Organic Chemistry

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Organic Chemistry

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Outline

• Introduction
• Special nature of carbon
• Classification of Organic Chemistry
• Homologous Series General Characteristics
• Separation of Petroleum Cracking
• Types of formula
• Isomerism
• I.U.P.A.C Nomenclature
• Compounds of different functional groups

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Introduction

• Organic chemistry is the study of carbon
  compounds. There are around 6 millions compounds
  of C already known.
• Not all C-compounds are organic
• CO, CO2 considered inorganic
• Organic compounds ? covalently bonded compounds
  containing carbon, excluding carbonates and
  oxides

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Special nature of carbon

• Carbon can join with other carbon atoms to form
• Long chain carbon atoms
• Branch chain carbon atoms
• Rings of carbons
• Multiple bonds between carbon atoms and atoms of
  other elements

Why is it possible for carbon to do so?
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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.
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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
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THE SPECIAL NATURE OF CARBON
MULTIPLE BONDING AND SUBSTITUENTS CARBON-CARBON
COVALENT BONDS CAN BE SINGLE, DOUBLE OR TRIPLE
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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
CARBON SKELETON FUNCTIONAL
GROUP
GROUP The chemistry of an organic
compound is determined by its FUNCTIONAL GROUP
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THE SPECIAL NATURE OF CARBON
MULTIPLE BONDING AND SUBSTITUENTS ATOMS/GROUPS
CAN BE PLACED IN DIFFERENT POSITIONS ON A CARBON
SKELETON
THE CC 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
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Classification of Organic Compounds

• Hydrocarbons Compounds containing carbon and
  hydrogen only
• Non-hydrocarbons Compounds that may also
  contain other elements such as nitrogen, sulphur,
  halogen or oxygen atoms besides hydrogen and
  carbon.

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Homologous Series

• A series of compounds with the same general
  formula (e.g. Alkanes CnH2n2) and functional
  group (e.g. CC, OH)
• Each member differs from the next by CH2
• Members have the same chemical properties.
• Members show a gradation in physical properties.

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Some functional groups
Homologous Series Condensed structural formula Structure of Functional Group
Alkanes -CH2CH2-
Alkenes -CHCH- C C
Halogenoalkanes -X ( X F, Cl, Br, I) -X ( X F, Cl, Br, I)
Alcohols -OH O H
Aldehydes -CHO O C H
Ketones -CO- R CO R
Carboxylic acids -COOH O C O H
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alkene
alcohol
ketone
ester
carboxylic acid
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carboxylic acid
ester
aldehyde
ether
amine
nitrile
Page 425
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Influence of functional groups

• bonding and shape
• type and strength of intermolecular forces
• physical properties
• nomenclature
• chemical reactivity

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Homologous Series Polarity Intermoecular forces Boiling point Solubility in water
Alkane non-polar van der Waals low Insoluble
Alkene non-polar van der Waals Insoluble
Alcohol Lower members soluble H bonding to water
Aldehydes/ ketones Dipole-dipole gt alkane lt alcohol Lower members soluble polar and water can H bond with them.
Carboxylic acid Hydrogen bonding High gt alcohol (more H bonding) Lower members soluble H bonding to water
Halogenoalkane For same no. of C atoms, I gt Br gt Cl Van der Waals forces stronger if Mris higher Insoluble
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Isomerism

• Structural Isomers are 2 or more compounds with
  the same molecular formula but different
  structural formula.
• Example Isomers of butane
• 1st isomer 2nd isomer
• Condensed CH3CH2CH2CH3
  CH3CH(CH3)CH3
• formula
  (has a branched chain)

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• Pentane has 3 isomers
• 1st isomer 2nd isomer
  3rd isomer
• Condensed
• formula

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Some isomers of C5H12O

• -OH attached to C-1
• OH attached to C-2
• OH attached to C-3
• Many more isomers of alcohol.
• Some are not alcohol.
• E.g. ether containing C-O-C as a fnal group.
• CH3CH2CH2OCH2CH2CH3

