1. ALKANES
CnH2n+2

2. Alkanes or CnH2n+2 C3H8 H H H H–C–C–C–H CH3CH2CH3 Chemical Formula
Structural Formula
Condensed Structural Formula

3. Alkanes: base unit CH4 CH3CH3 or C2H6 CH3CH2CH3 or C3H8
CH3CH2CH2CH2CH3 or C5H12
Difference between each is CH2

4. Properties of Alkanes Change systematically with number of C’s
As number of C’s increases, boiling point ↑
molecules get heavier & it’s harder to change into gas phase

5. Properties of Alkanes Low Reactivity
Except readily undergo combustion – fuels
Nonpolar – Don’t dissolve well in water
Low mp’s & bp’s
mp & bp ↑ with ↑ molecular mass
High vapor pressures

6. Which property is generally characteristic of an organic compound?
Low melting point
High melting point
Soluble in polar solvents
Insoluble in nonpolar solvents
Correct response = A

7. Which of the following compounds has the highest boiling point?
Correct answer = D
bp depends on strength of forces holding molecules together [forces ↑as size of molecule ↑]

8. Naming
Hydrocarbons

9. Naming straight-chain Alkanes
Name describes molecule so can draw it
All alkanes have the suffix –ane
prefix tells how many C’s

10. 10
Dec 9
Non 8
Oct 7
Hept 6
Hex 5
Pent 4
But 3
Prop 2
Eth 1
Meth
# of C atoms
Prefix

11. C5H12
C4H10
C3H8
C2H6
Meth + ane
CH4
Name
Formula
Ethane
Propane
Butane
Pentane

12. Branched-chain alkanes
Beginning with butane, C4H10, more than 1 way to arrange the atoms H
H–C–H
H H
H–C–C–C–H
H H H

13. Branched alkane
- can’t link all C’s without lifting pencil off paper
Methyl propane

14. Isomers Compounds with same molecular formula
but different structural arrangement
more C atoms in the formula, the more isomers  more possible ways to arrange them

15. Isomers
Different structures, different properties
Isomers have different chemical and physical properties

16. A note about isomers ---
If comparing 2 structural formulas & you can superimpose them, then not isomers = same molecule!
If can rotate or flip one of structural formulas & superimpose it on the other, they are not isomers – they are the same molecule!

17. These diagrams represent the same molecule
Represents bond to H

18. These diagrams represent the same molecule

19. These diagrams represent the same molecule

20. Two different molecules!

21. Branched Hydrocarbons
Naming
Branched Hydrocarbons

22. Naming Branched-Chain Alkanes
goal of name: to describe molecule so can draw it

23. Naming branched-chain alkanes
find longest continuous chain (backbone) of C atoms (Bends don’t count!)
base name derived from # of C’s in longest chain
branches named in prefix
Branches also named by number of C’s
“branch” part of name ends in “yl”
location of branch shown by assigning #’s to C’s in backbone
number from end that gives lowest # for branch
if more than 1 of same type branch:
use di, tri, tetra

24. Branch: 1 carbon – methyl
Branch at C #2:
- can’t be on any other C so doesn’t need #
Methyl propane
C4H10
CH3CH(CH3)CH3 H
H–C–H
H H
H–C–C–C–H
H H H
Longest continuous chain has 3 carbon atoms = propane

25. Longest continuous chain: 6 C’s = hexane
branch is 1 carbon long – methyl.
branch located at C #2
2-methyl hexane
C7H16
CH3CH(CH3)CH2CH2CH2CH3 H
H–C–H
H H H
H–C–C–C–C–H
H H H

26. A note about branches
If have several branches with same # C’s can condense name a bit
2-methyl 3-methyl pentane becomes
2,3-dimethyl pentane
every branch must have a #

27. Longest continuous chain has 6 C’s: hexane -branch 1 C = methyl
-branch located at C #3
3-methyl hexane
C7H16
CH3CH2CH2CH(CH3)CH2CH3
CH3(CH2)2CH(CH3)CH2CH3 H
H – C – H
H H H
H – C – C – C – C – H
H H
H–C–H H–C–H
H H