Organic Molecules Flashcards

Question 1

Q

What is a hydrocarbon?

Answer

A

Molecule consisting of only hydrogen and carbon

Question 2

Q

Give me an example of a alkane?

Answer

A

Propane, it has 3 Carbons and 8 Hydrogens. Alkanes end in -ane

Question 3

Q

Give me an example of an alkene?

Answer

A

Propene, it has 3 Carbons and 6 Hydrogens. It has the functional group of C=C double bond. The ending -ene means it’s an alkene.

Question 4

Q

Give me an example of an alcohol?

Answer

A

Propanol has 3 Carbons, 7 Hydrogens and 1 OH group. The functional group of alcohols is the OH bonded to one of the carbons. Alcohols all end in -ol.

Question 5

Q

Give me an example of a carboxylic acid?

Answer

A

Propanoic acid has 2 carbons, 5 Hydrogens and a COOH group. The functional group is COOH end. Carboxylic acids end with -oic.

Question 6

Q

Give me an example of an ester?

Answer

A

Methyl Propanoate has 3 carbons, 8 hydrogens and a COO group. Esters have a functional group of -COO- in the middle of the chain. Because they have carbon ‘chains’ they get two parts to the name. Endings in esters are -yl-anoate.

Question 7

Q

What is 1-chloropropane?

Answer

A

1-chloropropane, is a halogenoalkane or haloalkane (both are
valid names for these). Now we have a ‘prefix’ denoting the
functional group, not an ending or ‘suffix’. Again, the number shows
the location of the chlorine. Haloalkanes can include any halogen:
that chlorine could instead be an F, Br or I and it would still count,
just have a different name. The shorthand for ‘any halogen’ in
organic is ‘X’, so we can say the functional group is -X.

Question 8

Q

What is propanal?

Answer

A

Propanal, is an aldehyde (spot the linguistic link: that ‘al’ bit).
This one gets an ending again. It looks a little like a carboxylic acid,
and in fact aldehydes can be converted into carboxylic acids by
oxidation – you’ll learn about this later.
The functional group here is written as -CHO to differentiate it from
an alcohol where we would write OH.

Question 9

Q

What is propanone?

Answer

A

Propanone, is a ketone. These are similar to aldehydes, as they
both have C=O, but in ketones that group appears in the middle of the
chain instead of at the end.
This functional group is written as -CO-.

Question 10

Q

What is propanenitrile?

Answer

A

Propanenitrile, is a nitrile. You’ll notice that the name looks a
bit weird. Naming rules, which you will learn, dictates that if the
suffix (ending) starts with a vowel, you remove any vowel from the
first part (which is why we say ‘propanol’ not ‘propaneol’) but if the
suffix starts with a consonant, you leave any ending vowel. Hence,
instead of ‘propannitrile’ we say ‘propanenitrile’.
The functional group is the −C≡N

Question 11

Q

What is propan-1-amine?

Answer

A

Propan-1-amine or propylamine (don’t worry about the
nuance here yet), is an amine. The functional group is -NH2.

Question 12

Q

Alkane:
What is the functional group?
What is the suffix?
what is an example name?

Answer

A

C-C

-ane

ethane

Question 13

Q

Alkene:
What is its functional group?
What is it’s suffix?
What is an example?

Answer

A

C=C

-ene

ethene

Question 14

Q

Alcohol:
What is it’s functional group?
What is its suffix and prefix?
What is an example?

Answer

A

R-O-H

suffix: -ol
prefix: hydroxy-

ethanol

Question 15

Q

Carboxylic acid:
What is its functional group?
What is its suffix?
What is an example?

Answer

A

R-C=O
-O-H

-oic acid

ethanoic acid

Question 16

Q

Ester:
What is the functional group?
What is its suffix?
What is an example?

Answer

A

R-C=O
-O-R

yl -anoate

ethyl ethanoate

Question 17

Q

Haloalkene:
What is the functional group?
What is its prefix?
What is an example?

Answer

A

R-X

fluoro-
chloro-
bromo-
iodo-

fluoroethane

Question 18

Q

Aldehyde:
What is the functional group?
What is the suffix and prefix?
What is an example?

Answer

A

R-C=O
-H

suffix: -al
prefix: formyl-

ethanal

Question 19

Q

Ketone:
What is a the functional group?
What is its suffix and prefix?
What is an example?

Answer

A

O
||
R-C-R

suffix: -one
prefix: oxo-

prpanone (can’t exist with less than 3 carbons

Question 20

Q

Nitrile:
What is the functional group?
What is its suffix and prefix?
What is an example?

Answer

A

R-C=N

suffix: -nitrile
prefix: cyano-

ethanenitrile

Question 21

Q

Amine:
What is the functional group?
What is its suffix and prefix?
What is an example?

