L2 - Branched Alkane..

Branched Alkanes
– The simplest alkane is methane (CH4) – the primary
compound in natural gas.
– Ethane (C2H6) – a minor component of natural gas.
– Propane (C3H8) – a fuel for heating homes and
cooking.
– Octane (C6H14) – a fuel used for automobile
combustion
– Dodecadecane (C20H22) – solid wax used for making
candles and as a lubricant
All of these are straight-chained
hydrocarbons (CnH2n+2).
Many structural isomers of these exist,
known as branched alkanes.
Isomerism
Conformations are not the same as isomers!
–Isomers:
Isomers: Compounds that have identical
molecular formulas, but different arrangement of
atoms.
•Structural
Structural isomers:
isomers (AKA Constitutional
isomers) molecules having the same
molecular formula but different arrangement
of atoms and bonds
– Conformations refer to the arrangement of atoms in
space due to bond rotation
– Isomers have a different arrangement of atoms in
relationship to one another
C
|
C—C—C
|
C
branched alkane
C—C—C—C—C
normal alkane
•Ball-and-stick models of the isomers of C2H6O.
•The physical properties of isomers can be
drastically different.
•Ethyl alcohol is a liquid at room temperature and
completely soluble in water, whereas dimethyl
ether is a gas at room temperature and only
partially soluble in water.
1
Number of
Structural Isomers
Possible for Alkanes
of Various CarbonChain Lengths.
–Which of the following pairs represent
structural isomers, and which are simply the
same compound?
–Which are normal alkanes and which are
branched alkanes?
BONUS:
Draw and name all
of the constitutional
isomers of C9H20.
Due Mon.
•Straight-chained alkanes are easy to name…
ethane, hexane, etc… However, how do we
name branched alkanes
•Notice below, a single carbon group attached to
a long carbon chain
Branched alkane – straight-chained hydrocarbon
that has had a hydrogen on the parent carbon
chain replaced by an alkyl substituent.
•Substituent – atom or group of atoms that
have replaced hydrogen in organic
compounds
•Alkyl group –
saturated hydrocarbon
substituent
Alkyl groups are named
using the same alkane
prefixes, however, isomers
exist.
Root Name
Methethpropbutpenthexheptoctnondec-
# of Carbons
1
2
3
4
5
6
7
8
9
10
Organic Nomenclature
• Three parts to a compound name:
Base: Tells how many carbons are in the longest
continuous chain.
Memorize These !!!
2
Organic Nomenclature
• Three parts to a compound name:
Base: Tells how many carbons are in the longest
continuous chain.
Suffix: Tells what type of compound it is.
To Name a Compound…
1. Find the longest
chain in the
molecule.
2. Number the chain
from the end nearest
the first substituent
encountered.
3. List the substituents
as a prefix along
with the number(s)
of the carbon(s) to
which they are
attached.
Organic Nomenclature
• Three parts to a compound name:
Base: Tells how many carbons are in the longest
continuous chain.
Suffix: Tells what type of compound it is.
Prefix: Tells what groups are attached to chain.
To Name a Compound…
• For multiple branches of the
same type, modify the name
with di-, tri-, …
• List multiple branches
alphabetically – the di-, tri-,
sec-, t-… don’t count.
• However, iso- is used for
alphabetizing.
• Numbers are separated from
each other using commas;
numbers are separated from
letters using hyphens.
Example:
1CH
3—
2CH
—3CH —4CH —5CH2 —6CH2 —7CH3
|
|
|
CH3 CH
CH–CH3
|
CH3
4-isopropyl-2, 3-dimethylheptane
3
Let’s name this together:
Now write the name
Number the parent chain and identify the
substituents.
1.
2.
3.
4.
5.
6.
4
7. Draw and name all of the possible
constitutional (structural) isomers for
C6H14.
5