Epoxides - nomenclature, chemical reactions, physical and chemical properties, mechanisms

1. UNIVERSITY OF
GUYANA
DIVISION OF NATURAL SCIENCES
ORGANIC CHEMISTRY (CHM 2201)
EPOXIDESLECTURER: ……………..
GROUP MEMBERS
………………………………..

2. OBJECTIVES
DEFINITION
STRUCTURE
PHYSICAL PROPERTIES
NOMENCLATURE
REACTIVITY
PREPARATION

3. DEFINITION
An epoxide is a cyclic ether with a three-
atom ring (heterocyclic system). This ring
is similar to an equilateral triangle, which
makes it strained (unstable), and hence
highly reactive, more so than other
ethers.

4. STRUCTURE

5. PHYSICAL PROPERTIES
Similar to analogous ethers
Low molecular weight
Colourless
Nonpolar
Often volatile

6. NOMENCLATURE
There are two methods for naming epoxides
1. Alkene oxide style
(As the oxide of the corresponding
alkene)
The root name is for the corresponding
alkene (think of removing the oxygen and
adding a C=C at that location). Add the suffix
oxide. This is common for very simple
epoxides.

7. 2. Epoxy style
(Using the prefix epoxy- to indicate the
epoxide as a substituent)
The root name is based on the longest chain
with the two C-O bonds attached. The chain is
numbered so as to give the epoxide unit the
lowest possible locant (again like alkenes)
The epoxide prefix is inserted prior to the root
name along with both locants e.g. 1,2-
epoxypropane. Both locants are included since
this method is also used for naming other cyclic
ethers.

8. EXAMPLES
Alkene oxide style:
Functional group is an epoxide,
therefore suffix = -ene oxide
The longest continuous chain is
C3 therefore root = prop
Location of "alkene" is
unambiguous, so no locant
needed.
propene oxide

9. EXAMPLES
Epoxy style:
The longest continuous chain is
C3 therefore root = prop
The epoxide is a substituent
therefore prefix = epoxy
Number to give epoxide (only
group present) the lowest
locants = 1,2-
1,2-epoxypropane

10. EXAMPLES
Alkene oxide style:
Functional group is an epoxide,
therefore suffix = -ene oxide
The longest continuous chain is
C6 therefore root = hex
The system is cyclic therefore
prefix = cyclo
Location of "alkene" is
unambiguous, so no locant
needed.
cyclohexene oxide

11. EXAMPLES
Epoxy style:
The longest continuous chain is C6
therefore
root = hex
The root system is cyclic therefore
prefix = cyclo
The epoxide is a substituent therefore
prefix = epoxy
Number to give epoxide (only group
1,2-epoxycyclohexane

12. EXAMPLES
Alkene oxide style:
Functional group is an epoxide, therefore
suffix = -ene oxide
The longest continuous chain is C3
therefore root = prop
There is a C3 halide substituent = chloro
The halide group locant = 3-
Location of "alkene" is unambiguous, so
no locant needed.
3 – chloro propene oxide

13. EXAMPLES
Epoxy style:
The longest continuous chain is C3 therefore
root = prop
There is a C3 halide substituent = chloro
The halide group locant = 3-
The epoxide is a substituent therefore prefix =
epoxy
Number to give epoxide (only group present)
the lowest locants = 1,2-3- chloro-1,2-epoxypropan

14. EXAMPLES
Alkene oxide style:
Functional group is an epoxide, therefore
suffix = -ene oxide
The longest continuous chain is C6 therefore
root = hex
There is a C1 alkyl substituent = methyl
The first point of difference rule requires
numbering from the right as drawn to make
the "alkene" locant = 2-
5-methyl-2-hexene oxide

15. EXAMPLES
Epoxy style:
The longest continuous chain is C6 therefore
root = hex
There is a C1 alkyl substituent = methyl
The first point of difference rule requires
numbering from the right as drawn
The epoxide is a substituent therefore prefix =
epoxy
Number to give epoxide (only group present)
the lowest locants
2,3-epoxy-5-methylhexane

16. REACTIVITY
Epoxides are significantly more
reactive than simple ethers.
The small ring system has high ring
strain that can be relieved by opening
the ring.
Nucleophiles attack the C of the C-O
bond causing the C-O bond to break,
resulting in ring opening.

17. PREPARATION OF EPOXIDES
Epoxides are most commonly
prepared by either of two ways:
Epoxidation of Alkenes
Synthesis from halohydrins

18. EPOXIDATION OF ALKENES
Reaction type: Electrophilic Addition
1. Start at the C=C as the nucleophile,
make a bond to the slightly electrophilic
O.
2. Break the weak O-O bond and form a
C=O.
3. Break the original C=O to make a new O-
H bond.
4. break the original O-H to form the new C-
O bond

19. GENERAL MECHANISM
N.B. epoxidation of alkenes usually
produce a carboxylic acid as an end
product
1
2 3
4

20. EPOXIDATION OF CYCLOHEXENE MECHANISM
+

21. SYNTHESIS FROM HALOHYDRIN
Reaction type: Electrophilic Addition then
Nucleophilic Substitution
Step 1:
An acid/base reaction. The base
deprotonates the alcohol forming an
alkoxide intermediate that has enhanced
nucleophilicity.Step 2:
An intramolecular SN2 reaction where the
alkoxide nucleophile attacks the electrophilic
C displacing the leaving group, the halide ion.
The nucleophile has to attack anti to the C-X
bond.