Answer

A

R-N-H
-H

suffix: -amine
prefix: amino-

ethanamine

Question 22

Q

What is a general formula?

Answer

A

An algebraic formula that can describe any member of a family of compounds

Question 23

Q

What is an empirical formula?

Answer

A

The simplest whole number ratio of atoms of each element in a compound

Question 24

Q

What is a molecular formula?

Answer

A

The actual number of atoms of each element in a molecule

Question 25

Q

What is a structural formula?

Answer

A

Shows the arrangement of atoms carbon by carbon, with all attached hydrogens and functional groups

Question 26

Q

What is a skeletal formula?

Answer

A

Shows the bonds off the carbon skeleton only, with any functional groups. The hydrogen and carbon atoms aren’t shown. This is handy for drawing large complicated substances, like cyclic hydrocarbons.

Question 27

Q

What is a displayed formula?

Answer

A

Show how all the atoms are arranged, and all the bonds between them

Question 28

Q

What is the stem for 1-10 carbons?

Answer

A

Meth-
Eth-
Prop-
But-
Pent-
Hex-
Hept-
Oct-
Non-
Dec-

Question 29

Q

What is an addition reaction?

Answer

A

Joining two or more molecules together to form a larger molecule

Question 30

Q

What is a polymerisation reaction?

Answer

A

Joining together lots of simple molecules to form a giant molecule

Question 31

Q

What is an elimination reaction?

Answer

A

When a small group of atoms breaks away from a larger molecule

Question 32

Q

What is a substitution reaction?

Answer

A

When one species is replaced by another

Question 33

Q

What is a hydrolysis reaction?

Answer

A

Splitting a molecule into new molecules by adding H+ and OH- derived from water

Question 34

Q

What is an oxidation reaction?

Answer

A

Any reaction in which a species loses electrons

Question 35

Q

What is a reduction reaction?

Answer

A

Any reaction in which a species gains electrons

Question 36

Q

What do curly arrows represent in mechanisms?

Answer

A

How electron pairs move around

Question 37

Q

What types of mechanisms are there?

Answer

A

nucleophilic addition
electrophillic addition
radical addition

Question 38

Q

What happens in radical addition?

Answer

A

Radical substitution of halogens in alkanes to form halogenoalkanes

Question 39

Q

What happens in electrophilic addition?

Answer

A

Electrophilic addition of halogens and hydrogen halides to alkanes to make halogenoalkanes

Question 40

Q

What happens in nucleophilic addition?

Answer

A

Nucleophilic substitution of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols and with ammonia to make amines

Question 41

Q

What are nucleophiles?

Answer

A

nucleophiles are electron pair donors
they’re often negatively charged ions (e.g.halide ions) or species that contain a lone pair of electrons (e.g. the oxygen atoms in water).
they’re electron rich, so they’re attracted to places that are electron poor.
so they’re like to react with positive ions
molecules with polar bonds are often attacked by nucleophiles too, as they have delta+ area
↪️ nucleophiles are attracted to the delta + carbon atom in a polar carbon-halogen bond. The carbon-halogen bond breaks and the nucleophiles takes the halogen’s place-and that’s nucleophilic substitution

Question 42

Q

What are electrophiles?

Answer

A

electrophiles are electron pair acceptors
they’re often positively charged ions (e.g. H+), or delta+ areas (e.g. H delta + in a hydrogen halide H-X bond)
they’re electron poor, so they’re attracted to places that are electron rich
they like to react with negative ions, atoms with lone pairs and the electron-rich area around C=C bond
↪️ alkene molecules undergo electrophilic addition. In a molecule with a polar bonds are often, like HBr, the H delta + acts as an electrophile and is strongly attracted to the C=C bond (which polarises the H-Br bond even more, until it finally breaks)

Question 43

Q

What are radicals?

Answer

A

radicals have an unpaired electron, e.g. the chlorine atoms produced when UV light splits a Cl2 molecule
because they have unpaired electrons, they’re very, very reactive
unlike electrophiles and nucleophiles, they’rell react with anything, positive, negative, or neutral
↪️ radicals will even attack stable non-polar bonds, like C-C and C-H (so they’re one of the few things that will react with alkanes).

Question 44

Q

What is an isomer?

Answer

A

Two molecules are isomers if they have the same molecular formula, but the atoms are arranged differently
there are two types of isomers - structural isomers and stereoisomers

Question 45

Q

What is a structural isomer?

Answer

A

the atoms are connected in different ways; same molecular formula but different structural formula
there are 3 types: chain isomers, position isomers and functional group isomers

Question 46

Q

What are chain isomers?

