Transcript Chapter 21

Chapter 21
Fuels and Heats of Reaction
Organic chemistry
• Organic chemistry is defined as the study of the
compounds of carbon.
• A hydrocarbon is a compounds of carbon and hydrogen
only.
Types of hydrocarbon.
• Aliphatic- have molecules in chains or rings of carbon
atoms.
• Aromatic - hydrocarbons with a Benzene ring of 6 carbon
atoms, where the bonds are intermediate between single
and double bonds.
Aliphatic hydrocarbons.
• A homologous series is a group of compounds with similar
chemical properties due to having the same functional group.
They have a gradual variation in physical properties and they
differ from each other by CH2.
• A functional group is a group of atoms within the molecule
which, due to its structure, gives the molecule its
characteristics.(-OH functional group gives alcohols their
characteristics)
• The 3 main classes of Hydrocarbons are Alkanes, Alkenes
and Alkynes.
Alkanes
• Formerly known as the ‘paraffins’ (from the Latin meaning
‘lacking affinity’) the alkanes are a group of hydrocarbons
which conform to the general formula CnH2n+2, where n is
greater than or equal to 1. They are saturated compounds.
They consist of carbon atoms joined by four single
covalent bonds to either hydrogen or other carbon atoms.
• The first member of the group is methane (CH4), the
second is ethane (C2H6), and the third is propane (C3H8), as
illustrated in Fig. 3.2. By drawing their structural formulae
we can see that each differs from the next by replacing a
hydrogen with a CH3 group, i.e. an extra CH2 is inserted in
the chain.
ALKANES
General
members of a homologous series
general formula is CnH2n+2 - for non-cyclic alkanes
saturated hydrocarbons - all carbon-carbon bonding is single
bonds are spaced tetrahedrally about carbon atoms.
Isomerism
the first example of structural isomerism occurs with C4H10
BUTANE
2-METHYLPROPANE
Structural isomers have the SAME MOLECULAR FORMULA BUT
DIFFERENT STRUCTURAL FORMULA
They possess different physical properties such as boiling point,
melting point and density
THE STRUCTURE OF ALKANES
In ALKANES, the four sp3
orbitals of carbon repel each
other into a TETRAHEDRAL
arrangement with bond angles
of 109.5º.
Each sp3 orbital in
carbon overlaps with
the 1s orbital of a
hydrogen atom to form
a C-H bond.
109.5º
Nomenclature of alkanes
Naming straight-chain alkanes
• Naming of straight chain alkanes (alkanes that do not branch) is a
straightforward process. To give an alkane a name, a prefix indicating the
number of carbons in the molecule is added to the suffix ane, identifying
both the kind of molecule (an alkane) and how many carbons the
molecule has (the prefix). The name pentane, for example, tells you that
the molecule is an alkane (thus the ane ending) and that it has five
carbons (pent indicates five). Prefixes for alkanes that have 1-4 carbons
are rooted historically. These are methane, ethane, propane, and butane,
respectively. On the other hand, for 5 carbons and up a prefix derived
from greek is given. (An easy way to remember the first four names is the
anagram, standing for methane, ethane, propane, butane). Learning the
prefixes for up to twelve carbons is a good idea, and they are listed in the
figure below.
Molecular Formula
Structural Formula
IUPAC Name
CH4
CH4
Methane
C2H6
CH3-CH3
Ethane
C3H8
CH3-CH2-CH3
Propane
C4H10
CH3-(CH2)2-CH3
Butane
C5H12
CH3-(CH2)3-CH3
Pentane
C6H14
CH3-(CH2)4-CH3
Hexane
C7H16
CH3-(CH2)5-CH3
Heptane
C8H18
CH3-(CH2)6-CH3
Octane
C9H20
CH3-(CH2)7-CH3
Nonane
C10H22
CH3-(CH2)8-CH3
Decane
Naming branched alkanes
• There are several rules that you must follow to give the
alkane the correct name.
1. Find the longest chain of carbons in the molecule. The
number of carbons in the longest chain becomes the
parent name (refer to the above table)
2. After finding the parent chain, you number the parent
chain starting with the end nearest the first substituent (a
substituent is any fragment that juts off the main chain).
