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a level chemistry > module 4: alcohols, haloalkanes and organic synthesis > Flashcards

module 4: alcohols, haloalkanes and organic synthesis Flashcards

1
Q

outline the combustion of alcohols

A

they burn completely to form CO2 and H2O in a plentiful oxygen supply

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2
Q

can alcohols be oxidised? if so, outline the oxidation

A

primary - can be oxidised to produce an aldehyde through gentle heating with acidified potassium dichromate; it has to be distilled as it forms because if not further heating can cause it to become a carboxylic acid

secondary - oxidised by acidified potassium dichromate ions to produce ketones

acidified potassium dichromate goes from orange to green when it is reduced

tertiary alcohols are resistant to oxidation

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3
Q

what are the physical properties of alcohols and why

A

relatively high melting and boiling points; alcohols form hydrogen bonds between the -O-H groups of neighbouring molecules; these give alcohols a lower volatility than alkanes with a similar molecular mass

soluble in water: hydrogen bonds form between the polar -O-H groups of alcohol and the H of water
the first three members of the alcohol homologous series are water soluble

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4
Q

why does solubility of alcohols decrease with chain length

A

a larger part of the molecule is made of a non-polar, hydrocarbon chain, which doesn’t form hydrogen bonds with water molecules, that’s why only the 1st 3 member of the alcohol homologous series are soluble

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5
Q

how do you classify alcohols (p, s , t)

A

primary - OH group and one or no alkyl group
secondary - has OH and two alkyl groups
tertiary - OH and 3 alkyl groups

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6
Q

what are some uses of esters?

A

in the chemical industry - as adhesives and solvents

the fragrances and flavours of various esters are used widely to produce flavourings and perfumes

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7
Q

outline esterification

A

warming an alcohol with a carboxylic acid in the presence of an acid catalyst (often conc sulfuric acid) forms an ester

the O-H bond in the alcohol is broken and the H reacts with an OH group from the carboxylic acid to form water

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8
Q

how is an alcohol dehydrated

A

alcohols can be dehydrated to form an alkene and water by heating them in the presence of an acid catalyst

eg. aluminium oxide/ concentrated sulfuric acid/ concentrated phosphoric acid

this is an elimination reaction

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9
Q

what are the uses of mass spectronomy

A

in chemistry:
- identifying unknown compounds
- determining the abundance of each isotope in an element
- to gain further info about the structure and chemical properties of molecules

generally:
- detecting banned substances like steroids in athletes
- analysing molecules in space
- detecting traces of toxic chemicals in contaminated marine life

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10
Q

how does a mass spectrometer work

A
  1. vaporised/gaseous molecules are bombarded with a beam of high speed electrons that knock off an electron from some compounds, creating Positive Molecular Ions
  2. excess energy from the ionisation process can transfer to the ion and make it vibrate, this causes bonds to weaken and the ion splits into pieces
  3. these ions are propelled into a mass analyser
  4. they are separated due to their mass to charge ratio (m/z) , this can be done with a magnetic field
  5. the ions are detected and a mass spectrum is detected by computer software
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11
Q

how do you analyse a mass spectrum

A

the spectrum will show multiple peaks, based on the compound fragments formed during the ionisation process; the peak with the largest m/z value is the M+, the rest are fragments

the fragments form because excess energy from the ionisation process can be transferred to the ion and make it vibrate, causing the weakening of bonds so that the ion splits into pieces

the small peak next to the M+ is caused by the carbon-13 isotope

the structure of each fragment can be deduced by trying to see what part of the molecule would give that m/z value (Mr)

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12
Q

how does infrared spectroscopy work

A

IR radiation causes covalent bonds to vibrate more and absorb energy

IR spectroscopy identifies compounds based on changes in vibrations of atoms when they absorb IR of certain frequencies

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13
Q

what is the fingerprint region in IR spectroscopy and how can it be used

A

it is below 1500cm^-1
it’s unique for every compounds, it can be compared with that of a known compound to help with identification
comparing the region with a pure version of the compound can tell you if it’s impure (pure would be identical)

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14
Q

what are functional group signals in IR spectroscopy and how can they be used

C=O
O-H
ketones
aldehydes

A

above 1500^-1
the wavenumbers of bonds to know are given on the data sheet
also remember that
C=O is very strong and goes right down
O-H is obvious and smooth with a bumpier CH alongside
O-H acid is very broad and O-H combines with C-H
ketone/aldehyde has a little bumpy lump at the start

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15
Q

describe the bonding in haloalkanes

A

they contain polar bonds because the halogens are more electronegative than the carbon atom

this means electron density is drawn to the halogen, forming delta+ and delta- regions

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16
Q

how do primary, secondary and tertiary haloalkanes react

A

only primary and secondary haloalkanes can have nucleophilic substitution reactions

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17
Q

describe and explain the trend in reactivity of haloalkanes

A

reactivity increases as you go down the group

electronegativity of the halogens decreases as you go down and the bonds get longer; so they are weaker and easier to break

the Mr of the halogen in the polar bond increases as you go down so the bond enthalpy is lower and the bond can be broken more easily, reactivity increases

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18
Q

how can you react a haloalkane to make an alcohol, what is the mechanism

A

react with aqueous NaOH
has to be warmed bc of slow rate of reaction
nucleophilic substitution reaction mechanism
hydrolysis reaction

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19
Q

what is a nucleophile

A

an electron pair donor, it contains a lone electron pair that’s attracted to delta+ regions of a molecule

