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Chem Eng - Y1.S1 > CE 10224A - Science for CE (Organic Chemistry) > Flashcards

CE 10224A - Science for CE (Organic Chemistry) Flashcards

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1
Q

What are stereoisomers?

A

Molecules with the same molecular formula and order of atoms bound together but differ in their 3-D spatial orientation.

Same molecular and structural formula but different arrangement in space

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2
Q

What are olefins?

A

Alkenes

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3
Q

What are alkynes?

A

Compounds with C-C triple bonds

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4
Q

What are aromatics?

A

Compounds containing a benzene ring

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5
Q

What are properties of aromatics?

A

They contain a benzene ring - electrons are delocalised across the ring.

Most have a pleasant smell

Addition reactions are possible (however the ring is very stable)

Common naming of aromatic rings is to label from the first substituted carbon then use subsequent numbering
Traditional naming system uses ortho-, meta- and para- prefixes

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6
Q

What are the properties of: short chain alkanes, long chain alkanes, aromatics, alkenes and branched components?

A

Short chain alkanes:

  • poor energy content
  • excellent low temp’ properties
  • very volatile
  • good lubricant

Long chain alkanes:

  • greatest energy content
  • poor low temp’ properties
  • poor volatility
  • poor lubricant

Aromatics:

  • poor energy content
  • good low temp properties if short chain
  • poor volatility
  • good lubricant

Alkenes:

  • good energy content
  • good low temp properties
  • good volatility
  • poor lubricant

Branched components:

  • lower energy content than straight chain
  • greatest low temp properties
  • poor volatility
  • poor lubrication
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7
Q

What is acetone?

What’s its formula?

A

A ketone, also known as propanone

Formula: CH3COCH3

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8
Q

What is acetaldehyde?

What’s its formula?

A

An aldehyde, also known as ethanal

Formula: CH3CHO

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9
Q

What is formic acid?

What’s its formula?

A

A carboxylic acid, also known as methanoic acid

Formula: HCOOH

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10
Q

What’s acetic acid?

A

A carboxylic acid also known as ethanoic acid

Formula: CH3COOH

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11
Q

What is ethyl acetate?

What’s its formula?

A

An ester, also known as ethyl ethanoate

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12
Q

What is ether/diethyl ether?

A

An ether, also known as ethoxyethane

Formula: C2H5OC2H5

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13
Q

What’s benzene?

A

A hydrocarbon (aromatic) with formula C6H6.

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14
Q

What is toluene?

What’s its formula?

A

Aromatic hydrocarbon, methyl benzene

C6H5CH3

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15
Q

What is phenol?

What’s its formula?

A

Aromatic hydrocarbon with formula C6H5OH

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16
Q

What is pyridine?

What’s its formula?

A 
Heteroaromatic compound (azine)
Formula: C5H5N
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17
Q

What is THF?

What’s its formula?

A

Heterocyclic compound, TetraHydroFuran

Formula: C4H8O

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18
Q

What is DMF?

What’s its formula?

A

Dimethylformaldehyde

Formula: (CH3)2NCHO

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19
Q

What is DMSO?

What’s its formula?

A

Dimethylsulfoxide

Formula: (CH3)2SO

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20
Q

What is formaldehyde?

What’s its formula?

A

An aldehyde, also known as methanal

Formula: CH20

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21
Q

What are the 4 main analytical techniques used to determine organic structures?

A

NMR

X-ray crystallography

FT-IR (fourier transform infra-red)

Mass spectroscopy

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22
Q

What’s x-ray crystallography?

What are its limitations?

A

An analytical technique which can be used to determine structures of crystalline solids.

The technique works by firing X-rays at a structure.
The X-rays will interact with the electron cloud around atoms and diffract.
By assessing how the X-rays have diffracted and the pattern they produce we can determine the structure of a compound.

Limitations:

  • Only works on crystalline solids
  • Can’t see H atoms
  • Expensive and time consuming
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23
Q

How does NMR work?

A

Nuclei are held in a powerful magnetic field.
If the nuclei have the correct spin state, and can align with the magnetic field then they can be detected by NMR.

A radiowave at set frequency is used to excite the target atoms from a low energy state to a high one
As the nuclei relaxes back to its ground state it emits radiowaves, this can be detected and gives the information needed.

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24
Q

What does a carbon C13 spectra suggest?

left to right

A

200-150ppm: Unsaturated C next to O atom e.g. C=O

150-100ppm: Unsaturated C atoms e.g. C=C

100-50ppm: Saturated C atoms next to O e.g. RO-CH3

50-0ppm: saturated C atoms e.g. R-CH3

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25
Q

What’s mass spectroscopy?

