Here are the key factors that determine the major product of free radical halogenation of alkanes: - Halogens prefer to substitute at tertiary > secondary > primary carbon atoms. This is because tertiary radicals are more stable than secondary which are more stable than primary. - For isomeric structures with the same degree of substitution (e.g. 2-methylbutane vs 3-methylbutane), the major product will be the one where the halogen substitutes to give a more substituted structure. - Markovnikov's rule states that for addition to alkenes and alkynes, halogens will add on the side of the carbon atom that has the most hydrogen atoms. This

1. Organic Chemistry
Alkanes &
cycloalkanes

2. Alkanes
Alk
general formula CnH2n+2
alkanes are saturated
(each C is bound to 4 other atoms)

3. Alkanes
• Hydrocarbon chains where all the bonds
between carbons are SINGLE b d
b t b bonds
• Name uses the ending –ane
• Examples: Methane, Propane, Butane, Octane,
Methane, Propane, Butane, Octane,
2-methylpentane
methylpentane

4. Summary: IUPAC Rules for Alkane
Nomenclature
1. Find and name the longest continuous carbon chain.
This is called the parent c a . (Examples: methane,
s s ca ed e pa e t chain ( a p es e a e,
chain.
propane, etc.)
2. Number the chain consecutively, starting at the end
nearest an attached group (substituent).
g p (substituent). )
3. Identify and name groups attached to this chain.
(Examples: methyl-, bromo-, etc.)
methyl- bromo-
4. Designate the location of each substituent group with
the number of the carbon parent chain on which the
group is attached. Place a dash between numbers and
letters. (Example: 3-chloropentane)
3-
5. Assemble the name, listing groups in alphabetical order.
The prefixes di, tri, tetra etc., used to designate several
groups of the same kind, are not considered when
alphabetizing. Pl
l h b ti i Place a comma b t between multiple
lti l
numbers. (Example: 2,3-dichloropropane)
2,3-

5. Step 1 Find the parent chain
1. chain.
• Where is the longest continuous chain of
carbons?

6. Prefixes for # of Carbons
1 Meth 6 Hex
2 Eth 7 Hept
p
3 Prop 8 Oct
4 But 9 Non
5 Pent 10 Dec

7. IUPAC Names for Alkanes
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7

8. Endings
• Alkanes (all C-C single bonded parent chain)
C-
end in –ane
– Methane CH4
Methane
– Ethane C2H6
Ethane
– Propane C3H8
Propane
• Attached carbon groups (substituents) end i –yl
Att h d b (substituents) d in l
b tit t
– Methyl CH3 -
Methyl
– Ethyl CH3CH2-
Ethyl
l
– Propyl CH3CH2CH2 –
Propyl
3-ethylpentane

9. Step 2. Number the parent chain.
• Number the parent chain so that the attached
groups are on the lowest numbers
Methyl is on carbon #2 of the parent chain
Methyl is on carbon #4 of the parent chain
1 2 3 4 5 GREEN is the right
5 4 3 2 1 way for this one!
1 8 27
3 6 7 2 8 1 1 2 3 4 5 6
4 5 5 4 6 3 7 6 5 4 3 72
1
Groups on 4, 6, and 7 Groups on 2 and 5
Groups on 2, 3, and 5 Groups on 3 and 6

10. Step 3. Name the attached groups
3 groups.
• Carbon (alkyl) groups
( y
(alkyl) g p
– Methyl CH3 -
Methyl
– Ethyl CH3CH2-
Ethyl
y
– Propyl CH3CH2CH2 –
Propyl
• Halogens
– Fluoro (F-)
(F-
– Chloro (Cl-)
Cl-
– Bromo (Br-)
(Br-
– Iodo (I-)
(I-

12. Step 4. Designate where the group
is
i attached to the parent chain.
h d h h i
• Use the numbers of the parent chain from step 2
to designate the location of the attached groups
to the parent chain.
2-methyl
1 2 3 4 5

13. Step 5. Alphabetize the groups,
combine lik groups, and assemble.
bi like d bl
• The prefixes di, tri, tetra
di,
etc., used to designate
several groups of the same
kind
ki d
• Prefixes are not considered
when alphabetizing
1,1,1-trichloro-1- 1,1-dichloro-1,1-
(Example: dimethyl = m for fluoromethane difluoromethane
alphabetizing)
• Parent chain goes LAST

14. Draw Some Simple Alkanes
• 2-methylpentane
• 3-ethylhexane
th lh
• 2,2-dimethylbutane
2,2-
• 2,3-dimethylbutane
2,3-

16. Order of Priority
• IN A TIE halogens get the lower number
TIE,
before alkyl groups
4-chloro-2-methylpentane or
chloro-
2-chloro-4-methylpentane?
chloro-

17. Order of Priority
• IN A TIE between SIMILAR GROUPS the
GROUPS,
group lower ALPHABETICALLY gets the
lower number
4 bromo 2 chloropentane
4-bromo-2-chloropentane or
2-bromo-4-chloropentane ?