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20
Q

how can you test for a haloalkane

A

add ethanol and silver nitrate solution to the haloalkane

the water in the solution reacts with the haloalkane to form an alcohol and releases halide ions into the solution

chloroalkane - white
bromoalkane - cream
iodoalkane - yellow

iodo is fastest bc C-I bond is weakest and easiest to break

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21
Q

what are some environmental concerns with haloalkanes

A

CFC’s (haloalkanes containing only chlorine, fluorine and carbon) are stable, volatile non-flammable and non-toxic and were used in fridges, aerosol cans and air conditioning

upper atmosphere UV radiation can form halogen radicals that catalyse the breakdown of the ozone layer

NO free radicals do the same and can be produced by car and aircraft engines and thunderstorms

22
Q

describe the mechanism of the reaction related to concerns with CFC’s

A

the chlorine regenerated in propagation 2 is catalytic in the ozone breakdown, so a small amount of CFC released can cause a lot of damage

23
Q

what are some alternatives to CFC’s

A

alternatives were needed after they were banned because the advantages they provided didn’t outweigh the issues that were caused ; under the Montreal Protocol of 1989 which was an intentional treaty to phase out CFC use by 2000

instead;
HCFC’s - they break down in 10-20 years
HFC’s - they don’t contain chlorine so they ozone isn’t damaged
some hydrocarbons are being used in fridges - also greenhouse gas
these are both temporary alternatives but they are greenhouse gases that are 1000x worse than CO2

ozone holes do still form in spring but are slowly shrinking

24
Q

give an example of a reaction done using distillation

A

oxidising primary and secondary alcohols to aldehydes and ketones

quickfit apparatus is used where temperature can be measured

25
Q

give an example of a reaction where you heat under reflux

A

organic reactions can be completed by heating under reflux until you form an organic liquid
it allows the mixture to react as fully as possible without losing any reactants, solvent or products

eg. production of a carboxylic acid from a primary alcohol using acidified potassium dichromate
+ production of an ester from an alcohol and acid in the presence of an acid catalyst

26
Q

how can an organic liquid be purified with a separating funnel

A
  • invert the funnel and open the stopcock to release any pressure
  • repeat a few times
  • allow the aqueous layer and organic layer to settle
  • open the stopcock to drain away the aqueous layer and pour the organic liquid into another beaker
  • may have to then dry with an anhydrous salt

work out which is organic using: density data/ add water and see it is the layer that doesn’t increase

used with an insoluble product

27
Q

how can an organic liquid be purified with an anyhdrous salt
+ examples of anhydrous salts

A

an anhydrous inorganic salt is a drying agent that hydrates readily in the presence of water

anhydrous CaCL2 - used to dry hydrocarbons
anhydrous Ca/MgSO4 - more general purpose drying agents

the drying agent is added until it no longer clumps together; the excess drying agent is then decanted or filtered off
- if the organic liquid is dry it will appear clear

28
Q

how can an organic liquid be purified using redistillation

A

redistillation - used if an organic liquid obtained via distillation still has traces of other liquids
aim for a narrower boiling point range for the distillate so that you obtain only the desired organic liquid

29
Q

how does hydrogen bonding occur in alcohols

A

O-H
O is very electronegative and the more electronegative element in an O-H bond, it attracts the electrons and leaves the H delta+
the attraction between delta+ H atoms and delta- O atoms on different molecules is the hydrogen bond

30
Q

what are the conditions etc for alcohol to haloalkane

A

alcohol + NaX –> haloalkane
+ H2SO4

31
Q

reagents and conditions for a hydrolysis reaction

A

water and heat

32
Q

what modes of vibration can molecules have

A

asymmetric stretching
symmetric stretching
asymmetric bending
symmetric bending

33
Q

general equation for mechanism that breaks down the ozone layer

A

R* + O3 –> RO* + O2
RO* + O –> R* + O2

34
Q

how do you go from alkene to haloalkane

A

react with a hydrogen halide

35
Q

how do you go from an alcohol to a haloalkane

A

react with a sodium halide + sulphuric acid catalyst

36
Q

how do you go from a haloalkane to an alcohol

A

react with aqueous sodium hydroxide

37
Q

how do you go from an alkene to an alcohol

A

react with steam and a phosphoric acid catalyst

38
Q

how do you go from an alcohol to an alkene

A

react with sulphuric or phosphoric acid and heat

39
Q

how do you go from a carboxylic acid to an ester

A

react with an alcohol and concentrated sulfuric acid

40
Q

how do you go from an alcohol to an ester

A

react with carboxylic acid and concentrated sulfuric acid
OR acid anhydride

41
Q

how do you go from an alcohol to an aldehyde

A

distill a primary alcohol with acidified potassium dichromate and sulfuric acid

42
Q

how do you go from an alcohol to a carboxylic acid

A

react a primary alcohol with acidified potassium dichromate and sulfuric acid and reflux

43
Q

how do you go from an alcohol to a ketone

A

reflux secondary alcohol with potassium dichromate and sulfuric acid

44
Q

acidified potassium dichromate colour change

A

orange to green when it is reduced

45
Q

draw the apparatus used for refluxing

A
46
Q

draw the apparatus used for distillation

A
47
Q

draw the apparatus used for separation

A
48
Q

what can react with a tertiary alcohol

A

NaBr and H2SO4
the OH is substituted with Br

could also react with COOH to form an ester

and more!

49
Q

writing organic synthesis equations

A

usually can just write the ion that is reacting

50
Q

how does cooh react with a carbonate

A

loses the H and gets the carbonates positive ion

a level chemistry (15 decks)

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