Organic compounds can be classified based on their functional groups. Members of the same homologous series have similar chemical properties and their physical properties change gradually with increasing carbon chain length. Key factors that affect the physical properties of organic compounds include the structure of the functional group, length of carbon chains, and ability to form hydrogen bonds or dipole-dipole interactions. Non-polar compounds have lower boiling points than polar compounds due to weaker intermolecular forces.
2. O
O
OH
OH alizarin: the first naturally
occurring dye to be
synthesized (1868)
N
H
O
N
H
O
indigo: used to dye blue jeans
CH3CH2OH ethanol: a fermentation product
3. Vitamin B12
The synthesis of vitamin
B12 was finally completed
in 1972 by Woodward
and Eschenmoser after
10 years of work and the
assistance of roughly
one hundred graduate
students.
4. “A production of amino acids under possible
primitive earth conditions”
S.L. Miller, Science, 117, 528 (1953)
CH4 + NH3 + H2O + H2
electric
discharge
amino acids including
glycine and alanine
Proteins
E. coli contains ~5,000 different chemical compounds
of which 3,000 are proteins.
Man contains ~2,000,000 different proteins.
Biologists believe that there are in excess 10,000,000
of proteins which take part in the process of life.
5. Angiotensin II
Angiotensin II is a blood pressure regulating
hormone. It contains 8 amino acid residues.
Its structure is actually:
Asp-Arg-Val-Tyr-Ile-His-Pro-Phe.
It is possible to arrange these in 40,320
different ways; only one of which
corresponds to the hormone
6. Organic ChemistryOrganic Chemistry
• Chemistry of the compounds present
in living organisms.
• They all contain carbon.
• Organic Chemistry is the Chemistry
of Carbon.
7. Living
things
Carbohydrates /
Proteins / Fats /
Vitamins /
Antibiotics
Natural Sources of Organic CompoundsNatural Sources of Organic Compounds
Crude oil
or coal
Fractional distillation /
destructive distillation
Alkanes /
Alkenes /
Alkynes /
Aromatic
hydrocarbons
8. In the past
…,
Chemistry
Organic
compounds
obtained from
living organisms
Inorganic
compounds
obtained from
non-living sources
Development of Organic Chemistry as a ScienceDevelopment of Organic Chemistry as a Science
9. (Inorganic compound) (Organic compound)
In 1828, Friedrich Wohler (a German chemist)
Development of Organic Chemistry as a ScienceDevelopment of Organic Chemistry as a Science
The ammonium cyanate was synthesized from bones
The Kolbe synthesis of acetic acid in 1845 put the
theory to rest.
10. Organic chemistry is the study of carbon
compounds (except CO, CO2, carbonates,
hydrogencarbonates, carbides and
cyanides) obtained from natural sources
or synthesized in the laboratories.
Development of Organic Chemistry as a ScienceDevelopment of Organic Chemistry as a Science
12. Ability to form fourAbility to form four strongstrong covalent bondscovalent bonds
Carbon (ground state)
• Electronic configuration of carbon
(ground state) : 1s2
2s2
2p2
13. • Each carbon atom has four unpaired
electrons when excited
• Tend to form four strong covalent bonds
Carbon (excited state)
Ability to form fourAbility to form four strongstrong covalent bondscovalent bonds
14. • Carbon atoms link together to form
chains of varying length, branched
chains and rings of different sizes
• Catenation:
Ability of atoms in forming stable
bonds with itself, hence joining up
into chains or rings
Ability to CatenateAbility to Catenate
15. Ability to CatenateAbility to Catenate
C – C > Si – Si > Ge – Ge > Sn – Sn
Bond strength ↓ as bond length ↑
C – C > N – N > O – O
Bond strength ↓ as the number of lone pairs ↑
16. Ability to CatenateAbility to Catenate
CnH2n+2 n = 1,2,3,…(no limit for n)
SinH2n+2 n = 1 to 6 only → silanes
GenH2n+2 n = 1 to 3 only → germanes
SnnH2n+2 Only SnH4 (stannane) exists
17. Carbon (excited state)
Ability to Form Multiple BondsAbility to Form Multiple Bonds
sp
2π bonds, 2σ bonds
sp2
1π bond, 3σ bonds
sp3
4σ bonds
19. Carbon
• Carbon can form multiple bonds to itself and
with atoms of other elements.
