Organic Chemistry
•
http://chemmaster.co.in/showchapter.php?id=20&id2=161&title=Hydrocarbons
Origins
• Originally defined as the chemistry of living
materials or originating from living sources.
• Wohler synthesized urea from non organic
sources (1800 – 1882)
• Now generally defined as the chemistry of carbon
and its compounds.
• Why is carbon so special?
Carbon can form single, double and
triple bonds with itself
•
http://wps.prenhall.com/wps/media/objects/3311/3391006/blb0809.html
•
The bond length is defined as the distance between the nuclei of
the atoms involved in the bond.
• The bond enthalpy is the enthalpy
change, H, for the breaking of a
particular bond in a mole of gaseous
substance.
Carbon can catenate
One of the remarkable property of carbon atom is its unique
capacity to link with other carbon atoms. This property of
linking of atoms of one element with one another forming
chains of identical atoms is called catenation. Carbon
exhibits catenation to maximum extent because of strong
carbon-carbon bond and tetracovalency.
• Complete combustion of a hydrocarbon
produces CO2 and H2O, incomplete combustion
produces CO, C and H2O.
•
C produces a 'dirty' flame leaving carbon
deposits on everything, CO is toxic and CO2 is a
greenhouse gas.
• Incomplete combustion is where the carbon is
not completely oxidized.
Hydrocarbons
Hydrocarbons are organic compounds that
contain only hydrogen and carbon
Types :




Alkanes
Alkenes
Alkynes
Aromatic
8
Naming Hydrocarbons
using the IUPAC System
A series of prefixes are used to designate the
number of carbon atoms in a carbon chain:
meth
1C
hex
6C
eth
2C
hept
7C
prop
3C
oct
8C
but
4C
non
9C
pent
5C
dec
10 C
9
Alkane Structures
•
Alkanes have only carbon to carbon single bonds.
General Formula CnH2n+2
10
•
http://www.ivy-rose.co.uk/Chemistry/Organic/Homologous-Series.php
• A Homologous Series is a group of
organic compounds, usually listed in
order of increasing size,
that have a similar structure (and
hence also similar properties) and
whose structures differ only by the
number of CH2 units in the main
carbon chain.
Homologous Series:
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
C5H12
Pentane
A homologous
series of alkanes
Each compound in
this series differs
from the previous
compound by a
–CH2 –
Alkane Structures
• Structural Isomers are compounds with the same chemical
formula but a different structural formula.
• As the number of carbon atoms in an alkane molecule
increases, so do the possibilities for isomerism of this kind.
There are three isomeric pentanes, all with the C5H12, five
isomeric hexanes, C6H14
14
General Properties of Alkanes
• The boiling points of alkanes are very low for
their molecular mass. This is because the
molecule is completely nonpolar( inertness)
• It increases with an increase in mass.
• Alkanes are not soluble in water.
Boiling Points of Alkanes
http://wiki.chemeddl.org/index.php/8.2_Organic_Compounds:_Hydrocarbons
• The more spherical the isomer, the lower boiling point due
to less surface area to form intermolecular bonds.
Alkenes
•
Alkenes have one carbon to carbon
double bond C=C
•
Since there are fewer hydrogen atoms in
alkenes as a result of the double bond,
alkenes are referred to as unsaturated.
•
Alkanes on the other hand have the
maximum number of hydrogen atoms.
They are referred to as saturated.
17
Alkene Structures
•
Like alkanes, alkenes can have branched or
consecutive chains. In the larger alkenes there are
also multiple locations for the C=C. Hence multiple
structural isomers are possible.
Straight chain.
Straight chain.
Branched
chain
18
Alkynes
•
•
Alkynes have one (or more) carbon
to carbon triple bonds
Since there are fewer hydrogen
atoms in alkynes as a result of the
triple bond, alkynes like alkenes are
referred to as unsaturated.
19
Alkyne Structures
•
Like alkanes and alkenes, alkynes can have
branched or consecutive chains. In the larger
alkenes there are also multiple locations for the
C=C. Multiple structural isomers are possible. The
branch cannot originate on one of the carbons
making up the triple bond
Straight chain. The
triple bond is
between the first and
second carbon
Straight chain. The
triple bond is
between the second
and third carbon
Branched chain. The triple
bond can occur in one of the
branches but branches cannot
be attached to any carbon in
20
the triple bond
Table of Functional Groups
Functional groups
are groups of
atoms in a
molecule that give
the molecules
specific
characteristics
Resonance –Polarity of
Carboxylic acids
Ring Structures
• Hydrocarbons that exist in chains are
known as aliphatic hydrocarbons
• The ends of a chain may be joined to
form a ring structure.
• These compounds are known as
cyclic structures
23
Aromatic Structures
• The benzene ring is a
common structure in organic
molecules
• It consists of 6 carbon atoms
and 6 hydrogen atoms.
• One would predict that there
should also be 3 C=C bonds
in a benzene ring
24
Aromatic Structures
• Further investigation reveals
that the double bonds are not
distinct in benzene. Rather it
is a resonance hybrid.
• Either of these structures
could be used to represent
benzene.
25
Aromatic Structures
• Research shows that
there are no differences
in the C to C bonds in
benzene.
• The current view of
benzene holds that there
are 6 C-C single bonds
and 3 pairs or 6
delocalized electrons
26
Aromatic Structures
• The structure of benzene
is shown as either of these
two structures, or as a
circle in a hexagon which
depicts that the electrons
are delocalized
27
Halogenoalkanes or Alkyl
Halides
• Halogenoalkanes are compounds in which one or
more hydrogen atoms in an alkane have been
replaced by halogen atoms (fluorine, chlorine,
bromine or iodine).
• Halogenoalkanes are commonly known as alkyl
halides
28
Halogenoalkanes or Alkyl
Halides
• Depending on the location of the halogen atom,
halogenoalkanes may be primary secondary or
tertiary
29
Boiling Points of
Halogenoalkanes
• The boiling point
depends on the
halide
Cl < Br < I
• The boiling
points increase
as the chain
length increases
30
Solubility of Halogenoalkanes
• The halogenoalkanes are only very
slightly soluble in water.
• The attractions between the
halogenoalkane molecules (van der
Waals dispersion and dipole-dipole
interactions) are relatively strong
• Halogenoalkanes are only slightly polar
and do not effectively break the
hydrogen bonds between water
molecules.
• Halogenoalkanes are soluble in non
polar or less polar organic solvents
such as alcohol, ether, and benzene .
31
Functional Groups
• http://www.ivy-rose.co.uk/Chemistry/Organic/HomologousSeries.php
33
Alcohols
• http://www.physchem.co.za/OB12mat/organic2.htm#alkanols
Carboxylic Acids
• http://www.physchem.co.za/OB12mat/organic2.htm#acids
• Carboxylic acids have a higher boiling boint than the
alkanols with the same number of carbon atoms.
• This is not solely due to an increase in molar mass (14
units), but rather because carboxylic acids tend to be more
strongly hydrogen bonded than alkanols, and even have a
tendency to form dimers.
Aldehydes and Ketones
• http://www.physchem.co.za/OB12mat/organic2.htm#ketones
Amines and Amides
• http://www.physchem.co.za/OB12mat/organic2.htm#amines
Esters
• http://www.physchem.co.za/OB12mat/organic2.htm#acids
Halogenoalkanes
• Have the general
formula R-X where
R is an alkyl group
and X is a halogen
H
H
H
C
C
H
H
Chloroethane
Cl