3. Next, determine the names of all substituents. Substituents are named
as if the piece were a separate molecule, except that the suffix of yl is
used rather than ane. Thus, a two-carbon substituent would be an ethyl
substituent (not an ethane substituent).
4. Put the substituents in alphabetical order (ie. ethyl before methyl) in
front of the parent name.
5. Next, identify the positions of all substituents in the name by placing the
carbon number where the substituent attaches to the parent chain in
front of it. For example, 2-methylheptane indicates that a methyl
substituent is attached to the number 2 carbon
Mary eats peanut butter
PHYSICAL PROPERTIES OF ALKANES
Boiling point
increases as they get more carbon atoms in their formula
more atoms = greater intermolecular Van der Waals’ forces
greater intermolecular force = more energy to separate the molecules
greater energy required = higher boiling point
CH4 (-161°C)
C2H6 (-88°C)
C3H8 (-42°C)
C4H10 (-0.5°C)
difference gets less - mass increases by a smaller percentage
straight chains molecules have greater interaction than branched
“The greater the branching, the lower the boiling point”
Melting point
general increase with molecular mass
the trend is not as regular as that for boiling point.
Solubility
alkanes are non-polar so are immiscible with water
they are soluble in most organic solvents.
CHEMICAL PROPERTIES OF ALKANES
Introduction
- fairly unreactive; (old family name, paraffin, meant little reactivity)
- have relatively strong, almost NON-POLAR, SINGLE covalent bonds
- they have no real sites that will encourage substances to attack them
Combustion
- make useful fuels - especially the lower members of the series
- react with oxygen in an exothermic reaction
BUT
Handy tip
complete
combustion
CH4(g)
+
2O2(g)
incomplete
combustion
CH4(g)
+ 1½O2(g)
——>
CO2(g) +
2H2O(l)
——>
CO(g)
2H2O(l)
+
the greater the number of carbon atoms, the more energy produced
the greater the amount of oxygen needed for complete combustion.
When balancing equations involving complete combustion, remember...
every carbon in the original hydrocarbon gives one carbon dioxide and
every two hydrogen atoms gives a water molecule.
Put the numbers into the equation, count up the O’s and H’s on the RHS
of the equation then balance the oxygen molecules on the LHS.
POLLUTION
Processes involving combustion give rise to a variety of pollutants...
power stations
internal combustion engines
Removal
SO2
CO and NOx
SO2 emissions produce acid rain
CO, NOx and unburnt hydrocarbons
react effluent gases with a suitable compound (e.g. CaO)
pass exhaust gases through a catalytic converter
Catalytic converters
In the catalytic converter ... CO is converted to CO2
NOx are converted to N2
Unburnt hydrocarbons are converted to CO2 and H2O
e.g.
2NO
+
2CO
———>
N2
+
2CO2
• catalysts are made of finely divided rare metals Rh, Pd, Pt
• leaded petrol must not pass through the catalyst as the lead
deposits on the catalyst’s surface and “poisons” it, thus blocking
sites for reactions to take place.
Alkenes
Alkenes
General Formula
• Ethene C2H4
• Propene C3H6
• But-1-ene C4H8
• But-2-ene C4H8
CnH2n
Alkenes
• Alkenes are unsaturated hydrocarbons, as
they contain a carbon-carbon double bond
Ethene
C2H4
Propene
C3H6
But-1-ene
C4H8
But-2-ene
C 4 H8
Alkenes
• Alkene molecules are
planar, e.g. ethene
Physical properties
• Physical state: Gases
• Insoluble in water
• Soluble in non-polar solvents such as
cyclohexane
Uses
• Used to make plastics, e.g. ethene is used to
make polythene
• Ethene is used to make ethanol for
industrial use
CRACKING
Involves the breaking of C-C bonds in alkanes
Converts heavy fractions into higher value products
THERMAL
CATALYTIC
proceeds via a free radical mechanism
proceeds via a carbocation (carbonium ion) mechanism
CATALYTIC
SLIGHT PRESSURE
HIGH TEMPERATURE ... 450°C
ZEOLITE CATALYST
CARBOCATION (IONIC) MECHANISM
HETEROLYTIC FISSION
PRODUCES BRANCHED AND CYCLIC ALKANES, AROMATIC HYDROCARBONS
USED FOR MOTOR FUELS
ZEOLITES are crystalline aluminosilicates; clay like substances
CRACKING
Involves the breaking of C-C bonds in alkanes
Converts heavy fractions into higher value products
THERMAL
CATALYTIC
proceeds via a free radical mechanism
proceeds via a carbocation (carbonium ion) mechanism
THERMAL
HIGH PRESSURE ... 7000 kPa
HIGH TEMPERATURE ... 400°C to 900°C
FREE RADICAL MECHANISM
HOMOLYTIC FISSION
PRODUCES MOSTLY ALKENES ... e.g. ETHENE for making polymers and ethanol
PRODUCES HYDROGEN ... used in the Haber Process and in margarine manufacture
Bonds can be broken anywhere in the molecule by C-C bond fission or C-H bond fission
Petrol
Petrol is formed by the fractional distillation of crude oil.
