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Chapter 3
Hydrocarbons:
Nomenclature and Reactions
Chapter 3 Problems
• Review Section 3.9
• Read Essays on petroleum (p 204-207)
and gasoline (p 221-223) for interest.
• I recommend that you do all problems
except Prob. 8, 14, 33, 34 and 41
• Skip ethenyl, 2-propenyl etc on p. 200
• Read Section 3.15 and 3-16, but don’t
take them too seriously.
Sect. 3.1: IUPAC nomenclature
systematic nomenclature
I nternational
U nion of
P ure and
A pplied
C hemistry
colloquially:
“eye-you-pac”
Sect. 3.2: the alkanes
• Hydrocarbons
• “Paraffins”
• Alkanes: formula CnH2n+2
The alkanes: table 3-2
CH4
CH3 CH2 CH2 CH2 CH2 CH3
Methane
(CH4)
CH3 CH3
Ethane
(C2H6)
(C3H8)
(C4H10)
CH3 CH2 CH2 CH2 CH3
Pentane
Heptane
(C7H16)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH3
Butane
(C6H14)
CH3 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH3
Propane
Hexane
(C5H12)
Octane
(C8H18)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Nonane
(C9H20)
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Decane
(C10H22)
Sect. 3.4: IUPAC nomenclature of alkanes
Single substituent group
1. Find the longest continuous chain of
carbon atoms and name it (use linear names).
2. Number the chain starting from the end
nearest a branch.
3. Give the substituent a name based on the
number of carbon atoms it has. replace the
-ane ending with -yl
4. Give the substituent a number determined
on its location on the chain.
5. Assemble the name.
Finding the longest continuous chain
of carbon atoms is not always simple
all possibilites
must be examined
C-C
C-C-C-C-C-C-C-C-C
C
it won’t always be
the horizontal one
as shown here
9
try these also ……..
C-C
C-C
C- C-C-C-C-C-C-C-C
C
6
C-C-C- C-C-C-C-C-C
C
8
Sect. 3.3: Common alkyl groups
(C1 through C4): table 3-3
CH3
CH3 CH2 CH2 CH2
Methyl
CH3 CH CH2
Butyl
CH3
Isobutyl
CH3 CH2
(2-Methylpropyl)
Ethyl
CH3 CH2 CH2
Propyl
CH3 CH
CH3
Isopropyl
(1-Methylethyl)
CH3
CH3 CH2 CH
CH3
CH3 C
CH3
sec-Butyl
tert-Butyl
(1-Methylpropyl)
(1,1-Dimethylethyl)
Name this alkane
4
3
2
1
CH3 CH2 CH CH3
CH3
2-methylbutane
Find the longest continuous
carbon chain
1
2
3
CH3 CH2 CH CH3
CH2 CH3
4
3-methylpentane
5
You must choose the longest
continuous carbon chain
4
3
2
1
CH3 CH2 CH CH2 CH2 CH3
CH2 CH2 CH3
5
6
7
4-ethylheptane
Two different substituents
• number chain from end closest to a group,
regardless of alphabetical order
• locate where groups are on chain with
numbers
• place groups in alphabetical order, with the
appropriate number
• assemble the complete name, using
hyphens to separate numbers from “text”
Number from the end nearest
the first substituent
CH2 CH3
CH3 CH2 CH2 CH CH CH2 CH3
7
6
5
4
3
2
CH3
4-ethyl-3-methylheptane
1
Number from the end nearest
the first substituent
CH3
CH3 CH2 CH2 CH CH2 CH CH2 CH3
8
7
6
5
4
3
2
CH2 CH3
3-ethyl-5-methyloctane
1
Two or more identical
substituent groups
• for two identical groups, use prefix di with the
name of the group: dimethyl, diethyl, etc.
• dimethyl alphabetized as methyl, not dimethyl
• use numbers to locate groups on chain
• use commas to separate numbers
• prefixes: di = 2 tri = 3 tetra = 4 penta = 5
Use “di-” with two substituents
CH3
CH3 CH CH CH3
1
2
3
4
CH3
2,3-dimethylbutane
Every substituent must get a
number
CH3
CH3 CH2 C
1
2
3
CH2 CH2 CH3
4
5
CH3
3,3-dimethylhexane
6
You need numbers, even though
it appears on the same carbon!