• Carbon can only make four bonds since it has 4
valence electrons and most often bonds to H, O,
N and S.
• Because the C-C single bond (348 kJ mol-1
) and
the C-H bond (412 kJ mol-1
) are strong, carbon
compounds are stable.
• Carbon can form chains and rings.
21. • Organic compounds are classified by the
presence of characteristic functional
groups.
Functional GroupsFunctional Groups
A functional group is defined as an atom
or a group of atoms that effectively
determines the chemical properties of an
organic compound.
23. • have similar chemical properties
they contain the same functional group –OH
they are classified into the same
homologous series — alcohols
and
Functional GroupsFunctional Groups
24. Homologous SeriesHomologous Series
A homologous series is a series of compounds
that have the same functional group, and each
member differs from the next member by a –
CH2 – unit in their formulae.
CH4 C2H6 C3H8 C4H10
CH2 CH2 CH2
27. • Members in the same series can be
represented by a general formula.
e.g. alkanes: CnH2n+2
alkenes: CnH2n
alkynes: CnH2n-2
Homologous SeriesHomologous Series
e.g. alkanols: CnH2n+1OH
alkanals: CnH2n+1CHO
alkanoic acids: CnH2n+1COOH
28. Functional group of an organic compound
Members of a homologous series have similar
chemical properties
Homologous SeriesHomologous Series
Chemical properties
• The physical properties change gradually along the
homologous series
• e.g. the longer the carbon chain in the molecule ( or the
greater the molecular mass)
the greater the attractive force between molecules
the higher the melting point, boiling point and density
29. Number
of
carbon
atom(s)
Molecular
formula
State (at
room
temperature
and
pressure)
Melting
point (°C)
Boiling
point (°C)
Density of
solid / liquid at
20°C (g cm–3
)
1
2
3
4
5
6
7
8
9
10
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
Gas
Gas
Gas
Gas
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
–183
–172
–188
–135
–130
–95
–91
–57
–54
–30
–161
–89
–42
0
36
69
98
126
151
174
–
–
–
–
0.626
0.657
0.684
0.703
0.718
0.730
Some physical properties of the first 20 members of
straight-chain alkanes
30. Number
of
carbon
atom(s)
Molecula
r formula
State (at
room
temperature
and
pressure)
Melting
point (°C)
Boiling
point (°C)
Density of
solid / liquid at
20°C (g cm–3
)
11
12
13
14
15
16
17
18
19
20
C11H24
C12H26
C13H28
C14H30
C15H32
C16H34
C17H36
C18H38
C19H40
C20H42
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
Solid
Solid
Solid
–26
–10
–7
–3
10
18
22
28
32
37
196
216
233
260
271
287
302
316
330
344
0.740
0.749
0.753
0.761
0.769
0.773
0.778
0.777
0.777
0.785
Some physical properties of the first 20 members of
straight-chain alkanes
31. Factors Affecting theFactors Affecting the
Physical Properties ofPhysical Properties of
Organic CompoundsOrganic Compounds
32. 1. Structure of the functional group
1.1 Dipole moment of the molecule
1.2 Formation of hydrogen bonding
2. Length of carbon chains (London
dispersion forces)
Main Factors Affecting the PhysicalMain Factors Affecting the Physical
Properties of Organic CompoundsProperties of Organic Compounds
33. • Molecules having a polar functional group
have a higher b.p. than others with a non-
polar functional group of similar molecular
masses
Stronger intermolecular attraction
among molecules
Structure of Functional GroupStructure of Functional Group
34. Structure of Functional GroupStructure of Functional Group
Molecule Relative
molecular
mass
Boiling point
(o
C)
Molecules
with polar
functional
groups
CH3CH2CH2OH 60 97.2
CH3CH2CH2NH2 59 48.6
CH3CH2Cl 64.5 12.5
CH3CH2COOH 60 141
Molecules
with non-
polar
functional
groups
CH3CH2CH2CH3 58 -0.5
CH3CH2CH=CH2 56 -6.2
CH3CH2C≡CH 54 8.1
35. Polarity and Polar Bonds
The atoms in a nonpolar covalent bond have
electronegativity differences of 0.4 or less.
