Physics and chemistry
Unit 3: Organic compounds
Unit 3.Part II. Organic compounds
Index
1. The uniqueness of carbon.................................................................................................................2
2. The allotropes of carbon...................................................................................................................3
Diamond...........................................................................................................................................3
Graphite...........................................................................................................................................4
Buckminster Fullerene.....................................................................................................................4
Amorphous carbon...........................................................................................................................5
3. Types of formulas.............................................................................................................................6
4. Simple hydrocarbons........................................................................................................................8
Alkanes............................................................................................................................................8
Alkenes............................................................................................................................................9
Alkynes............................................................................................................................................9
5. Other functional groups..................................................................................................................14
Practice exam......................................................................................................................................18
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Physics and chemistry
Unit 3: Organic compounds
To understand life as we know it, we must first understand a little bit of organic chemistry. Organic
molecules contain both carbon and hydrogen. Though many organic chemicals also contain other
elements, it is the carbon-hydrogen bond that defines them as organic. Organic chemistry defines
life. Just as there are millions of different types of living organisms on this planet, there are millions
of different organic molecules, each with different chemical and physical properties. There are
organic chemicals that make up your hair, your skin, your fingernails, and so on. The diversity of
organic chemicals is due to the versatility of the carbon atom. Why is carbon such a special
element? Let's look at its chemistry in a little more detail.
1. The uniqueness of carbon
Carbon (C) appears in the second row of the periodic table and has four bonding electrons in its
valence shell. Similar to other non-metals, carbon needs eight electrons to satisfy its valence shell.
Carbon therefore forms four bonds with other atoms (each bond consisting of one of carbon's
electrons and one of the bonding atom's electrons). Every valence electron participates in bonding.
These bonds form a tetrahedron (a pyramid with a spike at the top), as illustrated below:
Organic chemicals get their diversity from the many different ways carbon can bond to other atoms.
The simplest organic chemicals, called hydrocarbons, contain only carbon and hydrogen atoms; the
simplest hydrocarbon (called methane) contains a single carbon atom bonded to four hydrogen
atoms : CH4
But carbon can bond to other carbon atoms in addition to hydrogen, as illustrated in the molecule
ethane below:
Ethane - a carbon-carbon bond
In fact, the uniqueness of carbon comes from the fact that it can bond to itself in many different
ways. Carbon atoms can form long chains:
Hexane - a 6-carbon chain
branched chains:
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Physics and chemistry
Unit 3: Organic compounds
Isohexane - a branched-carbon chain
rings:
Cyclohexane - a ringed hydrocarbon
There appears to be almost no limit to the number of different structures that carbon can form. To
add to the complexity of organic chemistry, neighboring carbon atoms can form double and triple
bonds in addition to single carbon-carbon bonds:
Single bonding
Double bonding
Triple bonding
Keep in mind that each carbon atom forms four bonds. As the number of bonds between any two
carbon atoms increases, the number of hydrogen atoms in the molecule decreases (as can be seen in
the figures above).
2. The allotropes of carbon
The term “ allotrope” means: substances that have different physical properties due to different
atomic structures only
Three forms (or 'allotropes') of pure carbon are diamond, graphite and fullerene (or 'buckyballs'). In
all three allotropes the carbon atoms are joined by strong covalent bonds but in such different
arrangements that the properties of the allotropes are very different.
Diamond
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Physics and chemistry
Unit 3: Organic compounds
A diamond is one giant molecule of carbon atoms.
Diamonds are colourless and clear (transparent). They sparkle and reflect light – they're lustrous.
These properties make them desirable in items of jewellery.
Diamond is extremely hard and has a high melting point. For this reason it's very useful in cutting
tools. The cutting edges of discs used to cut bricks and concrete are tipped with diamonds. Heavyduty drill bits, like those used in the oil exploration industry to drill through rocks, are made with
diamonds so that they stay sharp for longer.
Diamond is insoluble in water. It does not conduct electricity.
Every atom in a diamond is bonded to its neighbours by four strong covalent bonds leaving no
free electrons and no ions. That's why diamond does not conduct electricity. The bonding also
explains the hardness of diamond and its high melting point. A lot of energy would be needed to
separate atoms so strongly bonded together.
Graphite
Graphite is formed from carbon atoms in layers.
