1. Isomers

2. C11-5-14 NAMING AND DRAWING Vocabulary & Concepts Structural isomers
OUTCOME QUESTION(S):
C NAMING AND DRAWING
Name and draw structural models of simple and
branched alkanes.
Include: complete structural formula, molecular
formula, general formula, isomers
Name and draw structural models of simple and branched
alkenes and alkynes.
Compare and contrast the structure and uses of aromatic
and aliphatic hydrocarbons.
Vocabulary & Concepts
Structural isomers

3. Isomer: Compounds with the same molecular formula but different arrangement of bonded atoms.
Like all concepts this course – we are just scratching the surface – the same with isomers…we will focus on structural isomers only
(C3H7F)
(C3H7F)

4. Carbon atoms in alkanes can rotate (twist) freely around in the single bonds.
Don’t believe it? Follow the rules and name them both…
C - C C
C - C -
C - C C
C - C -
Which means these two compounds are really the exact same.
Structural isomer: a constitutional isomer in which molecules have the same molecular formula but a different organization of atoms.

5. C4H10 Draw butane and 2-methylpropane. C H3 C – C – C – C H3 H2 H2 H3
structural isomers

6. They all look different…name them to be sure
Draw and name 2 different structural isomers for a pentane.
C - C C
C -
C - C C
C - C -
They all look different…name them to be sure
2-methylbutane
2,2-dimethylpropane
C - C C
C - C -
C - C C
C - C -
2-methylbutane
pentane
Common mistakes
Counting from the wrong end
Bent parent chains
Wrong parent chain
Branching off the end carbon

7. Obviously, the more carbon atoms – the more structural isomers*
Octane (C8H18) structural isomers
Decane (C10H22) structural isomers
Eicosane (C20H42) structural isomers!
*Cycloalkanes are not considered isomers: 4 1
C – C – C – C H3 H2 H2 H3 H2 C H2 1 2 3 4 3
butane H2 H2
C4H10 2
cyclobutane
With the connecting end carbons - cycloalkanes have too few hydrogen
C4H8

8. C9H20 3-ethyl-2-methylhexane C H3 The alkane with 9 carbons is nonane.
3-ethyl-2-methylhexane is a structural isomer of which straight chained alkane?
Remember: isomers have the same number of carbons – so just use that…
3-ethyl-2-methylhexane
2 carbon
1 carbon
6 carbon
2 carbons + 1 carbons + 6 carbon = 9 carbons C H3
The alkane with 9 carbons is nonane. C H3 H2
C9H20
C – C – C – C – C – C H3 H H H H2 H3 1 2 3 4 5 6

9. Present in unhealthy “trans fats”
Stereoisomer: a specific type of isomer with a different spatial arrangement around the double bond. (Carbons can’t rotate around in double bonds)
Commonly called Cis/Trans isomers
(C4H8)
(C4H8)
cis form
trans form
Present in unhealthy “trans fats”

10. Make a prediction of how branching may affect this property
Melting/Boiling Points
Isomers show a decrease in melting/boiling point with increased branching.
Branching creates space  weakens IMF
 lowers energy needs
Make a prediction of how branching may affect this property
C6H14
Name
Boiling Point
Linear
Hexane
69oC
1 branch
2-methylpentane
60oC
2 branches
2,2-dimethylbutane
50oC
linear alkane
branched alkane

11. C11-5-14 NAMING AND DRAWING Vocabulary & Concepts Structural isomers
CAN YOU / HAVE YOU?
C NAMING AND DRAWING
Name and draw structural models of simple and
branched alkanes.
Include: complete structural formula, molecular
formula, general formula, isomers
Name and draw structural models of simple and branched
alkenes and alkynes.
Compare and contrast the structure and uses of aromatic
and aliphatic hydrocarbons.
Vocabulary & Concepts
Structural isomers