UNSW School of Chemistry CHEM1021/CHEM1041/CHEM1061 Lab. Manual (Term 3, 2020) Page 99
Reactions of Organic Functional
Groups
Tasks
Pre–lab work (MUST BE COMPLETED BEFORE YOUR LAB CLASS) – get safety information for
the chemicals used in this laboratory class and read the introduction, experimental procedure etc. for the
class.
In the laboratory class you will:
• write a
ief summary of what you need to do to improve your lab work, based on your demonstrator's
comments on your previous report.
• have your demonstrator check that you have written out the hazards of the chemicals used in this lab
class (if you haven't done this, you won't be allowed to do the experiment).
• complete a worksheet about organic functional groups.
• complete the 'Reactions of Organic Functional Groups' experiment.
• complete and submit the report for this lab class.
Main learning outcomes
At the end of this lab class you should:
• know the structures and names of several organic functional groups.
• be able to identify functional groups in a molecule.
• be able to write chemical equations for organic reactions.
Page 100 CHEM1021/CHEM1041/CHEM1061 Lab. Manual (Term 3, 2020) UNSW School of Chemistry
INTRODUCTION
Organic compounds can be classified according to their functional groups. The functional groups present in a compound
give the compound certain characteristic reactions, which allow it to be distinguished from other compounds. In this lab class
some characteristic reactions of simple functional groups (including alcohols, aldehydes, and ketones) will be examined.
Understanding the reactions of functional groups is important not only for identifying compounds but also for planning the
way compounds can be used in the synthesis of more complicated substances.
The table below lists some common functional groups where the rest of the molecule is written as –R, –R', etc.
When naming a molecule, many functional groups are identified by a suffix, often with a number in front of it to indicate
which ca
on atom the functional group is attached to. For alkyl halides, the halogen is named as a prefix, with a number
indicating which ca
on atom it is attached to. Esters have an alcohol part and an acid part and these are both in the name
(similar to an inorganic salt such as sodium sulfate, see example below).
Functional
Group
Lewis Structure Suffix Examples: Lewis structures, condensed formulae and names
alkene
ene
CH3CH=CHCH3 but–2–ene
alkyne yne HCºCCH2CH3 but–1–yne
alcohol ol
CH3CHOHCH2CH2CH3 pentan–2–ol
alkyl halide
(X is F, Cl, Br, or I)
–
CH3CHBrCH2CH3 2–
omobutane
aldehyde
al
CH3CHO ethanal
ketone
one
CH3CH2COCH2CH3 pentan–3–one
ca
oxylic
acid
oic acid
CH3CH2COOH propanoic acid
este
oate
CH3CH2COOCH3 methyl propanoate
amine amine
CH3CH(NH2)CH2CH3 butan–2–amine
amide
amide
CH3CH2CONH2 propanamide
ether –
CH3CH(OCH3)CH3 2–methoxypropane
C C
R
R'' R'''
R'
C C
H3C
H CH3
H
C C R'R C C CH3H
OHR
CH3-CH-CH2-CH2-CH3
OH
XR
CH3-CH-CH2-CH3
B
C
O
H
R C
O
H
H3C
C
O
R'R CH3-CH2-C-CH2-CH3
O
C
O
OH
R CH3 CH2 C
O
OH
C
O
O
R
R'
C
O
O
CH3-CH2
CH3
NH2R
CH3-CH-CH2-CH3
NH2
C
O
NH2R C
O
NH2CH2CH3
O R'R
CH3CHCH3
O CH3
UNSW School of Chemistry CHEM1021/CHEM1041/CHEM1061 Lab. Manual (Term 3, 2020) Page 101
There can be only one suffix in the name of a compound. There is a priority associated with each functional group, so that
the highest priority group is named as a suffix, and the other groups are named as prefixes. For example
CH3CH(NH2)CH2CH2OH is named 3–aminobutan–1–ol. The alcohol (–OH) group has a higher priority than the amine (it
is higher up the list of functional groups) so it takes the suffix and the amine is listed as a prefix (amino).
If a molecule contains a particular functional group then the molecule will be able to undergo chemical reactions associated
with that functional group. For example alkenes can react with
omine:
CH3CH=CHCH3 + Br2 ® CH3CHBrCHBrCH3
The same reaction is represented using condensed structures and Lewis diagrams above. This is an example of an addition
eaction. The two reactant molecules become joined by converting the double bond in one reactant into a single bond.
Another class of reactions are oxidation reactions. The definition of oxidation as a reaction where an atom or molecule loses
electrons is adapted in organic chemistry to refer to reactions where new ca
on – oxygen bonds form (and certain other bond
types too). When a ca
on – oxygen bond forms the ca
on atom partially loses electrons because the electrons in the new
ond are pulled towards the oxygen atom. Not all functional groups can be oxidized, and of those which can, some are more
easy to oxidize than others. Aldehydes are usually very easy to oxidize into ca
oxylic acids:
CH3CHO ® CH3COOH
Note the added C–O bond in the product of the reaction above. It is very common in organic chemistry to list only the organic
eactants and products in the equation, with any inorganic reactants listed over the a
ow. For the reaction above, the oxidizing
agent is the permanganate ion (MnO4–) in the presence of acid (H+). Ketones have a similar structure to aldehydes, but they
lack a hydrogen attached to the ca
on which is bonded to the oxygen. This makes ketones almost impossible to oxidize.