Some of the different fractions formed are:
Petroleum Gas - Mercaptans added for smell.
Petrol- light gasoline
Naphta - Petrochemical Industry
Kerosene - Aviation Fuel.
Diesel.
Lubricating Oil.
•
Octane Number
Knocking - early explosion due to petrol-air mixture. The petrol explodes
as it is compressed instead of being caused by a spark. (Auto-ignition).
Octane Number - Measure of the tendency of fuels to resist knocking.
2, 2-4 tri-methyl pentane (iso-octane) has an octane number of 100.
Heptane is not efficient and has an octane number of 0.
The shorter the alkane the higher the octane number.
The more branched the chain the higher the octane number.
Cyclic compounds have a higher octane number than straight chain
compounds.
Making Petrol
Knocking - early explosion due to petrol-air mixture. The petrol explodes as it is
compressed instead of being caused by a spark. (Auto-ignition).
Tetra-ethyl lead -Reduces knocking. However it caused health problems and is
poisoness.
4 ways to increase octane number.
1. Isomerisation. Branching caused by alkanes heated in the presence of a suitable
catalyst.
2. Catalytic Cracking. Long chained hydrocarbons broken down into short chain
molecules for which there is great demand. Large alkanes form alkanes and
alkenes.
3. Reforming (DeHydrocyclisation.) Reforming involves the use of catalysts to form
ring compounds.-Hydrogen given off.
4. Adding Oxygenates. Three oxygen containing molecules, methanol, ethanol, and
MTBE are added to petrol to increase its octane number.
MTBE stands for methyl tertiary butyl ether. (2-methoxy-2-methylpropane)
KNOCKHARDY PUBLISHING
ORGANIC CHEMISTRY
INTRODUCTION
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CONTENTS
ORGANIC CHEMISTRY
Organic chemistry is the study of carbon compounds. It is such a complex branch of
chemistry because...
• CARBON ATOMS FORM STRONG COVALENT BONDS TO EACH OTHER
• THE CARBON-CARBON BONDS CAN BE SINGLE, DOUBLE OR TRIPLE
• CARBON ATOMS CAN BE ARRANGED IN
STRAIGHT CHAINS
BRANCHED CHAINS
and RINGS
• OTHER ATOMS/GROUPS OF ATOMS CAN BE PLACED ON THE CARBON ATOMS
• GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON
CONTENTS
SPECIAL NATURE OF CARBON - CATENATION
CATENATION is the ability to form bonds between atoms of the same element.
Carbon forms chains and rings, with single, double and triple covalent bonds, because it
is able to FORM STRONG COVALENT BONDS WITH OTHER CARBON ATOMS
Carbon forms a vast number of carbon compounds because of the strength of the C-C
covalent bond. Other Group IV elements can do it but their chemistry is limited due to
the weaker bond strength.
BOND
ATOMIC RADIUS
BOND ENTHALPY
C-C
0.077 nm
+348 kJmol-1
Si-Si
0.117 nm
+176 kJmol-1
The larger the atoms, the weaker the bond. Shielding due to filled inner orbitals and greater
distance from the nucleus means that the shared electron pair is held less strongly.
