Organic Chemistry AS Level chemistry

water impact

global warming

Molecular formula

: The formula which shows the actual number of each type of atom

empirical formula

shows the simplest whole number ratio of atoms of each element in the compound

algebraic formula for a homologous series e.g. CnH2n

General formula

Displayed formula

show all the covalent bonds and atoms present in a molecule

Skeletal formula

A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.

formula that shows the arrangement of atoms in the molecule of a compound.

structural formula

Homologous series

Homologous series are families of organic compounds with the same functional

group and same general formula.

•They show a gradual change in physical properties (e.g. boiling point).

• Each member differs by CH2 from the last.

• same chemical properties.

alkane

CH3CH2CH2CH3

Alkenes

Hydrocarbons with one or more carbon-carbon double bonds

branched alkanes

Alkyl- (-yl)

Halogenoalkane

chloro-

bromo-

iodo-

Aldehydes

suffix -al

prefix formyl-

Ketones

suffix* -one

prefix oxo-

Carboxylic acids

suffix* -oic acid

Esters

-yl-oate

Alcohols

OH-

General rules for naming carbon chains

Count the longest carbon chain and name appropriately

Find any branched chains and count how many carbons they contain

Add the appropriate prefix for each branch chain

CH3

|

CH2

|

H3C - CH -- CH2 -- CH -- CH3

|

CH2

|

CH3

3,5-dimethylheptane

functional group rules

•When using a suffix, add in the following way :

If the suffix starts with a vowel- remove the -e from the stem alkane name

e.g. Propan-1-ol, butan-1-amine, ethanoic acid, ethanoylchloride, butanamide

If the suffix starts with a consonant or there are two or more of a functional group meaning di, or tri needs to be

used then do not remove the the -e from the stem alkane name

e.g. Propanenitrile, ethane-1,2-diol, propanedioic acid, propane-1,2,3-triol, pentane-2,4-dione.

skeletal formula for propane

skeletal formula for propene

methanoic acid skeletal formula

ethanal skeletal formula

propanone skeletal formula

1-chloropropane

displayed formula for 2,3-dibromopentane.

displayed formula for 2,3-dibromopentan

methylethanoate skeletal formula

ethanoic acid

Where can structural isomers arise from

Structural isomerism can arise from •Chain isomerism •Position isomerism •Functional group isomerism Same molecular formula different structures (or structural formulae)

chain isomer

Compounds with the same molecular formula but different structures of the carbon skeleton

position isomers

Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton

position isomer examples

propan-1-ol and propan-2-ol

functional group isomers

Compounds with the same molecular formula but with atoms arranged to give different functional groups

Homologous series

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

alkenes rules

The double bond will be between two carbons. Use the lower

number of the two to show the position of the double bond

The name for alkenes may include E or Z at start to show

the type of stereoisomer

If more than one double bond is present then suffix

ends diene or triene. The stem ends in a

The suffix-en for alkenes can go in front of other suffixes.

The alcohol and carboxylic acid groups have higher priority

than the alkene group so take precedence with numbering

alkanes rules

Class the halogen as a substituent on the C chain and use

the prefixes-fluoro,

-chloro,

-bromo, or-iodo. (Give the

position number if necessary)

2-bromobutane

alcohol

These have the ending-ol and if necessary the position

number for the OH group is added between the name

stem and the -ol

Ethane-1,2-diol

aldehydes

An aldehyde's name ends in-al

It always has the C=O bond on the first carbon of

the chain so it does not need an extra number. It is

by default number one carbon on the chain.

ketones

Ketones end in-one

When ketones have 5C's or more in a chain then

it needs a number to show the position of the

double bond. E.g. pentan-2-one

If two ketone groups then di is put before-

one and an e is added to the stem.

pentane-2,4-dione

What are stereoisomers?

Compounds with the same structural formula but with a different arrangement of the atoms in space. Stereoisomers have the same structural formulae but

have a different spatial arrangement of atoms.

Who can exhibit E-Z isomers and why

Alkenes can exhibit a type of isomerism

called E-Z stereoisomerism

E-Z isomers exist due to restricted

rotation about the C=C bond

When do E-Z isomers arise?

E-Z stereoisomers arise when:

(a) There is restricted rotation around the C=C double bond.

(b) There are two different groups/atoms attached both ends of the

E isomer

z isomer

Priority atom

The atom with the bigger

atomic number is classed as the priority atom

CIP Priority rules

1. Compare the atomic number of the

atoms directly attached to each side of the

double bond; the atom of higher atomic

number is given priority.

2. 2. If the atoms are the same, consider the

atoms at distance 2 from the double bond.