Answer

A

the carbon skeleton can be arranged differently - for example as a straight chain, or branched in different ways
these isomers have similar chemical properties - but their physical properties, like boiling points, will be different because of the change in shape of the molecule

Question 47

Q

What are positional isomers?

Answer

A

the skeleton and the functional group could be the same, only with the functional group attached to a different carbon atom
these also have different physical properties, and their chemical properties might be different too

Question 48

Q

What are functional group isomers?

Answer

A

the same atoms can be arranged into different function groups
these have very different physical and chemical properties

Question 49

Q

What is bond fission?

Answer

A

breaking a covalent bond is caked bond fission.
a single covalent bond is a shared pair of electrons between two atoms
it can break in two ways: homolytic or heterolytic

Question 50

Q

What is heterolytic fission?

Answer

A

in heterolytic fission the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair
two different substances can be formed - e.g. a positively charged cation (X+), and a negatively charged anion (Y-).

Question 51

Q

What is homolytic fission?

Answer

A

in homolytic, the bond breaks evenly and each bonding atom receives one electron from the bonding pair
two electrically uncharged ‘radicals’ are formed
radical are particles that have an unpaired electron
they are shown in mechanisms by a big dot next to the molecular formula (the dot represents the unpaired electron)
because of the unpaired electron, radicals are very reactive

Question 52

Q

What are the three stages of the radical substitution reaction?

Answer

A

➡️Initiation reaction (radicals are produced):
1) sunlight provides energy to break the Cl-Cl bond - this is photo dissociation Cl2->2⋅Cl
2). The bond splits equally and each atom gets to keep one electron - homolytic fission.
The atom becomes a highly reactive radical, ⋅Cl, because of its unpaired electron
➡️Propagation reaction (radicals are used up and created in a chain reaction):
1) ⋅Cl attacks a methane molecule: CH4+⋅Cl→⋅CH₃+HCl
2) the new methyl radical, ⋅CH₃, can attack another Cl2 molecule: ⋅CH₃+ Cl2 -> CH₃Cl + ⋅Cl
3) the new ⋅Cl can attack another CH4 molecule, and so on, until all the Cl2 and CH4 molecules are wiped out
➡️Termination reaction (radicals are destroyed here):
1) if two free radicals join together, that make a stable molecule
2) there are two heaps of possible termination reaction. Here are a couple:

⋅Cl + ⋅CH3 -> CH3Cl

⋅CH3 + ⋅CH3 -> C2H6

Question 53

Q

What is the problem with radical substitution?

Answer

A

1) you get a mixture of products
2) e.g. if your trying to make chloromethane and there’s too much chlorine , some of the hydrogen atoms on the chloromethane molecule will be swapped for chlorine atoms. The propagation reaction happens again, this time to make dichloromethane (CH2Cl2)

⋅Cl + CH3CL -> ⋅CH2Cl + HCl

⋅CH2Cl + Cl2 -> CH2Cl2 + ⋅Cl
3) another substitution reaction can take place to form trichloromethane (CHCl3)

⋅Cl + CHC,2 -> ⋅CHCl2 + HCl

⋅CHCl2 + Cl2 -> CHCl3 + ⋅Cl

4) tetra chloromethane is formed in the last possible substitution. There are no more hydrogen atoms connected to the carbon atom, so the substitution process has to stop
5) so the end product is a mixture of CH3Cl, CH2Cl2, CHCl3 and CCk4. You have to separate the chloromethane from the 3 unwanted by-products
6) the best way of reducing the change of these by-products is to have an exces of methane. This means there’s a greater chance of chlorine radical colliding only with methane molecules and not a chloromethane molecule.
7) another problem with radical substitution is that it can take place anywhere along a carbon carbon chain. So a mixture of structural isomers can be formed. E.g. reacting propane with chlorine will produce a mixture of 1-chloropropane and 2-chloropropane

Question 54

Q

What is crude oil?

Answer

A

Also known as petroleum, consists of a mixture of hydrocarbons. You can separate it through fractional distillation

Question 55

Q

How does fractional distillation work?

Answer

A

1) First, the crude oil is vaporised at about 350 °C.
2) The vaporised crude oil goes into a fractionating column and rises up through the trays. The largest hydrocarbons don’t vaporise at all, because their boiling points are too high-they just run to the bottom and form a gooey residue.
3) As the crude oil vapour goes up the fractionating column, it gets cooler.
Because the alkane molecules have different chain lengths, they have different boiling points, so each fraction condenses at a different temperature. The fractions are drawn off at different levels in the column.
4) The hydrocarbons with the lowest boiling points don’t condense.
They’re drawn off as gases at the top of the column.

Question 56

Q

What is the order of the fractions of crude oil, going up?

