carbocation
33
what does a mechanism show
the breaking and forming of covalent bonds using curly arrows
34
curly arrow
shows movement of pair of electrons
35
where must curly arrows start from
a lone pair or a covalent bond
36
what is the reagent in the reaction of alkanes with halogens
the halogen eg bromine
37
what does the reaction between ethane and bromine produce
1,2- dibromo ethane
38
what observations could be made during the reaction between ethene and bromine
bromine decolourises
39
what is the name of the mechanism in the reacton between ethene and bromine
electrophilic addition
40
what acts as the electrophile in the reaction between bromine and ethene
bromine
41
what does the high electron density in the c=c group do
polarises the bond in the bromine molecule
42
why does the br-br bond break
a pair of electrons is accepted by the delta plus br atom
43
how does the br-br bond break
heterolytic fission
44
what does the lone pair of electrons on the bromide ion form
a new c-br bond with the carbocation
45
what is bromine used for
to test for the presence of a C=C group
46
what is the reagent in the reaction of alkenes with hydrogen halides (same applies as halogen)
the hydrogen halide
47
What do hydrogen halides contain
A permanent dipole, h atom always delta plus
48
What is the reagent in the electrophilic addition reaction between sulphuric acid and lakebed
Concentrated sulphuric acid
49
Organic hydrogen sulfates are readily hydrolysed with warm water to form...
An alcohol
50
Hydrolysis
Breaking a bond using water
51
What are carbocations classified as
Primary secondary or tertiary
52
What is the classification of carbocations based on
The number of carbon atoms directly attached to the carbon with the positive charge
53
What does a primary carbocation have
1 variable group
54
What does a secondary carbocation have
2 variable groups
55
What does a tertiary carbocation have
3 variable groups
56
What do alkyl groups have a tendency to do
Release electrons
57
What does the tendency of alkyl groups to release electrons help with
Stabilising the positive charge of carbocations- called the positive inductive effect
58
What carbocations are the most stable and why
Tertiary as they have the most alkyl groups attached
59
Order of stability of carbocations
Tertiary>secondary>primary Most Least stable Stable
60
What does addition to an unsymmetrical Alkene produce
Two different organic products
61
Major product
Produced in the largest amount
62
Minor product
Produced in the smallest amount
63
What is the yield of a particular product related to
The stability of the carbocation it is formed from
64
What is produced when a hydrogen is added across a c=c bond
An alkane is produced (hydrogenation)
65
What is hydrogenation used for
Important industrial process e.g. Production of margarine
66
What catalyst is used in hydrogenation of alkenes
Nickel
67
When are polymers formed
When monomers join together to form a very large molecule
68
What do alkenesact as in addition reactions
Monomers, the c=c bond breaks allowing the monomers to add together
69
Repeating unit
A specific arrangement of atoms that occurs in the structure over and over again
70
What are simple polyalkenes
Unreactive
71
What does the backbone of single c-c bonds make polyalkenes
Saturated
72
What do the properties of polyalkenes depend on
Their structure and the intermolecular forces between neighbouring polymer chains
73
What does polyethene have between neighbouring chains
VDW forces
74
How can the properties of polymers like polyethene be modified
By increasing branching which decreases points of contact so the VDW forces are weakened- increased flexibility and lowers boiling point
75
What is polychloroethene
Rigid and brittle
76
What does polychloroethene contain
Polar c-Cl bonds and therefore has permanent dipole-dipole forces between polymer chains
77
Addition of what molecules make polymers like polychloroethene more flexible
Plasticisers
78
How do plasticisers make polychloroethene more flexible
They force neighbouring chains apart- allowing them to slide over each other
79
Where do plasticisers go when added to polyalkenes like polychloroethene
Get in between neighbouring chains and reduce intermolecular forces

Chemistry (42 decks)

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