CONTENTS
THE SPECIAL NATURE OF CARBON
CHAINS AND RINGS
CARBON ATOMS CAN BE ARRANGED IN
STRAIGHT CHAINS
BRANCHED CHAINS
and
RINGS
You can also get a combination of rings and chains
CONTENTS
THE SPECIAL NATURE OF CARBON
MULTIPLE BONDING AND SUBSTITUENTS
CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE
CONTENTS
THE SPECIAL NATURE OF CARBON
MULTIPLE BONDING AND SUBSTITUENTS
CARBON-CARBON COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE
DIFFERENT ATOMS / GROUPS OF ATOMS CAN BE PLACED ON THE CARBONS
The basic atom is HYDROGEN but groups containing OXYGEN, NITROGEN,
HALOGENS and SULPHUR are very common.
CARBON SKELETON
FUNCTIONAL
GROUP
CARBON SKELETON
FUNCTIONAL
GROUP
The chemistry of an organic compound is determined by its FUNCTIONAL GROUP
CONTENTS
THE SPECIAL NATURE OF CARBON
MULTIPLE BONDING AND SUBSTITUENTS
ATOMS/GROUPS CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON SKELETON
THE C=C DOUBLE BOND IS IN A DIFFERENT POSITION
PENT-1-ENE
PENT-2-ENE
THE CHLORINE ATOM IS IN A DIFFERENT POSITION
1-CHLOROBUTANE
2-CHLOROBUTANE
CONTENTS
TYPES OF FORMULAE - 1
MOLECULAR FORMULA
The exact number of atoms of each
element present in the molecule
C4H10
EMPIRICAL FORMULA
The simplest whole number ratio
of atoms in the molecule
C2H5
STRUCTURAL FORMULA
The minimal detail using conventional
groups, for an unambiguous structure
CH3CH2CH2CH3
DISPLAYED FORMULA
Shows both the relative placing of atoms
and the number of bonds between them
THE EXAMPLE BEING
USED IS...
BUTANE
CH3CH(CH3)CH3
there are two possible structures
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
H
H
C
C
C
H
H
H C H
H
CONTENTS
H
TYPES OF FORMULAE - 2
SKELETAL FORMULA
A skeletal formula is used to show a simplified organic formula by removing hydrogen
atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups
CH2
CH2
CH2
CH2
CH2
for
CH2
CYCLOHEXANE
THALIDOMIDE
CONTENTS
TYPES OF FORMULAE - 2
SKELETAL FORMULA
A skeletal formula is used to show a simplified organic formula by removing hydrogen
atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups
CH2
CH2
CH2
CH2
CH2
for
CH2
CYCLOHEXANE
GENERAL FORMULA
Represents any member of
a homologous series
THALIDOMIDE
for alkanes it is...
possible formulae...
CnH2n+2
CH4, C2H6 .... C99H200
The formula does not apply to cyclic compounds such as cyclohexane is C6H12
- by joining the atoms in a ring you need fewer H’s
CONTENTS
HOMOLOGOUS SERIES
A series of compounds of similar structure in which each member differs from the next
by a common repeating unit, CH2. Series members are called homologues and...
• all share the same general formula.
• formula of a homologue differs from its neighbour by CH2. (e.g. CH4, C2H6, ... etc )
• contain the same functional group
• have similar chemical properties.
• show a gradual change in physical properties as molar mass increases.
• can usually be prepared by similar methods.
ALCOHOLS - FIRST THREE MEMBERS OF THE SERIES
CH3OH
METHANOL
C2H5OH
ETHANOL
CONTENTS
C3H7OH
PROPAN-1-OL
FUNCTIONAL GROUPS
Organic chemistry is a vast subject so it is easier to split it into small sections for study.
This is done by studying compounds which behave in a similar way because they have
a particular atom, or group of atoms, FUNCTIONAL GROUP, in their structure.
Functional groups can consist of one atom, a group of atoms or multiple bonds
between carbon atoms.
Each functional group has its own distinctive properties which means that the
properties of a compound are governed by the functional group(s) in it.