A

Tool that gives the molecular weight of a compound, which works by measuring the mass of a charged compound.

The sample is volatised and ionised.
This is then sent as a beam of charged ions through a magnetic field which separates based on mass:charge ratio.
This then flows to the detector.

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26
Q

What’s FT-IR?

infra-red

A

Analytical technique can be used to assess functional groups.
All bonds vibrate and move. When moving these will absorb infra-red radiation.
We can pass radiation at different wavelengths through a sample and measure what is absorbed and what frequencies are not.
Stronger bonds vibrate faster (absorb more energy) as do lighter atoms.

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27
Q

What aspects can stabilise charged species?

A

Steric bulk around the charge (many atoms around the charged atom/ion which prevents it reacting easily

Electronic effects - groups can donate or remove electronic charge

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28
Q

What do EWG and EDG represent (electronic effects)?

A

EWG - electron withdrawing groups (have negative induction effect

EDG - electron donating groups (have positive induction effect)

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29
Q

What is indicative of leaving groups?

A

pKa

The lower the pKa the better the leaving group is.
This is also a good indication of the strength of a Nucleophile (in reverse) with large pKa meaning a stronger nucleophile.

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30
Q

What is epoxidation?

A

Any reaction that converts a compound (especially an alkene) into an epoxide.

An epoxide is an organic compound containing a three-membered ring consisting of an oxygen atom and 2 carbon atoms.

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31
Q

What are conjugated lipids.

A

Lipids have multiple double bonds, separated by a bisallylic carbon and essentially do not interact.

Some lipids, however, have double bonds on adjacent carbons
All of these compounds are brightly coloured and the bonds are said to be conjugated.

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32
Q

Why do lipids appear colourful?

A

The bonds have different energy characteristics and therefore absorb light at longer wavelengths than normal double bonds.

This means they absorb in the visible range (as opposed to the UV)
For example lycopene absorbs light in the green and blue and therefore appears red.
The more double bonds the longer the absorbed wavelength

33
Q

What are radicals?

A

Radicals are a unpaired electron caused by homolyses (as opposed to heterolysis when a compounds dissociates into ions)
(This is what causes lipids to go rancid).

Radicals can be formed from weak bonds splitting under the influence of temperature or UV light.
They’re extremely reactive and most are too quick to react to confirm by conventional analytical techniques.

34
Q

What’s an enolate?

A

The anion formed when an alpha hydrogen in the molecule of an aldehyde or a ketone is removed as a hydrogen ion.

35
Q

What happens in the coker unit (of refinery column)?

A

Temp is increased and heavy oil cracks into low Mr hydrocarbons.

Two stage thermal decomposition occurs (gas, liquid and coke).

In the first stage, thermal cracking takes place producing the gas and liquids. Condensation reactions result in the formation of semi-coke.
Steam is injected into the reaction to aid in the removal of the volatiles and minimise further cracking reactions.

In the second stage the semi-coke continues to undergo pyrolysis leading to more gas and liquid and coke.

36
Q

What (2) processes occur in cracking?

A

Free radical formation (producing a hydrocarbon (+R) radical and H radical)

Beta-scission (cracking)

37
Q

What’s FCC?

A

Fluid catalytic cracking

It cracks heavy gas oils (vacuum gas oils) into smaller chain olefins/aromatics/alkanes.

Zeolites (microporous aluminosilicates) are used as the catalyst.

There are 2 FCC mechanisms.

38
Q

What is the benefit of using zeolites in FCC?

A

They are good at extracting hydrogen (from alkanes.)
They’re microporous aluminosilicates.

They have strong acid sites internally that can abstract a H⁻.

39
Q

What happens in the FCC (fluid catalytic cracking) mechanism 1?

A

A zeolite is present, along with an alkane.
It removes a hydrogen atom, changing the alkane to a carbocation. [Hydrogen abstraction]

The carbocation can then start cracking to form olefins also. [Beta-scission / cracking]

Unstable carbocations will also rearrange to form more stable carbocations.
Another H⁽⁺⁾ is then also removed to form another olefin.
(You must end up with a proton, H+)

40
Q

What are the two main mechanisms of cracking?

A

Thermal process, requiring free radicals, high temperatures and no oxygen.

FCC (fluid catalytic cracking) which also involves 2 mechanisms and uses carbocations.

41
Q

What are the major products of FCC?

A

Alkanes
Alkenes
Aromatics

42
Q

What’s a paraffin?

A

An alkane

43
Q

What are napthenes?

A

Any of a group of cyclic aliphatic hydrocarbons (e.g. cyclohexane) obtained from petroleum.

