Notes Lecture - Introduction to Hydrocarbons
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Transcript of Notes Lecture - Introduction to Hydrocarbons
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Topic 4: Organic and Biological Chemistry
4.1 Systematic Nomenclature 4.2 Physical Properties 4.3 Alcohols 4.4 Aldehydes and Ketones 4.5 Carboxylic Acids 4.6 Amines 4.7 Esters 4.8 Amides 4.9 Proteins 4.10 Triglycerides 4.11 Carbohydrates
Organic Chemistry
Biological Chemistry
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Introduction to hydrocarbons
Alcohols, aldehydes, ketones and Carbohydrates
Carboxylic acids, esters and triglycerides (fats and oils)
Amines, amides and proteins
Topic 4: Organic and Biological Chemistry
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Organic chemistry - the study of hydrocarbons (compounds of hydrogen and carbon) and their derivatives.
Carbon:
the element of life on earth
4 valence electrons
it has room for 4 covalent bonds to 4 other atoms
Able to form single, double and triple bond
Organic compounds - molecules with carbon atoms as main elements.
7 million organic compounds
1.5 million inorganic compounds
Introduction
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Molecular Formula
- Number of atoms of each element present
Structural Formula
- Shows the individual atoms in a molecule and how they are arrange
Modeling Organic Compounds 1-hexanol C6H14O
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Molecular formula: C5H8O2
Other structural formula:
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Saturated & Unsaturated HC
When C=C or CC bonds are present in the hydrocarbon chain, where the hydrocarbon contain less than the maximum number of hydrogen atoms, its an unsaturated hydrocarbon.
If hydrocarbon chain contain only C-C bonds, it is refer to as saturated hydrocarbon.
Unsaturated Saturated Saturated
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Cyclics (cycloalkanes or cycloalkenes) are alkanes or alkenes which form into a ring structure.
Cyclics
CH2
CH2
CH2
CH2CH2
CH2
H2C
CH2
CH2 H2C
H2C CH2
CH2
CH2
CH2
CH2H2C
H2C
Cyclopropane Cyclobutane
Cyclopentane Cyclohexane
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An aromatic compound has aryl group/ benzene ring as its functional group:
In benzene ring, the electrons in the carbon to carbon double bond are not held between just two
carbon atoms, but are spread over the whole ring,
the electrons are said to be delocalised.
Aromatics
CH
CH
CH
CH
CH
CH
Molecular
formula:
C6H6
Structural formula:
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Physical Properties of Hydrocarbons
All hydrocarbons (HC) are non polar molecules,
HC molecules are attracted to each other only by
weak dispersion forces as secondary interactions.
As the length of hydrocarbon molecules increases,
the dispersion forces between molecules also
increases.
Small molecular mass hydrocarbons (< 5C), have
low boiling points and are gases at room
temperature (Eg. methane, propane, pentane).
Larger molecular mass hydrocarbons (> 5C) have
higher boiling point and usually liquid at room
temperature (Eg. hexane, octane, decane).
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Alkanes 1. General formula: R R
2. Functional group: none
3. Systematic naming / nomenclature: alkane
4. Physical properties:
Non polar molecules
Molecules are held by very weak dispersion forces
small molecular mass alkanes gases at r.t.p. but big molecular mass alkanes liquid at r.t.p. (more dispersion forces between molecules)
have very low MP and BP (weak DF betw mol.)
not soluble in water (cannot form H-bond with
very polar water molecules)
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5. Chemical properties:
Alkanes - generally considered chemically unreactive because they contain no reactive functional group.
But can undergo two main types of reaction:
(I) Complete combustion
CH4 + 2 O2 CO2 + 2 H2O
(II) Substitution forming haloalkanes, where hydrogen is substituted by a halogen in the presence of light.
