Title: Organic Chemistry
1Organic Chemistry
Chapter 1 Introduction
MOHD HASBI BIN. AB. RAHIM FKKSA
2Introduction 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 CC and CH bonds.
However, many organic molecules possess other
structural features - Heteroatomsatoms other than carbon or hydrogen.
- ? Bondsthe most common ? bonds occur in CC and
CO double bonds. - These structural features distinguish one organic
molecule from another. They determine a
molecules geometry, physical properties, and
reactivity, and comprise what is called a
functional group.
3Introduction to Organic Molecules and Functional
Groups
Functional Groups
- Heteroatoms and ? bonds confer reactivity on a
particular molecule. - Heteroatoms have lone pairs and create
electron-deficient sites on carbon. - ? Bonds are easily broken in chemical reactions.
A ? bond makes a molecule a base and a
nucleophile.
Dont think that the CC and CH bonds are
unimportant. They form the carbon backbone or
skeleton to which the functional group is
attached.
4Introduction to Organic Molecules and Functional
Groups
Functional Groups
- Ethane This molecule has only CC and CH bonds,
so it has no functional group. Ethane has no
polar bonds, no lone pairs, and no ? 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.
5Introduction to Organic Molecules and Functional
Groups
Functional Groups
Hydrocarbons are compounds made up of only the
elements carbon and hydrogen. They may be
aliphatic or aromatic.
6Introduction to Organic Molecules and Functional
Groups
Functional Groups
- 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 ? bonds of benzene
comprise a single functional group. - When a benzene ring is bonded to another group,
it is called a phenyl group.
7Introduction to Organic Molecules and Functional
Groups
Functional Groups
8Introduction to Organic Molecules and Functional
Groups
Functional Groups
Examples of Molecules Containing C-Z ? Bonds
9Functional Groups
10Introduction to Organic Molecules and Functional
Groups
Functional Groups
- Compounds Containing the CO Group
- This group is called a carbonyl group.
- The polar CO 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 ? bond that is
more easily broken than a CO ? bond.
11Introduction to Organic Molecules and Functional
Groups
Functional Groups
Molecules Containing the CO Functional Group
12Introduction to Organic Molecules and Functional
Groups
Functional Groups
It should be noted that the importance of a
functional group cannot be overstated.
A functional group determines all of the
following properties of a molecule bonding and
shape type and strength of intermolecular
forces physical properties nomenclature chemica
l reactivity
13Introduction to Organic Molecules and Functional
Groups
Biomolecules
- Biomolecules are organic compounds found in
biological systems. - There are four main families of small molecule
biomolecules - amino acids, simple sugars, lipids and
nucleotides - Biomolecules often have several functional groups.
14Introduction to Organic Molecules and Functional
Groups
Intermolecular Forces
- Intermolecular forces are also referred to as
noncovalent interactions or nonbonded
interactions. - There are several types of intermolecular
interactions.
- Ionic compounds contain oppositely charged
particles held together by extremely strong
electrostatic inter-actions. These ionic
inter-actions are much stronger than the
intermolecular forces present between covalent
molecules.
15Introduction to Organic Molecules and Functional
Groups
Intermolecular Forces
- 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 - van der Waals forces
- dipole-dipole interactions
- hydrogen bonding
16Introduction to Organic Molecules and Functional
Groups
Intermolecular Forcesvan 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 constituents van der
Waals forces.
17Introduction to Organic Molecules and Functional
Groups
Intermolecular Forcesvan der Waals Forces
- 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.
18Introduction to Organic Molecules and Functional
Groups
Intermolecular Forcesvan der Waals Forces
- 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.
19Introduction to Organic Molecules and Functional
Groups
Intermolecular ForcesDipole-Dipole Interactions
- Dipoledipole 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.
20Introduction to Organic Molecules and Functional
Groups
Intermolecular ForcesHydrogen 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.
21Introduction to Organic Molecules and Functional
Groups
Intermolecular ForcesHydrogen Bonding
Note as the polarity of an organic molecule
increases, so does the strength of its
intermolecular forces.
22Introduction to Organic Molecules and Functional
Groups
Physical PropertiesBoiling 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
23Introduction to Organic Molecules and Functional
Groups
Physical PropertiesBoiling Point
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.
24Introduction to Organic Molecules and Functional
Groups
Physical PropertiesBoiling Point
Consider the examples below which illustrate the
effect of size and polarizability on boiling
points.
25Introduction to Organic Molecules and Functional
Groups
Physical PropertiesBoiling Point
Liquids having different boiling points can be
separated in the laboratory using a distillation
apparatus, shown in Figure 3.4.
26Introduction to Organic Molecules and Functional
Groups
Physical PropertiesMelting Point
- 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.
27Introduction to Organic Molecules and Functional
Groups
Physical PropertiesMelting Point
- 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
28Introduction to Organic Molecules and Functional
Groups
Physical PropertiesMelting Point
- The trend in melting points of pentane, butanal,
and 1-butanol parallels the trend observed in
their boiling points.
29Introduction to Organic Molecules and Functional
Groups
Physical PropertiesMelting Point
- 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.
30Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- 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.
31Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- 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 since it
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.
32Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- 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.
33Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- Since butane and acetone are both organic
compounds having a CC and CH 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.
34Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- To dissolve an ionic compound, the strong ion-ion
interactions must be replaced by many weaker
ion-dipole interactions.
35Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- 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.
36Introduction to Organic Molecules and Functional
Groups
Physical PropertiesSolubility
- 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.
37Introduction to Organic Molecules and Functional
Groups
ApplicationVitamins
Vitamins are either lipid or water soluble.
38Introduction to Organic Molecules and Functional
Groups
ApplicationSoap
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.
39Introduction to Organic Molecules and Functional
Groups
ApplicationThe Cell Membrane
40Introduction to Organic Molecules and Functional
Groups
ApplicationThe Cell Membrane
- Transport Across a Cell Membrane
- Polar molecules and ions are transported across
cell membranes encapsulated within molecules
called ionophores. - Ionophores are organic molecules that complex
cations. They have a hydrophobic exterior that
makes them soluble in the nonpolar interior of
the cell membrane, and a central cavity with
several oxygens whose lone pairs complex with a
given ion.
41Introduction to Organic Molecules and Functional
Groups
ApplicationThe Cell Membrane
Transport Across a Cell Membrane
42Introduction to Organic Molecules and Functional
Groups
ApplicationThe Cell Membrane
Several synthetic ionophores have also been
prepared, including one group called crown
ethers. Crown ethers are cyclic ethers
containing several oxygen atoms that bind
specific cations depending on the size of their
cavity.
43Introduction to Organic Molecules and Functional
Groups
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 ?
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.
44Introduction to Organic Molecules and Functional
Groups
Influence of Functional Groups on Reactivity
45Introduction to Organic Molecules and Functional
Groups
Influence of Functional Groups on Reactivity
An electron deficient carbon reacts with a
nucleophile, symbolized as Nu in reactions. An
electron-rich carbon reacts with an electrophile,
symbolized as E in reactions. For example,
alkenes contain a CC double bond, an
electron-rich functional group with a
nucleophilic ? bond. Thus, alkenes react with
electrophiles E, but not with other electron
rich species like OH or Br.
46Introduction to Organic Molecules and Functional
Groups
Influence of Functional Groups on Reactivity
On the other hand, alkyl halides possess an
electrophilic carbon atom, so they react with
electron-rich nucleophiles.