7. 1. Geometry [3.4 Lewis structures]
Four groups of electrons
Ethane
tetrahedral
extend toward the corners of a regular tetrahedron
bond angle = 109.5o
14. 1. Physical properties
In each case, the alkyne has a higher boiling point than the
alkene.
Its structure is more linear.
The molecules pack together more efficiently.
Intermolecular forces are stronger.
Tegrity lecture video
15. 2. Nomenclature
The root name is based on the longest chain that
includes both carbons of the multiple bond.
The –ane ending is changed to –ene for double bonds
and –yne for triple bonds.
ethyne
ethene
propyne
propene
16. 2. Nomenclature
The chain is numbered from the end nearest the multiple
bond.
2-pentyne
1-butene [not 3-pentyne]
[not 3-butene]
The position of the multiple bond is indicated with the
lower-numbered carbon in the bond.
17. 2. Nomenclature
Determine the name and number of each substituent
and add in front of the name of the parent compound.
5-chloro-4-methyl-2-hexene
2,6-dimethyl-3-octene
5-bromo-4-ethyl-2-heptene
18. 2. Nomenclature
Alkenes with more than one double bond are called
alkadienes (2 double bonds)
alkatrienes (3 double bonds)
etc…
Each double bond is designated by its lower-numbered
carbon.
2,4-hexadiene
19. 2. Nomenclature
Cycloalkenes must be numbered so the double bond is
between carbons one and two.
3-chloro-cyclopentene
4-ethyl-5-methylcyclooctene
22. 2. Nomenclature
Write a structural formula for each of the following
compounds.
1-hexene
1,3-dicholoro-2-butene
4-methyl-2-hexyne
pencast
1,4-cyclohexadiene
23. 2. Nomenclature
Draw a structural formula for each of the following
compounds:
1-bromo-3-hexyne
2-butyne
pencast
dichloroethyne
9-iodo-1-nonyne
24. 3. Geometric isomers
Rotation around a double bond is restricted, in much the
same was as rotation is restricted for the cycloalkanes.
In the alkenes, geometric isomers occur when there are
two different groups on each of the double-bonded carbon
atoms.
1,2-dichloroethene
25. 3. Cis-trans isomers
If both constituents are on the same side of the double
bond, the isomer is cis-.
cis-1,2-dichloroethene
If the constituents are on opposite sides of the double bond,
the isomer is trans-.
trans-1,2-dichloroethene
26. 3. Cis-trans isomers
Alkenes without substituents also may exhibit cis-trans
isomerism.
cis-4-octene
trans-4-octene
27. 3. Cis-trans isomers
In order for cis and trans isomers to exist, neither double-
bonded carbon may have two identical substituents.
2-methyl-2-butene
no cis/trans isomerism
1-butene
no cis/trans isomerism
29. 3. Cis-trans isomers
Which of the following compounds can exist as geometric
isomers?
1-bromo-1-chloro-2,2-dimethylpropene
1,1-dichloroethene
1,2-dibromoethene
3-ethyl-2-methyl-2-hexene
30. 5. Reactions of alkenes and alkynes
The most common reactions of alkenes and alkynes are
addition reactions.
Hydrogenation: addition of H2
Halogenation: addition of X2
Hydration: addition of H2O
Hydrohalogenation: addition of HX
31. 5. General addition reaction
A double bond consists of
a sigma bond: two electrons
concentrated on a line between the two
connected atoms;
a pi bond: two electrons concentrated in
planes above and below the sigma bond.
33. 5. General addition reaction
In an addition reaction, the pi bond is lost and its electrons
become part of the single bonds to A and B.
34. 5. General addition reaction
For hydrogenation, halogenation, hydration, and
hydrohalogenation, identify the A and B portions of what is
being added to the double bond.
hydrogenation, H2
halogenation, X2 (where X = F, Cl, Br, or I)
hydration, H2O
hydrohalogenation, HX (where X = F, Cl, Br, or I)
35. 5. Hydrogenation
In hydrogenation of an alkene, one molecule of hydrogen
(H2) adds to one mole of double bonds.