Answer

A

➡️Petroleum gases - Fuel for domestic heating / cooking (1-4 carbons)
➡️Gasoline / petrol - Fuel for cars (5-12 carbons)
➡️Naptha - Making chemicals (7-14 carbons)
➡️Kerosene - Jet fuel (11-15)
➡️Diesel (gas oil) - Fuel for cars and some trains (15-19)
➡️Lubricating/ mineral oil - Reduces friction in machinery (20-30)
➡️Fuel oil - Fuel for ships and power stations (30-40 carbons)
➡️Bitumen - Surfacing roads and roofs (50+ carbons)

Question 57

Q

What is cracking?

Answer

A

There’s a higher demand for shorter hydrocarbons than for longer chain hydrocarbons. Cracking is breaking long chain alkanes into smaller hydrocarbons (which include alkenes). It involves breaking the C-C bonds. There are two types: thermal cracking and catalytic cracking.

Question 58

Q

What is thermal cracking?

Answer

A

1) Thermal cracking takes place at high temperature (up to 1000 °C) and high pressure (up to 70 atm). 2) It produces a lot of alkenes.
3) These alkenes are used to make heaps of valuable products, like polymers (plastics). A good example is poly(ethene), which is made from ethene.

Question 59

Q

What is catalytic cracking?

Answer

A

1) Catalytic cracking uses something called a zeolite catalyst (hydrated aluminosilicate), at a slight pressure and high temperature (about 450 °C). 2) It mostly produces aromatic hydrocarbons and motor fuels.
3) Using a catalyst cuts costs, because the reaction can be done at a low pressure and a lower temperature. The catalyst also speeds up the reaction, saving time (and time is money).

Question 60

Q

What are aromatic compounds?

Answer

A

Aromatic compounds contain benzene rings. Benzene rings contain a ring of 6 carbon atoms with delocalised ring of electrons.

Question 61

Q

What is knocking?

Answer

A

Knocking is where alkanes explode of their own accord when their fuel/ air mixture in the engine is compressed. Straight chain alkanes are the most likely hydrocarbons to cause knocking. Adding branched chain and cyclic hydrocarbons to the petrol mixture makes knocking less likely to happen, so combustion is more efficient.

Question 62

Q

How can alkanes be reformed?

Answer

A

Alkanes can be reformed into cyclohexanes and aromatic hydrocarbons. Straight chain alkanes can be converted into branched chain alkanes and cyclic hydrocarbons by reforming. This uses a catalyst (e,g. Platinum stuck on aluminium oxide).
↪️hexane can be reformed into cyclohexane and hydrogen gas, which can be reformed into benzene (C6H6) and hydrogen gas
↪️octane can be reformed into 2,5-dimethylhexane

Question 63

Q

What are combustion reactions with alkanes?

Answer

A

If your burn (oxidise) alkanes with oxygen, you carbon dioxide and water - this is a combustion reaction. Incomplete combustion is when there’s not enough oxygen, so the products will be carbon monoxide or carbon, and water. Combustion reactions happen between gases, so liquid alkanes need to be vaporised first. Smaller alkanes turn into gas more easily as are more volatile. Combustion is an exothermic reactions. Larger alkanes release more energy per mole because they have more bonds to react.

Question 64

Q

What harmful emissions are produced from alkanes in combustion reactions?

Answer

A

CO is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death. The CO binds well to haemoglobin which therefore cannot bind oxygen and carbon dioxide
sulfur impurities can cause acid rain
nitrous oxide can cause nitric acid
soot causes breathing problems and asthma

Answer 65

A

1) Catalytic converters sit quietly in a car exhaust and stop some pollutants from coming out.
2) Without catalytic converters, cars spew out lots of bad stuff, like carbon monoxide, oxides of nitrogen and unburnt hydrocarbons.
3) Catalytic converters get rid of theses pollutants by using a platinum catalyst to change them to harmless gases, like water vapour and nitrogen, or to less harmful ones like carbon dioxide.
4) For example, nitrogen monoxide and carbon monoxide
can be converted to nitrogen and carbon dioxide:
2NO+2CO→ N2(g) +2CO2 (g)

Answer 66

A

Fuels made from living matter over a short period of time:
↪️bio ethanol is ethanol made by fermentation of sugar from crops such as maize
↪️biodiesel is made by refining renewable fats and oils such as vegetable oil
↪️biogas is produced by the breakdown of organic waste matter

Answer 67

A

1) biofuels are classed as carbon neutral, as although they produce CO2 when burnt, they absorb CO2 when growing
2) biodiesel and biogas can also be made from waste that would have otherwise gone to landfill

Answer 68

A

1) a problem with switching from fossil fuels to biofuels is that petrol car engines will need to be modified to use fuels with high ethanol concentrations
2) also the land used to grow crops for fuel can’t be used to grow food

