Organic Chemistry
Chemistry A.S. 2.5 (91165)
4 External credits
Organic Chemistry
The branch of chemistry that deals with
carbon compounds.
– fats, proteins, carbohydrates
– fabrics
– wood and paper products
– plastics
– medicinals
Carbon has four valence
electrons
C
1s2, 2s2, 2p2
Carbon forms four single covalent
bonds by sharing electrons with
other atoms.
H
HCH
H
Carbon forms four single covalent
bonds by sharing electrons with
other atoms.
H
HCH
H
The bonds between carbon and
other atoms are often drawn at right
angles.
H
HCH
H
Actually the angle between the
bonds is 109.5o
Hydrocarbons
• Hydrocarbons are compounds composed entirely of carbon
and hydrogen atoms bonded to each other by covalent bonds.
• Saturated hydrocarbons have only single bonds between
carbon atoms.
C C
• Unsaturated hydrocarbons contain a double or triple bond
between two carbon atoms.
C C
C C
Groups of Hydrocarbons
carbon to carbon
single bonds
carbon to carbon carbon to carbon
double bonds
triple bonds
19.3
Alkanes
• Alkanes are saturated hydrocarbons.
• They are straight or branched-chain
hydrocarbons.
• There are only single covalent bonds between
the carbon atoms.
• Each successive member of the alkane series
differs from the next by a CH2 group.
• Successive members are similar in structure
but differ in formula.
The general formula of alkanes is CnH2n+2
If n = 7 formula = C7H16
Names of Straight-chain Alkanes
Formula
• Molecular – gives the type and number of each
atom
– e.g. C2H6
• Structural – shows how each atom is balanced
in molecule H H
– e.g.
H
C
C
H
H
H
• Condensed structural – abbreviated structural
formula
– e.g. CH3CH3
Carbon Bonding
Long chains of carbon atoms form by linking one carbon
atom to another through covalent bonds.
C
C
C
C
C C
C
C
C
C
nine carbon chain
C
Carbon Bonding
Chains of carbon atoms
may also form branches by
linking one carbon atom to
another through covalent
bonds.
C
C
nine carbon
branched chain
Covalent
network solids
like diamond and
graphite are
formed like this
C
C
C
C
C
C
C
Functional Groups
Hydrocarbons often have the following functional
groups
•
•
•
•
•
R
C=C
CΞC
Halogens F, Cl, I, Br
-OH
•
•
•
•
•
Represents an alkyl
Alkene
Alkyne
Form haloalkanes
Form alcohols
O
• -COOH
• -NH2
C
O
H
• Form carboxylic acid
• Form amines
O
• -COO
C
O
• Form esters
Naming Alkanes
1. Identify the longest C chain and any groups
2. Write number for the functional group(s) keep
the numbers as small as possible
3. Write name of group(s) alphabetically
4. Use di, tri, tetra to distinguish identical
branches
5. Write prefix for long chain
6. Finish with –ane.
2-chloro pentane
CH4
There is 1 possible
structure for CH4.
H
line
space
structure
filling
form of
methane
H C H
H
19.4
19.4
CH3CH3
There is 1 possible
structure for C2H6.
H H
space
filling
line
structure
form of
ethane
H C C H
H H
19.4
CH3CH2CH3
There is 1 possible structure
for C3H8.
line
space
structure
filling
form of
propane
H H H
H C C C H
H H H
19.4
CH3CH2CH2CH3
There are 2 possible structures
for C4H10
line structure
space
filling
form
of
form butane
of butane
H H H H
H C C C C H
H H H H
unbranched chain
19.4
CH3
CH2CHCH3
H H
H
H C H
space
filling
line
structure
form of methyl
propane
branched chain
branched chain
H C C C H
H H H
19.4
There are 2 possible structures
for C4H10.
Structural (constitutional) Isomers
• The properties of an organic substance are dependent
on its molecular structure.
normal butane
H H H H
(n-butane)
b.p. 0.5CoC
4H10
m.p. -138.3oC
H C C C C H
Isomers are compounds with
Normal butane and 2-methyl
the same molecular formula but
propane are isomers.
different structural formulas.
H H H H
H H
H
H C H
methyl propane
C
4H10-159.5oC
m.p.
H C C C H
b.p. -11.7oC
H H H
Draw the structural isomers of Pentane
(C5H12).
This is the is
Hydrogen
carbon
addedskeleton
to each carbon
with theto
longest
form
four
continuous
bonds. carbon chain. It is
the first isomer of pentane.
H H H H H
H C C C C C H
H H H H H
pentane
Pentane (C5H12) has 3 isomers.
