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					Organic 1

                                     A2 ORGANIC Chemistry

Isomerism & Naming organic compounds

    Naming compounds has been covered in the AS course – make sure you
     know how to name compounds using the IUPAC rules.
    Isomerism has been covered in the AS syllabus. Make sure you know the

      know and understand the meaning of the term structural isomerism
      know that E-Z isomerism and optical isomerism are forms of stereoisomerism
      know that an asymmetric carbon atom is chiral and gives
       rise to optical isomers which exist as non super-imposable
       mirror images and differ only in their effect on plane
       polarised light
      understand the meaning of the terms enantiomer and
      understand why racemates are formed
      be able to draw the structural formulae and displayed
       formulae of isomers
      Appreciate that drug action may be determined by the
       stereochemistry of the molecule and that different optical
       isomers may have very different effects e.g Thalidomide

Carbonyl Compounds
Compounds that contain the (C=O) functional group.

   -   Aldehydes & Ketones
   -   Carboxylic Acids
   -   Esters
   -   Anhydrides
   -   Acyl halides(chlorides)

Making Carbonyl compounds:

Aldehydes and Ketones
These are also known as carbonyl compounds and contain the carbonyl (C=O) functional group.

Functional Group:

                                 O              O
                                 C              C
                                     H      C    C
                         ALDEHYDE           KETONE
Organic 2

Primary and secondary alcohols may be oxidised using an oxidising agent such as acidified
potassium dichromate(VI) or acidified potassium manganate(VII).

Primary Alcohols
Primary alcohols are oxidised first of all to an aldehyde (partial oxidation) and then the aldehyde is
oxidised further to a carboxylic acid (complete oxidation).
                                                                          Carboxylic acids have the
                      Cr2O72-/H+               Cr2O72-/H+                              O
          Primary                                         Carboxylic
                                  Aldehyde                                           C
          alcohol      HEAT                      HEAT     acid
                                                                                        O H
                          Aldehydes contain the                                functional group

                               functional group

Cr2O72- is the oxidising agent and is therefore reduced during the reaction. Cr 2O72- is orange and it
is reduced to the green Cr3+(aq) ion. The half equation for the reduction is:

        Cr2O72- + 14H+ + 6e-  2Cr3+ + 7H2O                  Colour change: ORANGE  GREEN

If the reaction mixture is heated under reflux ethanoic acid
is obtained as the main product and the aldehyde is not           Aldehydes have a lower boiling point
usually isolated. However, it is possible to set up the           than alcohols as they do not have an
experiment so that the aldehyde is distilled off as soon as       H attached directly to an O and
it is formed and before it can be oxidised further.               therefore do not participate in
                                                                  hydrogen bonding.

If we look at the reactions in terms of                                 O                     O
the functional group change it is easier          OH     Cr2O72-/H+              Cr2O72-/H+
to generalise the reaction to other                C H                  C                      C
molecules:                                               HEAT               H      HEAT            O H

Secondary Alcohols
Secondary alcohols are also oxidised by acidified potassium dichromate(VI). They are oxidised to
ketones, which cannot be oxidised any further.

                Cr2O72-/H+                                  Ketones contain the
Secondary                    Ketone                                 O
alcohol          HEAT                     HEAT                   C C C
                                                              functional group

In terms of functional group change the reaction can be represented as:

    OH          Cr2O72-/H+       O
C C         C                C C      C
Organic 3

Tertiary Alcohols
Tertiary alcohols are resistant to oxidation.

      H OH H
    H C C      C H                   No Reaction
      H CH3 H

Identification test for the carbonyl group
Addition-Elimination reactions
The reaction of aldehydes and ketones with 2,4-dinitrophenylhydrazine (2,4-DNPH) is an
example of an addition-elimination reaction and is used as a test for the presence of the carbonyl
(C=O) group in aldehydes and ketones.

                                                                                     Water is

This reaction may be used to distinguish aldehydes and ketones         Yellow-orange
from other species. The product of the reaction with aldehydes and
                                                                       crystals produced -
ketones is yellow/orange crystals.
                                                                       test for carbonyl
If the melting point of these crystals is determined and the values    group
compared with those in tables exactly which aldehyde/ketone was
originally present may be determined.
Draw out the structures of the organic products formed when the following
aldehydes/ketones react with 2,4-dinitrophenylhydrazine.