44
Q

What happens when an olefin and napthene react? (alkene and cycloalkane)

A

It forms a paraffin (alkane) and cyclo-olefin (cycloalkene)

45
Q

What happens when an olefin and cyclo-olefin react? (alkene and cycloalkene)

A

It forms a paraffin (alkane) and cyclo-di-olefin (cyclo-dialkene)

46
Q

What happens when an olefin and cyclo-di-olefin react? (alkene and cyclo-dialkene)

A

It forms a paraffin (alkane) and an aromatic

47
Q

What is alkylation?

A

The transfer of an R-group from one molecule to another.

This can be done by free radicals, carbocations or carbene.

48
Q

What happens in alkylation?

A

The double bond of an alkene will react with the strong acid, forming a carbocation, and a H+ is extracted from the acid.

This carbocation can then react with another molecule/alkane and make something more stable (but also changing the alkane to a carbocation). This will happen again and again and will result in branching.

49
Q

What happens at the reformer unit (in refineries)?

A

Larger molecules and ‘better’ gasoline products are produced/reformed. It converts linear hydrocarbons into cyclic species

This requires high temperatures, pressures, a lot of hydrogen and catalysts.

50
Q

What happens at the reformer unit (in refineries)?

A

Linear hydrocarbons are converted into cyclic species, and alkanes are isomerised.

Hydrogen (H2) is removed from the species, forming double bonds, until cyclic structures can be formed.
In the second stage, hydrogen is removed and a carbocation is formed.
This is then rearranged to become more stable and isomerisation occurs.

This requires high temperatures, pressures, a lot of hydrogen and catalysts.

51
Q

Why is the reformer unit necessary (for refineries)?

A

Larger molecules and ‘better’ gasoline products are produced/reformed. It converts linear hydrocarbons into cyclic species.
Alkanes are also isomerised.

This requires high temperatures, pressures, a lot of hydrogen and catalysts.

BTEX (benzene, toluene, ethyl benzene and xylenes) are produced.

52
Q

What is hydrocracking?

A

A method for breaking down large molecules into smaller molecules, similar to normal cracking.
However, hydrogen is also present, and any double bonds are hydrogenated (before they can cyclise).

This forms saturated hydrocarbons

53
Q

What happens in hydrocracking (brief)?

A

Hydrogen H2 molecules break and bond to the metal surface catalyst.

The double bond of the alkene present will also break and bond with the metal catalyst surface.

The bonds between the catalyst and alkene, and catalyst and hydrogen, are broken and the alkene accepts the hydrogen atoms to form an alkane.

54
Q

What is hydrodesulfurization, HDS?

What happens?

A

The removal of sulphur from crude oil.
The most common catalyst is Molybdenum, in MoS2.

When hydrogen is added to the catalyst (which is full of sulphur), H2S is produced. Therefore, a sulphur atom is removed from the catalyst, leaving a ‘vacant space’ on the catalyst.
Then, in the presence of hydrogen, if a sulphur-containing molecule in crude oil is passed over the catalyst, it will bind to the Mo atom of the catalyst in that ‘vacant space’.

The hydrocarbon (without the sulphur atom) can then be removed, and the catalyst would be reformed (it would've gained the sulphur from the molecule in the crude oil).
(It is done in the presence of hydrogen, which will hydrogenate any C=C bonds).
55
Q

What is the overall hydrodesulfurization, HDS, reaction?

A

sulphide catalyst + thiol species -> H2S + alkane + sulphide catalyst

The H2S can then be removed by adding oxygen (which will form SO2 and H2O and eventually just sulphur and water).

56
Q

What is polyethylene?

A

A synthetic polymer, the largest produced polymer in the world.
It is produced by polymerisation of ethene (ethylene).

57
Q

What is PTFE and PVC?

A

Polytetra-fluoroethylene (from polymerisation of C2F4)
It is a good insulator.

Poly(vinyl chloride) (from polymerisation of C2H3Cl)
It is a solid, brittle polymer.

58
Q

What are homo and co-polymers?

A

Homopolymer - consists of repeating chains of the same type of monomer.

Co-polymer - Chains composed of 2+ different repeating units

59
Q

What is the functionality of a polymer?

A

It indicates the number of bonds a monomer can form (e.g. ‘bifunctionality’)

60
Q

What are isotactic stereoisomers?

A

Stereoisomers which have their R groups on the same side of the chain.
These have the greatest melting points

61
Q

What are syndiotactic stereoisomers?

A

Stereoisomers with R groups on alternate sides of the chain.

These have the 2nd highest melting points

62
Q

What are atactic stereoisomers?