Hydrogen
Add
the fifth
added
carbon
toatom
each
to
carbon
either
toof
To form
theis next
isomer
write
a four
the
form
middle
four
bonds.
carbon atoms.
carbon
chain.
H
H
H
H C H
C H
H C C C C H
H H H H
2-methylbutane
Pentane (C5H12) has 3 isomers.
Hydrogen
addedisomer
to each
carbon
To form
Add
the remaining
theis third
two
carbon
write
aatoms
3 to
form
bonds.
carbon
to
thefour
central
chain.
carbon atom.
H
H
H
H C
H C C C H
H C H
H
H
H
2,2-dimethylpropane
Cycloalkanes
• Draw and name the
structural isomers of C4H8
• Did you get all 3?
• But -1-ene
• But -2- ene
• Cyclobutane
• Cycloalkanes have the
same general formula as
alkenes CnH2n
• Chains longer than 4C’s
can form cyclic molecules
• Alkyl side chains maybe
attached
• Name the side chain first
then the cyclic group
• Ethyl-cyclopentane
Physical Properties of Alkanes
•
•
•
•
•
Colourless
Soluble in water? Why?
Non-polar
Like dissolves like – solvents
Less dense than water so
they float
• Conductors? Why?
• No free charged particles
Physical Properties of Alkanes
• What is the trend in boiling and melting points?
• Both increase with chain length because of greater wif
between molecules
• Not much energy is needed to break wif between small
chains so they are more volatile.
Chemical Properties of Alkanes
•
•
•
•
•
Combustion (used as fuels)
C3H8 + 5O2
3CO2 + 4H2O
Burns completely hot blue flame
C33H88 + 2O
3C + 4H2O
3.5O
3CO
2 2
Burns incompletely yellow flame Soot
Halogenation of alkanes
A substitution reaction
uv
RH + X2 → RX + HX
light
When a specific halogen is used the name reflects this:
Chlorination, Bromination uv
CH3CH3 + Cl2 → CH3CH2Cl + HCl
light
Name
1, chloroethane
of Haloalkane?
Damp
blue
litmus
test?
Reaction can continue so further Hydrogens can be replaced
forming di, tri, tetra etc. (only monosubstitution in the exam)
Classification
Primary haloalkane (X attached to C that is attached to one other
carbon
Secondary RX (X attached to C that is attached to two other carbons
Tertiary RX ....
Chemical Properties of
Haloalkanes
•
•
•
•
•
•
Substitution reactions with KOH(aq) form alcohols
CH3F + KOH(aq)
CH3OH + KF
Name the products and the type of bonding in each
Substitution reactions with conc. NH3 form amines
CH3F + 2NH3 high pressure
CH3NH2 + NH4F
Name the products, what is the bond angle between N –
H in the amine
• Name and classify these Haloalkanes
Chemical Properties of
Haloalkanes
• Elimination reactions involve the removal of a hydrogen
and halogen atom to form a hydrogen halide and an
alkene.
Heat and conc. KOH (alc)
• CH3CH2CH2I
CH3CHCH2 + HI
• Consider the elimination reaction of 2-Bromobutane,
what products are formed?
• But-2-ene and HBr and … But-1-ene
• Markovnikoff’s rule “The rich get richer, poor get poorer”
• Hydrogen is eliminated from the C with least H’s already
• But-2-ene is the major product and But-1-ene the minor
Alkenes and Alkynes
• Alkenes and alkynes are unsaturated hydrocarbons.
• They contain fewer than the maximum number of hydrogens.
• Name as for alkanes, the longest chain containing the multiple
bond is the parent.
Alkene
Alkyne
Alkenes contain a carbon-carbon double bond.
General formula for alkenes: CnH2n
Alkynes contain a carbon-carbon triple bond.
General formula for alkynes: CnH2n-2
• When naming
you must state
the position of
the multiple
bond
• What about
cycloalkenes?
Geometric Isomers
• Double bonds cannot rotate
about the C atoms
• Each carbon in the double bond
must have 2 different groups
attached
• Draw the formula for But-2-ene
H
C =C
CH3
CH3
H
Trans but-2-ene
CH3
H
C =C
CH3
H
Cis but-2-ene
•If the Carbon chain is on
different sides of the
multiple bond it is trans
otherwise cis
Reactions of Alkenes
• Combustion reactions are not as “clean” as the
corresponding alkanes
• Alkenes are more reactive than their corresponding
alkanes.
• This greater reactivity is due to the carbon-carbon
double bonds.
• Addition reactions at the carbon-carbon double bond are
the most common.
Halogenation
C=C bond is broken to make 2 new C- bonds
Addition
e.g.