Page 428 Practice Qns
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Physical Properties of Alkanes

• First 4 members are gases at room temperature
  pressure (r.t.p.)
• All members are insoluble in water but soluble in
  organic solvent.
• Reasons
• Made up of covalent molecules held by weak
  intermolecular forces, so less energy is required
  to overcome the forces to separate the molecules.
• Like dissolve like

Do you expect isomers to have similar physical
properties?
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• Isomers have different physical properties e.g.
  boiling point or melting point because the
  different structures will affect the physical
  properties.
• Isomers have the same chemical properties because
  there are the same number and kind of atoms in
  each isomer.

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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.
Prefix C atoms Alkane meth- 1 methane eth- 2
ethane prop- 3 propane but- 4 butane pent- 5 pent
ane hex- 6 hexane hept- 7 heptane oct- 8 octane no
n- 9 nonane dec- 10 decane
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.
Working out which is the longest chain can pose a
problem with larger molecules.
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I.U.P.A.C. NOMENCLATURE
How long is a chain? Because organic molecules
are three dimensional and paper is two
dimensional it can be 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
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.
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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.
THE ANSWERS ARE ON THE NEXT SLIDE
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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.
LONGEST CHAIN 5
LONGEST CHAIN 6
LONGEST CHAIN 6
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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
Functional group Suffix ALKANE - ANE ALKENE -
ENE ALKYNE - YNE ALCOHOL - OL ALDEHYDE -
AL KETONE - ONE ACID - OIC ACID
1-CHLOROBUTANE 2-CHLOROBUTANE
SUBSTITUENTS Many compounds have substituents
(additional atoms, or groups) attached to the
chain. Their position is numbered.
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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). 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.
2-methylheptane Numbers are separated from
numbers by a COMMA e.g. 2,3-dimethylbutane
Alkyl radicals methyl CH3 -
CH3 ethyl CH3- CH2- C2H5 propyl CH3-
CH2- CH2- C3H7
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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). 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. 2-methylheptane 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
Alkyl radicals methyl CH3 -
CH3 ethyl CH3- CH2- C2H5 propyl CH3-
CH2- CH2- C3H7
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I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
THE ANSWERS ARE ON THE NEXT SLIDE
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I.U.P.A.C. NOMENCLATURE
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
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I.U.P.A.C. NOMENCLATURE
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain 5 so it is a pentane A CH3,
methyl, group is attached to the third carbon
from one end... 3-methylpentane
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I.U.P.A.C. NOMENCLATURE
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain 5 so it is a pentane A CH3,
methyl, group is attached to the third carbon
from one end... 3-methylpentane
Longest chain 6 so it is a hexane A CH3,
methyl, group is attached to the second carbon
from one end... 2-methylhexane
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I.U.P.A.C. NOMENCLATURE
I.U.P.A.C. NOMENCLATURE
Apply the rules and name these alkanes
Longest chain 5 so it is a pentane A CH3,
methyl, group is attached to the third carbon
from one end... 3-methylpentane
Longest chain 6 so it is a hexane A CH3,
methyl, group is attached to the second carbon
from one end... 2-methylhexane
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
Discuss examples Page 430
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• Name the following hydrocarbons
• C(CH3)4
• CH3CH(C2H5)CH3
• CH3CH2CH(C2H5)CH2CH3

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Alkanes

• Belongs to the homologous series of saturated
  hydrocarbons
• Contain only single covalent bonds between atoms
  in molecules.
• Contain only hydrogen and carbon atoms

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Alkanes

• Alkanes ? hydrocarbons that contain only single
  bonds
• Each one different from previous by
• 1 C and 2 H

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General Characteristics

• Can be represented by a general formula.
• Physical property changes gradually as the number
  of CH2 group increases.
• Have similar chemical properties (since they have
  the same functional groups)

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• For alkanes with 3 or less C atoms, only 1
  molecular structure possible
• In alkanes with more than 3, chains can be
  straight or branched
• So, alkanes with 4 or more C have structural
  isomers