A

Stereoisomers with randomly positioned R groups.

These have the lowest melting points.

63
Q

What are the 3 types of stereoisomers?

A 
Isotactic (highest melting point)
Syndiotactic
Atactic (lowest melting point)
64
Q

What are cis and trans isomers?

A

Cis structure - highest priority groups about the double bond are on the same side

Trans structure - the groups are on opposite sides of the double bond.

65
Q

What are the main types of polymer molecular structures?

A

Linear
Branched
Cross-linked (aka vulcanisation in rubber)
Network

66
Q

What is vulcanisation?

A

When cross links are formed between polymer chains.
This is done with additional compounds e.g. sulphur compounds, by reacting them under high temperatures.

This makes them stronger.

67
Q

What are the 2 types of polymers, typed by processing?

A

Thermoplastics - can be processed by melting and can undergo several cycles of heating and cooling

Thermosets - can’t be melted or dissolved. They’ll chemically decompose before softening.

68
Q

How is number average molar mass calculated?

A

Mn = ΣXᵢMᵢ ; Mn = ΣNᵢMᵢ / ΣNᵢ

where Xᵢ is the mole fraction and Mᵢ is the average molecular weight in the range i.

69
Q

How is weight average molar mass calculated?

A 
Mw = ΣwᵢMᵢ ; 
where wi, weight fraction, is
wᵢ = NᵢMᵢ / ΣNᵢMᵢ ; 
therefore
Mw = ΣNᵢMᵢ²/ΣNᵢMᵢ
70
Q

What is molar mass dispersity?

A

A measure of the distribution of molecular mass in a given polymer sample.
It is the ratio of weight-average molar mass to number-average molar mass.

Dₘ = Mw / Mn

The larger the D number, the more skewed the distribution is and the worse the polymer properties will be.
Therefore it identifies if polymerisation has been done properly.

71
Q

What are nucleation sites?

A

Regions where, on cooling of the polymers, crystals begin to form. From here, they will crystalise outwards,

72
Q

How is % crystallinity measured?

A

By comparing the density of the sample to the densities of a completely crystalline and completely amorphous polymer;

% crystallinity = [ ρc(ρs - ρa) / ρs(ρc-ρa) ] *100

where:

ρs is density of sample
ρa is density of completely amorphous polymer
ρc is density of completely crystalline polymer

73
Q

What does % crystallinity depend on?

A

Rate of cooling - faster cooling results in less crystallinity

Type of polymer - simple structures means more crystallinity, and copolymers results in less crystallinity

Linear polymers form crystals more easily

74
Q

What is condensation polymerisation?

A

They produce polymers with repeat units that have different atoms to those within the monomers (as they form from more than one monomer) due to the elimination of small molecules e.g. H2O and HCl.

It’s a form of step growth polymerisation!

“Small molecules react with each other to form larger structural units while releasing smaller molecules as a byproduct, such as water or methanol”

75
Q

What’s addition polymerisation?

A

An addition polymer is a polymer that forms by simple linking of monomers without the co-generation of other products.

The [C=C] double bond breaks and the molecule bonds to more monomers, forming a polymer.

It is a form of chain growth polymerisation!

76
Q

What are the 2 main types of polymerisation mechanisms?

A

Step-growth (e.g. condensation polymerisation) where polymer chains grow step wise by reactions that can occur between any 2 molecular species.
- The graph shows an increase then plateu

Chain-growth (e.g. addition polymerisation) where polymer chains grow only by reaction of monomers with a reactive end group on the growing chain.
- The graph shows a constant increase

77
Q

What are properties of step growth polymerisation?

A

They’re simple extensions.
The links contain a heteroatom (not C or H)
It is difficult to obtain high molecular weight with it.
It involves successive reactions between pairs of mutually-reactive functional groups.

78
Q

What are polycondensations and polyadditions?

A

Polycondensations - Step polymerisations involving elimination of small molecules

Polyadditions - Step polymerisations involving elimination of small molecules

79
Q

How does chain growth occur by free radical polymerisation?

A

An initiator or catalyst is needed to start the chain polymerisation.

Initiation:

  • free radicals are formed from an initiator via homolytic scission (homolysis) or photolysis, causing single e- transfer.
  • A free radical is then added to a monomer

Propagation:
- This describes the ‘chain’ part of chain reactions. Once a reactive free radical is generated, it can react with stable molecules to form new free radicals. These new free radicals go on to generate yet more free radicals, and so on.

Termination:

  • When 2 radical species come together, they react to form a single bond
  • It stops in the absence of an active centre.

Chem Eng - Y1.S1 (10 decks)

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