1      butanone

2      2-methylpentanal
Organic 4

Distinguishing between Aldehydes and Ketones.

Use is made of the oxidation reaction to tell the difference between Aldehydes (can be oxidised)
and ketones(cannot be oxidised)

   1. Tollens Reagent – ‘silver mirror’(Ag) Uses ammonical silver nitrate solution (AgNO3/NH3)

   2. Fehlings solution – Brick red precipitate (Cu2O) Uses copper(II) chloride in sodium
      hydroxide (CuCl2/NaOH)

Reduction of Aldehydes and Ketones (H)

Using (H- ion ) HYDRIDE ION , aldehydes and ketones can be reduced back into alcohols.

Reducing agent: sodium borohydride (NaBH4) or lithium aluminium hydride (LiALH4)

**(LiAlH4 reaction is carried out in a non aqueous environment at low temperature (exothermic))

*(NaBH4 can be carried out in water)

Reaction is an example of NUCLEOPHILLIC ADDITION
Carboxylic acids can also be reduced back into primary alcohols.

Organic 5

Aldehydes and ketones reaction with HYDROGEN CYANIDE (HCN)

Another example of ‘nucleophillic addition ‘ involving the carbonyl group involves reacting
aldehydes and ketones with hydrogen cyanide. The product is a HYDROXYNITRILE or

** (HCN is a very weak acid – In practice a KCN/H2SO4 solution is used)

NOTE!! KCN is extremely toxic!!! (HCN is also VERY toxic and flammable) Death = 100ppm


Nitrile groups may be hydrolysed to form a carboxylic acid:
                                          +   H2O/H reflux        CH3     C         + NH4+
              CH3    C N + H2O + H3O
                                                                              O H
Or – hydrolysis of a cyanohydrin:

Hydrolysis is also brought about by refluxing with aqueous alkali. In this case the product is the
salt of the acid and ammonia:
        OH                                                   OH
                                  H2O/OH reflux    CH3       C H      + NH3
CH3     C H + H2O + NaOH
                                    hydrolysis                    -   +
        CN                                                   COO Na
Organic 6

Carboxylic acids
                                                                         Functional Group:                   C
                                                                                                                 O H
                                                                             Boiling Point of carboxylic acids, aldehydes and alcohols
Physical properties of carboxylic                                  250

                                              Boiling point / oC

                                                                         0        20        40        60         80        100   120     140
                                                                                                 relative molecular mass

Lower relative molecular mass carboxylic acids are generally soluble in water because

However, the solubility decreases as the length of the hydrocarbon chain increases because

Carboxylic acids readily liberate CO2 from carbonate compounds

Carboxylic acids react with alcohols in the presence of an acid catalyst to give an ESTER.

Condensation Reactions
These are reactions in which two molecules join together with the elimination of the elements of
water. They are part of a more general class of reactions called addition-elimination reactions,
where molecules other than H2O are eliminated.

When an alcohol is heated with a carboxylic acid in the presence of a small amount of
concentrated sulphuric acid as a catalyst an ester is formed:

                                              conc H2SO4
        alcohol     +       carboxylic acid             ester                                     +        water
For example:

The alcohol and the carboxylic acid have been joined together and water has been eliminated – 1
H atom from the alcohol and –OH from the carboxylic acid molecule.
Organic 7

Complete the table:

            Alcohol           Carboxylic Acid                     Ester
                H H            O        H H H
            H C O                  C C C C H
              H              H O        H H H
            H H H H                      O
        H C C C O                  H C
            H H H                        O H
            H OH H            H H       H H     O
        H C C       C H     H C C       C C C
             H H H            H CH3 H H         O H
            H      H          H     CH3 H      O
                            H C     C    C C
    H    C      C   C   H
                              H     CH3 H      O H
            H   CH3 H

                                                                  O       H
                                                              H         C C CH3
                                                         H3C C O          H

                                                                    O      H H    H
                                                        H CH3 H         C C C     C H
                                                      H C C   C O          H H    H
                                                        H CH3 H

                                                                      O       H
                                                              CH3         C C H
                                                         H3C C      O         H
Organic 8