CH3
CH3
CH3 CH CH2 C
5
4
3
2
CH3
1
CH3
2,2,4-trimethylpentane
Number from the end nearest
first substituent
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3
10
9
8
7
6
5
4
3
CH3
2,7,8-trimethyldecane
2
CH3
1
Number from the end which has
the “first difference”
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3
1
2
3
4
CH3
5
6
7
8
CH3
3,4,8-trimethyldecane
9
10
Number from the end nearest
the “first difference”
Dimethyl alphabetized as methyl, not dimethyl
CH3
CH3 CH2 CH CH CH2 CH CH2 CH3
1
2
3
CH3
4
5
6
7
CH2 CH3
6-ethyl-3,4-dimethyloctane
8
If you can name this,
you can name almost anything!
CH3
CH3
CH3 CH CH2 CH CH2 C
1
2
3
4
CH3 CH
CH3
5
6
CH3
CH2
7
CH2 CH3
8
9
4-isopropyl-2,6,6-trimethylnonane
The isopropyl group can be named
as a “complex” substituent
CH3
CH3 CH
2
1
1-methylethyl
Now, rename the isopropyl group.
Notice the alphabetical order!
CH3
CH3
CH3 CH CH2 CH CH2 C
1
2
3
4
CH3 CH
CH3
5
6
CH3
CH2
7
CH2 CH3
8
9
2,6,6-trimethyl-4-(1-methylethyl)nonane
Deciding on alphabetical order
for complex groups
• Complex groups are alphabetized under
the first letter of the name
• (1,3-dimethylbutyl) = d
• (1,1,2-trimethylpropyl) = t
• (1-ethyl-1,2-dimethylbutyl) = e
Naming complex substituents -this one is aphabetized under d
C H3
CH3
CH3 C H
C H2 C H
4
2
3
1
1,3-dimethylbutyl
Naming complex substituents
CH3 CH2 CH3
CH3 C
1
CH CH2 CH3
2
3
4
2-ethyl-1,1-dimethylbutyl
Name this compound!
CH3
CH3 CH2 C
CH3 CH2 CH2 CH2
1
2
3
4
C
5
1
CH2 CH3
2
3
CH2 CH2 CH2 CH3
6
7
8
CH2 CH2 CH3
5-(1-ethyl-1-methylpropyl)-5-propylnonane
9
Name this two ways -- (the complex
group)
CH3
CH3 C
CH3
CH2
CH3
CH
CH2
CH2
CH2
CH2
C
CH3
CH2
CH2
CH3
CH3
7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane
7-tert-butyl-3-ethyl-7-methyldecane
Sect. 3.5: Common names of
alkanes
•
•
•
•
•
butane
isobutane
pentane
isopentane
neopentane
Sect. 3.6: the cycloalkanes
• The names of the cycloalkanes always
contain the prefix cyclo
• Cycloalkanes have the general formula
CnH2n
Cyclic molecules
H
H
H
H
C
H
H
CH2 CH2
H
H
C
C
H
CH2 CH2
H
C
C
H
CH2 CH2
H
Cyclobutane
H
H
C
C
H
H
HH
C
H
H
H
H
C
C
C
C
C
H
CH2
Cyclopentane
C
H
CH2
CH2 CH2
H
H
H
H
CH2
C
C
Cyclopropane
H
H
H
CH2
C
C
H
H
H
CH2
H
H
CH2
CH2
CH2
CH2
CH2
Cyclohexane
Nomenclature of the substituted
cycloalkanes
• If there is only one substituent, do not use the “1”.
• If there is more than one substituent, you must
use all numbers, including “1”!
• Number around the ring in a direction to get from
the first substituent to the second substituent by
the shorter path.
• For equivalent degrees of substitution, number in
a direction that follows the alphabetical sequence.
• A carbon with greater substitution has precedence
in numbering.
CH3
CH3
1,1-dimethylcyclohexane
CH3
CH3
CH3 CH2
4-ethyl-1,1-dimethylcyclohexane
Some
cycloalkanes
1,3-dimethylcyclopentane
CH3
1
2
3
CH3
CH3
CH3
Drawn
differently
but same
name.