Answer 69

A

E/Z nomenclature is used to distinguish between the isomers
Z isomers have functional groups on the same side of the double bond/carbon ring
E isomers have functional groups on opposite sides of the double bond/carbon ring
if the atoms attached to the carbon are different, give the highest priority to atoms with a higher atomic number, then decide if it’s an E or Z isomer

Answer 70

A

Stereoisomers are compounds that have the same atoms connected to each other, however the atoms are differently arranged in space

Answer 71

A

Cis-Trans isomerism is a special type of E/Z isomerism in which both of the carbon atoms of the C=C group have at least one substituent group in common. Cis isomers will have the equal groups on the same side and trans isomers will have the equal groups on different sides.

Answer 72

A

In an electrophilic addition reaction, the alkene double bond opens up and atoms are added to the carbon atoms. 1) Electrophilic addition reactions happen because the double bond
has got plenty of electrons and is easily attacked by electrophiles.
2) Electrophiles are electron-pair acceptors - they’re usually a bit short of electrons,
so they’re attracted to areas where there are lots of electrons about.
3) Electrophiles include positively charged ions, like H+ and NO2+, and polar molecules (since the 8+ atom is attracted to places with lots of electrons).

Answer 73

A

alkenes will react with hydrogen gas in an addition reaction to produce an alkane. It needs a nickel catalyst and a temperature of 150 degrees Celsius

Answer 74

A

Alkenes decolourise bromine water when shaken with it

Answer 75

A

alkenes can be hydrated by steam at 300 degrees Celsius and a pressure of 60-70atm. The reaction needs a phosphoric (V) catalyst

Answer 76

A

if you shake an alkenes with acidified potassium manganate (VII), the purple solution is decolourised. The alkenes has been oxidised, and a diol has been made (alcohol with 2 -OH groups).

Answer 77

A

adding hydrogen halides to unsymmetrical alkenes can form two possible products
the amount of each product depends on how stable the carbocation formed in the middle of the reaction is
carbocations with more alkyl groups are more stable, because the alkyl groups feed electrons towards the positive charge. The more stable carbocation is much more likely to form
the major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached

Answer 78

A

double bonds in alkenes can open up and make long chains called polymers, the individual, small alkenes are called monomers
this is called addition polymerisation

Answer 79

A

Waste Plastics can be Buried:
1) Landfill is used to dispose of waste plastics when the plastic is:
⚫ difficult to separate from other waste,
⚫ not in sufficient quantities to make separation financially worthwhile,
⚫️ too difficult technically to recycle.
2) But because the amount of waste we generate is becoming more and more of a problem, there’s a need to reduce landfill as much as possible.
Waste Plastics can be Reused:
1) Many plastics are made from non-renewable oil-fractions,
so it makes sense to reuse plastics as much as possible.
2) There’s more than one way to reuse plastics.
After sorting into different types:
some plastics (poly(propene), for example) can
be recycled by melting and remoulding them,
some plastics can be cracked into monomers, and these can be used as an organic feedstock to make more plastics or other chemicals.
Waste Plastics can be Burned:
1) If recycling isn’t possible for whatever reason, waste plastics can be burned and the heat can be used to generate electricity.
2) This process needs to be carefully controlled to reduce toxic gases. For example, polymers that contain chlorine (such as PVC) produce HCI when they’re burned- this has to be removed.
3) Waste gases from the combustion are passed through scrubbers which can neutralise gases, such as HCI, by allowing them to react with a base.
4) Plastics can also be sorted before they are burnt to separate out any materials that will produce toxic gases.

Answer 80

A

Use reactant molecules that are as safe and environmentally friendly as possible.
Use as few other materials, like solvents, as possible.
If you have to use other chemicals, choose ones that won’t harm the environment.
Renewable raw materials should be used wherever possible.
Energy use should be kept to a minimum. - Catalysts are often utilised in polymer synthesis to lower energy use.
Limit the waste products made, especially those which are hazardous to human health or the environment.
Make sure the lifespan of the polymer is appropriate for its use. If you make a polymer that just keeps breaking, you’ll end up having to make loads more than if you create a more enduring polymer.

Answer 81

A

Raw materials aren’t going to run out like oil will.
When polymers biodegrade, carbon dioxide (a greenhouse gas) is produced. If your polymer is plant-based, then the CO, released as it decomposes is the same CO, absorbed by the plant when it grew. But with an oil-based biodegradable polymer, you’re effectively transferring carbon from the oil to the atmosphere.
Over their ‘lifetime’ some plant-based polymers save energy compared to oil-based plastics.