H H H H H
H H H H H
H C C C C C
H C C C C C
NH2
H H H H H
H H H H H
Carbon
skeleton
OH
Functional
Group = AMINE
CONTENTS
Carbon
skeleton
Functional
Group = ALCOHOL
COMMON FUNCTIONAL GROUPS
GROUP
ENDING
ALKANE
- ane
ALKENE
ALKYNE
GENERAL FORMULA
RH
EXAMPLE
C2H6
ethane
- ene
C2H4
ethene
- yne
C2H2
ethyne
HALOALKANE
halo -
RX
C2H5Cl
chloroethane
ALCOHOL
- ol
ROH
C2H5OH
ethanol
-al
RCHO
CH3CHO
ethanal
KETONE
- one
RCOR
CH3COCH3
propanone
CARBOXYLIC ACID
- oic acid
RCOOH
CH3COOH
ethanoic acid
ACYL CHLORIDE
- oyl chloride
RCOCl
CH3COCl
ethanoyl chloride
AMIDE
- amide
RCONH2
CH3CONH2
ethanamide
ESTER
- yl - oate
RCOOR
CH3COOCH3
methyl ethanoate
NITRILE
- nitrile
RCN
CH3CN
ethanenitrile
AMINE
- amine
RNH2
CH3NH2
methylamine
NITRO
nitro-
RNO2
CH3NO2
nitromethane
ALDEHYDE
SULPHONIC ACID
- sulphonic acid
RSO3H
C6H5SO3H
benzene sulphonic acid
ETHER
- oxy - ane
ROR
C2H5OC2H5
ethoxyethane
CONTENTS
COMMON FUNCTIONAL GROUPS
ALKANE
CARBOXYLIC ACID
ALKENE
ALKYNE
ESTER
HALOALKANE
ACYL CHLORIDE
AMINE
NITRILE
AMIDE
ALCOHOL
ETHER
NITRO
ALDEHYDE
SULPHONIC ACID
KETONE
CONTENTS
HOW MANY STRUCTURES?
Draw legitimate structures for each molecular formula and classify each one according
to the functional group present. Not all the structures represent stable compounds.
carbon atoms have
oxygen atoms
nitrogen atoms
hydrogen
halogen atoms
4 covalent bonds surrounding them
2
3
1
1
C2H6
ONE
C3H9Br
TWO
C4H8
FIVE - 3 with C=C and 2 ring compounds with all C-C’s
C2H6O
TWO - 1 with C-O-C and 1 with C-O-H
C3H6O
SIX - 2 with C=O, 2 with C=C and 2 with rings
C2H7N
TWO
C2H4O2
SEVERAL - Only 2 are stable
C2H3N
TWO
CONTENTS
HOW MANY STRUCTURES?
Draw legitimate structures for each molecular formula and classify each one according
to the functional group present. Not all the structures represent stable compounds.
carbon atoms have
oxygen atoms
nitrogen atoms
hydrogen
halogen atoms
4 covalent bonds surrounding them
2
3
1
1
C2H6
ONE
C3H9Br
TWO
C4H8
FIVE - 3 with C=C and 2 ring compounds with all C-C’s
C2H6O
TWO - 1 with C-O-C and 1 with C-O-H
C3H6O
SIX - 2 with C=O, 2 with C=C and 2 with rings
C2H7N
TWO
C2H4O2
SEVERAL - Only 2 are stable
C2H3N
TWO
CONTENTS
NOMENCLATURE
Ideally a naming system should tell you everything about a structure without ambiguity.
There are two types of naming system commonly found in organic chemistry;
Trivial :
Systematic :
based on some property or historical aspect;
the name tells you little about the structure
based on an agreed set of rules (I.U.P.A.C);
exact structure can be found from the name (and vice-versa).
trivial name
paraffin
olefin
fatty acid
trivial name
methane
butane
acetic acid
HOMOLOGOUS SERIES
systematic name
example(s)
alkane
methane, butane
alkene
ethene, butene
alkanoic (carboxylic) acid
ethanoic acid
INDIVIDUAL COMPOUNDS
derivation
systematic name
methu = wine (Gk.)
methane (CH4)
butyrum = butter (Lat.)
butane (C4H10)
acetum = vinegar (Lat.)
ethanoic acid (CH3COOH)
CONTENTS
I.U.P.A.C. NOMENCLATURE
A systematic name has two main parts.
