chapter 3 hydrocarbons: nomenclature and reactions
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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.
I nternational
U nion of
P ure and
A pplied
C hemistry
Sect. 3.1: IUPAC nomenclaturesystematic nomenclature
“eye-you-pac”
colloquially:
Sect. 3.2: the alkanes
• Hydrocarbons
• “Paraffins”
• Alkanes: formula CnH2n+2
The alkanes: table 3-2
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
Pentane (C5H12)
Hexane (C6H14)
Heptane (C7H16)
Octane (C8H18)
Nonane (C9H20)
Decane (C10H22)
CH4
CH3 CH3
CH3 CH2 CH3
CH3 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Sect. 3.4: IUPAC nomenclature of alkanes
1. Find the longest continuous chain of carbon atoms and name it (use linear names).
3. Give the substituent a name based on the number of carbon atoms it has. replace the -ane ending with -yl
2. Number the chain starting from the end nearest a branch.
4. Give the substituent a number determined on its location on the chain.5. Assemble the name.
Single substituent group
Finding the longest continuous Finding the longest continuous chain chain of carbon atoms is not always of carbon atoms is not always simplesimple
C-C-C-C-C-C-C-C-CC-C-C-C-C-C-C-C-C
C
C-C
C-C-CC-C-C
C-CC-C
CC
-C-C-C-C-CC- C-C-C-C-C-CC-C-C-C-C-C
C-CC-C
C-C-C-
C
all possibilitesmust be examined
it won’t always bethe horizontal one as shown here
try these also ……..
99
66 88
Sect. 3.3: Common alkyl groups (C1 through C4): table 3-3
Methyl
Ethyl
Propyl
Butyl
Isopropyl
Isobutyl
(1-Methylethyl)
(2-Methylpropyl)
sec-Butyl
(1-Methylpropyl)
tert-Butyl
(1,1-Dimethylethyl)
CH3
CH3 CH2
CH3 CH2 CH2
CH3 CH2 CH2 CH2
CH3 CH
CH3
CH3 CH CH2
CH3
CH3 CH2 CH
CH3
CH3 C
CH3
CH3
CH3 CH2 CH CH3
CH3
Name this alkane
4 3 2 1
2-methylbutane
CH3 CH2 CH CH3
CH2 CH3
Find the longest continuouscarbon chain
1 2 3
4 5
3-methylpentane
CH3 CH2 CH CH2 CH2 CH3
CH2 CH2 CH3
You must choose the longestcontinuous carbon chain
4 3 2 1
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”
CH3 CH2 CH2 CH CH CH2 CH3
CH3
CH2 CH3
Number from the end nearestthe first substituent
7 6 5 4 3 2 1
4-ethyl-3-methylheptane
CH3 CH2 CH2 CH CH2 CH CH2 CH3
CH2 CH3
CH3
Number from the end nearestthe first substituent
8 7 6 5 4 3 2 1
3-ethyl-5-methyloctane
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
CH3 CH CH CH3
CH3
CH3
Use “di-” with two substituents
1 2 3 4
2,3-dimethylbutane
CH3 CH2 C CH2 CH2 CH3
CH3
CH3
Every substituent must get a number
1 2 3 4 5 6
3,3-dimethylhexane
CH3 CH CH2 C CH3
CH3 CH3
CH3
You need numbers, even though it appears on the same carbon!
