Chapter 3 Alkanes and Their Stereochemistry-1-1
Chapter 3 Alkanes and Their Stereochemistry-1-1
Chapter 3 Alkanes and Their Stereochemistry-1-1
Organic Compounds:
Alkanes and Cycloalkanes
Classification of Organic Compounds
Organic compounds are classified into different types based
on the kinds of functional groups present in its structure
A functional group is an atom or groups of atoms that
determine the types of chemical reactions that the compound
participates in.
For example, the double bonds in simple and complex
alkenes react with bromine in the same way
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Types of Functional Groups: Multiple
Carbon–Carbon Bonds
Alkenes have a
C=C double bond
Alkynes have a
CC triple bond
In Arenes or
aromatic
hydrocarbons, the
functional group is
the benzene ring
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Alkane Isomers
CH4 = methane, C2H6 = ethane, C3H8= propane
Isomers of alkanes are of 2 types: straight chain or normal
alkanes and branched chain alkanes.
Straight-chain or normal alkanes have all n C atoms attached
in a single connected chain. That is, no C atom is attached to
more than 2 other C atoms. For any alkane with n 4, there is
only one straight chain isomer.
Branched-chain alkanes have one or more C atoms
connected to 3 or 4 other C atoms. C4H10 has one branched
isomer. For all alkanes with n > 4, there are more than one
branched isomers.
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Examples of Constitutional Isomers
Compounds other than alkanes can be constitutional isomers of
one another
They must have the same molecular formula to be isomers
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3.6 Cycloalkanes
Cycloalkanes are alkanes that have carbon atoms attached to form a
ring
In simple cycloalkanes, all n C atoms are attached to form a ring. The
general molecular formula of a cycloalkane with n C atoms is C nH2n
The condensed structural formula of a simple cycloalkane with n C
atoms is a regular polygon with n vertices
The boiling points of cycloalkanes also increases with increase in ring
size.
Cycloalkanes exhibit structural isomerism. A cycloalkane has the
same general formula as an alkene with the same number of C atoms
and 1 double bond.
In addition, any cycloalkane with more than 3 C atoms will also have
cyclic structural isomers
cyclobutane cyclohexane
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cyclopropane cyclopentane
Complex Cycloalkanes
Naturally occurring materials contain cycloalkane structures
Examples: chrysanthemic acid (cyclopropane), prostaglandins
(cyclopentane), steroids (cyclohexanes and cyclopentane)
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Structural Isomers & Stereoisomers