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Alkanes
Names Molecluar Formula Mr Empirical Formula Condensed Formula Bpt /0 C State Full structural formula
Methane CH4 16 CH4 CH4 -164 Gas
Ethane 30 -89 Gas
Propane C3H8 44 C3H8 CH3CH2CH3 -42 Gas
Butane 58 -0.5 Gas
Pentane C5H12 72 36 Liquid
Hexane C6H14 CH3 (CH2) 4CH3 liquid
Name ends with ane and has a general molecular
formula CnH2n2
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Physical states

• Alkanes with lowest molecular mass (1-4 C atoms)
  are gases
• Natural gas ?fossil fuel made primarily of
  alkanes containing 1-4 C atoms
• C-H bonds are nonpolar
• Only forces of attraction between nonpolar
  molecules are weak intermolecular forces

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• The strength of the forces is related to the no.
  of electrons involved in the structure and the
  surface area of the molecules over which the
  interactions can be spread.
• Increasing the chain length of the molecules
  increase both these features and so the strength
  of the van der Waals forces increases with the
  increasing molecuar size.
• Physical properties dependent on these
  interactions, such as mpt, bpt and enthalpy of
  vaporisation will also increase with the length
  of chain.

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• Larger alkanes are liquid
• Gasoline, kerosene made mostly of liquid alkanes
• Stronger forces hold together enough to form
  liquids
• Alkanes with very high molecular mass are solid
• Paraffin wax contains solid alkanes (candles)

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Boiling points

• Increase with increasing molecular mass
• As the strength of the van der Waals forces
  increases, more energy (heat) required to break
  them
• This property used in separation of petroleum
  (major source of alkanes)
• Petroleum ? complex mixture of different
  hydrocarbons that varies greatly in composition

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Separation of Petroleum

• Petroleum is a mixture of hydrocarbon molecules
  from 1 to more than 50 C atoms is heated in a
  furnace. Oil vaporizes and passes up the
  fractionating column.
• The different fractions come out of the column
  at different heights depending on their boiling
  points.
• Substances with low boiling points are collected
  near the top of the column

A hydrocarbon with a long chain has
__________________than one with a shorter carbon
chain
higher boiling point
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General Properties
Fractions Boiling (0C) Approx no. of C atoms
Petroleum gas Below 40 1-4
Petrol (gasoline) 40-75 5-10
Naphtha 75-150 7-14
Kerosene (paraffin) 160-250 11-16
Diesel Oil 250-300 16-20
Lubricating Oil 300-350 20-35
Bitumen Above 350 More than 70

• As the no. of C atoms
• increases,
• boiling point increases
• liquids are more viscous
• liquids burn less easily

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Cracking

• To meet the demands for fractions like petrol and
  kerosene, a process called cracking is carried
  out.
• This involves the use of high temperature,
  pressure and catalyst to split the larger
  molecules (of higher boiling points) into smaller
  ones (of lower boiling points)
• Example
• C10H2 ? C10H22 C10H22

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Alkenes

• Belongs to the homologous series of unsaturated
  hydrocarbons.
• Contains double covalent bonds between C atoms in
  molecules.
• Contain only H and C atoms.

Draw the dot and cross diagram of ethene
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Alkenes
Name formula Mr Full structural formula
Ethene C2H4 28
Pro-1-pene C3H6 42
But-1-ene C4H8 56
Pent-1-ene C5H10 70
Hex-1-ene
Important plant hormone induces flowering and
ripening of fruit
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Isomerism

• Butene has 3 isomers
• 1st isomer 2nd isomer
  3rd isomer
• Condensed
• formula

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• Draw all the isomers of C5H10 and write their
  condensed formulae.

