Chapter 3 Hydrocarbons: Nomenclature and Reactions

1
Chapter 3Hydrocarbons Nomenclature and
Reactions
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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 dont take them
  too seriously.

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Sect. 3.1 IUPAC nomenclature
systematic nomenclature
I nternational U nion of P ure and A pplied C
hemistry
colloquially
eye-you-pac
4
Sect. 3.2 the alkanes

• Hydrocarbons
• Paraffins
• Alkanes formula CnH2n2

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The alkanes table 3-2
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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.
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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
it wont always be the horizontal one as shown
here
C
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try these also ..
C-C
C-C
C-C-C-C-C-C
C-C-C-
C-C-C
-C-C-C-C-C
C-
C
6
8
C
8
Sect. 3.3 Common alkyl groups (C1 through C4)
table 3-3
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Name this alkane

• 4 3 2 1
• 2-methylbutane

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Find the longest continuouscarbon chain

• 1 2 3
  4 5
• 3-methylpentane

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You must choose the longestcontinuous carbon
chain

• 4 3 2
  1 5 6 7
• 4-ethylheptane

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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

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Number from the end nearestthe first substituent

• 7 6 5 4 3
  2 1
• 4-ethyl-3-methylheptane

14
Number from the end nearestthe first substituent

• 8 7 6 5 4 3
  2 1
• 3-ethyl-5-methyloctane

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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

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Use di- with two substituents

• 1 2 3 4
• 2,3-dimethylbutane

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Every substituent must get a number

• 1 2 3 4 5
  6
• 3,3-dimethylhexane

18
You need numbers, even though it appears on the
same carbon!

• 5 4 3 2 1
• 2,2,4-trimethylpentane

19
Number from the end nearestfirst substituent

• 10 9 8 7 6 5
  4 3 2 1
• 2,7,8-trimethyldecane

20
Number from the end which hasthe first
difference

• 1 2 3 4 5 6
  7 8 9 10
• 3,4,8-trimethyldecane

21
Number from the end nearestthe first
difference Dimethyl alphabetized as methyl, not
dimethyl

• 1 2 3 4 5
  6 7 8
• 6-ethyl-3,4-dimethyloctane

22
If you can name this,you can name almost
anything!

• 1 2 3 4 5
  6
  7
  8 9
• 4-isopropyl-2,6,6-trimethylnonane

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The isopropyl group can be named as a complex
substituent

• 1-methylethyl

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Now, rename the isopropyl group. Notice the
alphabetical order!

• 1 2 3 4 5
  6
  7
  8 9
• 2,6,6-trimethyl-4-(1-methylethyl)nonane

25
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

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Naming complex substituents -- this one is
aphabetized under d

• 1,3-dimethylbutyl

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Naming complex substituents

• 2-ethyl-1,1-dimethylbutyl

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Name this compound!

• 1 2
  3
• 1 2 3 4 5
  6 7 8 9
• 5-(1-ethyl-1-methylpropyl)-5-propylnonane

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Name this two ways -- (the complex group)

• 7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane
• 7-tert-butyl-3-ethyl-7-methyldecane

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Sect. 3.5 Common names of alkanes

• butane
• isobutane
• pentane
• isopentane
• neopentane

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Sect. 3.6 the cycloalkanes

• The names of the cycloalkanes always contain the
  prefix cyclo
• Cycloalkanes have the general formula
• CnH2n

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Cyclic molecules
33
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.

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1,1-dimethylcyclohexane
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4-ethyl-1,1-dimethylcyclohexane
36
Some cycloalkanes
1,3-dimethylcyclopentane
Drawn differently but same name.
1
2
1

2
3
3
4
3
1
2
2
1
3
3-ethyl-1,1-dimethylcyclobutane
1-ethyl-4-methylcyclohexane
The more substituted carbon takes precedence even
though E comes before M.
E before M
37
Two ways of naming this

• 1-isopropyl-2-methylcyclohexane
• 1-methyl-2-(1-methylethyl)cyclohexane

38
Numbering starts at the most highly-substituted
carbon
2 1 3
7 4 6
5
2-chloro-1,1,6-trimethylcycloheptane
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Sect. 3.7 cycloalkyl groups
40
3-cyclobutyl-3-methylpentane
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Rings with one substitutent
(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!
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Another name of a group
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3-methyl-2-phenylpentane
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Sect. 3.8 Degree of Substitution
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Example
A hydrocarbon containing carbon atoms
with differing degrees of substitution
PRIMARY
QUATERNARY
TERTIARY
SECONDARY
All of the methyl groups (CH3) are primary.
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Sect. 3.9 -- review