18. Isomers
• St i ht chain alkanes: A alkane
Straight h i alkanes: An lk
lk
that has all its carbons connected in a
row.
row.
• Branched chain alkanes: An alkane
alkanes:
that has a branching connection of
carbons.
carbons.
• Isomers: Compounds with same
Isomers:
molecular formula but different
structures.
structures.

19. • There is only one possible way that the
carbons in methane (CH4), ethane (C2H6),
and propane (C3H8) can be arranged.
arranged.

21. However,
However carbons in butane (C4H10) can be
arranged in two ways; four carbons in a row
ways;
(linear alkane) or a branching (branched
alkane)
alkane)
alkane). These two structures are two
isomers for butane.
butane.

22. Isomers
methane ethane propane
1 isomer 1 isomer 1 isomer

23. Isomers
normal butane
isobutane
(n-butane)
(n butane)

24. Different isomers are completely different
compounds.
compounds. They have different structures,
different physical properties such as melting
p y p p g
point and boiling point, and may have different
physiological properties.
properties.

25. Learning Check
• Draw all possible structural isomers of C5H12

26. Types of Carbon Atoms
• Primary carbon
y ( o)
(1
H
– a carbon bonded to C C H
one other carbon
H
• Secondary carbon (2o) H
– a carbon bonded to
C C C
two other carbons
H
H
• Tertiary carbon(3o)
– a carbon bonded to C C C
three other carbons
C

29. Alkanes
Example: Name the following compounds:
CH3 CH3
CHCH3 CH CH3
CH3 CH CH CH2 CH CH3
CH3 C CH2 CH2Br
CH3 C CH3 CH2CH3
CH2CH3 CH3

30. Structural Formulas
Alkanes are written with structural formulas that are
• Expanded to show each bond
bond.
• Condensed to show each carbon atom and its
attached hydrogen atoms
atoms.
• Line to show bonds as lines and omit hydrogens
H H H
H2
H C C C H H3C C CH3
H H H
30

31. Expanded and Condensed
Structures
St t
TABLE 11.3
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31

32. Line Bond
Line-Bond Formulas
• Because each C atom has a tetrahedral
arrangement, the order of atoms is not a
straight line, but a zigzag pattern.
• A line-bond formula abbreviates the carbon
atoms and shows only the zigzag pattern of
bonds from carbon atom t carbon atom.
b d f b t to b t
32

33. Alkanes
Example: Write the condensed
structure for the following compounds:
t t f th f ll i d
3,3-
3,3-dimethylpentane
2-methyl-4-sec-butyloctane
methyl- sec-bu y oc a e
e y
1,2-dichloro-
1,2-dichloro-3-methylheptane

34. Cycloalkanes
Are cyclic alkanes
alkanes.
Have 2H fewer than the open chain.
Are named by using the prefix cyclo before
cyclo-
the name of the alkane chain with the same
number of carbon atoms.
34

35. Cycloalkanes
The structural formulas of cycloalkanes are usually
y y
represented by geometric figures,
Cyclopropane CH2
CH2 CH2
Cyclobutane
CH2 CH2
CH2 CH2
35

36. Cycloalkanes
=
cyclopropane

37. Cycloalkanes
cyclobutane
cyclopentane
cyclohexane

38. Cycloalkanes

39. Naming Cycloalkanes with
Substituents
S b tit t
The name of a substituent is placed in front
of the cycloalkane name.
CH3
methylcyclobutane
Number ring with two substituents
1-bromo-2-chlorocyclopentane
1 bromo 2 chlorocyclopentane Br
B
Cl
39

40. Nomenclature of Cycloalkanes

42. Name each of the following :

43. Name each of the following :

44. Name each of the following :

45. Name each of the following :

46. Some Properties of Alkanes
The properties of alkanes include
being
• N
Nonpolar.
l
• Insoluble in water.
• L
Less d
dense th water
than t
• Flammable in air.
• Relatively unreactive. Copyright © 2007 by Pearson Education, Inc.
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46