Naming Esters
Esters are named according to the carboxylic acid from which they are derived.
        O     H H                       O      H H H                          O   H
    H      C C C H          H H H          C C C C H                      H     C C CH3
H C O         H H       H C C C O              H H H                H3C C O       H
    H                       H H H                                         H

            O     H
                                             CH3                                 O     H H        H
       H        C C H                  O
                                   H C C C CH3                      H CH3 H          C C C        C H
 H3C C O          H                      H2
                               H C O   H                         H C C       C O       H H        H
                                 H                                  H CH3 H

Uses of esters
Esters often have a sweet-fruity smell and they are used as artificial flavours and odours. Other
uses are as plasticizers (added to polymers to make them easier to process and reduce
brittleness) and as solvents.
Animal Fats and Vegetable oils are esters of propane-1,2,3-triol (glycerol) and long chain
carboxylic acids (fatty acids). (Vegetable oils and animal fats can be hydrolysed to give soap,
glycerol and long chain carboxylic(fatty) acids)

Esters can be ‘HYDROLYSED’ back into carboxylic acid and alcohol. This is done by
heating(refluxing) with either an acid or a base (H2SO4 or NaOH)

Biodiesel is a mixture of methyl esters of long chain carboxylic acids

Vegetable oils can be converted into biodiesel by reaction with methanol in the presence of an
acid catalyst

Polyesters may be formed in a condensation polymerisation
                                                                    The type of polymerisation is
reaction when a dicarboxylic acid reacts with dihydric alcohol
                                                                    condensation polymerisation as
(alcohol with 2 –OH groups). It is the presence of two
                                                                    a water molecule is eliminated
functional groups on each monomer that allows the production
                                                                    each time two monomers are
of a polymer chain as an ester is formed on both sides of both
                                                                    joined together.
Organic 9

It can be seen from this reaction that, when four monomer molecules join together three water
molecules are produced. The total number of water molecules is always one less than the total
number of monomer molecules that join together.

If we then
look at a

The polymer chain as a whole can be represented by the unit shown in brackets in the equation.
This is called the repeat unit or repeating unit of the polymer. The whole polymer chain could be
built up by just joining these units together
Organic 10

From which monomers could the following polymers be formed?

  O H H O             H H H H H            O H H O           H H H H H                O H H O
  C C C C O C C C C C                  O C C C C O C C C C C                  O C C C C
      H H             H H H H H                H H           H H H H H                  H H

  O H H CH3 H H        O       H H CH3 H H      O H H CH3 H H        O       H H CH3 H H
  C C C C      C C     C O     C C C    C C O C C C C         C C    C O     C C C      C C O
     H H H      H H            H H CH3 H H           H H H    H H            H H CH3 H H

Acylation reactions – Reactions involving Anhydrides and Acid
Chlorides (Acylating agents)

Acid Anhydrides                                        O
                                                 R C
The basic structure of an acid anhydride is:           O
                                                 R C
This can be regarded as being formed from two molecules of carboxylic acid with water removed:

Naming acid anhydrides:
                           O                                                  O
                   H3C C                                            CH3CH2    C
                           O                                                      O
                   H3C C                                            CH3CH2    C
                           O                                                      O

Acid anhydrides are acylating agents, that is they react by adding the acyl
                                                                                          R C
group to other species. The reactions are called addition-elimination
Organic 11


Acid anhydrides react with nucleophiles:

1      Reaction with water
Acid anhydrides react violently with water to from carboxylic acids

2      Reaction with alcohols
Acid anhydrides react with alcohols to form esters.
Organic 12

Phenol does not react directly with acid anhydrides but must first be dissolved in sodium hydroxide
solution, to generate the phenoxide ion, which reacts readily with the anhydride to form an ester.

This reaction is used in the formation of aspirin from 2-hydroxybenzoic acid
       OH    O                                                            H3C C
             C                                                                  O       O

2-hydroxybenzoic acid                                                                   aspirin
** Ethanoic anhydride is used instead of ethanoyl chloride on an industrial scale because it is
cheaper, easier to handle, reacts more slowly and does not produce HCl as a by product.

3      Reactions with ammonia
When concentrated ammonia solution is added to an acid anhydride a primary amide is formed.