• We already did this in Chapter 1

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Sect. 3.10 and 3.11 nomenclature of halides and
nitro compounds
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bromoethane (IUPAC)
ethyl bromide (common)
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bromocyclopropane
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2-chloro-2-methylpropane (IUPAC)
tert-butyl chloride (common)
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2-bromo-3-methylpentane
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iodocyclohexane (IUPAC)
cyclohexyl iodide (common)
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1-bromo-2-chlorocyclohexane
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2-nitropropane
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Sect. 3.12 Block diagram for nomenclature
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Sect. 3.13 alkene nomenclature

• ending is ene
• identify the longest chain with the CC
• number from the end closest to the CC and assign
  a number - - i.e. 2-pentene
• CC is more important than groups!
• now number the attached groups and place them in
  alphabetical order

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ethene (IUPAC)
propene (IUPAC)
ethylene (common)
propylene (common)
1-butene
2-butene
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2-methyl-2-butene
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6-methyl-2-heptene
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trans-6-methyl-3-propyl-2-octene
(Dont worry about trans until Chapter 4)
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4,4-dimethylcyclohexene
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2-methyl-1,3-cyclohexadiene
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2,5-diethyl-1,3-cyclooctadiene
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Very important!
benzene
It is never cyclohexatriene!!!
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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

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ethyne
propyne
acetylene
1-butyne
2-butyne
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ALKYNES ( -YNE )
The functional group has precedence in numbering.
2-hexyne
functional group
The suffix has precedence over any substituents
4-methyl-2-pentyne
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4-chloro-4-methyl-2-pentyne
5-bromo-2-methyl-3-heptyne
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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 5 4 3
2 1
CH3-CH2-C C-CH2-CHCH-CH3
2-octen-5-yne
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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 Nomenclature
Organic
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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.

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Sect. 3.16 Combustion of alkanes
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Sect. 3.17 Halogenation of Alkanes
chlorination
free-radical substitution reaction
examples
CH4 Cl2 CH3Cl HCl
CH3CH2CH3 Cl2 CH3CHCH3 HCl
Cl
takes place at a refinery or a chemical plant -
not easy to do in the lab
CH3CH2CH2-Cl
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The previous examples given assumed
monochlorination
(one chlorine added)
BUT the reaction can repeat itself
COMMON NAMES
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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
..
..
..
.
Cl-Cl
hn



2
Cl
chlorine atoms
..
..
..
or D
(radicals)
diatomic molecule
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Abstraction of hydrogen atom
BY A CHLORINE FREE RADICAL (ATOM)
unpaired electron free radical
..
.
.
.
C H

Cl
HYDROGEN ABSTRACTION

..
Chlorine takes the hydrogen and one of its
electrons
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Mechanism of chlorination of methane
CHAIN REACTION
dissociation
REPEAT ING S TEPS
hydrogen abstraction
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4. Termination Steps
recombinations
These steps stop the chain reaction
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Monochlorination of propane Does one isomer
predominate?
CH3CH2CH3 Cl2 CH3CHCH3
CH3CH2CH2-Cl
Cl
limited amount
A
B
QUESTION
WHAT ARE THE RELATIVE AMOUNTS OF A AND B ?
IS IT STATISTICAL ( 2 6 ) (1 3 ) ?
DOES SOMETHING ELSE CONTROL THE OUTCOME ?
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Monochlorination of propane
STATISTICAL VERSUS EXPERIMENTAL RESULTS
CH3CH2CH2-Cl
A
B
STATISTICAL PREDICTION 25 75
CH3-CH2-CH3 6 2 or 31
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Experimental results show
Secondary hydrogens are energenically more easily
removed than primary hydrogens
CH3CH2CH3
CH3CHCH3
H
Primary H
Secondary H
more reactive hydrogen
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Stability of free radicals explains results!
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Stability of radicals TERTIARY gt SECONDARY gt
PRIMARY
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Another example isobutane Which product should
form in the largest amount?
There are 9 primary Hs and only 1 tertiary
H Statistically you could predict a 91 ratio
or a 90 yield of 1-chloro-2-methylpropane!
Wrong!!
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Isobutane gives only 62 of 2-chloro-2-methylpropa
ne! Why? Look at the stability of the
intermediate radical.
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The statistical factor predicts a 91 ratio
(90) However, the energy factor predicts that
the ratio will be less than 90 and turns out to
be 62.
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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!
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Here are 5 more isomeric products that are formed!
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Ethylcyclopentane monochlorination products
MONOCHLORINATION PRODUCTS
90
Hydrochlorofluorocarbons(HCFCs)
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Sect. 3.18 hydrogenation of alkenes
catalyst Pt, Pd, Ni
Hydrogenation is covered in more detail in Chap 4
- well cover it there.
Hydrogenation is included in this chapter
(briefly) because it is a method of making
ALKANES.