This document provides an introduction to organic chemistry, focusing on functional groups and how they influence molecular properties and reactivity. It defines functional groups as parts of molecules that determine geometry, physical properties, and reactivity. The document discusses common functional groups containing heteroatoms and pi bonds, and how these features create reactive sites. It also examines how functional groups influence intermolecular forces, physical properties like boiling point and solubility, and chemical reactivity.

1. Basics of Organic Chemistry
By-
Saurav K. Rawat
(Rawat DA Greatt) 1

2. Introduction to Organic Molecules and Functional Groups
Functional Groups
• A functional group is an atom or a group of atoms with
characteristic chemical and physical properties. It is the
reactive part of the molecule.
• Most organic compounds have C—C and C—H bonds.
However, many organic molecules possess other
structural features:
 Heteroatoms—atoms other than carbon or hydrogen.
 p Bonds—the most common p bonds occur in C—C
and C—O double bonds.
 These structural features distinguish one organic
molecule from another. They determine a molecule’s
geometry, physical properties, and reactivity, and
comprise what is called a functional group.
2

3. • Heteroatoms and p bonds confer reactivity on a particular
molecule.
Heteroatoms have lone pairs and create electron-deficient
3
sites on carbon.
p Bonds are easily broken in chemical reactions. A p
bond makes a molecule a base and a nucleophile.
Don’t think that the C—C and C—H bonds are unimportant.
They form the carbon backbone or skeleton to which the
functional group is attached.

4. • Ethane: This molecule has only C—C and C—H bonds, so it has
no functional group. Ethane has no polar bonds, no lone pairs,
and no p bonds, so it has no reactive sites. Consequently,
ethane and molecules like it are very unreactive.
• Ethanol: This molecule has an OH group attached to its
backbone. This functional group is called a hydroxy group.
Ethanol has lone pairs and polar bonds that make it reactive with
a variety of reagents.
The hydroxy group makes the properties of ethanol very
different from the properties of ethane.
4

5. Hydrocarbons are compounds made up of only the elements
carbon and hydrogen. They may be aliphatic or aromatic.
5

6. 6
OH
H2SO4
OH H OSO3H
OH2 + HSO4
H H2SO4 3C CH3 No Reaction
OH
NaH
OH
Na H O Na + H2
NaH
H3C CH3
No Reaction

7. • Aromatic hydrocarbons are so named because many of the
earliest known aromatic compounds had strong characteristic
odors.
• The simplest aromatic hydrocarbon is benzene. The six-membered
ring and three p bonds of benzene comprise a single
functional group.
• When a benzene ring is bonded to another group, it is called a
phenyl group.
7

8. 8

9. 9

10. Compounds Containing the C=O Group:
• This group is called a “carbonyl group”.
• The polar C—O bond makes the carbonyl carbon an
electrophile, while the lone pairs on O allow it to react
as a nucleophile and base.
• The carbonyl group also contains a p bond that is more
easily broken than a C—O s bond.
10

11. It should be noted that the importance of a functional
group cannot be overstated.
11
A functional group determines all of the following
properties of a molecule:
 Bonding and shape
 Type and strength of intermolecular forces
 Physical properties
 Nomenclature
 Chemical reactivity

12. 12
Which of the following is an aldehyde?
H3CH2CH2C
O
CH3 H3CH2CH2C
O
H
A B
H3CH2CH2C
O
OH
H3CH2CH2C
O
CH3
C
D
H3CH2CH2C
O
H
B

13. 13
Which of the following is an ester?
H3CH2CH2C
O
CH3 H3CH2CH2C
O
NH2
A B
H3CH2CH2C
O
OH
H3CH2CH2C
O
C
D
O
CH3
H3CH2CH2C
O
C
O
CH3

14. 14
Which of the following is an amide?
H3CH2CH2C
O
CH3 H3CH2CH2C
O
NH
A B
H3CH2CH2C
O
H2N OH
C
D
O
CH3
CH2CH3
H3CH2CH2C
O
NH
B
CH2CH3 H2N
O
C
CH3

15. Intermolecular Forces
• Intermolecular forces are interactions that exist between
molecules. Functional groups determine the type and
strength of these interactions.
• There are several types of intermolecular interactions.
• Ionic compounds contain
oppositely charged particles
held together by extremely
strong electrostatic inter-actions.
15
These ionic inter-actions
are much stronger
than the intermolecular forces
present between covalent
molecules.

16. • Covalent compounds are composed of discrete
molecules.
• The nature of the forces between molecules depends on
the functional group present. There are three different
types of interactions, shown below in order of
increasing strength:
16
 van der Waals forces
 dipole-dipole interactions
 hydrogen bonding

17. van der Waals Forces
• van der Waals forces are also known as London forces.
• They are weak interactions caused by momentary changes in
electron density in a molecule.
• They are 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
constitutes van der Waals
forces.
17

18. • All compounds exhibit van der Waals forces.
• The surface area of a molecule determines the strength of the
van der Waals interactions between molecules. The larger the
surface area, the larger the attractive force between two
molecules, and the stronger the intermolecular forces.
18
Figure 3.1
Surface area and
van der Waals forces

19. • 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.
19
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.

20. 20
Dipole-Dipole Interactions
• Dipole—dipole interactions are the attractive forces between
the permanent dipoles of two polar molecules.
• Consider acetone (below). The dipoles in adjacent molecules
align so that the partial positive and partial negative charges
are in close proximity. These attractive forces caused by
permanent dipoles are much stronger than weak van der Waals
forces.