Page 440
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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 CC bond 5
4 3 2 1 CH3CH2CHCHCH3
is pent-2-ene (NOT pent-3-ene) Side-chain
Similar to alkanes position is based
on the number allocated to the double bond 1
2 3 4
1 2 3
4 CH2 CH(CH3)CH2CH3 CH2
CHCH(CH3)CH3 2-methylbut-1-ene 3-methy
lbut-1-ene
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Naming alkenes (more than 1 CC)
Page 440
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• Name the following alkenes
• (a) (b)
  CH3CH2CH(CH3)CH CH2
• (c) (d)
  CH2 C(CH3)CH2CH CH2

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Alcohols
Name formula Full structural formula
Methanol
Ethanol C 2H5OH
Propan-1-ol C3H7OH
Butan-1-ol C4H9OH
Pentan-1-ol
general formula CnH2n1OH or R-OH Lower members
are very soluble in water because of hydrogen
bonding
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Alcohols

• Alcohols are the homologous series with the
  general formula CnH2n1OH.
• They all contain the functional group, OH, which
  is called the hydroxyl group.
• Alcohols can be classified as primary, secondary
  or tertiary, depending on the carbon skeleton to
  which the hydroxyl group is attached.

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RCH2OH 1 alkyl group on C next to OH so primary
alcohol, 1
R2CHOH 2 alkyl groups on C next to OH so
secondary alcohol, 2
R3COH 3 alkyl groups on C next to OH so tertiary
alcohol, 3
Draw out the structure, name and classify all the
alcohols with the formula C4H9OH.
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Butan-1-ol primary
Butan-2-ol secondary
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2-methylpropan-1-ol primary
2-methylpropan-2-ol tertiary
Page 448
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• Draw the isomers of propanol.

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Aldehydes (Carbonyl compound)
Name formula Full structural formula
Methanal HCHO
Ethanal CH3CHO
Propanal C2H5CHO
Butanal
general formula CnH2n1CHO or R-CHO
61

• Name and draw the full structural formula of
• CH3CH2CH2CH(CH3)CHO

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Ketones
Name formula Full structural formula
Propanone CH3COCH3
Butanone CH3COC2H5
general formula R-CO-R where R represents
either The same alkyl group as R or a differen
alkyl group
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Draw the full structural formula of pentan-2-one
and write its condensed formula.
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Physical properties ofaldehydes and ketones

• Aldehydes and ketones have very similar boiling
  points.
• Aldehyde has higher b. pt. than alkane of similar
  RMM and lower b. pt. than alcohols of similar RMM.

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• Aldehydes are polar due to the very
  electronegative O, whereas alkanes are non-polar.
  
• IMF between aldehyde molecules are stronger than
  those in alkane of similar RMM due to
  dipole-dipole interaction but only van der Waals
  forces are present between alkane molecules.
  Hence aldehydes have higher bpt than alkanes.
• Alcohols are polar and its O is joined directly
  to H able to form H bonding.
• Since strength of hydrogen bond gt dipole-dipole
  interaction, alcohol has higher bpt than
  aldehydes.

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Solubility

• Lower members (methanal, ethanal, propanal,
  propanone, butanone) are soluble in water since
  they form H bonding with water.
• Aldehyde cannot H bond to each other but able to
  form H bond with water.
• Solubilty decreases with increasing length of HC
  chains because of the non-polar nature of the HC
  chain.

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Carboxylic acids
Name formula Full structural formula
Methanoic acid HCOOH
Ethanoic acid CH3COOH
Propanoic acid C2H5COOH
general formula R-COOH or R-CO2H
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Name the following organic compound and write its
condensed formula.
Practice Page 455
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Physical properties ofcarboxylic acids

• Carboxylic acids have H bonding between
  molecules. They have higher bpt. than aldehydes
  and alcohols of similar RMM.
• Carboxylic acids have two O atoms per molecule,
  hence have stronger H bonding than alcohols which
  has only one O atom per molecule. Therefore,
  carboxylic acids have higher bpt. than alcohols.
• Carboxylic acids with lower RMM are generally
  soluble in water and less soluble when the HC
  chain increases.