47. Alkanes with 1-4 Carbon Atoms
14
Alkanes with 1-4 carbon atoms are
14
• Methane, ethane, propane, and
butane.
• Gases at room temperature.
• Used as heating fuels
fuels.
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47

48. Alkanes with 5-17 Carbon Atoms
Alkanes with 5-8 carbon atoms are
• Liquids at room temperature.
• Pentane, hexane, heptane, and octane.
• Very volatile.
• Used to make gasoline.
Alkanes with 9-17 carbon atoms
• Are liquids at room temperature
• Have higher boiling p
g g points.
• Are found in kerosene, diesel, and jet fuels. 48

49. Alkanes with 18 or more Carbon Atoms
Alkanes with 18 or more carbon atoms
• Have high molar masses.
• Are waxy solids at room temperature
temperature.
• Used in waxy coatings of fruits and
vegetables.
vegetables
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50. Crude Oil
The hydrocarbons in
crude oil are
• Separated by boiling
points.
• Heated to higher
temperatures to
produce
prod ce gases that
can be removed and
cooled.
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51. Alkane Reactions
1. Combustion
The
Th combustion of carbon compounds, especially h d
b ti f b d i ll hydrocarbons, h b
b has been th
the
most important source of heat energy for human civilizations throughout
recorded history.
CH3-CH2-CH3 + 5 O2 ——> 3 CO2 + 4 H2O + heat
Two points concerning this reaction are important:
1. Since all the covalent bonds in the reactant molecules are broken,
the quantity of heat evolved in this reaction is related to the strength
of these bonds (and of course, the strength of the bonds formed in
(and, course
the products).
2. The stoichiometry of the reactants is important. If insufficient oxygen
is supplied some of the p
pp products will consist of carbon monoxide, a ,
highly toxic gas.

52. Combustion of Alkanes
Alkanes
• Undergo combustion by
reacting with oxygen to
p
produce carbon dioxide, ,
water, and energy.
• Are typically not very
reactive d t strong C-
ti due to t C
C single bonds.
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alkane + O2 CO2 + H2O + energy
gy
52

53. Balancing A Combustion Equation
Write the equation
C5H12 + O2 CO2 + H2O
Balance C
C5H12 + O2 5CO2 + H2O
Balance H
C5H12 + O2 5CO2 + 6H2O
Balance O with O2
C5H12 + 8O2 5CO2 + 6H2O balanced
53

54. 2. Halogenation
Halogenation is the replacement of one or more hydrogen atoms in
an organic compound by a halogen (
g p y g (fluorine, chlorine, bromine or
, ,
iodine).
CH4 + Cl2 + energy ——> CH3Cl + HCl
When alkanes react with halogens:
• One or more hydrogens will be replaced with halogens
y g p g
• Halogens prefer to go to the more substituted (location
with more surrounding carbons) location
• Tertiary is more reactive than secondary which is more
reactive than primary
• Light or heat is required to form the radicals
• Radicals have unpaired electrons and violate the octet
rule (reactive)

55. Free Radical Halogenation
Mechanism
M h i
Light
Li ht
1. X X X + X
2.
2 R H + X R + X H
3. R + X X R X + X
used to indicate an unpaired electron (free radical)
X = shorthand for a halogen atom
R = shorthand for an organic compound or group
55

56. Free Radical Halogenation
g
Mechanism
1. inisiation
1 inisiation,

57. 2. propagation
radical reaction with Cl2:

58. 3. termination;

59. Predicting the Major Product of Free
Radical H l
R di l Halogenation
ti
• Halogens p
g prefer more substituted location on molecule
• Tertiary is more reactive than secondary which is more
reactive than primary
• Reactivity depends on ease of forming radical
• Below radicals listed from easiest to form to hardest
C H H H
C C C C H C H C
C C C H
tertiary secondary primary methyl
59

60. Predict the Major Product
H H H
H C C C H + Cl2
H H H
CH3
H2C CH
+ B2
Br
H2C CH2
+ Br2
60

61. Predict the Major Product
H H H H Cl H
H C C C H + Cl2 H C C C H + HCl
H H H H H H
CH3
CH3
Br
H2C CH H2 C C
+ Br2 + HBr
H2C CH2 H2 C CH2
+ Br2 Br + HBr
61