1. ALKENES

2. Alkenes CnH2n “unsaturated” hydrocarbons
C2H4 ethylene
Functional group = carbon-carbon double bond

3. C3H6 propylene
C4H8 butylene
CH3CH=CHCH3
β-butylene isobutylene
2-butene 2-methylpropene

4. there are two 2-butenes:
cis-2-butene trans-2-butene
Diastereomers

5. C=C are called “vinyl” carbons
If either vinyl carbon is bonded to two equivalent groups, then no geometric isomerism exists.
CH3CH=CHCH CH3CH2CH=CH2
yes no
CH3
(CH3)2C=CHCH3 CH3CH=CCH2CH3
no yes

6. E/Z system is recommended by IUPAC for the designation of geometric isomerism.
Use the sequence rules to assign the higher priority * to the two groups attached to each vinyl carbon.
2. * * * *
(Z)- “zusammen” (E)- “entgegen”
together opposite

7. * *
(Z)-
(E)- * *

8. Nomenclature, alkenes:
Parent chain = longest continuous carbon chain that contains the C=C.
alkane => change –ane to –ene
prefix a locant for the carbon-carbon double bond using
the principle of lower number.
Similar to alkanes
If a geometric isomer, use E/Z (or cis/trans) to indicate which isomer it is.

9. * * * * (Z)-3-methyl-2-pentene (3-methyl-cis-2-pentene)
(E)-1-bromo-1-chloropropene *

10. CH3
CH3CH CHCH2CH3
\ /
C = C 3-ethyl-5-methyl-3-heptene
/ \
CH3CH H (not a geometric isomer)

11. -ol has the priority when naming
CH2=CHCH2-OH 2-propen-1-ol
CH3CHCH=CH2 3-buten-2-ol OH

12. Physical properties:
non-polar or weakly polar
no hydrogen bonding
low mp/bp similar to alkanes
Insoluble in water
Importance:
common group in biological molecules

13. Preparation of alkenes:
dehydrohalogenation of alkyl halides
2. dehydration of alcohols
dehalogenation of vicinal dihalide

14. 2. dehydration of alcohols

15. dehydrohalogenation of alkyl halides
| | | |
— C — C — KOH(alc.)  — C = C — KX H2O
| |
H X

16. dehalogenation of vicinal dihalides
| | | |
— C — C — Zn  — C = C — ZnX2
| |
X X
eg.
CH3CH2CHCH Zn  CH3CH2CH=CH ZnBr2
Br Br

17. R-OH H+
R-X
KOH
Alkene
(alc.) Zn
vicinal
dihalide

18. Reduction of alkynes

19. Reactions of Alkenes
Addition of hydrogen

20. Addition of halogens

21. Addition of hydrogen halides

22. Addition of hydrogen halides

23. Additon of water

24. Halohydrin formation

25. Dimerization

26. Alklyation

27. Oxymercuration-Demercuration

28. Hydroboration-Oxidation

29. Polymerization

30. Hydroxylation