Examples:
Atoms Electronegativity Difference Type of Bond
N-N 3.0 - 3.0 = 0.0 Nonpolar covalent
C-P 2.5 - 2.1 = 0.4 Nonpolar covalent
H-C 2.1 – 2.5 = 0.4 Nonpolar covalent
Non-polar bonds:
36. The atoms in a polar covalent bond have
electronegativity differences of 0.5 to 1.6.
Examples:
Atoms Electronegativity Difference Type of Bond
O-H 3.5 – 2.1 = 1.4 Polar covalent
N-C 3.0 - 2.5 = 0.5 Polar covalent
O-S 3.5 - 2.5 = 1.0 Polar covalent
Polar Bonds:
38. • Metal elements have low electronegativity values
• Non-metal elements have high electronegativity values
Electronegativity increases
Electronegativityincreases
39. Dipole Moment of MoleculeDipole Moment of Molecule
• Tetrachloromethane has 4 polar bonds in the
molecule
• M.p. and b.p. are very low
the molecule is non-polar
the molecule is tetrahedrally
symmetrical
the dipole moments of the
C Cl bond cancel each other
40. Examples of Polar Molecules with NetExamples of Polar Molecules with Net
Dipole MomentDipole Moment
Examples of Non-polar Molecules withExamples of Non-polar Molecules with
No Net Dipole MomentNo Net Dipole Moment
41. Solubility of Organic MoleculesSolubility of Organic Molecules
• Depends on the polarity of organic molecules
and the solvent
• Non-polar or weakly polar compounds dissolve
readily in non-polar or weakly polar solvents
• Highly polar compounds dissolve readily in
highly polar solvents
• “Like dissolves like”
42. Solubility of Organic MoleculesSolubility of Organic Molecules
Hexane in
tetrachloromethane
Hexane in water
43. Hexane Dissolve Readily in TetrachloromethaneHexane Dissolve Readily in Tetrachloromethane
(CCL(CCL44))
Intermolecular forces among
hexane molecules and those
among CCl4 molecules
≈
Intermolecular forces between
hexane and CCl4 molecules
Hexane Insoluble in WaterHexane Insoluble in Water
44. Formation of Hydrogen BondingFormation of Hydrogen Bonding
• Molecules having OH or NH2 groups are
able to form hydrogen bonds
• Hydrogen bonds affect the physical properties
of alcohols and amines with low molecular
masses
Propan-1-ol have a Higher Boiling PointPropan-1-ol have a Higher Boiling Point
45. Formation of Hydrogen BondingFormation of Hydrogen Bonding
• Also affect the solubility of a molecule
• Molecules with OH groups are able to form
hydrogen bonds with surrounding water
molecules Soluble in water
Length of Carbon ChainsLength of Carbon Chains
• Molecules with higher molecular masses have
higher m.p., b.p. and density
Higher molecular masses
Large molecular sizes
Stronger London dispersion forces
among molecules
46. Length of Carbon ChainsLength of Carbon Chains
• Molecules with branched chains
b.p. and density lower than its straight-chain
isomer
Straight-chain isomers have greater surface area
in contact with each other
Greater attractive force among the molecules
• Molecules with branched chains
m.p. higher than its straight-chain isomer
Branched-chain isomers are more spherical
Packed more efficiently in solid state
Extra energy is needed to break down the
efficient packing
47. • Intermolecular forces
– Simple alkanes, alkenes, alkynes → van der Waals’ forces
(nonpolar) → lower b.p.
– Aldehydes, ketones, esters & presence of halogens (polar) →
dipole: dipole forces → slightly higher b.p.