STEM
number of carbon atoms in longest chain bearing the functional group +
a prefix showing the position and identity of any side-chain substituents.
Apart from the first four, which have trivial
names, the number of carbons atoms is indicated
by a prefix derived from the Greek numbering
system.
The list of alkanes demonstrate the use of prefixes.
The ending -ane is the same as they are all
alkanes.
Prefix
methethpropbutpenthexheptoctnondec-
C atoms
1
2
3
4
5
6
7
8
9
10
Alkane
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
Working out which is the longest chain can pose a problem with larger molecules.
CONTENTS
I.U.P.A.C. NOMENCLATURE
How long is a chain?
Because organic molecules are three dimensional and paper is two dimensional it
can confusing when comparing molecules. This is because...
1. It is too complicated to draw molecules with the correct bond angles
2. Single covalent bonds are free to rotate
All the following written structures are of the same molecule - PENTANE C5H12
CH3
CH3 CH2 CH2 CH2 CH3
CH2 CH2 CH2 CH3
CH3
CH2 CH2 CH2
CH3 CH2 CH3
CH3
CH2 CH2
A simple way to check is to run a finger along the chain and see how many carbon
atoms can be covered without reversing direction or taking the finger off the page.
In all the above there are... FIVE CARBON ATOMS IN A LINE.
CONTENTS
I.U.P.A.C. NOMENCLATURE
How long is the longest chain?
Look at the structures and work out how many carbon atoms are in the longest chain.
CH3
THE ANSWERS ARE
ON THE NEXT SLIDE
CH2
CH3 CH CH2 CH3
CH3
CH3 CH2 CH2 CH2 CH CH3
CH3
CH3 CH2
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
How long is the longest chain?
Look at the structures and work out how many carbon atoms are in the longest chain.
CH3
LONGEST CHAIN = 5
CH2
CH3 CH CH2 CH3
CH3
LONGEST CHAIN = 6
CH3 CH2 CH2 CH2 CH CH3
CH3
CH3 CH2
LONGEST CHAIN = 6
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
A systematic name has two main parts.
SUFFIX An ending that tells you which functional group is present
See if any functional groups are present.
Add relevant ending to the basic stem.
In many cases the position of the functional
group must be given to avoid any ambiguity
1-CHLOROBUTANE
SUBSTITUENTS
Functional group
Suffix
ALKANE
ALKENE
ALKYNE
ALCOHOL
ALDEHYDE
KETONE
ACID
- ANE
- ENE
- YNE
- OL
- AL
- ONE
- OIC ACID
2-CHLOROBUTANE
Many compounds have substituents (additional atoms, or groups)
attached to the chain. Their position is numbered.
CONTENTS
I.U.P.A.C. NOMENCLATURE
SIDE-CHAIN
carbon based substituents are named before the chain name.
they have the prefix -yl added to the basic stem (e.g. CH3 is methyl).
Alkyl radicals
methyl
CH3 -
CH3
ethyl
propyl
CH3- CH2CH3- CH2- CH2-
C2H5
C3H7
Number the principal chain from one end to give the lowest numbers.
Side-chain names appear in alphabetical order
butyl, ethyl, methyl, propyl
Each side-chain is given its own number.
If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa
Numbers are separated from names by a HYPHEN
e.g.
Numbers are separated from numbers by a COMMA
e.g. 2,3-dimethylbutane
CONTENTS
2-methylheptane
I.U.P.A.C. NOMENCLATURE
SIDE-CHAIN
carbon based substituents are named before the chain name.
they have the prefix -yl added to the basic stem (e.g. CH3 is methyl).
Alkyl radicals
methyl
CH3 -
CH3
ethyl
propyl
CH3- CH2CH3- CH2- CH2-
C2H5
C3H7
Number the principal chain from one end to give the lowest numbers.
Side-chain names appear in alphabetical order
butyl, ethyl, methyl, propyl
Each side-chain is given its own number.
If identical side-chains appear more than once, prefix with di, tri, tetra, penta, hexa
Numbers are separated from names by a HYPHEN
e.g.