22. GENERAL MECHANISM
X
X
X
X, H2O
Na+ OH-
-
HH
Formation of
halohydrin step
1
32
H
HH
H

23. SYNTHESIS OF CYCLOHEXENE OXIDE VIA
HALOHYDRIN
Cl2 , H20
Na+ OH-
-
Acts as
the base
1
2 3

24. REACTIONS INVOLVING EPOXIDES
The most common reactions involving
epoxides are the ring opening
reactions.The ring opening reactions
of epoxides can take place under
basic conditions or acidic conditions

25. RING OPENING REACTIONS
ACIDIC CONDITIONS
•EPOXIDES OPEN IN A “SN1
LIKE” FASHION
•THE NUCLEOPHILE WILL
ATTACKTHE MOST
SUBSTITUTED CARBON
•WEAK NUCLEOPHILE
REQUIRED
BASIC CONDITIONS
• EPOXIDES OPEN IN A
“SN2 LIKE” FASHION
•THE NUCLEOPHILE WILL
ATTACKTHE LEAST
SUBSTITUTED CARBON
•STRONG NUCLEOPHILE
REQUIRED

26. ACIDIC CONDITIONS (SN1):
GENERAL MECHANISM

27. ACIDIC CONDITIONS (SN1):
EXAMPLE ((1,2 EPOXY-1- METHYL CYCLOHEXANE))
,
1
2
3
Ethanol (CH3CH2OH) is the nucleophile (weak)
in this reaction

28. BASIC CONDITIONS (SN2):
GENERAL MECHANISM

29. BASIC CONDITIONS (SN2):
EXAMPLE (1,2 EPOXY-1- METHYL CYCLOHEXANE)
-
-
1
2
Ethoxide ion (CH3CH2O-) is the nucleophile
(strong) in this reaction

30. BASIC CONDITIONS (SN2):
EXAMPLE (USING GRIGNARD REAGENT)
-
Grignard reagent
acting as the
nucleophile
Carbon is more
electronegative than
Mg, thus gaining the
electrons
1
2

31. STEREOCHEMISTRY
Compound 1
Compound 2
enantiomers
R & S CONFIGURATION
In terms of cis & trans
isomerism
These epoxides would fall
under trans isomerism,
since their bulky groups
are on opposite sides,
which is also highlighted in
the alkene (alternate sides

32. COMPOUND 1
1 21 2
Considering C1 Considering C2
R – Configuration S – Configuration X
In terms of C2 the lowest priority atom (H) is
not in the back, therefore we assign using the
normal rules backwards. i.e. 1-2-3
anticlockwise is R and not S
R – Configuration
1
3
2
4
1
2 4
3
(R) 1-Chloro-1,2-epoxy-2-
methylethane

33. COMPOUND 2
1 2
Considering C1 Considering C2
1 21 2 1 2
S – ConfigurationR – Configuration X
S – Configuration
In terms of C1 the lowest priority atom (H) is
not in the back, therefore we assign
configuration using the normal rules
backwards. i.e. 1-2-3 clockwise is S and not R
1
2
3
4
1
2
3
4
(S) 1-Chloro-1,2-epoxy-2-
methylethane

34. CIS – TRANS ISOMERISM
Cis- trans isomerism has to do with the
arrangement of the atoms in space.
When two like groups are on the same
side of the epoxy substituent, it is said
to be a cis- isomer, whereas when the
two groups are on opposite sides, it is
said to be trans isomer.

36. SUMMARY
• An epoxide is a cyclic ether with a three
membered ring
• Epoxides are commonly named by either of
two styles
- Alkene oxide style
- Epoxy Style
• Epoxides are most commonly prepared by
- Epoxidation of Alkene
- Synthesis from halohydrin

37. SUMMARY
• Due to epoxides being a three membered ring
chain and its structure is somewhat of a
triangle, it undergoes high ring strain.
• Due to its high ring strain, epoxides commonly
undergo ring opening reactions.
• Ring opening reactions that epoxides undergo
can occur under both basic and acidic
conditions depending on the strength of the
nucleophile.

38. SUMMARY
• The structure of epoxides can also be
looked at in terms of stereochemistry; R
& S configuration, cis-trans isomerism

39. REFERENCE
1. Hunt, I. (n.d.). Basic IUPAC Organic Nomenclature. Retrieved from Epoxides:
http://www.chem.ucalgary.ca/courses/351/orgnom/ethers/ethers-02.html
2. Hunt, I. (n.d.). Chapter 16: Ethers, Epoxides and Sulfides. Retrieved from ch 16-HO-C-
C-X: http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch16/ch16-5-2.html
3. James. (2016). Master in Organic Chemistry. Retrieved from Opening of epoxides with
acids-Master in organic chemistry:
http://www.masterorganicchemistry.com/2015/02/02/opening-of-epoxides-with-acid/
4. March, J. (2013, September 24). New World Encyclopdedia. Retrieved from Epoxide-
New Wold Encyclopedia:
http://www.newworldencyclopedia.org/entry/Epoxide#Reactions
5. Reusch, W. (2013, May 5). Reactions of Alkenes Part II. Retrieved from Alkene
Reactivity: https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/addene2.htm
6. Soderburg, T. (n.d.). CHEMWIKI. Retrieved from Section 8 16 Epoxides as electrophiles
in nucleophilic substitution reaction:
http://chemwiki.ucdavis.edu/Core/Organic_Chemistry/Organic_Chemistry_With_a_Biol
ogical_Emphasis/Chapter_08%3A_Nucleophilic_substitution_reactions_I/Section_8.6%3
A_Epoxides_as_electrophiles_in_nucleophilic_substitution_reactions
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https://www.universalclass.com/articles/science/organic-chemistry/understanding-ethers-
and-epoxides.htm
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compound|Britannica.com: http://www.britannica.com/science/epoxide