Bromine
reaction
addsof
across
bromine
the double
to pent-2-ene
bond.
Geometric isomer?
double bond breaks
saturated
2,3-dibromopentane
Distinguishing test for alkene Vs alkane
Orange/Brown liquid decolourises
Alkene gases
will need to be
bubbled through
bromine water
Reaction with HCl
Hydrogen
chloride
adds
across
the
double
Addition of hydrogen chloride to But-1-ene
bond.
In an unsymmetrical alkene there are 2 possible
products
double bond breaks
saturated
2-chlorobutane
(major product)
Hydrogen usually attaches to
the Carbon with most
Hydrogen atoms already
CH2ClCH2CH2CH3
1- chlorobutane
(minor product)
Hydrogenation
Hydrogen adds across the double bond to form
Addition
an
alkane. of hydrogen to But-1-ene
double bond breaks
CH2=CH-CH2-CH3 + H-H
Pt at
room
temp
saturated
CH3-CH2-CH2-CH3
butane
Name? But-1-ene
Hydration
Addition of water to But-1-ene
Water (as steam at 3000C) adds across the
double bond to form an alcohol.
Classification
of the
alcohols?
double bond breaks
saturated
+
heat/H
CH2=CH-CH2-CH3 + H-OH
CH2OH-CH2-CH2-CH3
Butan1- ol
Name?
Catalyst
Is this the major or
minor product?
Oxidation
Addition of oxygen to but-1-ene
Alkene is oxidised under acidified
conditions to form an alcohol (diol).
double bond breaks
H+
CH2=CH-CH2-CH3 + MnO4
saturated
CH2OH-CHOH-CH2-CH3
Butan-1,2- diol
Distinguishing test for alkene Vs alkane
purple solution turns colourless
Polymers from Alkenes
• A polymer (macromolecule) is a natural
or synthetic giant molecule formed from
smaller molecules (monomers).
• Monomers are the small units that
undergo addition polymerisation to
form a polymer ( very large molecule
Addition polymers
of high molar mass)
Formation of Polymers
H
H
C
C
H
H
H
High
C
temp and
H pressure
C
H
H
Ethene
Ethene
H
H
H
H
C
C
C
C
H
H
H
H
Poly(e)thene
General formula for addition polymerisation:
n
C
C
C
C
n
• n = the number of monomer units.
• n ranges from 2,500 to 25,000
e.g. Polypropylene
15000
H
CH3
H
CH3
C
C
C
C
H
H
H
H
15000
Polymers
• Chain lengths are 500 - 25000
monomers in length
• Longer chains get tangled
• Weak intermolecular forces
increase with chain length
so…
• Melting point increases and …
• Polymer becomes stronger
Reactions of Alkynes
• Addition reactions occur with halogens and hydrogen to
produce alkenes and then alkanes.
Hydrogenation
0
• H-C=C-H + H2 Ni/150 C CH2=CH2
0
• CH2=CH2 +H2 Ni/150 C CH3-CH3
Halogenation
• H-C=C-H + Br2 Br2
CHBr=CHBr
Br2
• CHBr=CHBr +Br2
CHBr2-CHBr2
• Name the products
• 1,2 – dibromoethene and 1,1,2,2 - tetrabromoethane
Alcohols
• Alcohols are organic molecules
whose molecules contain the –
OH (hydroxyl) functional group.
• The general formula for alcohols
is ROH.
• Alcohol molecules with 4 or less
C are soluble in water because
EN difference between OH makes the molecule polar
• Longer chain alcohols are non-polar and insoluble in
water.
• Alcohols burn in air to produce water and carbon
dioxide.
Naming Alcohols
• Find the longest C
chain containing –OH
• Identify any branches
• Number C atoms so –
OH has the lowest
number
Name
2-
Location of branch -
methyl
Name of branch
but
Prefix of long chain
an-
OH
2CH3
C
CH3
CH2
CH3
Location of OH ol
Name:
an -
ol
Polyhydroxy Alcohols
• Alcohols that contain more than one OH group
attached to different carbons are called
polyhydroxy alcohols.
• Monohydroxy: one OH group per molecule.
• Dihydroxy: two OH groups per molecule.
• Trihydroxy: three OH groups per molecule.
Name?
Ethan-1,2 -diol
Classifying Alcohols
Alcohols are classified as:
primary (1o)
• (C atom with –OH is
bonded to 1 other C)
secondary (2o)
• (C atom with –OH is
bonded to 2 other C)
tertiary (3o)
• (C atom with –OH is
bonded to 3 other C)
Name the alcohols and draw the
isomers of the secondary alcohol
Alcohol reactions
• Alcohols combust in the same way as other
hydrocarbons
• Alcohol can be dehydrated to form an alkene
CH2OH-CH2-CH3
Conc.