21. • 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.
21
Hydrogen Bonding

22. Note: as the polarity of an organic molecule increases, so
does the strength of its intermolecular forces.
22

23. What type of intermolecular forces are exhibited by each
molecule?
23
N
VDW VDW and DD
O
OH
VDW, DD
and HB
VDW

24. 24
Physical Properties—Boiling Point
• The boiling point of a compound is the temperature at which
liquid molecules are converted into gas.
• 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:

25. Consider the example below. Note that the relative
strength of the intermolecular forces increases from
pentane to butanal to 1-butanol. The boiling points of
these compounds increase in the same order.
For two compounds with similar functional groups:
• The larger the surface area, the higher the boiling point.
• The more polarizable the atoms, the higher the boiling
point.
25

26. Consider the examples below which illustrate the effect of
size and polarizability on boiling points.
26
Figure 3.2
Effect of surface area and
polarizability on boiling point

27. 27
Which has the higher boiling point and why?
O
A B
O
B
A has only VDW, while B has both
VDW and DD interactions

28. 28
O
H OH 3CH2C
O
H OCH3 3CH2C
A B
O
H OH 3CH2C
A
A had VDW, DDD and H-bonding, while B
lacks H-bonding

29. 29
H3C
(CH2)5
H3C
H3C
(CH2)20
H3C
A B
H3C
(CH2)20
H3C
B
Both A and B only have VDW interactions, but
B has the higher bp b/c of a larger surface
area.

30. • The melting point is the temperature at which a solid is
converted to its liquid phase.
• 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.
30
Melting Point

31. • Because ionic compounds are held together by
extremely strong interactions, they have very high
melting points.
• With covalent molecules, the melting point depends
upon the identity of the functional group. For
compounds of approximately the same molecular
weight:
31

32. • The trend in melting points of pentane, butanal, and 1-
butanol parallels the trend observed in their boiling
points.
32

33. • Symmetry also plays a role in determining the melting points of
compounds having the same functional group and similar
molecular weights, but very different shapes.
• A compact symmetrical molecule like neopentane packs well into
a crystalline lattice whereas isopentane, which has a CH3 group
dangling from a four-carbon chain, does not. Thus, neopentane
has a much higher melting point.
33

34. 34
Which has the higher melting point and why?
NH2
A B
NH2
B
B has stronger intermolecular forces (DD and
HBZ).

35. 35
A B
A
Both only have VDW forces, so A has the higher
mp b/c it is more symmetrical. Closer packing
means higher mp.

36. • 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.
36
Solubility

37. • Compounds dissolve in solvents having similar kinds of
intermolecular forces.
• “Like dissolves like.”
• Polar compounds dissolve in polar solvents. Nonpolar or
weakly polar compounds dissolve in nonpolar or weakly
polar solvents.
• Water and organic solvents are two different kinds of
solvents. Water is very polar and is capable of hydrogen
bonding with a solute. Many organic solvents are either
nonpolar, like carbon tetrachloride (CCl4) and hexane
[CH3(CH2)4CH3], or weakly polar, like diethyl ether
(CH3CH2OCH2CH3).
• Most ionic compounds are soluble in water, but insoluble
in organic solvents.
37

38. • 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.
38

39. • Since butane and acetone are both organic compounds
having a C—C and C—H backbone, they are soluble in
the organic solvent CCl4. Butane, which is nonpolar, is
insoluble in H2O. Acetone is soluble in H2O because it
contains only three C atoms and its O atom can
hydrogen bond with an H atom of H2O.
39

40. • To dissolve an ionic compound, the strong ion-ion
interactions must be replaced by many weaker ion-dipole
interactions.
40
Figure 3.4
Dissolving an ionic
compound in H2O

41. • The size of an organic molecule with a polar functional group
determines its water solubility. A low molecular weight alcohol
like ethanol is water soluble since it has a small carbon
skeleton of £ five C atoms, compared to the size of its polar
OH group. Cholesterol has 27 carbon atoms and only one OH
group. Its carbon skeleton is too large for the OH group to
solubilize by hydrogen bonding, so cholesterol is insoluble in
water.
41

42. • 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.
42

43. 43
Which of the following are water soluable?
A B
O
N
C
O atom, 5 or
less Cs
soluable
No O, N or F, nonpolar,
not soluable
Has N, but more
than 5 C’s, so not
soluable

44. Influence of Functional Groups on Reactivity
Recall that:
• Functional groups create reactive sites in molecules.
• Electron-rich sites react with electron poor sites.
All functional groups contain a heteroatom, a p bond
or both, and these features create electron-deficient (or
electrophilic) sites and electron-rich (or nucleophilic)
sites in a molecule. Molecules react at these sites.
44

45. 45

46. • An electron-deficient carbon reacts with a
nucleophile, symbolized as :Nu¯.
• An electron-rich carbon reacts with an electrophile,
symbolized as E+.
For example, alkenes contain an electron rich
double bond, and so they react with electrophiles E+.
46

47. On the other hand, alkyl halides possess an
electrophilic carbon atom, so they react with electron-rich
47
nucleophiles.

48. 48
Considering only electron density, will each reaction
occur?
Cl
+ OH
E+ Nu-
Yes
+ Br-
Nu- Nu-
No
O
ClO
+ OCH3
Nu-
E+
Yes

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