Make a list of each atom bonded to the one

directly attached to the double bond.

Arrange list in order of decreasing atomic

number. Compare the lists atom by atom; at

the earliest difference, the group containing

priority

the atom of higher atomic number is given

priority

chain isomer examples

butane and 2-methyl propane

Explain the differences between structural isomerism and stereoisomerism. Use

examples to show how compounds with the molecular formula C4H8 exhibit

stereoisomerism and the three types of structural isomerism.

Stage 1

Difference between structural & stereoisomers

1a structural isomers = molecules with same molecular formula but different

structure

1b stereoisomers = molecules with same structural formula but different

arrangement of atoms in space

Stage 2

Stereoisomers

2a lack of rotation around C=C

2b structures of E- and Z-but-2-ene

2c correct identity of E and Z isomers

Stage 3

Structural isomers

3a different C chain, e.g. methylpropene & but-1-ene / but-2-ene

3b different position of functional group e.g. but-1-ene & but-2-ene

3c different functional group, e.g. cyclobutane & but-1-ene / but-2-ene /

methylpropene

general formula for alkene

CnH2n

unsaturated

double bonds, so they tend to undergo addition reactions

what does a carbon double bond consist of

a sigma (2 s-orbitals) bond and

a pi bond (2 p-orbitals)

which area of double bond is vulnerable and why

the pi bond. They are therefore vulnerable to attack

by species which 'like' electrons: these

species are called electrophiles.

π bonds are exposed and have high electron density

what shape is the double bond

The arrangement of bonds around the

>C=C< is planar and has the bond angle 120o

in reaction with hydrogen bromide with alkenes, which is the electrophile

Electrophile, H(delta)+

which is attracted to who in reaction with hydrogen bromide with alkenes

The H δ + is

attracted to the

electron-rich pi bond

what sort of molecule is HBr

is a polar

molecule because

Br is more electronegative than H.

what is the intermediate formed in reaction alkene --> halogenoalkene

carbocation

What becomes a nucleophile alkene --> halogenoalkene

reaction of hydrogen bromide with alkenes

what will form when alkene is assymetrical (reaction of hydrogen bromide with alkenes)

This reaction can lead to two products when the alkene is unsymmetrical, 90% major product and 10% minor product

order of stability of carbocations

tertiary > secondary > primary

mechanism of markovnikov's rule

how is a product formed in electrophilic addition to alkenes

In electrophilic addition to alkenes, the major product is formed via the more stable carbocation intermediate

why is secondary carbocation more stable

Because it has two methyl groups releasing electrons towards the positive carbon

functional group

Functional group is an atom or group of atoms which when present in different molecules

causes them to have similar chemical properties

cycloalkanes and alkenes

aldehydes and propane

addition polymerisation

Addition polymers are formed from alkenes

Example of addition polymerisation

why are polymers unreactive

they are saturated

reaction of bromine with alkenes

Reagent: Bromine

Conditions: Room temperature (not in UV light)

Mechanism: Electrophilic addition

Type of reagent: Electrophile, Br+

3. Reaction of sulfuric acid with alkenes

Change in functional group

alkene alkyl hydrogensulfate

Reagents: concentrated H2SO4

Conditions: room temperature

Mechanism: Electrophilic addition

Type of reagent: Electrophile, H2SO4

CH2=CH2 + H2SO4 CH3CH2OSO2OH

Primary halogenoalkane

One carbon attached to the carbon atom adjoining the halogen

Secondary halogenoalkane

A halogenoalkane which has two carbon atoms directly bonded to the carbon atom that is bonded to the halogen.

Tertiary halogenoalkane

A halogenoalkane which has three carbon atoms directly bonded to the carbon atom that is bonded to the halogen.

Direct hydration of ethene

Ethene reacts with steam at a temperature of 300°C, a pressure of 65 atm (6500kPa) and in

the presence of a catalyst of either concentrated phosphoric acid or concentrated

sulphuric acid.

(CH2)2CHCH2CH3, structural formula, name

2-methylbut-1-ane

nucleophilic substitution reaction hydroxide ions

NaOH (AQ) + Heat.