CH4 + Br2 CH3 Br + HBr
6. Preparation: through fractional distillation of petroleum.
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Alkene & Alkyne 1. General formula: R R RCCR RCCR
2. Functional group: Carbon to carbon Carbon to carbon
double bond triple bond
2. Systematic nomenclature: alkene alkyne
3. Physical properties:
Non polar molecules
Molecules are held by very weak dispersion forces
small molecular mass alkenes gasses at r.t.p. but big molecular mass alkanes liquid at r.t.p.
have very low MP and BP
not soluble in water
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5. Chemical properties: More reactive than alkanes
(I) Complete combustion
CH3CH=CHCH3 + 6 O2 4 CO2 + 4 H2O
(II) Addition reaction
Hydrogenation add H2 across the double bond, with metal catalyst (nickel or platinum); used commercially to convert unsaturated vegetable oils to saturated fat. [Fats and Oils]
CH3CH=CHCH3 + H2 CH3CH2CH2CH3
Halogenation react with halogens (Br2, Cl2)
Bromine Test: Bromine water (Br2 / H2O), a reagent used to test the presence of double bonds because orange bromine solution will be decolorised.
CH3CH=CHCH3 + Br2 CH3CHBrCHBrCH3
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Hydrohalogenation the hydrogen halides (HBr, HCl) can added across a double bond.
CH3CH=CHCH3 + HBr CH3CH2CHBrCH3
Hydration the addition of water (catalysed by an acid) to alkenes is an important reaction industrially, eg. to
produce ethanol (alcohol) from ethene.
CH3CH=CHCH3 + H2O CH3CH2CHOHCH3
Addition polymerization many alkenes and alkenes can add to themselves to form very long-chained
macromolecules called polymers. [Topic 5: Materials]
6. Preparation: cracking of short chain alkanes with the
presence of platinum as catalyst
C C + A B CA C B
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Systematic naming / Nomenclature IUPAC naming
Identify longest chain of carbon atoms containing functional group (parent name).
Number the carbon atoms - start with C nearer to the functional group.
Determine functional groups location and type.
When two same functional groups are present on the same carbon atom, use the number twice.
When two or more functional groups are identical, indicates this by the use of prefixes di-, tri-, tetra-, and so on.
When branching first occurs at an equal distance from either end of the longest, choose the name of that gives the lower number at the first point of difference.
When two or more chains of equal length compete for selection as the parent chain. Choose the chain with greater number of substituents.
Between a number and a number:
Between a number and an alphabet:
Between an alphabet and an alphabet:
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3-bromo-2-chloro-3-methylpentane
2-chloro-5-methylhexane-3-ene
2,4-dibromo-3,5-dichloropentan(e)-1,3-diene
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Derivatives of Hydrocarbons
R = hydrocarbons (saturated / unsaturated /
cyclic / aromatic) or hydrogen atom
X = functional group / reactive site
atoms or groups of atoms that govern
the physical and chemical properties of
an organic compound
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Organic Families
Each family has a functional group to identify it.
1. Alcohols (-OH, hydroxyl group)
2. Aldehydes (-CHO, aldehyde group)
3. Ketones (-CO-, ketone group)
4. Carboxylic acids (-COOH, carboxyl group)
5. Esters (-COO-, ester group)
6. Amines (-NH2, amino group)
7. Amides (-CONH2, amide group)
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Homologous Series Homologous series has an associated functional group.
The formula of each member conforms to the same general formula.
The formula of each member contains more CH2 group than that of the previous member.
The physical properties of the members of a series gradually changes as the molecules become heavier and more complex
Physical state changes from gas to liquid to solid
Boiling point and melting point gradually increases
Solubility in a given solvent gradually decreases
The chemical properties of all the members of a series are similar. If the chemical properties of the first members are known then those of later members can be deduced.
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Types of Organic Reactions
Combustion
Condensation (eg: esterification)
Addition (eg: hydrogenation, hydration, bromination, chlorination)
Acidic hydrolysis
Alkaline hydrolysis (eg: saponification)
Redox reaction
Most organic reaction require special apparatus set-
up to carry out the reaction due to volatile organic
compounds and also the very slow reaction rate.
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Organic reactions apparatus
Reflux apparatus
To prevent the loss of volatile
organic compound and to
increase the rate of organic
reaction by giving extended
heating
Reflux process: repeated
vaporisation and condensation
Most organic reaction require special apparatus set-up
to carry out the reaction because organic compounds
are volatile and also to speed up the rate reaction.
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2. Distillation apparatus Fractional distillation: To separate two miscible liquid with different boiling point, so as to purify / concentrate one of the organic compound.
Buchner filtration apparatus
To separate precipitate formed in an aqueous solution.
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Separation apparatus
To separate two immiscible liquid
Boiling chips
To prevent over heating, bumping of solution and to
make sure heat is distributed evenly throughout the
liquid during reaction.