Numbers are separated from numbers by a COMMA
e.g. 2,3-dimethylbutane
Example
longest chain 8 (it is an octane)
3,4,6 are the numbers NOT 3,5,6
order is ethyl, methyl, propyl
3-ethyl-5-methyl-4-propyloctane
2-methylheptane
CH3 CH3
CH3 CH2 CH2 CH
CH2
CH3 CH2 CH2 CH
CH
CONTENTS
CH2
CH3
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
THE ANSWERS ARE ON THE NEXT SLIDE
CH3
CH2
CH3 CH CH2 CH3
CH3
CH3 CH2 CH2 CH2 CH CH3
CH3
CH3 CH2
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
CH3
CH2
CH3 CH CH2 CH3
CH3
CH3 CH2 CH2 CH2 CH CH3
CH3
CH3 CH2
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain = 5 so it is a pentane
CH3
A CH3, methyl, group is attached to the
third carbon from one end...
CH2
CH3 CH CH2 CH3
3-methylpentane
CH3
CH3 CH2 CH2 CH2 CH CH3
CH3
CH3 CH2
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain = 5 so it is a pentane
CH3
A CH3, methyl, group is attached to the
third carbon from one end...
CH2
CH3 CH CH2 CH3
3-methylpentane
CH3
CH3 CH2 CH2 CH2 CH CH3
Longest chain = 6 so it is a hexane
A CH3, methyl, group is attached to the
second carbon from one end...
2-methylhexane
CH3
CH3 CH2
CH3 CH2 CH CH CH3
CONTENTS
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain = 5 so it is a pentane
CH3
A CH3, methyl, group is attached to the
third carbon from one end...
CH2
CH3 CH CH2 CH3
3-methylpentane
CH3
CH3 CH2 CH2 CH2 CH CH3
Longest chain = 6 so it is a hexane
A CH3, methyl, group is attached to the
second carbon from one end...
2-methylhexane
CH3
CH3 CH2
CH3 CH2 CH CH CH3
Longest chain = 6 so it is a hexane
CH3, methyl, groups are attached to the
third and fourth carbon atoms
(whichever end you count from).
3,4-dimethylhexane
CONTENTS
NAMING ALKENES
Length
In alkenes the principal chain is not always the longest chain
It must contain the double bond
the name ends in -ENE
Position
Count from one end as with alkanes.
Indicated by the lower numbered carbon atom on one end of the C=C bond
5
4
3
2
1
CH3CH2CH=CHCH3
Side-chain
is pent-2-ene
(NOT pent-3-ene)
Similar to alkanes
position is based on the number allocated to the double bond
1
2
3
4
CH2 = CH(CH3)CH2CH3
2-methylbut-1-ene
CONTENTS
1
2
3
4
CH2 = CHCH(CH3)CH3
3-methylbut-1-ene
WHICH COMPOUND IS IT?
Elucidation of the structures of organic compounds - a brief summary
Organic chemistry is so vast that the identification of a compound can be involved. The
characterisation takes place in a series of stages (see below). Relatively large amounts
of substance were required to elucidate the structure but, with modern technology and
the use of electronic instrumentation, very small amounts are now required.
Elemental composition
One assumes that organic compounds contain carbon and hydrogen but it can be
proved by letting the compound undergo combustion. Carbon is converted to carbon
dioxide and hydrogen is converted to water.
Percentage composition by mass
Found by dividing the mass of an element present by the mass of the compound
present, then multiplying by 100. Elemental mass of C and H can be found by allowing
the substance to undergo complete combustion. From this one can find...
mass of carbon
mass of hydrogen
=
=
12/44 of the mass of CO2 produced
2/18 of the mass of H2O produced
CONTENTS
INVESTIGATING MOLECULES
Empirical formula
The simplest ratio of elements present in the substance. It is calculated by dividing the
mass or percentage mass of each element by its molar mass and finding the simplest
ratio between the answers. Empirical formula is converted to the molecular formula
using molecular mass.
CONTENTS
INVESTIGATING MOLECULES
Empirical formula
The simplest ratio of elements present in the substance. It is calculated by dividing the
mass or percentage mass of each element by its molar mass and finding the simplest
ratio between the answers. Empirical formula is converted to the molecular formula
using molecular mass.