Answer 82

A

these polymers still need the right conditions before they’ll decompose
this means that you still need to collect and separate the biodegradable polymers from non-biodegradable plastics. At the moment, they’re are also more expensive than non-biodegradable equivalents

Answer 83

A

Alkanes with at least one halogen atom in place of a hydrogen atom

Answer 84

A

1) A primary halogenoalkane has two
hydrogen atoms and just one alkyl group.
2) A secondary halogenoalkane has just one hydrogen atom and two alkyl groups.
3) A tertiary halogenoalkane has no hydrogen atoms and three alkyl groups.

Answer 85

A

halogenoalkanes can be hydrolysed to alcohols in a nucleophilic substitution reaction, one way to do this is to use water:
R-X + H2O -> R-OH + H+ + X-
and with bromoethane:
CH3CH2Br + H2O -> C2H5OH + H+ + Br-
halogenoalkanes can also be hydrolysed to alcohols with aqueous potassium hydroxide

Answer 86

A

1) When you mix a halogenoalkane with
water, it reacts to form an alcohol.
R-X + H2O → R-OH + H+ + X-
2) If you put silver nitrate solution in the mixture too, the silver ions react with the halide ions as soon as they form, giving a silver halide precipitate .
Ag+(aq) + X (aq) → AgX (9)
3) To compare the reactivities of different halogenoalkanes, set up three test tubes each containing a different halogenoalkane, ethanol (as a solvent) and silver nitrate solution (this contains the water).
4) Time how long it takes for a precipitate to form in each test tube. The more quickly a precipitate forms, the faster the rate of hydrolysis is for that halogenoalkane.
↪️tertiary halogenoalkanes are the most reactive

Answer 87

A

1) In order to hydrolyse a halogenoalkane, you have to break the carbon-halogen bond.
2) How quickly different halogenoalkanes are hydrolysed depends
on the carbon-halogen bond enthalpy - see page 110 for more on this.
3) Weaker carbon-halogen bonds break more easily so they react faster.
4) Bond enthalpy depends on the size of the halogen- the larger the halogen, the longer the C-X bond, and the lower the bond enthalpy.
5) The size of the halogen increases down Group 7, so iodoalkanes have the weakest bonds, and are hydrolysed the fastest. Fluoroalkanes have the strongest bonds, so they’re the slowest at hydrolysing.
6) You can compare the reactivity of chloroalkanes, bromoalkanes and iodoalkanes using an experiment

Answer 88

A

1) Halogens are generally more electronegative than carbon. So, the carbon-halogen bond is polar.
2) The 8+ carbon doesn’t have enough electrons. This means it can be attacked by a nucleophile.
A nucleophile’s an electron-pair donor. It donates an electron pair to somewhere without enough electrons
3) OH, NH, and CN- are examples of nucleophiles that react readily with halogenoalkanes.
Water is also a weak nucleophile.
4) A nucleophile can bond with the 8+ carbon of a halogenoalkane, and be substituted for the halogen. This is called nucleophilic substitution:
Here’s what happens. It’s a nice
simple one-step mechanism:
↪️X is the halogen. Nuc is the nucleophile, which provides a pair of electrons for the Co+.
↪️The C-X bond breaks heterolytically both electrons
from the bond are taken by the halogen.
↪️The halogen falls off as the nucleophile bonds to the carbon.
5) There are three examples of nucleophilic
substitution you need to know.
↪️halogenoalkanes react with aqueous KOH to form alcohols
↪️cyanide ions react with halogenoalkanes to form nitriles
↪️halogenoalkanes react with ammonia to form amines

Answer 89

A

1) halogenoalkanes react with hydroxide ions by nucleophilic substitution to form alcohols. You can use warm aqueous potassium hydroxide and do the reaction under reflux, otherwise it won’t work
2) here’s the general equation for the reaction: R-X + KOH -> ROH + KX
↪️R represents an alkyl group. They’re alkanes with on H removed, e.g. -CH3, -C2H5. X stands for one of the halogens (F, Cl, Br or I).
3) here’s how the reaction happens:
➡️the C-Br bond is polar. The C delta+ attracts a lone pair of electrons from the OH- ion.
➡️the C-Br bond breaks heterolytically, and a new bond forms between the C and the OH- ion
➡️the charges of each step has to balance - here, each step has an overall charge of -1
4) you can use water to hydrolyse halogenoalkanes and form alcohols. Water is a worse nucleophile than hydroxide ions, so the reaction with water is slower

Answer 90

A

If you regular a halogenoalkane with potassium cyanide in ethanol, then the cyanide ions react with the halogenoalkane by nucleophilic substitution to form a nitriles
R-X + CN- -> R-C≡N + X-
↪️this results in the length of the carbon chain increasing by one

