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ORGANIC CHEMISTRY
Classes of Organic Compounds
Classification of Hydrocarbons
1. Aromatic Hydrocarbons-contain one or
more benzene rings
2. Aliphatic Hydrocarbons - all other
hydrocarbons
Aliphatic Hydrocarbons
Carbon atoms can be bonded in straight
chains, branched chains, or rings.
Chains may contain single, double, or triple
bonds.
A saturated compound contains only
single bond between carbons. These are
alkanes.
ALKANES
Simplest hydrocarbon
Each differs from the next by a -CH2group.
Compounds whose structures differ from
each other by a specific structural unit is
called a homologous series.
ALKANES
Simplest alkane is methane. CH4
General formula of alkane is CnH2n+2
All end in -ane
Soluble in nonpolar solvents,
C to C bonds have sp3 hybridization.
Hydrocarbon Prefixes
ALKANES
When a hydrogen along with its associated
electrons is removed from a hydrocarbon
molecule, a radical is left.
CH3 is a radical. It is named methyl.
Radicals end in -yl.
Alkanes form alkyl groups.
Branched Chain Alkanes
1. Find longest continuous chain or parent chain.
2. Add the name of the branches (substituents) attached in
alphabetical order using prefixes.
3. Number Carbon atoms in parent
4. Insert position # of each substituent group
5. Punctuate name - separate position # with hyphens,
more than one # is separated by commas.
Cycloalkanes
Alkane rings
General formula is CnH2n
Example cyclopentane C5H10
Isomers
Isomerism is the existence of two or more
substances with the same molecular
formula, but different molecular structures.
Important because structure determines
properties and function.
There are two main types of isomers.
Structural Isomers
Structural Isomers
Also called constitutional isomers.
Atoms are bonded in different
arrangements--thus different properties.
Longer chains have higher boiling points
(BP) and melting points (MP)
Having branches on the chain serves to
lower the BP but it raises the melting point.
Stereoisomers
All atoms are bonded in the same order but
are arranged differently in space.
There are two types:
a. Geometric isomers
b. Optical isomers
Geometric Isomers
Structural isomers have a different
arrangement of groups around a double
bond.
In alkenes with double bonds, the carbon is
locked in place and cannot rotate freely as it
could in alkanes with single bonds. Pi bonds
Geometric isomers
Optical Isomers
Optical Isomerism (Chiralty) occurs when
there is an asymmetric carbon (C has 4
different atoms or groups attached)
Chiral Molecules
Chirality is important in drugs and enzymecatalyyzed rxns. Only L-form of ascorbic
acid functions as vitamin C.
Geometric Isomers
Properties and Uses of Alkanes
1. C-H bonds are nonpolar
2. Strength of London dispersion forces
increases as mass increases--# of C
determines state of matter.
3. Longer the chain, higher the boiling point.
Properties and uses of alkanes
4. Alkanes less reactive than other
hydrocarbons due to stability of single
covalent bonds.
5. Most important rxn is combustion.
Fractional Distillation
Gasoline is a component of fossil fuel. Is can be extracted
by fractional distillation.
Combustion
Straight-chain alkanes ignite more
spontaneously than branched chains but
cause knocking in autos.
Octane rating is a measure of burning
efficiency and antiknock properties.
2,2,4-trimethyl pentane (isooctane) resists
knocking
C8H18
2,2,4-trimethylpentane
octane
Unsaturated Hydrocarbons
Contain double and triple carbon to carbon
bonds.
Include Alkenes and Alkynes
ALKENES
Olefin is another name.
Contain double bonds.
General formula CnH2n
Double bond is shorter than a single bond
and it is also stronger and more reactive.
Double C bonds have sp2 hybridization.
Naming Alkenes
End in -ene.
The double bond location takes precedence
in naming.
If there is more than one double bond, the
location is numbered and a prefix is used
2 = adiene 3 = atriene
Alkenes are numbered so that the lowest
position number is assigned to the first
carbon atom to which the double bond is
attached.
1,4-pentadiene
Ethene
#1 organic chemical in industry
Product of petroleum refining
Makes plastics and
synthetics
ALKYNES
Contain triple bonds.
General formula is CnH2n-2
End in -yne
Ethyne or acetylene
Naming Alkynes
The numbering system follows the same
pattern used for naming alkenes.
4,4-dimethyl-2-pentyne
If a compound has both double and triple
bonds, the double bonds take precedencein
numbering.
The double bond is given the lowest number
and named first.
Benzene Ring
Kekule’s snake
AROMATIC HYDROCARBONS
Contain Benzene ring
Most have distinctive odors.
Thousands of compounds are derived from
benzene.
Ways to diagram benzene
Important in making plastics and fibers
Naphthalene
2 benzene rings
Phenyl Radical
Methyl Benzene or Toluene
improves quality of gasoline
used in production of
explosives
TNT
Functional Groups
A substituent group that is not made up of
only carbon and hydrogen is a functional
group.
-OH is hydroxide