Molecular mass
Traditionally found out using a variety of techniques such as ... volumetric analysis or
molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass
spectrometry is now used. The m/z value of the molecular ion and gives the molecular
mass. The fragmentation pattern gives information about the compound.
CONTENTS
INVESTIGATING MOLECULES
Empirical formula
The simplest ratio of elements present in the substance. It is calculated by dividing the
mass or percentage mass of each element by its molar mass and finding the simplest
ratio between the answers. Empirical formula is converted to the molecular formula
using molecular mass.
Molecular mass
Traditionally found out using a variety of techniques such as ... volumetric analysis or
molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass
spectrometry is now used. The m/z value of the molecular ion and gives the molecular
mass. The fragmentation pattern gives information about the compound.
Molecular formula
The molecular formula is an exact multiple of the empirical formula. Comparing the
molecular mass with the empirical mass allows one to find the true formula. e.g.
if the empirical formula is CH (relative mass = 13) and the molecular mass is 78
the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 .
CONTENTS
INVESTIGATING MOLECULES
Empirical formula
The simplest ratio of elements present in the substance. It is calculated by dividing the
mass or percentage mass of each element by its molar mass and finding the simplest
ratio between the answers. Empirical formula is converted to the molecular formula
using molecular mass.
Molecular mass
Traditionally found out using a variety of techniques such as ... volumetric analysis or
molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass
spectrometry is now used. The m/z value of the molecular ion and gives the molecular
mass. The fragmentation pattern gives information about the compound.
Molecular formula
The molecular formula is an exact multiple of the empirical formula. Comparing the
molecular mass with the empirical mass allows one to find the true formula. e.g.
if the empirical formula is CH (relative mass = 13) and the molecular mass is 78
the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 .
Structural formula
Because of the complexity of organic molecules, there can be more than one structure
for a given molecular formula. To work out the structure, different tests are carried out.
CONTENTS
INVESTIGATING MOLECULES
Empirical formula
The simplest ratio of elements present in the substance. It is calculated by dividing the
mass or percentage mass of each element by its molar mass and finding the simplest
ratio between the answers. Empirical formula is converted to the molecular formula
using molecular mass.
Molecular mass
Traditionally found out using a variety of techniques such as ... volumetric analysis or
molar volume methods (Dumas, Victor-Meyer or gas syringe experiments). Mass
spectrometry is now used. The m/z value of the molecular ion and gives the molecular
mass. The fragmentation pattern gives information about the compound.
Molecular formula
The molecular formula is an exact multiple of the empirical formula. Comparing the
molecular mass with the empirical mass allows one to find the true formula. e.g.
if the empirical formula is CH (relative mass = 13) and the molecular mass is 78
the molecular formula will be 78/13 or 6 times the empirical formula i.e. C6H6 .
Structural formula
Because of the complexity of organic molecules, there can be more than one structure
for a given molecular formula. To work out the structure, different tests are carried out.
CONTENTS
INVESTIGATING MOLECULES
Chemical
Chemical reactions can identify the functional group(s) present.
Spectroscopy
IR
detects bond types due to absorbance of i.r. radiation
NMR
gives information about the position and relative
numbers of hydrogen atoms present in a molecule
By
comparison of IR or NMR spectra and
mass spectrometry
Confirmation
CONTENTS
REVISION CHECK
What should you be able to do?
Recall and explain the reasons for the large number of carbon based compounds
Be able to write out possible structures for a given molecular formula
Recognize the presence of a particular functional group in a structure
Know the IUPAC rules for naming alkanes and alkenes
Be able to name given alkanes and alkenes when given the structure
Be able to write out the structure of an alkane or alkene when given its name
Recall the methods used to characterise organic molecules
CAN YOU DO ALL OF THESE?
CONTENTS
YES
NO
You need to go over the
relevant topic(s) again
Click on the button to
return to the menu
CONTENTS
WELL DONE!
Try some past paper questions
CONTENTS
AN INTRODUCTION TO
ORGANIC CHEMISTRY
THE END
© 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING