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Chemistry OCR A-Level > Topic 4 > Flashcards

Topic 4 Flashcards

(67 cards)

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1
Q

alkenes are which kind of hydrocarbons

A

unsaturated

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2
Q

what is the general formula for alkenes

A

CnH2n

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3
Q

what prohibits rotation in alkenes

A

the pi bond
it locks the 2 carbon atoms into position

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4
Q

what is the shape around the carbon atoms in the double bond and why

A

120 degree bond angle
repel each other equally
in the same plane
trigonal planar
3 regions of electron density

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5
Q

what is stereoisomerism

A

same structural formula but a different arrangement of atoms in space

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6
Q

what are the 2 types of stereoisomerism

A

E/Z isomerism
Optical isomerism

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7
Q

when is cis/trans isomerism applicable

A

when molecules has C=C double bonds
Each carbon atom in double bond is attached to 2 different groups

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8
Q

what is the cis isomer

A

hydrogen atoms on each carbon are on the same side

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9
Q

what is the trans isomer

A

hydrogen atoms are diagonally opposite each other

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10
Q

what are the Cahn-Ingold Prelog rules for deciding E/Z isomerism

A

higher atomic number = higher priority
groups of higher priority on the same side of the double bond of the Z isomer

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11
Q

describe hydrogenation of alkenes

A

an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K forming an alkane

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12
Q

describe halogenation of alkenes

A

Rapid addition reaction between an alkene and Cl/Br at room temperature to form a halogenalkane

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13
Q

how do you test for alkenes

A

orange bromine water turns clear

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14
Q

describe hydration of alkenes

A

an alkene is reacted with steam in the presence of a phosphoric acid catalyst, forming an alcohol
2 products can be formed

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15
Q

what is the mechanism for addition reaction

A

electrophilic addition

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16
Q

outline an electrophilic addition reaction between an alkene and hydrogen bromide

A

H-Br is a polar molecule
electron pair in a pi bond is attracted to it
double bond breaks
bonds forms H and C atoms
H-Br bond breaks by heterolytic fission
bromide ion and carbocation formed
Br- reacts with carbocation

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17
Q

how does electrophilic addition take place with molecules with molecules that are non-polar

A

when the molecule approaches the pi bond, the electrons in the bond are repelled and this induces polarity

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18
Q

what is the Markownikoff’s rule

A

In electrophilic addition, when the carbocation is formed, it can be primary, secondary, tertiary.
Tertiary is the most stable so is the most likely product

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19
Q

what is carbocation

A

positively charged molecule of carbon

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20
Q

why is tertiary carbocation the most stable

A

connecting alkyl groups donate and push electrons towards the positive charge of the carbocation
therefore more alkyl groups = a more stable ions

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21
Q

what is the name of the reaction for a polymer’s formation from alkenes

A

addition polymer

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22
Q

how is the monomer unit displayed

A

displayed formula with an (n) before it to signify many units

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23
Q

how is the repeat unit of the polymer are displayed

A

displayed formula, in square brackets, an (n) is placed after to signify a large number of repeats

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24
Q

what are the conditions for a polymerisation reaction

A

high temperature and pressure

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25
what are the uses of polypropene
Toys, packing crates, guttering, rope fibre
26
what are the uses of polyphenylethene - polystyrene
packaging materials food trays + cups
27
what are the uses of polytetra fluroethene
coating for non-stick pans permeable membrane for clothing cable insulation
28
downside of current disposal of waste of polymers?
very unreactive non-biodegradable with serious environmental effects
29
what are the benefits of recycling polymers
reduces environmental impacts by conserving fossil fuels and decreasing waste
30
how is a double bond formed
3 sigma bonds formed 1 electron left in a p-orbital a pi bond forms from the sideways overlap of 2 p-orbitals
31
what is an elimination reaction
the removal of a small molecule from a larger one
32
what is the functional group and suffix for an alkene alcohols aldehyde ketones carboxylic acids
c=c -ene OH -ol -CHO -al C(CO)C -one COOH -oic acid
33
functional group and prefix for haloalkane
-Cl/-Br/-I Chloro- Bromo- Iodo-
34
what is the difference between a saturated and unsaturated hydrocarbon
saturated = only single bonds unsaturated = mutiple bonds
35
what is a homologous series
family of compounds with similar chemical properties differing by the addition of a group
36
what is a functional group
part of the organic molecule that is responsible for the molecules chemical properties
37
what is an aliphatic hydrocarbon
carbon atoms are joined to each other in a straight chain
38
what is an alicyclic hydrocarbon
carbon atoms are joined to each other in a ring (cyclic) structure
39
what is an aromatic hydrocarbon
some/all carbon atoms are found in a benzene rings
40
what is the difference between alkanes, alkenes and alkynes
ane - single C-C bonds ene - one+ C=C double bond yne - 1+ C-C triple bond
41
what is a general formula
simplest algebraic formula for any member of a homologous series
42
what is displayed formula
shows relative positioning of all of the atoms in a molecule + the bonds
43
what is the structural formula
shows which groups are bonded together CH3CH2CH3
44
hwo is skeletal formula formed
remove all of the carbon and hydrogen labels from the carbon chain remove any bonds to hydrogen atoms
45
how does skeletal formula work
one line = a single bond intersection of 2 lines = a carbon atom end of a line = -CH3 group
46
what is a structural isomer
compounds with the same molecular formula but different structural formula
47
what is homolytic fission and what is formed after
when a covalent bond breaks, each of the bonded atoms takes 1 electron from the shared pair 2 atoms with an unpaired electron - radicals
48
what is heterolytic fission and what is formed after
whena covalent bond breaks, 1 bonded atom takes both of the electrons fro the shared pair a positive ion ad a negative ion
49
what are curly arrows used to show
movement of electron pairs when bonds are broken or made
50
what is an addition reaction
2 reactants form 1 product after being joined together
51
what is a substitution reaction
an atom/group of atoms is replaced by a different atoms/group ofatoms
52
what is the main use of alkanes
fuel
53
what is the general formula of alkanes
CnH2n+2
54
what kind of covalent bonds are formed in alkanes
sigma bonds
55
what is a sigma bond
the overlap of 2 orbitals
56
how are alkanes separated
fractional distillation
57
how does chain length affect bp and why
longer chain length raises boiling point as there is a greater surface area of contact which means stronger London forces which require more energy to overcome
58
what is the effect of branching on bp and why
lowers boiling point as there is less surface area of contact which means weaker London forces which require less energy to overcome
59
why are alkanes fairly unreactive
C-C, C-H sigma bonds are strong C-C bonds are non polar Similar electronegativity of carbon and hydrogen
60
what is complete combustion and what are the products
alkanes burn completely to produce CO2 and H2O
61
what are the 2 products from incomplete combustion of alkanes
carbon monoxide and water
62
name the mechanism for bromination of alkanes
free radical substitution
63
what are the 3 stages of free radical substitution
initiation propagation substitution
64
describe initiation of free radical substitution
covalent bond in a bromine molecule is broken by homolytic fission energy is provided by UV radiation Br-Br -> *Br + *Br
65
describe propagation stage of free radical substitution
CH4 + Br* --> CH3 + HBR CH3 + Br2 --> CH3BR + Br*
66
describe termination stage of free radical substitution
2 radicals collide forming a molecule with all electrons paired 1. Br* + Br* --> Br2 2. *CH3 + *CH3 --> C2H6 3. CH3 + Br --> CH3Br
67
what can occur after a radical substitution reaction
further substitution

Chemistry OCR A-Level (2 decks)

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