Haloalkane + NaOH mixed in ethanol to make miscible

nucleophilic substitution cyanide ions

KCN + Heat

This reaction increases the length of the carbon chain (which is reflected in the name) In the above example butanenitrile includes the C in the nitrile group

which halogenoalkane is unreactive

The iodoalkanes are the fastest to substitute and the fluoroalkanes are the slowest. The strength of the C-F bond is such that fluoroalkanes are very unreactive

The rate of these substitution reactions depends on the strength of the C-X bond The weaker the bond, the easier it is to break and the faster the reaction

nucleophilic substitution with ammonia

HALOGENOALKANE to AMINE

Reagent: NH3 dissolved in ethanol

Conditions: heat under pressure

Mechanism: nucleophilic substitution

Type of reagent: Nucleophile, :NH3

CH3CH2Br + 2NH3 → CH3CH2NH2 + NH4Br

nucleophilic elimination

The formation of alkenes from haloalkanes happens when the same sodium or potassium hydroxide is used as before, but this time the conditions are alcoholic (dissolved in ethanol). This means an elimination mechanism occurs rather than the nucleophilic substitution seen previously. e.g. the formation of propene from 2-bromopropane

Chlorination of methane

Methane does not react with chlorine at room temperature, or in the dark. In the presence of

ultraviolet light, however, a mixture of methane and chlorine will explode forming hydrogen

chloride and a mixture of chlorinated methane's.

Free radical substitution mechanism's take place in several steps.

Initiation

The ultraviolet light (sunlight) provides the energy needed to break the Cl-Cl bond, splitting

some chlorine molecules into two atoms (radicals). This bond breaks as it is weaker than the

alternative C-H bonds

Propagation

In each step above, a radical is used and a new radical is formed, this leads to a chain

reaction as the process continues. Each step is exothermic so the chain reaction produces an

explosion.

The overall reaction is the sum of these two propagation steps.

Termination

When two radicals combine (the two individual electrons form a covalent bond) they form a

stable molecule and the reaction stops. Two possible termination steps are:

The second termination step forms an impurity of ethane that can be formed in this reaction.

Two chlorine atoms (radicals) could recombine but this is not likely as they would just

separate again

draw the possible isomers for C5H12 (6)

draw chain isomers for c4h10

relative ease of substitution

the ease of substitution depends on bond enthalpy

Bond Enthalpy Table

bond enthalpy and bond strength

the lower the C-X bond enthalpy, the weaker the bond, the more reactive it is, the easier it is to substitute

uses of chloromethane

Halo alkanes have been used as anaesthetics, refrigerants, aerosol propellants, insecticides

and solvents. Their use is now no longer encouraged or in some cases allowed as it has been

discovered that haloalkanes are toxic and some have negative effects on the atmosphere.

Toxicity of haloalkanes

1,1,1-trichloroethane, CH3CCl3, was used as a dry cleaning solvent to remove grease on

clothes and also as the thinner in tippex. Tetrachloromethane (carbon tetrachloride), CCl4,

was also used by dry cleaners and as a solvent. Both of these compounds are now considered

so toxic that their use is banned.

what are CFCs

A chlorofluorocarbon or CFC is a compound where all of the hydrogen atoms have been

replaced with either a chlorine or fluorine atom as in the examples below.

trichlorofluoromethane, CCl3F.

dichlorodifluoromethane, CCl2F2

why are CFCs unreactive

CFCs are very unreactive compounds due to the large amount of energy needed to break the

C-Cl or C-F bonds, (338kJmol-1 and 484kJmol-1 respectively). Their inertness and volatility

made them really useful as refrigerants and aerosol propellants. However it was eventually

discovered that their use caused a hole in the ozone layer in the upper atmosphere so their use

is now banned.

ozone

Ozone, O3, is an allotrope of oxygen. It is formed when ultraviolet radiation from the sun

breaks down oxygen molecules, O2, into two oxygen atoms (radicals). These oxygen radicals

then react with more oxygen to form ozone.

what will UV do to ozone

Ultraviolet radiation will decompose ozone into an oxygen molecule and oxygen radical. This

radical then further reacts with another ozone molecule reforming O2 molecules. This natural

cycle of reactions above results in harmful UV radiation from the sun being absorbed by the

ozone layer and hence much less of it reaches the Earth's surface.

However it was discovered, in the 1970s, that the ozone layer was much thinner over

Antarctica than expected due to the reaction of ozone with chlorine radicals in the upperatmosphere. These chlorine radicals were formed in the atmosphere as a result of the

breaking of C-Cl bonds in CFCs when exposed to UV radiation:

chlorines reaction with ozone

alcohol general formula

CnH2n+1OH

examples and properties of alcohols (SOME BONDING)

Methanol, ethanol, propanol, butanol

PERMANENT DIPOLE ACROS O-H BOND

VSHAPED, 104.5, water solubility

Fermentation

Ethanol is produced by fermentation which converts glucose into ethanol and carbon dioxide

by using yeast as a catalyst.

This reaction is carried out between 30-40°C (optimum temperature for the yeast) in an

oxygen free environment, anaerobic conditions, and in neutral pH.