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Unsaturation
Recall:pentane – C5H12
We refer to pentane as a saturated compound because the carbon atoms have the maximum number of possible substituents
cyclopentane – C5H10
We refer to cyclopentane as an unsaturated compound because the carbon atoms do not have the maximum number of possible substituents
Can you think of any other ways to make an unsaturated molecule?
Double & Triple Bonds
C5H10
C5H10
C5H8
C5H8
C5H12
0° of unsaturation
Degree of unsaturation = (# of double bonds) + (2 × # of triple bonds) + (# of rings)
1° of unsaturation 2° of unsaturation
Multiple sites of unsaturation:
Double & Triple Bonds
C5H10
C5H10
C5H8
C5H8
C5H12
0° of unsaturation
Degree of unsaturation = (# of double bonds) + (2 × # of triple bonds) + (# of rings)
1° of unsaturation 2° of unsaturation
CnH2×n+2 CnHn CnH2×n-2
Double & Triple Bonds
C5H10
C5H10
C5H8
C5H8
C5H12
0° of unsaturation 1° of unsaturation 2° of unsaturation
Degree of unsaturation = [2 + (2 x #Cs) + #Ns - #Hs - #Halogens]/2
CnH2×n+2 CnHn CnH2×n-2
C6H10BrCl
C8H10NOBr
1°
4°
Double & Triple Bonds
Alkenes Alkynes
C5H10
C5H10
C5H8
C5H8
Alkanes
C5H12
pentane(n-pentane)
1-pentene
How do we name these guys?
2-pentene
1-pentyne
2-pentyne
Rules for Naming Alkenes and Alkynes
1) Find the longest carbon chain containing the multiple bond
2) Start numbering from the end closest to the multiple bond
3) Finish as if you were naming an alkane only use the appropriate suffix(e.g., -ene for a double bond, -yne for a triple bond)
Let’s try a practice problem
Nomenclature of Alkenes
Common Terms You Should Know:
vinylic carbons
allylic carbons
vinyl group
allyl group
2-pentene 12 3 4 5 6 7 8 9
10
5-allyl-4-vinyl-decane
Alkenes are also called olefins.
Alkene Factoids
Recall:CH3
H HCH3
H HH
H CH3CH3
H HH
H3C HCH3
H Hrotate rotate
butane(n-butane)
Now let’s look at 2-butene
H3C
H CH3
H
Alkene Factoids
The barrier to rotation is very large. This leads to the possibility of cis and trans isomers, stable, separable compounds with different properties.
E,Z Nomenclature
(The higher the molcular weight, the higher the priority)
Sometimes cis and trans are ambiguous; in such cases we resort to the more formal E,Z nomenclature.
cis or trans?
•Z if highest priority substituents on same side of double bond
•E if highest priority substituents on opposite side of double bond
A way to remember: Ecross, Zame Zide
•Look at each carbon atom and assign each group a priority