4      Reactions with amines
When acid anhydrides are reacted with amines substituted amides are formed.
Organic 13

This reaction is used in the formation of paracetamol.


                                                                H3C        N
                                                                       C        H

Draw out equations, using structural formulae for the following reactions:

1      Butanoic anhydride + ammonia

2      Propanoic anhydride + water

3      Ethanoic anhydride + 2-methylbutylamine
Organic 14

Acyl chlorides
The basic structure of an acyl chloride is:            R C
These are extremely reactive and react in basically the same way as acid anhydrides to add an
acyl groups to nucleophiles with the elimination of HCl.

1      Reaction with water
       Acyl chlorides react violently with water to from carboxylic acids

2      Reaction with alcohols
       Acyl chlorides react with alcohols to form esters.

Phenol does not react directly with acyl chlorides but must first be dissolved in sodium hydroxide
solution, to generate the phenoxide ion, which reacts readily with the acyl chloride to form an

*This reaction may also be used in the formation of aspirin from 2-hydroxybenzoic acid.
(Frequent exam question)
Organic 15

3      Reactions with ammonia
       When concentrated ammonia solution is added to an acyl chloride a primary amide is

4      Reactions with amines
       When acyl chlorides are reacted with amines substituted amides are formed.

The addition-elimination mechanism
The mechanism of these reactions involves two steps:
     1     initial addition of a nucleophile
     2     elimination of a molecule/ion
IB Further Organic Option 16

                               AROMATIC CHEMISTRY
Benzene and Aromatic compounds
Benzene has the formula C6H6 and is usually represented by a skeletal formula:
Compounds which contain a benzene ring are called aromatic whereas
compounds without benzene rings are called aliphatic.

When determining molecular formulae or condensed structural formulae for
compounds containing benzene rings it must be remembered that there is a C
and, if there is nothing else attached, an H atom at each vertex.

                           Therefore methyl benzene

                           Has the molecular formula

                           The condensed structural formula may be written as
                           C6H5CH3 or may be shown as a benzene ring with CH3

As long as a particular functional group is not attached directly to the benzene ring the
reactions of compounds containing a benzene ring will be basically the same as the reactions
encountered in other sections.

Benzene and Aromatic Compounds
The structure originally proposed for benzene (C6H6) was due to Kekulé:


The structure was accepted for many years but eventually the weight of evidence against it
became too great and a modified structure was proposed.

Evidence for a different structure of benzene:
X-ray crystallographic data
C-C bond lengths may be determined by x-ray crystallography.
    IB Further Organic Option 17

         Bond            Compound          Bond length
                                                         All C-C bond lengths are equal in
          C=C             ethene             0.133
          C-C             ethane             0.154
          C--C           BENZENE             0.139

                                                         cyclohexane (C6H12)
    Thermochemical evidence

                           +         H2                                H = -120 kJ mol-1

                            +        3H                                H =                 .



                       +           3H2                                 H = -207 kJ mol-1

    Actual benzene

                                                  Therefore actual benzene is 153 kJ mol-1 more
                                                  stable than “expected” if it were made up of 3
                                                  C=C double bonds.
IB Further Organic Option 18

Heat of Combustion Data
The enthalpy change for the combustion of Kekulé benzene may be worked out from the following
bond enthalpies:
                                 Bond               Energy /kJ mol-1
                                 C=C                     612
                               C=O (CO2)                 805
                                 O-H                     464
                                 O=O                     496
                                 C-H                     413
                                 C-C                     347

This value can be compared with the heat of combustion of actual benzene (in the gaseous state),
-3242 kJ mol-1.

The value for the extra stability of benzene here is not exactly the same as the value from
hydrogenation data. Why not? Which value is more reliable?