Graphite is black, shiny and opaque (not transparent). It's also a very slippery material. It's used in
pencil leads – it slips easily off the pencil onto the paper and leaves a black mark. It's a component
of many lubricants, for example bicycle chain oil. Graphite is insoluble in water. It has a high
melting point and is a good conductor of electricity, which makes it a suitable material for the
electrodes needed in electrolysis.
Each carbon atom is bonded into its layer with three strong covalent bonds. This leaves each atom
with a spare electron, which together form a delocalised ‘sea’ of electrons loosely bonding the
layers together. These delocalised electrons can all move along together – making graphite a good
electrical conductor. Because the layers are only weakly held together they can easily slip over one
another: hence the slipperiness of graphite. Melting graphite is not easy however. It takes a lot of
energy to break the strong covalent bonds and separate the carbon atoms.
Buckminster Fullerene
Structure of a buckminsterfullerene molecule - a large ball of 60 atoms
Buckminster Fullerene is one type of fullerene. Fullerenes are made from carbon atoms joined
together to make balls, ‘cages’ or tubes of carbon. The molecules of Buckminster Fullerene are
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Physics and chemistry
Unit 3: Organic compounds
spherical and are also known as 'buckyballs' – formula C60.
Buckminster Fullerene is a black solid although it's deep red when in solution in petrol.
The tube fullerenes are called nanotubes which are very strong and are conductors of electricity.
Their unusual electrical properties mean that nanotubes are used as semiconductors in electronic
circuits. Their strength makes them useful in reinforcing structures where exceptional lightness and
strength are needed for example, the frame of a tennis racket. They're also used as a platform for
industrial catalysts.
Amorphous carbon
It is the name used for carbon that does not have any crystalline structure. As with all glassy
materials, some short-range order can be observed, but there is no long-range pattern of atomic
positions.
While entirely amorphous carbon can be made, most of the material described as "amorphous"
actually contains crystallites of graphite or diamond with varying amounts of amorphous carbon
holding them together, making them technically polycrystalline or nanocrystalline materials.
Commercial carbon also usually contains significant quantities of other elements, which may form
crystalline impurities.
Coal (carbón) and soot (hollín) are both informally called amorphous carbon. The coal industry
divides coal up into various grades depending on the amount of carbon present in the sample
compared to the amount of impurities. The highest grade, anthracite, is about 90 percent carbon and
10% other elements. Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal
that is around 55 percent carbon.
Activities:
1) Define allotrope
2) What structure is shown in the diagram?
3) One property that diamond and graphite have in common is:
4) Why is diamond used on drilling bits?
5) Why is graphite used in pencils?
6) What type of structure do diamond and graphite have?
7) Why graphite is able to conduct th electricity?
8. Complete the table
allotrope
structure
properties
diamond
graphite
fullerene
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uses
Physics and chemistry
Unit 3: Organic compounds
9. Find information about th discovery, structure, properties and uses of : fullerene, graphene and
nanotubes
3. Types of formulas
A chemical formula is a way of expressing information about the proportions of atoms that
constitute a particular chemical compound, using a single line of chemical element symbols,
numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and
plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may
include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no
words
The simplest types of chemical formulas are called empirical formulas, which use letters and
numbers indicating the numerical proportions of atoms of each type. Molecular formulas
indicate the real numbers of each type of atom in a molecule, with no information on structure.
For example, the empirical formula for glucose is CH2O (twice as many hydrogen atoms as carbon
and oxygen), while its molecular formula is C6H12O6 (12 hydrogen atoms, six carbon and oxygen
atoms).
Condensed formula (or condensed molecular formula, occasionally called a "semi-structural
formula") conveys additional information about the particular ways in which the atoms are
chemically bonded together, either in covalent bonds, ionic bonds, or various combinations of
these types. This is possible if the relevant bonding is easy to show in one dimension. An example is
the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH.
However, even a condensed chemical formula is necessarily limited in its ability to show complex
bonding relationships between atoms, especially atoms that have bonds to four or more different
substituents.
Since a chemical formula must be expressed as a single line of chemical element symbols, it often
cannot be as informative as a true structural formula, which is a graphical representation of the
spatial relationship between atoms in chemical compounds.