H2SO4
heat
CH2=CH-CH3 + H2O
• This is an example of an elimination reaction
• How can you test that the product is an
alkene?
Alcohol reactions
• Primary and secondary alcohols can be oxidised
by oxidants.
• Alcohol + oxidising agent
carboxylic acid
H+
2• CH3CH2OH + Cr2O7
CH3COOH
• Cr6+(orange)
Cr3+(green)
• Breathalyser test
Oxidation of
primary alcohols
forms carboxylic
acids
Alcohol reactions
• Substitution reactions of alcohols occur when –OH is
replaced by a halogen atom to form a haloalkane.
H H
H H
• H-C-C-H
H OH
Reagent*
H-C-C-H
H Cl
• Reagents* for this reaction are:
– PCl3 phosphorous trichloride
– PCl5 phosphorous pentachloride
– SOCl2 thionyl chloride
Carboxylic Acid
carbonyl group
OH bonded to
a carbonyl
carbon.
or
Carboxylic acids contain the
carboxyl group.
• Open-chain carboxylic acids form a
homologous series.
• The carboxyl group is always at the
beginning of a carbon chain.
• The carbonyl carbon atom is always
designated as C-1.
3
2
1
Naming Carboxylic acids
• The name of a carboxylic acid is derived
from the name of the alkane
corresponding to the longest carbon
chain that contains the carboxyl group.
• The parent name is formed by
changing the –e ending of the alkane
to –oic acid.
methane
methanone
oic acid
Naming Carboxylic acids
• The name of a carboxylic acid is derived
from the name of the alkane
corresponding to the longest carbon
chain that contains the carboxyl group.
• The parent name is formed by
changing the –e ending of the alkane
to –oic acid.
propane
propanone
oic acid
Formulas and Names of Saturated Carboxylic Acids
Physical properties of carboxylic
acids
• Colourless liquids or white solids at room temp
• Methanoic and ethanoic acid are soluble because the
–COOH group is polar.
• Solubility decreases with increasing chain length.
• Short chain molecules tend to be “smelly”
• Higher m.p and b.p than equivalent hydrocarbons and
alcohols due to stronger intermolecular bonding
Reactions of Carboxylic Acids
• Behave like weak inorganic acids as they partially ionise
in water
Ethanoate and
hydronium ions
•
•
•
•
•
What would the pH be? How would indicators change?
Why do solutions of carboxylic acid conduct electricity?
Acid + base
salt + water
Acid + metal
salt + hydrogen
Acid + carbonate
salt + water + carbon dioxide
Reactions of Carboxylic acids
• Lithium + methanoic acid
• 2Li + 2H-COOH
• 2Li + 2H-C
O
O
O-H
Lithium methanoate + Hydrogen
2H-COOLi + H2
2H-C
𝛿+
𝛿…
O Li
+ H-H
• Complete balanced structural formula equations for the following:
• Zinc oxide + 2ethanoic acid
Zinc ethanoate + water
• Iron (II) carbonate + 2propanoic acid
Iron propanoate + water +
carbon dioxide
Amines
• Amines are derived from ammonia
• If the N is attached to one carbon chain it
is a primary amine
• Secondary amines have 2 alkyl groups
and tertiary have 3 (not in the exam)
Naming Amines
• The name of primary amines is derived from the
corresponding alkane.
• The parent name is formed by changing the –e
ending of the alkane to –amine.
• State the position of the amine group or groups
• Multiple groups are signified by di, tri or tetra
ethane
name
amine
ethanone
draw
1-chloropropan 1,2 diamine
Physical properties of Amines
• Higher mp and bp than
similar molecular mass
alkane due to…
• High E.N. difference
between N and H causing
polarity of NH2 and
greater intermolecular
attraction.
• Methanamine and
ethanamine are gases,
propanamine is liquid
• Low mass amines are
soluble in water
Chemical reactions of Amines
•
•
•
•
•
•
•
Methylammonium
ion
Amines are weak bases
CH3NH2 (aq) + H2O
CH3NH3+ + OHIndicator colours?
Name?
Neutralisation reaction with acids to form salts
CH3CH2NH2 (aq) + HCl (aq)
CH3CH2NH3+ + ClName?
CH3CH2NH3+ + ClCH3CH2NH3+ClWhat is the name of the product formed when
propanamine reacts with methanoic acid?
• Propylammonium methanoate
• Why does lemon juice reduce the fishy smell?