Edexcel A Level Chemistry, topic 6: Organic Chemistry 1

What are the options for types of bonds around a carbon atom? (5)

Four single

Two single and one double

One single and one triple

Two double

Three single and one ionic

What is a hydrocarbon?

a compound made of hydrogen and carbon only

What is a general formula?

The simplest algebraic formula of a member of a homologous series

What is a homologous series? (3)

A series of organic compounds with the same functional group, but each successive member differing by CH2

What is a functional group?

a group of atoms responsible for the characteristic reactions of a particular compound.

What are the six different formulas used to represent molecules? (6)

Empirical

Molecular

Structural

Displayed

Skeletal

3D displayed

What is a structural formula? (2)

The minimal written detail that shows the arrangement of atoms in a molecule

What is the displayed formula?

Diagram showing the relative positioning of the atoms and bonds between them

What is a skeletal formula?

Diagram showing the bonds of the carbon skeleton only with any functional groups

General formula for alkanes

CnH2n+2

Functional group for alkenes

C=C

General formula for alkenes

CnH2n

Functional group of halogenoalkanes

-X, where X is a halogen

General formula for halogenoalkanes

CnH2n+1X

General formula for cycloalkanes

CnH2n

Functional group of alcohols

-OH

Suffix for alcohols (2)

-ol, or if another functional group is present a prefix of hydroxy-

Functional group for aldehydes

CHO

suffix for aldehydes

-al

Functional group for ketones

C=O

Suffix for ketones

-one

Functional group of carboxylic acids

COOH

Suffix for carboxylic acids

-oic acid

What does aliphatic mean?

Straight chain of carbons

What are the steps for naming an organic compound? (3)

Identify longest unbranded carbon chain to give stem name

Name any substituent groups, if more than one order alphabetically

Identify position of substituent groups

What are the rules for identifying the position of substituent groups? (4)

Count from the end that gives the lowest numbers

If two of the same on one carbon, repeat number and add di- as prefix to group

If more than one of same on diff carbons, number and add di-, tri- or tetra-

Commas between numbers, dashes between numbers and letters

What is the general formula of cycloalkanes?

CnH2n

What is the first member of the cycloalkane homologous series? (+formula)

Cyclopropane, C3H6

What is an unsaturated hydrocarbon?

Have at least one double or triple C-C bond

What is a saturated hydrocarbon?

Single C-C bonds only, alkane

What is an alkene?

An unsaturated hydrocarbon

What is the general formula of alkenes?

CnH2n

How is the naming of alkenes different from that of alkanes?

Must specify the location of the double bond

What is structural isomerism?

Compounds with the same molecular formula but different structural

What are the different types of structural isomerism? (3)

Carbon-chain isomers

Positional isomers

Functional-group isomers

What are carbon chain isomers? (+ one example) (5)

The length of the main carbon chain

Similar chemical properties because same functional group

Slightly different physical properties

More branches results in lower boiling point

Butane and methylpropane

What are positional isomers? (+ one example) (4)

The functional group is in a different location on the carbon framework

Similar chemical properties

Different physical properties

Propan-1-ol and propan-2-ol

What are functional-group isomers? (+ one example) (4)

A different functional group but same molecular formula

Different chemical properties

Different physical properties

Propanone and propanal

What is stereoisomerism? (1)

Atoms making up the isomers are joined in the same order but have a different arrangement

What must happen for a geometric isomer to be able to occur?(3)

There must be restricted movement somewhere in the molecule, often a double bond or in a cyclic compound

Why does a C=C bond result in the potential for geometric isomers? (3)

The pi bond formed by sideways overlap of p orbitals fixes the carbon atoms in position resulting in no free rotation

What is a trans isomer?

The priority groups are on opposite sides of the carbon chain

What is a cis isomer?

The priority groups are on the same side of the carbon chain

What is an E (entgegen) isomer?

The priority groups are on opposite sides of the carbon chain

What is a Z (zusammen) isomer?

The priority groups are on the same side of the carbon chain

When can cis/ trans or E/ Z notation be used in isomers?

When there is a priority and a non priority group on each side of the double bond

How do you identify a priority group (in the context of isomerism)?