The “extra” stability of benzene comes from the

  delocalised 
  electron system
The spreading out of electrons (delocalisation) stabilises the molecule.
IB Further Organic Option 19

Reactions of Benzene
                               A feature of the extra stability associated with the benzene aromatic
                               ring is that benzene does not react like alkenes, i.e. it does not
                               undergo addition reactions under normal conditions (and will not
                               decolourise bromine water).
The stability of the aromatic ring means that it is regenerated in reactions, therefore benzene
undergoes SUBSTITUTION reactions.
e.g. benzene reacts with chlorine at room temperature in the presence of a catalyst such as
aluminium chloride:

Naming aromatic compounds
                         CH3                              NO2                           OH

                  O                                                                     O
                       C OH                                     Cl                       C CH3
Organic 20

Relative rates of nucleophilic substitution in halogenated benzene compounds

Chlorobenzene does not undergo nucleophilic substitution (hydrolysis) reactions with sodium
hydroxide under normal conditions.

Halogen atom
directly to the                +    NaOH                      NO REACTION under normal conditions

Chloroethane undergoes the reaction much more readily:

To all extents and purposes halogenated benzene compounds with the halogen atom
attached directly to the ring are inert to nucleophilic substitution.

                                              overlap of a lone pair on the halogen
                                             with the benzene  system.
                                              strengthens the C-Cl bond
                                              nucleophiles are repelled from the C
                                               attached to the Cl.

When the halogen atom is not attached directly to the benzene ring but is rather in the side-chain,
hydrolysis occurs much more readily, e.g.

          H        H
          C    C
               H Cl

What is the organic product formed when the following compound is heated with excess sodium
hydroxide solution

                   H H H
 Cl                C C C H
                       H Cl

Organic 21

Electrophilic Substitution Reactions

General mechanism

The Nitration of Benzene

                           Reflux 60 oC
                           conc. HNO                            The
              + HNO3                                  + H2O     electrophile is
                           conc. H SO4
                                  2                             the NO2+ ion

                                             pale yellow
     C6H6 + HNO3  C6H5NO2 + H2O

Formation of the
                                HNO3 + 2H2SO4  NO2+ + H3O+ + 2HSO4-

                                 Or    HNO3 + H2SO4  NO2+ + H2O + HSO4-
Organic 22

Chlorination of benzene

Overall equation:

Benzene does not react with halogens in the dark because the halogen molecule is non-polar.
Therefore a catalyst is required which polarises the molecule. The catalysts used are AlCl3 or
FeCl3, these are known as HALOGEN CARRIERS.
Aluminium chloride is electron deficient and accepts a pair of electrons from the Cl 2:

Formation of the electrophile         Cl2 + AlCl3  AlCl4- + Cl+


                                                                                  For bromination
                                                                                  FeBr3 would be

Alkylation (also known as Friedel Crafts alkylation)
Halogenoalkanes react with benzene in the presence of a halogen carrier catalyst:

Overall Reaction:

Formation of the electrophile:

The mechanism is the same as for halogenation.
Organic 23

Acylation (also known as Friedel Crafts acylation)
Acyl halides react with benzene in the presence of a halogen carrier:

Overall Reaction:

Formation of the electrophile:

The mechanism is the same as for alkylation.
Organic 24

Naming substituted benzene rings

When more than one group is present in a benzene ring the groups are first of all numbered to
give the lowest possible numbers and then in alphabetical order.

                           CH3                                                  CH3

                           CH3                               H3C

                           CH3                                                  CH3

                           Cl                               O2N


Organic 25

Reactions of methylbenzene
Methylbenzene reacts in the same way as benzene, via an electrophilic substitution mechanism.
The conditions for the reactions of methylbenzene are slightly milder than those for the reactions
of benzene and the methyl group is an activating group. The methyl group donates electron
density into the benzene ring (positive inductive effect). This increase the amount of electron
density in the ring so that it is more attractive to electrophiles and reacts more readily.

The methyl group is a 2,4-directing group and so the major products of substitution are:

Nitration of methylbenzene

The methylbenzene is heated under reflux with a mixture of concentrated sulphuric and
concentrated nitric acid:

Mono nitration occurs readily easily, further nitration is possible but because of the
deactivating effect of the nitro group the 2nd and 3rd nitrations are slow and more
difficult to achieve.

Multiple nitrated compounds:

2,4,6, trinitromethylbenzene(trinitrotoluene/TNT)

2,4,6 trinitrohydroxybenzene(trinitrophenol/picric acid)
Organic 26

Chlorination of methylbenzene

Methylbenzene is reacted with chlorine in the presence of a halogen carrier catalyst (AlCl 3) at
room temperature. This is chlorination in the ring.

