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chemistry module 4 > basics + alkanes + alkenes > Flashcards

basics + alkanes + alkenes Flashcards

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1
Q

general formula definition

A

the simplest algebraic formula of a member of a homologous series

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2
Q

homologous series definition

A

a group of organic compounds with the same functional group and general formula, where each successive member differs by CH2

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3
Q

functional group definition

A

an atom/group of atoms responsible for the characteristic reactions of a compound

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4
Q

hydrocarbon definition

A

a compound containing only C and H atoms

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5
Q

alkyl group definition

A

an organic group with the formula CnH2n+1

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6
Q

aliphatic definition

A

a hydrocarbon compound consisting of straight chains, branched chains or non aromatic rings

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7
Q

alicyclic definition

A

a hydrocarbon compound arranged in non aromatic rings

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8
Q

aromatic definition

A

a compound containing a benzene ring

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9
Q

saturated definition

A

an organic compound with only single C-C bonds

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10
Q

unsaturated definition

A

an organic compound with C=C double bonds, C≡C triple bonds or an aromatic ring

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11
Q

nucleophile definition

A

an electron pair donator

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12
Q

electrophile definition

A

an electron pair acceptor

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13
Q

structural isomerism definition

A

molecules with the same molecular formula but different structural formulae

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14
Q

what are the 3 types of structural isomerism

A
  • chain isomerism
  • positional isomerism
  • functional isomerism
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15
Q

chain isomerism definition + example

A

molecules with the same molecular formula but different carbon arrangements in straight or branched chains
e.g. butane and methylpropane

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16
Q

positional isomerism definition + example

A

molecules with the same molecular formulas and carbon skeleton and functional group, but different positions of the functional group
e.g. but-1-ene and but-2-ene

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17
Q

functional isomerism definition

A

molecules with the same molecular formulae but different functional croups
e.g. butene and cyclobutane

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18
Q

what are the 3 naming steps

A

1- identify longest carbon chain/longest chain with priority functional group
2- identify functional groups and the numbered C they are attached to
3- arrange in alphabetical order

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19
Q

what is the priority ranking for naming/identifying carbon chains - from lowest to highest

A

carboxylic acid (HIGHEST)
ester
amide
nitrile
aldehyde
ketone
alcohol
amine
alkene
alkyne
alkane (LOWEST)

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20
Q

homolytic fission definition

A

when a bond is broken and each bonding atom received on electron from the bonded pair, forming 2 radicals

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21
Q

heterolytic fission definition

A

when a bond is broken and just one bonding atom received both electrons from the bonded pair

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22
Q

radical definition

A

a species with an unpaired electron

23
Q

3 types of reactions

A

elimination
addition
substitution

24
Q

elimination definition

A

a reaction involving the removal of a small molecule from a larger one, usually a single bond is turned into a double bond

25
Q

addition definition

A

a reaction where 2 reactants join to form one product, usually a double bond is turned into 2 single bonds

26
Q

substitution definition

A

a reaction where an atom/molecule is replaced by another atom/molecule

27
Q

what is the shape and bond angle around a C atom in alkanes

A

tetrahedral
angle = 109.5

28
Q

explain the trend in boiling points in alkanes

A

as chain length increases boiling point increases as longer chains = more atoms with electrons = more london forces which require more energy to overcome

29
Q

explain how branching affects boiling point

A

as branching increases boiling point decreases as branched alkanes cannot pack as closely together = decreased london forces between molecules which requires less energy to overcome

30
Q

why do alkanes have low reactivity

A

C-C and C-H bond enthalpies are high so lots of energy is needed to break them
these bonds also have a low polarity so they do not attract nucleophiles or electrophiles easily

31
Q

give 1 use for alkanes

A

complete combustion of alkanes is used as fuel

32
Q

why might incomplete combustion occur + what is dangerous about it

A

incomplete combustion occurs in a limited supply of oxygen
it forms CO which is a toxic gas as it binds to haemoglobin irreversibly therefore preventing oxygen transport around the body