5 4 3 2 1
2,2,4-trimethylpentane
CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3
CH3CH3
CH3
Number from the end nearestfirst substituent
10 9 8 7 6 5 4 3 2 1
2,7,8-trimethyldecane
CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3
CH3
CH3
CH3
Number from the end which hasthe “first difference”
1 2 3 4 5 6 7 8 9 10
3,4,8-trimethyldecane
CH3 CH2 CH CH CH2 CH CH2 CH3
CH3
CH3
CH2 CH3
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
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
CH3 CH CH2 CH CH2 C CH3
CH3
CH
CH3
CH3
CH3
CH2
CH2 CH3
The isopropyl group can be named as a “complex” substituent
1-methylethyl
CH3 CH
CH3
2 1
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
CH3 CH CH2 CH CH2 C CH3
CH3
CH
CH3
CH3
CH3
CH2
CH2 CH3
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
1,3-dimethylbutyl
C H 3 C H C H 2 C H
C H 3C H 3
4 3 2 1
Naming complex substituents
2-ethyl-1,1-dimethylbutyl
CH3 C CH CH2 CH3
CH3 CH2 CH3
1 2 3 4
CH3 CH2 CH2 CH2 C CH2 CH2 CH2 CH3
C
CH2 CH2 CH3
CH3
CH2CH2 CH3CH3
Name this compound!
1 2 3
1 2 3 4 5 6 7 8 9
5-(1-ethyl-1-methylpropyl)-5-propylnonane
CH2CH2
CH2CH
CH2CH3 C
CH2CH2
CH3
CH2CH3
CH3
CCH3 CH3
CH3
Name this two ways -- (the complex group)
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 formulaCnH2n
Cyclic molecules
Cyclopropane
Cyclobutane
Cyclopentane
Cyclohexane
CC
C
H H
H
H
H
H
CH2
CH2
CH2
C
C C
C
H
H
H
H
H
H
H
H
CH2
CH2 CH2
CH2
C
C
C
C
C
H HH H
HH
HH
HH
CH2
CH2
CH2
CH2
CH2
C
CC
C
CC
H HH
H
H
H
HH
H
H
H
HCH2
CH2
CH2
CH2
CH2
CH2
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
CH2CH3
4-ethyl-1,1-dimethylcyclohexane
CH3
CH3
CH3
CH3CH3
CH2CH3
CH3
CH3
CH3CH2
1,3-dimethylcyclopentane
1-ethyl-4-methylcyclohexane
3-ethyl-1,1-dimethylcyclobutane
Some Some cycloalkanescycloalkanes
The more substituted carbontakes precedence even though E comes before M.
Drawndifferentlybut samename.
=
E before M
1 2
3
1
2
3
1
231
2
3
4
Two ways of naming this
1-isopropyl-2-methylcyclohexane
1-methyl-2-(1-methylethyl)cyclohexane
CH3
CH
CH3
CH3
Numbering starts at the most highly-substituted carbon
Cl CH3
CH3
CH3
2 13 74 6 5
2-chloro-1,1,6-trimethylcycloheptane
Sect. 3.7: cycloalkyl groups
cyclopropyl cyclobutyl
cyclopentyl cyclohexyl
C
CH3
CH2CH2CH3 CH3
3-cyclobutyl-3-methylpentane
CH CH2CH3CH3
(1-methylpropyl)cyclohexane or2-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!
Rings with one substitutentRings with one substitutent
Another name of a group
or
Phenyl
or C6H5
CH3 CH2 CH CH CH3
CH3
3-methyl-2-phenylpentane
Sect. 3.8: Degree of Substitution
methyl methylene
methine
CH3 R R CH2 R
R CH R
R
R C R
R
R
primary (1°) secondary (2°)
tertiary (3°) quaternary (4°)
CH3 C
CH3
CH3
CH CH2 CH3
CH3
QUATERNARY
PRIMARY
TERTIARY
SECONDARY
A hydrocarbon containing carbon atoms withdiffering degrees of substitution
All of the methyl groups (CH3) are primary.