The priority group has the largest atomic mass

What is the effect of geometric isomerism on physical properties?(2)

Z (cis) isomer has a higher boiling point

E (trans) isomer has a higher melting point

Why do Z isomers have higher boiling points than E?(2)

Both have same number of electrons (so Wan der Vaals the same) but Z isomers can be polar because they aren’t symmetrical

Why do E isomers have higher melting points than Z?(3)

The straighter shape of E isomers mean they can pack better than the U of Z isomers so intermolecular forces between Z isomers aren’t as strong as they should be

What is an addition reaction?

A molecule with a C=C double bond reacts with an other molecule to form one product

What is an elimination reaction?

A small molecule is lost from a larger molecule to produce two molecules, one with a C=C double bond

What is a substitution reaction?

An atom or small group is lost from a molecule to be replaced by a different atom or group

What is a hydrolysis reaction?

A covalent bond in a molecule is broken by adding a molecule of water, slitting it into two parts

What is heterolytic fission?(3)

When the covalent bond breaks, both electrons go to one species to form a cation and an anion (X-Y → X+ + Y-)

What is homolytic fission?(3)

When the covalent bond breaks, one electron goes to each species to form two radicals (X-Y → .X + .Y )

What do dots before a chemical symbol indicate?

Unpaired electrons

What a free radical substitution reaction?(3)

An atom or group in a molecule is replaced by a free radical, producing another free radical

What is a radical?

A species with an unpaired electron

What is the the first step of a free radical substitution reaction?

Initiation

Describe the initiation step of a free radical substitution reaction (using CH4 and Cl2 as examples)(4)

UV light provides energy to split Cl2 into free radicals by homolytic fission

Waves must be of a high enough energy to break the sigma (σ) bond

The radicals are so unstable that no more energy is needed

A chain reaction forms

A Cl-Cl bond breaks feather than a C-H because is has a lower bond enthalpy

What is the second step of a free radical substitution reaction?

Propagation

Describe the propagation step of a free radical substitution reaction (using CH4 and Cl2 as examples)(6)

The free radicals from the initiation step react with CH4 to form HCl and a .CH3 radical

Then the new .CH3 radical reacts with a Cl2 molecule to form CH3Cl and another .Cl radical

The new .Cl radical can now trigger another set of reactions

Unwanted side reactions also occur:

.Cl + .Cl → Cl2

.Cl + .CH3 → CH3Cl

.CH3 + CH3 → C2H6

What is the third step of a free radical substitution reaction?

Termination

Describe the termination step of a free radical substitution reaction (using CH4 and Cl2 as examples)(7)

As the concentration of Cl2 and CH4 falls, more free radicals react with each other

More side reactions

.Cl + .Cl → Cl2

.Cl + .CH3 → CH3Cl

.CH3 + CH3 → C2H6

Slows Down main reaction

When there are no radicals left, the reaction stops

What is the evidence for the free-radical mechanism?(using CH4 and Cl2 as examples)(2)

Production of C2H6 as a minor byproduct

Need for high frequency UV waves to produce 2.Cl from Cl2

What are the limitations of a free radical substitution reaction to produce the major product?

Will not just produce the desired product

Produces a range of side products (may not be useful)

What are the by products of the free radical substitution of CH4 and Cl2?(3)

Cl2

CH3Cl

C2H6

What is the hybridisation of orbitals in alkenes?(3)

One s-orbital and two p-orbitals combine to form three new sp² orbitals

All three are equivalent

Remaining p-orbital is unchanged

How do carbon atoms form double bonds?(3)

Hybridised sp² orbitals (one form each C) overlap to form a single C-C bond (σ bond)

2p orbitals overlap to form the second bond (π bond)

For maximum overlap, 2p orbitals overlap in a line

What are the main reactions of alkenes?(5)

Hydrogenation

Halogenation

Hydration

Addition of hydrogen halides

Oxidation to diols

What is common in all reactions of alkenes?(3)

Opening of a double bond to form a saturated product

Addition reactions

High electro density in the π bond attracts electrophiles

What is hydrogenation?

Electrophilic addition of H2 to an alkene across the C=C double bond

What are the conditions of hydrogenation?

Hydrogen gas

Nickel catalyst

150 degrees C

What are some of the uses of hydrogenation?(4)

Manufacturing margarine

Reduces the number of double bonds in polyunsaturated veg oils and fats

Increases solidity of the fat so easier for use in cooking

Produces partially hydrogenated oil/fat

What is halogenation?(3)

Electrophilic addition of a halogen to alkene across the C=C double bond

Often with bromine water to test for double bonds

Forms dihalogenoalkane

What are the conditions for halogenation?