If methylbenzene is reacted with chlorine in the presence of UV light then side chain substitution
occurs. This involves a free radical substitution mechanism as for alkanes.

Alkylation of methylbenzene

Methylbenzene is reacted with a halogenoalkane in the presence of a halogen carrier catalyst
(AlCl3) at room temperature.

Acylation of methylbenzene

Methylbenzene is reacted with an acyl chloride in the presence of a halogen carrier catalyst (AlCl3)
at room temperature.
Organic 27

***Reactions of Substituted Benzene Rings (NOT IN THE SYLLABUS)
Substituted benzene rings undergo basically the same reactions as a benzene ring, i.e.
electrophilic substitution. The nature of the substituent determines the position of further
substitution and the rate of the reaction relative to unsubstituted benzene.
Substituents on a benzene ring may be divided into two group: those which cause substitution
predominantly at positions 2 and 4 (and 6) (ortho and para) and those which cause substitution at
position 3 (and 5) (meta).

Substituents that cause substitution faster than with benzene are called activating groups and
those that cause substitution to occur more slowly than with benzene are called deactivating

                                                                        Rate of Substitution
  Substituent           Main Product of Halogenation
                                                                        relative to benzene
                                   CH3                  CH3

                       OH                OH                   OH
                             Cl                         Cl         Cl

                                         Cl                   Cl


      -NO2                                                                   SLOWER

 2,4-directing groups normally cause substitution faster than in benzene and 3-directing groups
 normally react more slowly than benzene

Rate of substitution
The rate determining step in the reaction is the attack of the electrophile on the ring. Attack, and
hence the reaction, occurs more quickly when there is more electron density in the ring so that an
electrophile is attracted more strongly. When the ring is deactivated by the withdrawal of electron
density the electrophile is attracted less strongly and reaction occurs more slowly.

Thus methylbenzene reacts more readily than benzene due to the electron-                   CH3
releasing effect of the -CH3 group (positive inductive effect).                            v
The methyl group activates the ring towards electrophilic substitution by donating
electron density into the ring. This makes the ring more negative, i.e. more
attractive towards electrophiles and the reaction occurs more quickly than with
Organic 28


        - Back to syllabus

Phenol is a significantly stronger acid than aliphatic alcohols such as ethanol
Dissociation of phenol:

                             +   H2O

   Consider the anion (phenoxide ion)
   Delocalisation of negative charge from O- into ring
   H+ not attracted back as strongly
   Anion (conjugate base) stabilised
   Greater dissociation
   Stronger acid

Delocalisation results in stabilisation of the anion, making it more likely to be formed than the
corresponding ion with ethanol, where no delocalisation can take place.
    OH       In general, for compounds of the form shown, if X (in any position) is an electron-
             withdrawing group the compound will be a stronger acid than phenol. The electron-
             withdrawing group reduces the amount of electron density on the O in the conjugate
             base – the charge is more delocalised in the anion – meaning that the H+ is less
             strongly attracted. If X is an electron-donating group the compound will be a weaker
    X        acid than phenol. In this case the charge is less delocalised in the anion – with the
             charge more localised on the O the H+ is attracted back more strongly.


The nitration of aromatic compounds, followed by the reduction of the nitro group to an amine are
the first steps to producing organic dyes.

Step 1. Nitration
Organic 29

Step 2. Reduction

Step3. Producing the diazonium salt

Step4. Making the Azodyes
Organic 30

Functional Group: -NH2 or -NHR or -NR2 or –NR3+

Solubility:               Lower members are soluble in water (H-bonding).                  HYDROGEN
                          Higher members increasingly less soluble.
Boiling Points:           Higher than alkanes of similar Mr (H-bonding) but lower than corresponding alcohols.

Nucleophilic Substitution:
                                                         conc. NH 3
             CH3       CH2Br + NH 3                                        CH3    CH2NH2   +   HBr
                                                    Heat in sealed tube

Further substitution is also possible to give secondary and tertiary amines and quaternary ammonium
salts(cationic surfactant).