ExampleExample
Sect. 3.9 -- review
We already did this in Chapter 1
Sect. 3.10 and 3.11: nomenclature of halides and
nitro compounds
fluoro chloro bromo iodo
nitro
F Cl Br I
NO2
CH 3 CH 2 Br
bromoethane (IUPAC)
ethyl bromide (common)
Br
bromocyclopropane
CH3 C Cl
CH3
CH3
2-chloro-2-methylpropane (IUPAC)
tert-butyl chloride (common)
CH3 CH CH CH2 CH3
Br CH3
2-bromo-3-methylpentane
I
iodocyclohexane (IUPAC)
cyclohexyl iodide (common)
Br
Cl
1-bromo-2-chlorocyclohexane
CH3 CH CH3
NO2
2-nitropropane
LOCANT PREFIX N STEM SUFFIX
numbers substituents number -ALK(AN)- ending
Sect. 3.12: Block diagram for nomenclature
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 CH3 CH CH2
CH3 CH2 CH CH2 CH3 CH CH CH3
ethene (IUPAC) propene (IUPAC)
1-butene 2-butene
ethylene (common) propylene (common)
C CH CH3
CH3
CH3
2-methyl-2-butene
CH3 CH CH2 CH2 CH CH CH3
CH3
6-methyl-2-heptene
C C
CH3
H
CH2
CH2
CH2CH3
CH2CHCH2
CH3
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!
benzeneIt 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 CH3 C C H
CH3 CH2 C CH CH3 C C CH3
ethyne propyne
1-butyne 2-butyne
“acetylene”
ALKYNES ( -YNE )ALKYNES ( -YNE )
C CCH3 CH2CH2CH3
CCH3 C CH
CH3
CH3
2-hexyne
4-methyl-2-pentyne
The suffix hasprecedenceover anysubstituents
The functional group has precedence in numbering.
functionalgroup
CH3 C C
CH3
Cl
C CH3
CH3 CH C
CH3
C CH CH2
Br
CH3
4-chloro-4-methyl-2-pentyne
5-bromo-2-methyl-3-heptyne
Number from the end closest to either the double bondor the triple bond, whichever is closest to the end.
ene vs. yne: which one wins?ene vs. yne: which one wins?
CH3-CH2-C C-CH2-CH=CH-CH3
2-octen-5-yne
8 7 6 5 4 3 2 1
Compounds are named: en-yne.
COMPUTER PROGRAM
““ORGANIC NOMENCLATURE”ORGANIC NOMENCLATURE”
Available in ChemistryComputer Lab - CB280
Go to ChemApps Folder :
optional, but recommended …..
then choose first and then Organic Nomenclature
Chem Apps
Organic
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
where n = number of carbons
+ HEAT!!!
Example:
2 C6H14 + 19 O2 12 CO2 + 14 H2O
light+ +R H Cl Cl R Cl H Cl
chlorination
examples
CH4 + Cl2 CH3Cl + HCl
CH3CH2CH3 + Cl2 CH3CHCH3 + HCl Cl
+ CH3CH2CH2-Cltakes place at a refineryor a chemical plant - noteasy to do in the lab
free-radicalsubstitution reaction
Sect. 3.17: Halogenation of Alkanes
The previous examples given The previous examples given assumed assumed monochlorinationmonochlorination
(one chlorine added)(one chlorine added)
BUT …the reaction can repeat itselfCOMMON 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 theIUPAC names ?
The reaction must be initiated
It does not occur in the dark.
Exposure to ultraviolet light (sunlight) will startthe reaction.
Heat will also start the reaction.
Once reaction starts, it is exothermic and continuesalmost explosively.
The first step is the dissociation of chlorine :
Cl-Cl 2 Cl....
..
......: : :.h
or chlorineatoms
diatomic molecule(radicals)
Abstraction of hydrogen atomAbstraction of hydrogen atom
Cl.. :...
BY A CHLORINE “FREE RADICAL” (ATOM)
+
C . H-Cl.. :..
+
Chlorine takes thehydrogen and one of its electrons
unpaired electron= “free” radical
HYDROGEN ABSTRACTION..C H
Cl Cllight
2 : Cl..
...
CH3 H + : Cl..
...
..:
..H Cl + . CH3
. CH3 +
..
..
..
..: :Cl Cl
..
..:CH3 Cl + : Cl
...
..
..
..
..
..: :
1. Initiation
2. Chain Propagation (first step)
3. Chain Propagation (second step)
a free radical
methyl radical
feeds back intostep two
REPEAT ING
STEPS
Mechanism of chlorination of methaneMechanism of chlorination of methaneCHAIN REACTION
“hydrogen abstraction”
“dissociation”
4. Termination Steps
Cl Cl2 : Cl..