Reaction conditions:
platinum, palladium, or nickel catalyst
[sometimes] heat and/or pressure
36. 5. Hydrogenation
In hydrogenation of an alkyne, two molecules of hydrogen
(H2) add to one mole of triple bonds.
Reaction conditions: same as for alkenes.
37. 5. Hydrogenation
Compare the products resulting from the hydrogenation of
trans-2-pentene and cis-2-pentene.
pencast
38. 5. Hydrogenation
Compare the products resulting from the hydrogenation of
1-butene and cis-2-butene.
pencast
39. 5. Vegetable oil and margarine
Why does hydrogenation make oils more solid?
MP = 13-14oC
MP = 69.6oC
MP = 62.9oC
40. 5. Halogenation
In halogenation of an alkene, one mole of a halogen (Cl2,
Br2, I2) adds to one mole of double bonds.
Since halogens are more reactive than hydrogen, no
catalyst is needed.
41. 5. Halogenation
In halogenation of an alkyne, two moles of a halogen (Cl2,
Br2, I2) add to one mole of double bonds.
42. 5. Halogenation
Draw the structure and write a balanced equation for the
halogenation of each of the following compounds.
3-methyl-1,4-hexadiene
4-bromo-1,3-pentadiene
3-chloro-2,4-hexadiene
pencast
43. 5. Halogenation
A solution of bromine in water
has a reddish-orange color.
A simple test for the presence
of an alkene or alkane is to
add bromine water.
If a double or triple bond is
present, the bromine will be
used up in a halogenation
Test of cyclohexane
reaction and the color will
and cyclohexene
disappear.
44. 5. Hydration
In hydration, one mole of water (H2O) is added to one mole
of double bonds.
A trace of acid is required as a catalyst.
45. 5. Hydration
Unlike hydrogenation and halogenation, hydration is not a
symmetric addition to a double bond.
If the double bond is not symmetrically located in the
molecule, there are two possible hydration products.
46. 5. Hydration
The predominant product is determined by Markovnikov’s
rule: The rich get richer.
OR: The carbon that already has more hydrogens will get
the hydrogen from the water.
Hydration of propene:
+ H 2O
47. 5. Hydration
Write a balanced equation for the hydration of each of the
following compounds:
2-butene
2-ethyl-3-hexene pencast
2,3-dimethylcyclohexene
Alkynes undergo a much more complicated hydration that you don’t need
to remember at this time!
48. 5. Hydrohalogenation
Like hydration, hydrohalogenation is an asymmetric addition
to a double bond.
Hydrohalogenation also follows Markovnikov’s rule.
50. 6. Aromatic compounds
Consider the following molecular formulas for unsaturated
hydrocarbons:
Hexane (all single bonds): C6H14
Cyclohexane (one ring): C6H12
Hexene (one double bond): C6H12
Hexadiene (two double bonds): C6H10
Cyclohexene (one ring, one double bond): C6H10
Hexatriene (three double bonds): C6H8
Cyclohexadiene (one ring, two double bonds): C6H8
51. 6. Aromatic compounds
The molecular formula for benzene is C6H6.
The structure must be highly unsaturated.
One ring, three double bonds?
Reactions of benzene:
Benzene does not decolorize bromine solutions.
Benzene does not undergo typical addition reactions.
Benzene reacts mainly by substitution.
The first three items are opposite from what is expected
from unsaturated compounds.
The last item is identical to what is expected for alkanes.
52. 6. Benzene structure
The benzene ring consists of:
six carbon atoms
joined in a planar hexagonal arrangement
with each carbon bonded to one hydrogen atom.
Two equivalent structures proposed by Kekulé are
recognized today as resonance structures.