Aliphatic amines can also be made by the reduction of nitriles:
(Nitriles made by substitution of haloalkane with CN-)

                                     (i)LiAlH4/dry ether then H2O
        CH3CN + 4[H]                                                  CH3CH2NH2
                                     (ii) H2 and Ni catalyst

             **Carbon chain extended by one carbon unit
Aromatic amines are made by the reduction of nitro compounds:

        C6H5NO2                                          C6H5NH2
                          (ii) H2/Ni

Functional Group:                    O
Organic 31

Solubility:            Soluble but solubility decreases as length of hydrocarbon chain
                       increases.                                                                  HYDROGEN
Boiling Points:        Solids except for methanamide. Higher boiling points than
                       corresponding carboxylic acids.

Acidity:               Very weakly basic

Basicity (General )
A base (Brønsted-Lowry definition) is a proton acceptor:
         B:    +   H+          HB+
The order of basicity for nitrogen-containing compounds is:
   Compound                    ethylamine                ammonia           phenylamine            ethanamide

      pKb                         3.33                     4.75                 9.38                  14.5
  Kb /mol dm-3                  5.4x10-4                 1.8x10-5              5x10-10               1x10-15
Amides are very weak bases and will not affect red litmus paper.

The base strength depends on:
                                         The charge on the N atom. A greater negative charge means
                                          that the H+ is more strongly attracted and the compound is a stronger

                                         The availability of the lone pair. The less available the lone
                                          pair for donation, the weaker the base.

Ethylamine is a stronger base than NH3 because of the electron-donating effect of the ethyl

                      -   H                       H                   ETHYLAMINE
    CH3       CH2 > N                               -
                                                                       alkyl group electron-donating
                           H                   H       H               N more -
                                                                       H+ attracted more strongly

Phenylamine and ethanamide are weak bases due to unavailability of the lone pair:
Organic 32

Delocalisation of the lone pair makes it less available for donation to H+

Amides: the N is also less - due to electron-withdrawing effect of the adjacent O atom

                                                                          Formation of SALTS
       NH3 + HCl  NH4+Cl-                                                Amines, like ammonia, form salts
                                                                          with acids, e.g.
       CH3NH2 + HCl  CH3NH3+Cl-
                    methylammonium chloride

Syntheses of amines actually often result in the formation of a salt.
                                                                           The free amine may be released
       CH3NH3+Cl- + NaOH  CH3NH2 + H2O + NaCl                             by adding a stronger base
The alkylammonium ion is acting as a Brønsted-Lowry acid.                  (e.g. NaOH)
Thus, if sodium hydroxide solution is added to a salt of an amine the free amine is released. This will be
noticed by a fishy smell or can be tested for by using moist litmus paper (amines are basic).

Peptides and Proteins
Peptides and proteins are naturally occurring polyamide polymers formed from amino acids ( bifunctional
                          (-amino acids) contain an amine and an carboxylic acid functional group.
2-amino acids
                           H           H    O
                                                             All 2-amino acids except glycine (aminoethanoic

                               N C C                         acid) are   optically active         (all naturally
                                                             occurring optically active amino acids in proteins
                           H           R   O H               are L-isomers)

                  H       H        O                                        H       H     O
                      N   C    C                                                N   C C
                  H       H        O H                                      H       CH3 O H
             AMINOETHANOIC ACID                                         2-AMINOPROPANOIC ACID
                   glycine                                                      Alanine
Organic 33

The carboxylic acid in amino acids donates it’s proton to the amine. This makes a doubly charged ion which
can act as both acid and base:

                                              + OH-

                              H2NCH2CO2H                     H3N+CH2CO2-
                                              + H+

At an intermediate pH it will exist as simultaneously as a cation and anion – Zwitterion. Each amino acid
has a unique pH value when this happens – Isoelectric pH. (The existence of the zwitterion makes amino
acids crystalline solids at room temperature)

Separating amino acids: simple chromatography is used to separate mixtures of amino acids, as they are
colourless compounds a staining agent is used to develop the chromatogram (ninhydrin) – amino acids stain
purple. This technique can be extended to a more sophisticated separative technique – Electrophoresis.