Empirical
Molecular
Condensed formula
Structural formula
formula
formula
Relationship
Real number (usually in a single
graphical representation of
between atoms of atoms
line) additional
the spatial relationship
information of the
between atoms
bonds
C2H6O
C2H6O
CH3-CH2OH
CH2O
C2H4O2
CH3-COOH
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Physics and chemistry
Unit 3: Organic compounds
Activities:
10. Write the molecular and the condensed formula of the following:
11. Complete the table:
Empirical
formula
Molecular
formula
Condensed formula Structural formula
CH3-CHOH-CH2OH
CH4
C2H6
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Physics and chemistry
Unit 3: Organic compounds
CH3-CH2-CH3
4. Simple hydrocarbons
The simplest hydrocarbons are those that contain only carbon and hydrogen. These simple
hydrocarbons come in three varieties depending on the type of carbon-carbon bonds that occur in
the molecule.
Alkanes
Alkanes are the first class of simple hydrocarbons and contain only carbon-carbon single bonds.
The alkanes are named by combining a prefix that describes the number of carbon atoms in the
molecule with the root ending "ane". The names and prefixes for the first ten alkanes are given in
the following table.
Chain Designation
No. of C Atoms
meth-
1
eth-
2
prop-
3
but-
4
pent-
5
hex-
6
hept-
7
oct-
8
non-
9
dec-
10
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Physics and chemistry
Unit 3: Organic compounds
Carbon
Atoms
Prefix
Alkane
Name
Chemical
Formula
Structural
Formula
1
Meth
Methane
CH4
CH4
2
Eth
Ethane
C2H6
CH3CH3
3
Prop
Propane
C3H8
CH3CH2CH3
4
But
Butane
C4H10
CH3CH2CH2CH3
5
Pent
Pentane
C5H12
CH3CH2CH2CH2CH3
6
Hex
Hexane
C6H14
...
7
Hept
Heptane
C7H16
8
Oct
Octane
C8H18
9
Non
Nonane
C9H20
The molecular formula for any alkane is given by the expression CnH2n+2. The condensed formula,
shown for the first five alkanes in the table, shows each carbon atom and the elements that are
attached to it. This condensed formula is important when we begin to discuss more complex
hydrocarbons. The simple alkanes share many properties in common. All enter into combustion
reactions with oxygen to produce carbon dioxide and water vapor. In other words, many alkanes are
flammable. This makes them good fuels. For example, methane is the main component of natural
gas, and butane is common lighter fluid.
CH4
+
2O2
→
CO2
+
2H20
Alkenes
The second class of simple hydrocarbons, the alkenes, consists of molecules that contain at least
one double-bonded carbon pair. Alkenes follow the same naming convention used for alkanes. A
prefix (to describe the number of carbon atoms) is combined with the ending "ene" to denote an
alkene. Ethene, for example is the two-carbon molecule that contains one double bond. The
chemical formula for the simple alkenes follows the expression CnH2n. Because one of the carbon
pairs is double bonded, simple alkenes have two fewer hydrogen atoms than alkanes.
Ethene
Alkynes
Alkynes are the third class of simple hydrocarbons and are molecules that contain at least one triplebonded carbon pair. Like the alkanes and alkenes, alkynes are named by combining a prefix with
the ending "yne" to denote the triple bond. The chemical formula for the simple alkynes follows the
expression CnH2n-2.
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Physics and chemistry
Unit 3: Organic compounds
Activities:
12. Formula of the following:
Pentane
Butane
Propene
2,3-dimethylbutane
2,2-dimethylbutane.
3-ethyl-2-methylhexane.
Propyne.
but-1-ene
3-methylhex-2-ene
ethane
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Physics and chemistry
Unit 3: Organic compounds
methylpropane.
Methane
2-methylprop-1-ene
ethyne
Oct-3-yne
2-methylpent- 1-ene
Non- 4-ene
pentan-1-yne
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Physics and chemistry
Unit 3: Organic compounds
Now if you have the formula and you have to write the name:
Types of compounds
alkanes
Hydrocarbons having no
double or triple bond
functional groups
1. Find and name the
longest continuous carbon
chain.
2. Identify and name
groups attached to this
chain.
3. Number the chain
consecutively, starting at
the end nearest a
substituent group.
alkene
Alkenes are hydrocarbons
which have carboncarbon double bond
1. The ene suffix (ending)
indicates an alkene or
cycloalkene.
2. The longest chain chosen for
the root name must include both
carbon atoms of the double bond.
3. The root chain must be
numbered from the end nearest a
double bond carbon atom.