1
=
2
3
CH3
CH3
4
3
1
2
1
CH2CH3
1-ethyl-4-methylcyclohexane
E before M
CH3CH2
3
CH3
2
3-ethyl-1,1-dimethylcyclobutane
The more substituted carbon
takes precedence even
though E comes before M.
Two ways of naming this
CH3
CH
CH3
CH3
1-isopropyl-2-methylcyclohexane
1-methyl-2-(1-methylethyl)cyclohexane
Numbering starts at the most
highly-substituted carbon
Cl
CH3
2
CH3
1
3
7
4
5
6
CH3
2-chloro-1,1,6-trimethylcycloheptane
Sect. 3.7: cycloalkyl groups
cyclopropyl
cyclopentyl
cyclobutyl
cyclohexyl
CH3 CH2 C
CH2 CH3
CH3
3-cyclobutyl-3-methylpentane
Rings with one substitutent
H3C
CH
CH2CH3
(1-methylpropyl)cyclohexane or
2-cyclohexylbutane
No locant is needed.
With one substituent on a ring , it is automatically on carbon 1.
1-(1-methylpropyl)cyclohexane is overkill, but OK!
Another name of a group
or
or C6H5
Phenyl
CH3
CH3 CH2 CH
CH
CH3
3-methyl-2-phenylpentane
Sect. 3.8: Degree of Substitution
methylene
methyl
CH3 R
primary (1°)
methine
R
R CH2 R
secondary (2°)
R
R
CH R
R
C
R
R
tertiary (3°)
quaternary (4°)
Example
A hydrocarbon containing carbon atoms with
differing degrees of substitution
PRIMARY
QUATERNARY
CH3
TERTIARY
CH3
C
CH CH2 CH3
CH3 CH3
SECONDARY
All of the methyl groups (CH3) are primary.
Sect. 3.9 -- review
We already did this in Chapter 1
Sect. 3.10 and 3.11:
nomenclature of halides and
nitro compounds
F
Cl
fluoro
NO2
nitro
Br
chloro
I
bromo
iodo
CH 3 CH 2 Br
bromoethane (IUPAC)
ethyl bromide (common)
Br
bromocyclopropane
CH3
CH3 C
Cl
CH3
2-chloro-2-methylpropane (IUPAC)
tert-butyl chloride (common)
CH 3 CH
Br
CH
CH 2 CH 3
CH3
2-bromo-3-methylpentane
I
iodocyclohexane (IUPAC)
cyclohexyl iodide (common)
Br
Cl
1-bromo-2-chlorocyclohexane
CH3 CH
CH3
NO2
2-nitropropane
Sect. 3.12: Block diagram for
nomenclature
LOCANT
PREFIX
N
STEM
SUFFIX
numbers
substituents
number
-ALK(AN)-
ending
Sect. 3.13: alkene
nomenclature
• ending is ene
• identify the longest chain with the C=C
• number from the end closest to the C=C
and assign a number - - i.e. 2-pentene
• C=C is more important than groups!
• now number the attached groups and place
them in alphabetical order
CH2 CH2
ethene (IUPAC)
CH3 CH CH2
propene (IUPAC)
ethylene (common) propylene (common)
CH3 CH2 CH CH2
1-butene
CH3 CH CH CH3
2-butene
CH3
C
CH
CH3
CH3
2-methyl-2-butene
CH3
CH3 CH
CH2 CH2 CH
CH
6-methyl-2-heptene
CH3
CH 3
CH 3 CH 2 CH
CH 2 CH2
C
CH 3 CH 2 CH2
H
C
CH3
trans-6-methyl-3-propyl-2-octene
(Don’t worry about “trans” until Chapter 4)
CH3 CH3
4,4-dimethylcyclohexene
CH3
2-methyl-1,3-cyclohexadiene
CH2 CH3
CH2
CH3
2,5-diethyl-1,3-cyclooctadiene
Very important!
benzene
It is never cyclohexatriene!!!