In living organisms enzymes catalyse the polymerisation of amino acids to form peptides and proteins:
                           H                               H         O
          H       O    H       O
                                                             N C C         H   O   +               H2O
            N C C    +   N C C
                                                           H   H      N C C
          H   H   O H H    CH3 O H
                                                                    H      CH3 O H
             SERINE               ALANINE                        a dipeptide
               CH2OH                                                                H     H
                   H                     H     H                  CH2OH O
           O                    O                             O                 C C N          +    H2O
             C C N           +    C C N                           C C N            CH3 H
         H O   H   H          H O   CH3 H                 H O        H      H

The dipeptides are different depending on which way round the amino acids are joined together.
The functional group present in peptides and proteins is an amide group called a peptide link.
Proteins are macromolecules (large long chain molecules) formed when amino acids polymerise. The
simplest level of protein structure is the sequence of the amino acids in the chain. This is known as primary
structure. There are 20 naturally occurring amino acids and, if just 100 are joined together to make a
polymer, there are 20100 combinations.

    H O          H O          H    O            part of a protein chain
    C C N C          C   N C       C    N
    R1       H R2        H R3           H
                                                There are three further levels of protein structure; secondary,
                                                tertiary, quaternary.
Organic 34

Addition Polymerisation


                                 C C

                                                      O2 200 oC
                                                       2000 atm.                 [ ]H H
                                                                                    C C
                                                                                    H H
                             MONOMER                                             POLYMER
                              Ethene                                             poly(ethene)

    H H          H H     H H          H H     H H        H H      H H       H H      H H        H H   H H
    C C          C C     C C          C C     C C        C C       C C       C C     C C        C C   C C
    H H          H H     H H          H H     H H        H H      H H       H H      H H        H H   H H

This is an example of addition polymerisation.

The mechanism is free radical addition involving opening of the double bond:

             C   C
                                      .   H H
                                          C   C
                                                  .            HOMOLYTIC FISSION
       H             H                    H H

PVC [Poly(vinylchloride)]

This is more properly known as poly(chloroethene)


                                      C   C

                                                      peroxide initiator     [ ]H Cl
                                                                                H H

                                 chloroethene                              poly(chloroethene)

Write an equation for the formation of poly(propene) and draw a length of the polymer chain showing three
repeat units.

** Addition polymers are non-biodegradeable
Organic 35

Condensation Polymerisation
The mechanism involved is addition-elimination, where a molecule of water is eliminated as each monomer is
linked to the chain.
                                                                  H H
       O                                  O
           C                          C              H O          C    C O H
 H O                                      O H                     H H
                                                                                              NEED 2 FUNCTIONAL
                                                                                              GROUPS ON THE
     benzene-1,4-dicarboxylic acid                          ethane-1,2-diol
                 CONDENSATION                        HEAT
                 POLYMERISATION                      acid cat.

                      [       O

                                  C                     C

                                                                  H H
                                                                  H H
                                                                                      + (2n-1)H O


                                  O                         O                 O                     O
                  H H                                             H H                                        H H
                                      C                 C                         C             C
             O    C       C       O                         O     C   C       O                     O        C   C O
                  H H                                             H H                                        H H

The functional group present is the            ester group and the polymer is a polyester.
In general, an diol and an dioic acid are required for formation of a polyester.
                      H H H H H H                                         O       H H H H                O
           NH2        C       C C         C    C C NH2                        C   C C     C    C C
                      H H H H H H                                     H O         H H H H                O H


                                                                      O       H H H H               O
                                      H H H H H H

                              [   N
                                      C     C C N
                                              C C
                                    H H H H H H H
                                                                          C   C C
                                                                              H H H H
                                                                                      C   C C
                                                                                                        ] n
                                                                                                        + (2n-1) H O
                                      NYLON-6,6                    amide link
Organic 36

        H H H H                                          O      H H H H           O    H H H H H H
O                         O    H H H H H H
    C C C C C C                                              C C C C C C               C C C C C C N
                               C C C C C C N
                          N                                     H H H H           N
        H H H H                H H H H H H H                                           H H H H H H H
                          H                                                       H

The functional group present is the amide group, therefore nylon is a polyamide.

** Condensation polymers are biodegradeable, the ester and amide link can be broken by acid hydrolysis (and bioorganisms)


       Know the arguments for and against the recycling of plastics
       The advent of biodegradable plastics
       Different methods used to dispose of plastics