33
Q

what are the 3 stages in radical substitution

A

initiation - the formation of a radical
propagation - maintaining radical concentration
termination - loss of radical concentration

34
Q

what are limitations of radical substitution

A

it doesn’t produce a very high yield of product, especially if a very specific compound is needed, due to:
- further substitution in excess halogen forming di/tri haloalkanes
- substitution can occur at different positions on the chain, products could be various isomers
- impurities as multiple products are formed in the termination steps so the product needed is mixed up with other stuff too

35
Q

a radical substitution question may give you a compound and then ask how many different isomers can be formed with just a single substitution - how can you work this out

A

the answer should be the same as the number of proton environments in the molecule - trick!
- good to think of as you might miss an isomer
- this will only work for single substitutions !

36
Q

summarise the 1 main reaction of alkanes

A

halogenation via free radical substitution with a halogen under UV to make haloalkanes

37
Q

what is the shape and bond angle around a double bond in an alkene

A

triagonal planar
angle = 120

38
Q

pi bond definition

A

a pi bond is formed by the sideways overlap of electrons in adjacent p-orbitals

39
Q

what bonds make up a C=C double bond

A

1 sigma bond and 1 pi bond

40
Q

stereoisomerism definition

A

molecules that have the same molecular and structural formulae but different spatial arrangement

41
Q

what are the 2 types of stereoisomerism

A

E/Z isomerism and optical isomerism

42
Q

why does stereoisomerism occur in alkenes

A

this is because double bonds restrict rotation around the C atom

E - high priority groups opposite each other
Z - high priority groups next to each other

43
Q

what conditions are needed for E/Z isomerism

A

a C=C double bond with 2 different groups attached to each carbon of the double bond

44
Q

cis-trans isomerism definition

A

a special case of E/Z isomerism where one of the groups on each carbon is a H atom

cis - Z - H atoms next to each other
trans - E - H atoms opposite each other

45
Q

outline the inductive effect

A

when a carbocation has alkyl groups attached (known as electrodonating groups) this will stabilise the carbocation, making it less positively charged

this is because alkyl groups push electron density towards the carbocation making it energetically more stable

therefore in terms of stability
tertiary carbocation > secondary carbocation > primary carbocation

46
Q

state markownikoffs rule

A

during electrophilic addition of HY to asymmetrical alkenes the H will bond to the C atom bonded to the most H atoms, whereas the other group Y will bond to the most substituted C atom (bonded to the least H atoms/most alkyl groups) which is the more stable carbocation therefore will remain as an intermediary long enough for the next step of the reaction to occur

if the addent contains 2 halogens e.g. Br-F the more electronegative halogen will bond to the most substituted C atom - in this case F

47
Q

why are alkenes more reactive than alkanes

A

pi bonds have lower enthalpy than sigma bonds, so less energy is needed to break a double bond into a single bond than to break a single bond
also double bonds have high electron densities therefore are more polarising and attract electrophiles

48
Q

summarise 3 main reactions of alkenes

A
  • hydrogenation via electrophilic addition with H2 + Ni catalyst to become alkanes
  • electrophilic addition with hydrogen halides to become haloalkanes
  • hydration via electrophilic addition with steam + H2SO4 catalyst at high temps and pressure to become alcohols
49
Q

QUALITATIVE ANALYSIS OF ORGANIC COMPOUNDS
outline the test for alkenes + equation

A
  • react with bromine water
    POSITIVE= the solution decolourises from orange-brown - colourless

alkene + Br2(aq)&raquo_space; dibromoalkane

50
Q

polymer definition

A

a long chain molecule made of many repeating units called monomers

51
Q

monomer definition

A

small molecules which can react together to form polymers

52
Q

what type of polymerisation can alkenes undergo + why

A

addition polymerisation by breaking the double bod into a single bond

53
Q

give 3 sustainable ways to process waste polymers

A
  • combust as a fuel source to produce energy
  • use as organic feedstock for the production of plastics
  • removal of toxic wastes formed from other reactions

chemistry module 4 (2 decks)

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