Sect. 3.14: nomenclature of
alkynes
• similar system used as with alkenes
• ending is yne
• identify the longest chain with the triple
bond
• everything else is the same as alkenes
H
C
C
H
ethyne
“acetylene”
CH3 CH 2 C
1-butyne
CH3 C
C
H
propyne
CH
CH3 C
C
2-butyne
CH 3
ALKYNES
( -YNE )
The functional group has precedence in numbering.
CH3
C C CH2CH2CH3
2-hexyne
CH3
functional
group
C C CH CH3
CH3
4-methyl-2-pentyne
The suffix has
precedence
over any
substituents
4-chloro-4-methyl-2-pentyne
CH3
CH3 C
C
C
CH3
Cl
CH3
CH3 CH
Br
C
C
CH
5-bromo-2-methyl-3-heptyne
CH2 CH3
ene vs. yne: which one wins?
Number from the end closest to either the double bond
or the triple bond, whichever is closest to the end.
Compounds are named: en-yne.
8
7
6
CH3-CH2-C
5
4
3
2
1
C-CH2-CH=CH-CH3
2-octen-5-yne
optional, but recommended …..
COMPUTER PROGRAM
“ORGANIC NOMENCLATURE”
Available in Chemistry
Computer Lab - CB280
Go to ChemApps Folder :
Chem Apps
then choose first
and then
Organic
Organic
Nomenclature
Sect. 3.15: physical
properties of hydrocarbons
• the longer the straight chain, the higher
the boiling point -- van der Waals forces
• isomers that are branched have lower
boiling points
• hydrogen bonding increases boiling
points
• Dipole-dipole attractions increase b.p.
Sect. 3.16: Combustion of
alkanes
CnH2n+2 + m O2
n CO2 + (2n+2)/2 H2O
+ HEAT!!!
where n = number of carbons
Example:
2 C6H14 + 19 O2
12 CO2 + 14 H2O
Sect. 3.17: Halogenation of Alkanes
chlorination
R
H
+
Cl
Cl
light
free-radical
substitution
reaction
R
Cl
+
H
examples
CH4 + Cl2
CH3CH2CH3 + Cl2
takes place at a refinery
or a chemical plant - not
easy to do in the lab
CH3Cl + HCl
CH3CHCH3 + HCl
Cl
+ CH3CH2CH2-Cl
Cl
The previous examples given assumed
monochlorination (one chlorine added)
BUT …the reaction can repeat itself
COMMON NAMES
CH4
+ Cl2
CH3Cl + HCl
methyl chloride
CH3Cl + Cl2
CH2Cl2 + HCl
methylene chloride
CH2Cl2 + Cl2
CHCl3
+ HCl
chloroform
CHCl3 + Cl2
CCl4
+ HCl
carbon tetrachloride
fully chlorinated product
What are the
IUPAC names ?
The reaction must be initiated
It does not occur in the dark.
Exposure to ultraviolet light (sunlight) will start
the reaction.
Heat will also start the reaction.
Once reaction starts, it is exothermic and continues
almost explosively.
The first step is the dissociation of
chlorine :
hn
or D
.. ..
:Cl
:
Cl
.. ..
diatomic molecule
..
:
2 . Cl
..
chlorine
atoms
(radicals)
Abstraction of hydrogen atom
BY A CHLORINE “FREE RADICAL” (ATOM)
unpaired electron
= “free” radical
C..H
C.
+
+
..
. Cl :
..
..
:
H-Cl
..
HYDROGEN ABSTRACTION
Chlorine takes the
hydrogen and one
of its electrons
Mechanism of chlorination of methane
CHAIN REACTION
1. Initiation
..
: Cl
..
..
Cl :
..
light
2
..
: Cl .
..
a free radical
“dissociation”
R
E
P
E
A
T
I
N
G
S
T
E
P
S
2. Chain Propagation (first step)
+
CH3 H
..
: Cl .
..
H
..
Cl :
..
+
. CH3
methyl radical
“hydrogen abstraction”
3. Chain Propagation (second step)
. CH3
+
..
: Cl
..
..
Cl :
..
CH3
..
Cl :
..
+
..
: Cl .
..
feeds back into
step two
4. Termination Steps
..
2 : Cl .
..
CH3.
..
: Cl .
..
+
+
. CH
3
. CH
3
“recombinations”
..
: Cl
..
..
Cl :
..