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Halogenoalkanes

• Named by using name of the alkane from which they
  are derived with the prefix chloro-, bromo- or
  iodo-.
• For example
• CH3CH2Br is bromoethane
• (CH3)2CHCH2Cl is 1-chloro-2-methylpropane

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Remember the position of the halogen atom must be
indicated using the appropriate number so
CH3CH2CH2Cl is 1-chloropropane and CH3CHClCH3 is
2-chloropropane Halogenoalkanes can be
classified in the same way as alcohols.
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Halogenoalkanes (halogen atom as fnal group)
Name formula Full structural formula
Iodomethane

1-bromo-3-fluoro-pentane

general formula R-X where X F, Cl, Br or I
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Primary, secondary and tertiary halogenoalkanes
Page 458
74
Key feature of halogenoalkanes is
C X
where X Cl, Br or I
What is notable about this bond compared with
say, C C and C H?
The halogen atom is more electronegative than C
so the bond is polarised
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ORDER OF BOND POLARITIES
?
?-
?
?-
?
?-
C Cl
C I
C Br
gt
gt
So is order of reactivity chloroalkane gt
bromoalkanes gt iodoalkanes?
Is there another factor that ought to be
considered before reaching a conclusion?
BOND ENERGIES
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Bond energies
Bond Bond energy in kJmol-1
C - Cl
C - Br
C - I
346
290
234
This suggests that the order of reactivity
is iodoalkane gt bromoalkanes gt chloroalkanes
77
Boiling points

• No. of C atoms
• Halogenoalkanes have higher bpt. than alkanes
  with the same no. of C atoms.
• Due to the higher RMM and hence stronger van der
  Waals forces.

Refer to table Page 456
78

• Compounds of same RMM
• Bromo- and iodo-compounds have substantially
  lower bpt. than alkanes of similar RMM.
• Alkanes have longer chain molecules in the
  liquid state more S. A. Of molecules in contact
  stronger IMF.
• Little difference between bpt of alkanes and
  chloroalkanes of similar RMM.
• The chloroalkanes are polar but alkanes are
  non-polar expect to have higher bpt but is
  balanced out by the long HC chain of alkanes.

Refer to table Page 456
79
Solubility

• Sparingly soluble or insoluble in water
• Soluble in organic solvent

80
Amines
Name formula Full structural formula
Methylamine

2-aminobutane
general formula R-NH2 Strong smelling substances
Page 465
81
Esters
Name formula Full structural formula
Methyl methanoate

Propyl ethanoate

general formula R-COOR, where R is an alkyl
group
82
Aromatic compounds (arenes)
Name formula Full structural formula
Benene C6H6
Methyl benzene


83
Primary, secondary and tertiary compounds

• Are the following molecules primary, secondary or
  tertiary?
• 3-methylpentan-3-ol
• Pentan-2-ol
• 1-chlorobutane

84

• Are the following molecules primary, secondary or
  tertiary?
• 3-methylpentan-3-ol
• Pentan-2-ol
• 1-chlorobutane

85
Additional notes
86
Intermolecular forces

• also referred to as noncovalent interactions or
  nonbonded interactions.
• several types of intermolecular interactions.

87
Physical Properties of Organic Molecules

• What type of intermolecular force would you
  expect to find between alkanes, halogenoalkanes,
  aldehydes, ketones, alcohols and carboxylic
  acids?
• Use this information to deduce the relative
  boiling points of these homologous series and
  their solubility in water.

88
Ion-ion interactions

• Ionic compounds contain oppositely charged
  particles held together by extremely strong
  electrostatic interactions.
• These ionic interactions are much stronger
• than the intermolecular forces present between
  covalent molecules.

89
Van der Waals forces (London forces)

• are weak interactions caused by momentary changes
  in electron density in a molecule.
• the only attractive forces present in nonpolar
  compounds.
• Even though CH4 has no net dipole, at any one
  instant its electron density may not be
  completely symmetrical, resulting in a temporary
  dipole. This can induce a
• temporary dipole
• in another molecule.
• The weak interaction
• of these temporary
• dipoles constituents
• van der Waals forces.