The real benzene molecule is a hybrid with each resonance
structure contributing equally to the true structure.
53. 6. Benzene structure
Sigma and pi bonding in benzene:
The sharing of six electrons over the entire ring gives the
benzene structure extra stability.
Removing any one of the six electrons would destroy that
stability.
54. 6. Nomenclature
Most single-substituent compounds are named as
derivatives of benzene.
Bromobenzene
Ethylbenzene
55. 6. Nomenclature
A few “common” names have been adopted as IUPAC
nomenclature.
toluene
phenol
aniline
xylene (any benzene ring with two methyl groups)
56. 6. Nomenclature
There are three ways for the methyl groups on xylene to be
arranged.
1,2 [ortho-xylene]
1,3 [meta-xylene]
1,4 [para-xylene]
57. 6. Nomenclature
The substituent created by removing one hydrogen from the
benzene ring is called phenyl-.
2-phenylhexane
3-phenylcyclopentene
58. 6. Nomenclature
The substituent consisting of a –CH2 attached to a benzene
ring is called benzyl-.
Benzyl chloride
59. 6. Polynuclear aromatic hydrocarbons
These consist of rings joined along one side.
Good news! You don’t have to memorize these names!
60. 6. Reactions of benzene
Because of the stability of benzene’s ring structure, only
substitution reactions are characteristic.
Halogenation: substitution of one or more halogen atoms for
hydrogen atoms.
Cl2 requires FeCl3 catalyst.
Br2 requires FeBr3 catalyst.
Nitration: substitution of one or more nitro- (-NO2) groups for
hydrogen atoms.
Requires nitric acid and concentration sulfuric acid.
Sulfonation: substitution of one sulfonic acid (-SO3H) group for a
hydrogen atom.
SO3 reactant and concentration sulfuric acid.
61. 7. Heterocyclic aromatic compounds
Heterocyclic aromatic compounds have at least one non-
carbon atom incorporated in an aromatic ring or polynuclear
aromatic compound.
Many of these compounds are biologically important.
Components of DNA and RNA
Components of hemoglobin and chlorophyll
Pharmaceuticals
pyridine
Notas del editor
1-bromo-1-chloro-2,2-dimethylpropene: Looking at the double bond, we can see that the right carbon has identical groups (methyls) attached to it, so there CANNOT be geometric (cis-trans) isomers.1,1-dichloroethene: The name itself gives this one away. There are 2 chlorines on the left carbon so there can’t be geometric isomers.1,2-dibromoethene: This molecule has cis-trans geometric isomers. It doesn’t matter that both carbons have the same two groups attached, as long as NEITHER carbon has 2 identical groups attached to it.3-ethyl-2-methyl-2-hexene: Because the double bond begins at carbon 2 and there is also a methyl attached to carbon 2, the left carbon has identical (methyl) groups and there cannot be cis-trans isomers.
Hydrogenation: A-B is H-H. Both A and B represent a hydrogen atom.Halogenation: A-B is X-X (F-F or Cl-Cl or Br-Br or I-I). Both A and B represent X (F or Cl or Br or I).Hydration: A-B is H-OH. So A represents H and B represents OH (or vice versa: A represents OH and B represents H).Hydrohalogenation: A-B is H-X (H-F or H-Cl or H-Br or H-I). So A represents H and B represents X (F or Cl or Br or I).
Linear molecules pack together very efficiently, which maximizes the intermolecular forces. Saturated oils have long, linear chains of carbons.Nonlinear molecules don’t pack together as efficiently and experience weaker intermolecular forces. The weaker the forces, the lower the melting point.Natural oils (vegetable oils) are unsaturated so the molecules are nonlinear. These oils are liquid at room temperature.Hydrogenation adds hydrogens to the double bonds, making the molecules more nearly linear. This increases the intermolecular forces and raises the melting point. So, the more an oil is hydrogenated, the higher its melting point and the more solid it is at room temperature.