CH3CH3
..
: Cl CH3
..
These steps stop
the chain reaction
Monochlorination of propane:
Does one isomer predominate?
CH3CH2CH3 + Cl2
limited
amount
CH3CHCH3 + CH3CH2CH2-Cl
Cl
A
QUESTION
WHAT ARE THE RELATIVE AMOUNTS OF A AND B ?
IS IT STATISTICAL ( 2 : 6 ) = (1 : 3 ) ?
DOES SOMETHING ELSE CONTROL THE OUTCOME ?
B
Monochlorination of propane
STATISTICAL VERSUS EXPERIMENTAL RESULTS
CH3CHCH3
Cl
STATISTICAL PREDICTION
CH3CH2CH2-Cl
A
B
25 %
75 %
CH3-CH2-CH3 = 6 : 2 or 3:1
ACTUALLY FOUND
50 %
Equal
amounts
50 %
Equal
amounts
Experimental results show:
Secondary hydrogens are energenically more easily
removed than primary hydrogens
CH3CHCH3
H
CH3CH2CH3
Primary H
Secondary H
more reactive hydrogen
Stability of free radicals
explains results!
H
H
H3C
C
CH 3
H3C
CH 2
C
H
secondary radical
primary radical
More stable and
easier to form!
Less stable and harder
to form
Stability of radicals: TERTIARY > SECONDARY > PRIMARY
CH 3
H3C
C
H
CH 3
H3C
C
H
CH 3
H3C
CH 2
C
H
tertiary radical
secondary radical
primary radical
Most stable and
easiest to form!
less stable than
tertiary but more
stable than primary
Least stable and
hardest to form
Another example: isobutane
Which product should form in the largest
amount?
CH 3
H 3C
C
CH 2
H
H
Cl2
CH 3
H 3C
There are 9 primary H’s
and only 1 tertiary H
Statistically you could predict
a 9:1 ratio or a 90% yield of
1-chloro-2-methylpropane!
Wrong!!
C
CH 2
H
Cl
Isobutane gives only 62% of 2-chloro-2-methylpropane!
Why? Look at the stability of the intermediate radical.
CH 3
H3C
Cl
CH 3
H-Cl
tertiary radical - more stable
CH 3
H3C
C
C
CH 2
H
H
CH 3
Cl
H3C
C
H
H
H-Cl
C
H
primary radical - less stable
The statistical factor predicts a 9:1 ratio (90%)
However, the energy factor predicts that the ratio
will be less than 90% and turns out to be 62%.
CH 3
H3C
C
CH 3
CH 3
Cl2
H3C
tertiary radical
CH 3
H3C
C
H
Cl
38%
CH 3
Cl2
H
H
CH 3
Cl
H
C
C
H3C
C
H
C
H
primary radical
62%
Cl
H
H
Cl
Draw the structure of all of the monochlorinated products.
There are 6 total products. The next slide shows the
remaining 5 products. Only ONE product is shown here!
Cl2
light or heat
The two circled methyl
groups are equivalent!!!!
Cl
same as
Cl
1-chloro-2-methylhexane
Here are 5 more isomeric products that are formed!
Cl2
light or heat
Cl
2-chloro-2-methylhexane
Cl
2-chloro-5-methylhexane
Cl
3-chloro-2-methylhexane
Cl
Cl
1-chloro-5-methylhexane
4-chloro-2-methylhexane
Ethylcyclopentane: monochlorination
products
CH2 CH3
MONOCHLORINATION
PRODUCTS
CH2 CH2 Cl
CH2 CH3
Cl
CH CH3
CH2 CH3
Cl
CH2 CH3
Cl
Cl
Hydrochlorofluorocarbons
(HCFC’s)
F
H
C
F
Cl
Depletes the ozone in the upper atmosphere
Sect. 3.18: hydrogenation of alkenes
C
+
C
H
H
catalyst
catalyst = Pt, Pd, Ni
C
C
H
H
Hydrogenation is covered in more detail in Chap 4 we’ll cover it there.
Hydrogenation is included in this chapter (briefly)
because it is a method of making ALKANES.
+
H2
Pd
H3C
CH3
+
H
H
Pt
H2
CH3CH2CH2CH3