– Alcohol, carboxylic acid & amine → hydrogen bonding (w/ O,
N, F) → even higher b.p.
• Volatility: how easily a substance turns into a gas
– The weaker the intermolecular force, the more volatile it is
– vdW › d-d › H
– alkane › halogenoalkane › aldehyde › ketone › amine › alcohol
› carboxylic acid
48. • Solubility: a solute’s ability to dissolve in a polar solvent (water)
– The more polar a substance is, the more soluble it is
• Solubility:
– If the functional group is soluble (hydrogen bonded), it will be
more soluble
– Solubility decreases as chain length increases
– Smaller alcohols, aldehydes, ketones & carboxylic acids are
typically soluble
– Halogenoalkanes are NOT soluble since they don’t form
hydrogen bonds
49. Resonance
Consider the carbonate ion, CO3
2-
. We can draw three equivalent
structures:
-
O O-
O -
O
-
O O O-
-
O
O
In reality the ion is perfectly symmetric.
All C-O bond lengths are identical and the negative charge is
delocalized over the three oxygens.
The structure is a hybrid of these three contributing structures.
• Whenever a molecule can be represented by 2 or more
structures which differ only in the arrangement of their
electrons, there may be resonance:
• The molecule is a hybrid of all the contributing structures and
cannot be adequately represented by any one of these
structures.
50. Atomic orbitals
Atomic orbitals are described by quantum numbers:
The most important is the principal quantum number, n.
It governs the energy of an orbital. It can be equal to any
positive integer except for zero.
The second is the angular momentum quantum number, l,
whose value depends on n: l = 0, 1, 2, …. n-1. It determines the
shape of the orbital.
The third is the magnetic quantum number, ml, which governs
the orientation of the orbital relative to the three axes. ml = -l, -l +
1 … 0 … l - 1, l.
51. Orbitals are classified (named) according to their values of n
and l using a number and a letter. The number represents the
value of n and the letter represents the value of l.
Electrons in an orbital having l = 0 are called s electrons.
Electrons in an orbital having l = 1 are called p electrons.
Electrons in an orbital having l = 2 are called d electrons.
Atomic orbitals
n = 1, l = 0, ml = 0 one 1s orbital
n = 2, l = 0, ml = 0 one 2s orbital
n = 2, l = 1, ml = -1, 0, or +1 three 2p orbitals!
54. Electron configurations
The aufbau principle: Orbitals of lowest energy are filled first.
The Pauli exclusion principle: Orbitals can accommodate a
maximum of two electrons but only if they are of opposite spin.
Hund’s rule: One electron is placed in each degenerate orbital
before adding a second electron to an orbital.
The electronic configuration of carbon is therefore
1s2
2s2
2p1
2p1
55. Hybrid atomic orbitals
Orbital hybridization is a mathematical approach that involves
the combination of individual orbital wave functions to obtain
wave functions for new orbitals.
These orbitals have, in varying proportions, the properties of the
original orbitals taken separately.
sp3
hybrid orbitals
1s 2s 2p
↑↓ ↑ ↑ ↑ ↑
The four orbitals are mixed (hybridized) to give four new sp3
hybrid orbitals which are oriented at angles of 109.5o
and are
more directional in character:
61. sp hybrid orbitals
sp hybridization leads to a linear structure. BeH2 is
an example of such a molecule. The 2s orbital and one
of the 2p orbitals are hybridized.
H Be H
180
o
64. NH3
Ammonia is pyramidal and its bond angles (H-N-H) are 107o
.
..
N
H H
H
H2O
:
..
O
H H
Oxygen has 8 valence electrons in the water molecule:
Its bond angle is 104.5°.
65. Bond dissociation energies
Energy is released when bonds are formed.
Energy is absorbed when bonds are broken.
This energy is called the bond dissociation energy, D.
A B A + B
Homolysis
free radicals
A B A + B
Heterolysis
ions
66. Breaking of bonds to carbon
C Z +
carbocation
+ :Z-
C Z C:-
+ Z+
carbanion
C Z
radical
+ Z