Some alcohols are also able to be oxidized, but this depends again on how many hydrogens are attached to the ca
on ca
ying
the –OH group. Alcohols with three ca
ons attached to the ca
on with the –OH (tertiary alcohols) are almost impossible to
oxidize (adding more C–O bonds to the C–OH would require
eaking ca
on–ca
on bonds). Alcohols with two ca
ons
and a hydrogen on the C–OH (secondary alcohols) are able to be oxidized to ketones and alcohols with one ca
on and two
hydrogens on the C–OH (primary alcohols) are easily oxidized to aldehydes and then to ca
oxylic acids. With many
oxidizing agents the ca
oxylic acid is the only product.
Alkyl halides can undergo substitution reactions where the halogen is displaced by an incoming species such as OH– or
CN–.
In a substitution reaction (and many other organic reactions) there may be no visible change during the reaction. The fact
that the reaction occu
ed can only be proven by subsequent reactions of the products. This applies to the substitution reaction
you will ca
y out in this experiment.
C C
H3C
H CH3
H
+ Br Br H3C C C CH3
Br B
H H
C
O
H
H3C
MnO4–/H+
C
O
OH
H3C
H3C C CH3
MnO4–/H+
CH3CH3C
OH
H
O
H3C CH2 C OH
H
H
MnO4–/H+
C
O
OH
CH2H3C
H3C CH2 OH–Br + H3C CH2 Br–OH +
H3C CH2 CN–Br + H3C CH2 Br–CN +
UNSW School of Chemistry CHEM1021/CHEM1041/CHEM1061 Lab. Manual (Term 3, 2020) Page 105
Materials Needed
cyclohexane
1-
omobutane
cyclohexene
utan-1-ol
propan-2-ol
2-methylpropan-2-ol
methanal (formaldehyde)
enzaldehyde
utanone
glacial acetic acid
utylamine (butan–1–amine)
2 M HNO3
2 M H2SO4
2 M HCl
2 M NaOH
5 M NaOH
0.1 M AgNO3
omine in CH2Cl2
0.02 M KMnO4
2 M NH3
1,6-diaminohexane
hexanedioyl chloride
litmus paper
semi-micro test tubes and racks
egular and large test tubes
squash pipettes
steam bath
disposable gloves
acetone (fume cupboard, for rinsing)
wire hook
watch glass
glass rod
non–halogenated organic waste container
halogenated organic waste container
heavy metals waste container
nylon waste containe
DISPOSE OF ALL ORGANIC WASTE IN THE FUME CUPBOARD
DO NOT discard waste organic substances in the sink. Dichloromethane residues (including
omine in dichloromethane) must be placed in the halogenated organic waste bottle in the
fume cupboard. Dispose of used gloves in the glove bin.
All test tubes must be clean for these tests. Use a wash bottle of acetone (in the fume cupboard)
to squirt a little acetone into the test tube and then empty the test tube into the non–halogenated
organic waste. Allow the acetone to evaporate to give a clean, dry test tube.
MANY ORGANIC COMPOUNDS ARE NOT MISCIBLE WITH WATER
The formation of two layers when you mix an organic compound with water is NOT an indication that
a reaction has happened. In this experiment you should be looking for colour changes, a precipitate,
dissolution of a solid or evolution of a gas as evidence of a chemical reaction.
Method – Part A (Reactions of alkanes, alkenes, alkyl halides)
Bromine addition reaction
1. Prepare three clean, dry semi–micro test tubes in an appropriate rack. In each test tube place 10 drops of
omine in
CH2Cl2 solution (this solution is prepared for you and is available in the fume cupboard). The CH2Cl2 is not a reactant
here, it is just a solvent for the
omine.
2. To test tube 1 add 10 drops of cyclohexane and shake well. To test tube 2 add 10 drops of cyclohexene and shake well.
Leave test tube 3 as a control. Observe if the colour of
omine fades immediately or does not fade by comparing test
tubes 1 and 2 with test tube 3. DO NOT HEAT. Record your observations along with appropriate equations.
Substitution reaction with an alkyl halide
1. Place 1-
omobutane (5 drops) in a clean regular size test tube. Add 2 M NaOH (15 drops) to this test tube and shake
the mixture vigorously. Heat the tube and contents in the steam bath for about 2 minutes with continual shaking.
2. At the end of the heating, acidify the mixture with 2 M HNO3 (checked using blue litmus paper on a watch glass with
a small amount of the solution picked up on a clean glass rod. DO NOT DIP LITMUS PAPER INTO SOLUTIONS).
3. Add 0.1 M AgNO3 dropwise and record any changes on your result sheet.
Silver
omide is insoluble, so the appearance of a white or creamy precipitate in step 3 is a positive test for
omide
ions in the solution. Record your observations and write the appropriate equation for each step in the procedure, in
particular explaining your observations at step 3.
Page 106 CHEM1021/CHEM1041/CHEM1061 Lab. Manual (Term 3, 2020) UNSW School of Chemistry
Method – Part B (Reactions of alcohols, aldehydes and ketones)
Oxidation reactions with Tollens' reagent ([Ag(NH3)2]
+)
TOLLENS TEST NEEDS CLEAN TEST TUBES
For the Tollens' reaction to