90

• van der Waals forces are also affected by
  polarizability.
• Polarizability is a measure of how the electron
  cloud around an atom responds to changes in its
  electronic environment.
• Larger atoms, like iodine, which have more
  loosely held valence electrons, are more
  polarizable than smaller atoms like fluorine,
  which
• have more tightly held
• electrons.
• Thus, two F2 molecules
• have little attractive
• force between them
• since the electrons are
• tightly held and
• temporary dipoles are
• difficult to induce.

91
Hydrogen bonding

• Hydrogen bonding typically occurs when a hydrogen
  atom bonded to O, N, or F, is electrostatically
  attracted to a lone pair of electrons on an O, N,
  or F atom in another molecule.

92
Physical properties Boiling points

• In boiling, energy is needed to overcome the
  attractive forces in the more ordered liquid
  state.
• The stronger the intermolecular forces, the
  higher the boiling point.
• For compounds with approximately the same
  molecular weight

93

• Consider the examples below which illustrate the
  effect of
• size and polarizability on boiling points.

94
In summary

• The intermolecular forces increase with
  increasing polarization of bonds.
• Strength of forces (and therefore impact on
  boiling points) is  ionic gt hydrogen bonding gt
  dipole dipole gt van der Waals forces
• Boiling point increases with molecular weight,
  and with surface area.

95
Volatility

• A measure of how easily a substance evaporates. A
  high volatile substance evaporates easily and has
  a low boiling point.
• 3 factors that affect the volatility
• Volaility decreases with the increasing molecular
  size. The longer molecule with increased
  molecular size has stronger van der Waals force
  between the molecules, hence increasing boiling
  point. Hence, the early molecules are gases and
  liquids while the later molecules are mostly
  soilds.

96

• A branched isomer of the compound is likely to
  have a lower boiling point than its straight
  chain isomer.
• The branching of a chain results in a more
  spherical overall shape to the molecule. This
  means there is less contact surface area between
  molecules and these branched isomers have weaker
  intermolecular forces and hence lower boiling
  points.

97

• The nature of the functional group present will
  influence the volatiity, depending on the effect
  of intermolecular forces.
• Polar groups will have stronger dipole-dipole
  interactions between molecules hence higher
  boiling points.
• Groups that are capable of forming hydogen bonds
  will result in even stronger forces between the
  molecules, giving rise to even higher boiling
  points.

98
Melting point

• In melting, energy is needed to overcome the
  attractive forces in the more ordered crystalline
  solid.
• The stronger the intermolecular forces, the
  higher the melting point.
• Given the same functional group, the more
  symmetrical the compound, the higher the melting
  point.

99

• The trend in melting points of pentane, butanal,
  and 1-butanol parallels the trend observed in
  their boiling points.

100
Solubility

• Solubility is the extent to which a compound,
  called a solute, dissolves in a liquid, called a
  solvent.
• In dissolving a compound, the energy needed to
  break up the interactions between the molecules
  or ions of the solute comes from new interactions
  between the solute and the solvent.

101

• An organic compound is water soluble only if it
  contains one polar functional group capable of
  hydrogen bonding with the solvent for every five
  C atoms it contains.
• For example, compare the solubility of butane and
  acetone in H2O and CCl4.

102

• To dissolve an ionic compound, the strong ion-ion
  interactions must be replaced by many weaker
  ion-dipole interactions.

103

• The nonpolar part of a molecule that is not
  attracted to H2O is said to be hydrophobic.
• The polar part of a molecule that can hydrogen
  bond to H2O is said to be hydrophilic.
• In cholesterol, for example, the hydroxy group is
  hydrophilic,
• whereas the carbon skeleton is hydrophobic.

104
Soap

• Soap molecules
• have two distinct
• partsa hydrophilic
• portion composed
• of ions called the
• polar head, and a
• hydrophobic
• carbon chain of
• nonpolar CC
• and CH bonds,
• called the
• nonpolar tail.

105
Influence of functional groups on reactivity
106

• On the other hand, alkyl halides possess an
  electrophilic carbon atom, so they react with
  electron rich nucleophiles.