...
. CH3CH3
..
..
..
..: :
. + CH3CH3
: Cl..
... . CH3+ : Cl
..CH3
..
These steps stopthe chain reaction
“recombinations”
CH3CH2CH3 + Cl2 CH3CHCH3
Cl+ CH3CH2CH2-Cl
limited amount
QUESTION
A B
WHAT ARE THE RELATIVE AMOUNTS OF A AND B ?
IS IT STATISTICAL ( 2 : 6 ) = (1 : 3 ) ?
DOES SOMETHING ELSE CONTROL THE OUTCOME ?
Monochlorination of propane: Monochlorination of propane: Does one isomer predominate?Does one isomer predominate?
CH3CHCH3
Cl CH3CH2CH2-Cl
A B
STATISTICAL PREDICTION 25 % 75 %
CH3-CH2-CH3 = 6 : 2 or 3:1
Monochlorination of propaneMonochlorination of propane STATISTICAL VERSUS EXPERIMENTAL RESULTS
ACTUALLY FOUND 50 % 50 %
Equal amounts
Equalamounts
Experimental results show:
Secondary hydrogens are energenically more easily removed than primary hydrogens
CH3CHCH3
H
CH3CH2CH3
Secondary HPrimary H
more reactive hydrogen
Stability of free radicals explains results!
H3C C CH3
H
secondary radical
More stable and easier to form!
H3C CH2 C
H
H
primary radical
Less stable and harderto form
Stability of radicals: TERTIARY > SECONDARY > PRIMARY
H3C C CH3
H
secondary radical
less stable than tertiary but more stable than primary
H3C CH2 C
H
H
primary radical
Least stable and hardest to form
H3C C CH3
CH3
tertiary radical
Most stable and easiest to form!
H3C C CH2
CH3
H H
H3C C CH2
CH3
H Cl
Cl2
Another example: isobutaneWhich product should form in the largest amount?
There are 9 primary H’sand only 1 tertiary H
Statistically you could predict a 9:1 ratio or a 90% yield of 1-chloro-2-methylpropane!
Wrong!!
H3C C CH3
CH3
tertiary radical - more stable
H3C C CH2
CH3
H H
H3C C C
CH3
H
ClH-Cl
primary radical - less stable
H
H
Cl H-Cl
Isobutane gives only 62% of 2-chloro-2-methylpropane! Why? Look at the stability of the intermediate radical.
The statistical factor predicts a 9:1 ratio (90%)However, the energy factor predicts that the ratiowill be less than 90% and turns out to be 62%.
H3C C CH3
CH3
tertiary radical
H3C C C
CH3
H
primary radical
H
H
Cl2
Cl2
H3C C CH3
CH3
Cl
ClH
H3C C C
CH3
H
H
H
Cl ClH
38%
62%
Cl2
light or heatCl
same as
Cl
1-chloro-2-methylhexane
The two circled methylgroups are equivalent!!!!
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 heatCl
Cl
Cl
Cl
Cl
1-chloro-5-methylhexane 4-chloro-2-methylhexane
2-chloro-5-methylhexane
2-chloro-2-methylhexane
3-chloro-2-methylhexane
Here are 5 more isomeric products that are formed!
Ethylcyclopentane: monochlorination products
MONOCHLORINATION PRODUCTS
CH2 CH3
CH2 CH2 Cl
CH CH3
Cl
CH2 CH3
Cl
CH2 CH3
Cl
Cl
CH2 CH3
Hydrochlorofluorocarbons(HCFC’s)
H C Cl
F
F
Depletes the ozone in the upper atmosphere
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.
Sect. 3.18: hydrogenation of alkenes
+Pd
H2
CH3
HH
CH3
+ H2 CH3CH2CH2CH3
Pt
catalyst = Pt, Pd, Ni
+C C H H C C
H H
catalyst
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