Room temp

What is an electrophile?

An electron deficient species that can accept a lone pair of electrons

What is the meaning of curly arrows in reaction mechanisms?(2)

Show the movement of a pair of electrons

Always from an electron pair or a double bond

Describe the mechanism for halogenation (use bromine and ethene as examples)(8)

As Br2 approaches the C=C bond, high electron density of the bond induces a dipole in Br2

Delta positive Br in now an electrophile

A pair of electrons from C=C are accepted by the electrophile (this is electrophilic attack)

C=C bond breaks to accept Br atom

Br-Br bond breaks through heterolytic fission

Creates a Br- ion and a carbocation intermediate

Br- will now attack C+ to form a second bond

Creates 1,2-dibromoethane

What is the general term for an oxidising agent?

[O]

Describe addition using acidified manganate (vii) (5)

An alkene reacts with water and an oxidising agent

Cold, dilute, acidified manganate (vii) used as a catalyst

Double C=C bond is oxidised to form a diol (two OH groups)

O of OH provided by MnO4- and water

H of OH provided by water

What is hydration of an alkene?

Alkene reacts with steam to form an alcohol

What are the conditions of hydration?

Concentrated phosphoric acid catalyst

600 K

6MPa (pressure)

Describe the mechanism for electrophilic addition of a hydrogen halide (use hydrogen bromide and propene as examples)

As HBr approaches the C=C bond, high electron density of the bond induces a dipole in HBr

Delta positive H in now an electrophile

A pair of electrons from C=C are accepted by the electrophile (this is electrophilic attack)

C=C bond breaks to accept H atom

H-Br bond breaks through heterolytic fission

Creates a Br- ion and a carbocation intermediate

Br- will now attack C+ to form a second bond

Creates 2-bromopropane as major product

When is there more than one possible addition product in electrophilic addition with an alkene?

If the alkene is unsymmetrical

What are the three types of carbocations (+explain)?

Primary: C+ is bonded to one other C atom

Secondary: C+ is bonded to two other C atoms

Tertiary: C+ is bonded to three other C atoms

What is the most stable type of carbocation?

Tertiary

What will the major carbocation intermediate be in an electrophilic addition reaction?

The one where the C+ is bonded to the highest number of other C atoms (the most stable one)

Why are tertiary carbocations more stable than secondary etc?

More alkyl groups 'push' the electrons in the covalent bonds towards the C+, stabilising it

State Makovnikov's rule

When compound HX is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon atom with the most hydrogen atoms attached to it

How are radicals formed?

By homolytic fission of a covalent bond

What is crude oil?(4)

Mixture of hydrocarbons, mainly alkenes

Varying viscosities, volatilities and carbon chain length

All dissolved in each other

Not very useful in raw form so must be separate and processed

What is fractional distillation?

Process of separating a mixture into different components (fractions) based on boiling points.

Describe the fractional distillation of crude oil (4)

Heated crude oil is led into a fractionating column

Decreases in temperature the further you go up

As soon as crude oil reaches the fractionating column, each fraction will evaporate

Once cool enough, each fraction will condense and fractions can be collected

What is cracking?(3)

Vaporising and breaking up large hydrocarbon molecules into smaller, more useful alkanes and alkenes

Combust more cleanly and are more volatile

Either high pressure and temperature with no catalyst, of lower pressure and temperature with a zeolite catalyst (500 degrees C)

What is reforming?(3)

Turning small hydrocarbons (often 5-10 carbon atoms) into cyclic hydrocarbon and hydrogen

Changes physical and chemical properties

Requires high pressure, temperature and either platinum or rhenium catalyst

What is a catalytic converter?(2)

Exhaust emission control system

Reduces toxic gases and pollutants form an internal combustion engine into less toxic pollutants by catalysing redox reaction

How do catalytic converters work?(3)

Reduce nitrogen oxides into N2 and O2

Oxidise CO into CO2 and water

Require oxidative and platinum or rhodium catalyst

What are alternative fuels?

Any material or substance that can be used as a fuel, other than conversational fuels such as fossil fuels and nuclear material