4. The smaller of the two
numbers designating the carbon
atoms of the double bond is used
as the double bond locator. If
more than one double bond is
present the compound is named as
a diene, triene or equivalent prefix
indicating the number of double
bonds, and each double bond is
assigned a locator number.
alkynes
alkynes are hydrocarbons
which have carbon-carbon
triple bond functional
groups
. The yne suffix (ending)
indicates an alkyne or
cycloalkyne.
Same rules than alkenes
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Physics and chemistry
Unit 3: Organic compounds
Activities:
13. Name the following
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Physics and chemistry
Unit 3: Organic compounds
CH3-CH2-CH2-CH2-CH3
CH3 – CH2- CH3
5. Other functional groups
Halocarbons
organic compounds containing CF3CHBrCl
one or more halogens
alcohols
An alcohol is a carbon chain
with a hydroxide (OH-)
CH3-CH2-CH2OH
attached
ethers
a carbon chain bonded to an
oxygen that is bonded to
another carbon chain
CH3OCH2CH3
aldehydes
An aldehyde is a carbon chain CH3CHO
with an oxygen double bonded
to the last/first carbon.
ketones
A ketone is a carbon chain
with an oxygen bonded to a
middle carbon
CH3-CH2-CH2-CO-CH3
carboxylic acids A carboxylic acid is a carbon CH3CH2COOH
chain with an oxygen double
bonded and a hydroxide
bonded to the last/first carbon
esters
An ester is a carbon chain
with an oxygen both double
and single bonded to one
carbon
CH3 COOCH2CH2CH2CH3
amines
An amine is a carbon chain
with an NH2 bonded to it
CH3CHNH2CH3
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Physics and chemistry
Unit 3: Organic compounds
14. Identify the following functional groups
CH3CH2CH=CH2
CH3CH2OH
CH3-CHOH-CH2-CH2OH
CH3CH2-COO-CH2CH3
CH3-CH2-CHO
CH3CH2-O-CH2CH2CH2CH3
CH3CH2CH2CH2COCH2CH3
COOH-CH2-CH2-COOH
HCOOH
CH3-CHCl-CH2-CH3
15. Identify the following functional groups
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Physics and chemistry
Unit 3: Organic compounds
CH3-CO-CO-CH2CH3
CH3-COO-CH3
CH3-COOH
CH2O
CH3 – CO- CH3
CH3-NH2
CH3CH2CH2-NH2
CH3 – O- CH3
CH3 – CO0- CH2CH2CH3
CClH2-CH3
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Physics and chemistry
Unit 3: Organic compounds
16. Complete with an example :
Halocarbons
alcohols
ethers
aldehydes
ketones
carboxylic acids
esters
amines
17. Identify the following functional groups
2-bromopentane
butanoic acid
ethyl methanoate
1-butanol
Propanal
1,1 dichloro-2,2-difluoroethane
methylamine
2-methyl-2-propanol
dimethylether
3-methyl-1-butanol
butenone
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Physics and chemistry
Unit 3: Organic compounds
Practice exam
1. Write the empirical, molecular, condensed and structural formula of the following:
a) butane
b) etyne
c) propanone d) pentane-2-ol
e) hexanoic acid
2. Answer:
a) What is the structural difference between aldehydes and ketones?
b) What are the three main allotropes of carbon? Write about its structure, hardness and
conductivity.
c) Why carbon can form so many compounds?
d) What is the difference between empirical and molecular formula?
3. Identify the functional groups in the following compounds:
CH3
CH3-CH2-CH-CH2Br
CH3-CH2-CH-CH2-CH3
C CH
CH3
CH3-CH CH-CH-CH-CH3
CH3
CH3-CH2-CH2-O-CH2-CH3
CH3-CH2-COOCH3
CH3
CH3
CH2-CH3
CH3-CH-COOCH2CH3
CH3-(CH2)3-COOH
CH3-CH-CH-CO-CH3
CH3-CH-CH-CH-CHO
CH3
.
CH3
CH3-N-CH3
CH3
CH3
4. Name the following:
CH3C≡C-CH2CH3
5. Formula of the following:
a) 2,2-dimethylbutane
b) 2-propylpent-1-ene
c) 1,4-penta-1,4- diene
d) Propene
e) 3-ethyl-2-methylhexane.
CH2=CH-CH2CH2CH3
f) 3-methylhex-2-ene.
h) 1-iodo-3-methylpent-2-ene.
i) pentan-3-one
j) 3-chloro - 2methylpentane
k) 5,5-dimethylhex-1-yne
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