Answer 91

A

1) Amines are organic compounds. They’re based on ammonia (NH3), but one or more of the hydrogen atoms are replaced by alkyl groups.
2) If you warm a halogenoalkane with excess ethanolic ammonia, the ammonia swaps places with the halogen to form a primary amine - yes, it’s another one of those nucleophilic substitution reactions.
↪️the first step is the same as in the mechanisms on the previous page, except this time the nucleophile is NH3
↪️in the second step, an ammonia molecule removes a hydrogen from the NH3 group to leave an amine

Answer 92

A

1) if you react a halogenoalkane with a warm alkali dissolved in ethanol, you get an alkene. The mixture must be heated under reflux or volatile stuff will be lost.
C2H5Br + KOH -> C2H4 + H2O + KBr
2) in elimination reactions,, the hydroxide ions are acting as a base to remove H+ ion from the halogenoalkane

Answer 93

A

An alcohol is primary, secondary or tertiary, depending on which carbon atom the -OH group is bonded to

Answer 94

A

alcohols can react in substitution reactions to form halogenoalkanes

1) If you react an alcohol with phosphorus pentachloride (PCI), a chloroalkane is produced. The general equation for this reaction is:

ROH + PCI5 → RCI + HCI + POCI3

2) You can also make chloroalkanes if you react an alcohol with hydrochloric acid.
The general equation for this reaction is:
ROH + HCI → RCI + H2O
3) For example, 2-methylpropan-2-ol reacts with hydrochloric acid
at room temperature to form 2-chloro-2-methylpropane:

(CH3)3COH + HCI → (CH3)3CCI + H2O

4) The reaction between alcohols and hydrochloric acid is fastest if the alcohol is a tertiary alcohol, and slowest if it is a primary alcohol (the rate for secondary alcohols is somewhere in between).

Answer 95

A

1) Alcohols will react with compounds containing bromide ions (such as KBr) in a substitution reaction.
2) The hydroxyl (-OH) group is replaced by the bromide, so the alcohol is transformed into a bromoalkane.
3) The reaction also requires an acid catalyst, such as 50% concentrated H2SO4

Answer 96

A

1) You can make an iodoalkane from an alcohol by reacting it with phosphorus triiodide (PI)3
2) Pl3 is usually made in situ (within the reaction mixture) by refluxing the alcohol with ‘red phosphorus’ and iodine.
3) This is the general equation:
3ROH+ PI3 -> 3RI + H3PO3

Answer 97

A

1) You can make alkenes by eliminating water from alcohols in an elimination reaction.
2) The alcohol is mixed with an acid catalyst such as concentrated
phosphoric acid (H3PO4). The mixture is then heated.
3) When an alcohol dehydrates it eliminates water. E.g. Ethanol dehydrates to form ethene.
C2H5OH → CH2=CH2 + H2O
4) The water molecule is made up from the hydroxyl group and a hydrogen atom
that was bonded to a carbon atom adjacent to the hydroxyl carbon.
5) This means that often there are two possible alkene products from one elimination reaction depending on which side of the hydroxyl group the hydrogen is eliminated from.
6) Also, watch out for if any of the alkene products can form E/Z isomers - if they can then a mixture of both isomers will form.

Answer 98

A

It doesn’t take much to set ethanol alight and it burns with a pale blue flame. The C-C and C-H bonds break and ethanol is completely oxidised to make carbon dioxide and water. This is a combustion reaction.
C2H5OH(l)+ 302(g)→ 2CO2(g) + 3H2O(g)
If you burn any alcohol along with plenty of oxygen, you get carbon dioxide and water as products.
But if you want to end up with something more interesting, you need a more sophisticated way of oxidising…

Answer 99

A

You can use the oxidising agent acidified dichromate(VI) (Cr2O7 2-/H+, e.g. K2Cr2O7/H2SO4) to mildly oxidise alcohols.
• Primary alcohols are oxidised to aldehydes and then to carboxylic acids.
• Secondary alcohols are oxidised to ketones only.
• Tertiary alcohols won’t be oxidised.
The orange dichromate (VI) ion is reduced to the green chromium(III) ion, Cr3

Answer 100

A

aldehydes and ketones have a functional group C=O and a general formula CnH2nO
aldehydes have a hydrogen and one alkyl group attached to the carbonyl carbon atom
E.g. propanal ~ CH3CH2CHO
ketones have two alkyl groups attached to the carbonyl carbon atom
E.g. propanone ~ CH3COCH3

Answer 101

A

Use a Benedict’s solution. It’s a blue solution of complexed copper (ll) ions dissolved in sodium carbonate. If it’s heated with an aldehyde the blue copper (ll) ions are reduced to a brick red precipitate of copper (l) oxide. If it’s heated with a ketone, nothing happens as ketones can’t be oxidised easily.

Answer 102

A

1) Gently heating ethanol with potassium dichromate(VI) solution and sulfuric acid in a test tube should produce “apple” smelling ethanal (an aldehyde). However, it’s really tricky to control the amount of heat and the aldehyde is usually oxidised to form “vinegar” smelling ethanoic acid.
2) To get just the aldehyde, you need to get it out of the oxidising solution as soon
as it’s formed. You can do this by gently heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus, so the aldehyde (which boils at a lower temperature than the alcohol) is distilled off immediately.
3) To produce the carboxylic acid, the alcohol has to be vigorously oxidised. The alcohol is mixed with excess oxidising agent and heated under reflux.

Answer 103

A

1) refluxing a secondary alcohol e.g. propane-2-ol, with acidified dichromate (VI) will produce a ketone
2) ketones can’t be oxidised easily, so even prolonged refluxing won’t produce anything

Answer 104

A

Burning them

Answer 105

A

1) Organic reactions are slow and the substances are usually flammable and volatile (they’ve got low boiling points). If you stick them in a beaker and heat them with a Bunsen burner they’ll evaporate or catch fire before they have time to react.
2) You can reflux a reaction to get round this problem.
3) The mixture’s heated in a flask fitted with a vertical Liebig condenser this continuously boils, evaporates and condenses the vapours and recycles them back into the flask, giving them time to react.
4) The heating is usually electrical hot plates, heating mantles, or electrically controlled water baths are normally used. This avoids naked flames that might ignite the compounds.

Answer 106

A

1) Distillation works by gently heating a mixture in a distillation apparatus. The substances will evaporate out of the mixture in order of increasing boiling point.
2) The thermometer shows the boiling point of the
substance that is evaporating at any given time.
3) If you know the boiling point of your pure product, you can use the thermometer to tell you when it’s evaporating and therefore when it’s condensing.
4) If the product of a reaction has a lower boiling point than the
starting materials then the reaction mixture can be heated so that
the product evaporates from the reaction mixture as it forms.
5) If the starting material has a higher boiling point than the product, as long as the temperature is controlled, it won’t evaporate out from the reaction mixture.
↪️Sometimes, a product is formed that will go on to react further if it’s left in the reaction mixture.
↪️For example, when you oxidise a primary alcohol, it is first oxidised to an aldehyde and then oxidised to a carboxylic acid. If you want the aldehyde product, then you can do your reaction in the distillation equipment. The aldehyde product has a lower boiling point than the alcohol starting material, so will distil out of the reaction mixture as soon as it forms. It is then collected in a separate container.
6) If a product and its impurities have different boiling points, then distillation can
be used to separate them. You use the distillation apparatus shown above, but this
time you’re heating an impure product, instead of the reaction mixture.
7) When the liquid you want boils (this is when the thermometer is at the boiling point of the liquid), you place a flask at the open end of the condenser ready to collect your product.
8) When the thermometer shows the temperature is changing, put another flask
at the end of the condenser because a different liquid is about to be delivered.

Answer 107

A

If a product is insoluble in water then you can use separation to remove any impurities that do dissolve in water such as salts or water soluble organic compounds (e.g. alcohols). 1) Once the reaction to form the product is completed,
pour the mixture into a separating funnel, and add water.
2) Shake the funnel and then allow it to settle. The organic layer and the aqueous layer (which contains any water soluble impurities) are immiscible, (they don’t mix), so separate out into two distinct layers.
3) You can then open the tap and run each layer off into a separate container. (In the example on the left, the impurities will be run off first, and the product collected second.)

Answer 108

A

1) If you use separation to purify a product, the organic layer will
end up containing trace amounts of water, so it has to be dried.
2) To do this you can add an anhydrous salt such as magnesium sulfate (MgSO) or calcium chloride (CaCl2). The salt is used as a drying agent-it binds to any water present to become hydrated.
3) When you first add the salt to the organic layer it will be lumpy. This means you need to add more. You know that all the water has been removed when you can swirl the mixture and it looks like a snow globe. 4) You can filter the mixture to remove the solid drying agent.

Answer 109

A

1) You can measure the purity of an organic, liquid product by looking at its boiling point.
2) If you’ve got a reasonable volume of liquid, you can
determine its boiling point using a distillation apparatus,
like the one shown on the previous page.
3) If you gently heat the liquid in the distillation apparatus, until it evaporates, you can read the temperature at which it is distilled, using the thermometer
in the top of the apparatus. This temperature is the boiling point.
4) You can then look up the boiling point of the substance in data books and compare it to your measurement.
5) If the sample contains impurities, then your measured boiling point will be higher than the recorded value. You may also find your product boils over a range of temperatures, rather than all evaporating at a single temperature.

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Organic Molecules Flashcards

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