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ORGANIC
CHEMISTRY 171
Section 201
2-1
Alkanes
and
Cycloalkanes
Chapter 2
2-2
Structure
 Hydrocarbon:
a compound composed only of
carbon and hydrogen
 Saturated hydrocarbon: a hydrocarbon
containing only single bonds
 Alkane: a saturated hydrocarbon whose carbons
are arranged in an open chain
 Aliphatic hydrocarbon: another name for an
alkane
2-3
Hydrocarbons
Hydrocarb on s
Saturated
Class
Carboncarbon
bondin g
Example
N ame
Un saturated
Alkan es
(Ch apter 2)
Alk enes
(Chap ters 5-6)
A lkynes
(Ch apter 7)
Arenes
(Ch apter 21-22)
Only carboncarbon sin gle
bond s
HH
H-C-C-H
HH
Ethan e
One or more
carb on -carbon
double b on ds
H
H
C C
H
H
One or more
carbon-carb on
trip le bonds
On e or more
ben zenelike
rin gs
Eth ene
Acetylen e
H-C C-H
Ben zene
2-4
Functional Groups
 Functional
group: An atom or group of atoms
within a molecule that shows a characteristic
set of physical and chemical properties.
 Functional
groups are important for three
reasons:
1. Allow us to divide compounds into classes.
2. Each group undergoes characteristic chemical
reactions.
3. Provide the basis for naming compounds.
2-5
Organic Molecules and Functional Groups
Functional Groups:
Hydrocarbons
Hydrocarbons are compounds made up of only the elements
carbon and hydrogen. They may be aliphatic or aromatic.
6
2-6
Organic Molecules and Functional Groups
Functional Groups:
Heteroatoms
7
2-7
Functional Groups:
Carbonyl groups
8
2-8
Alcohols
 Contain
an -OH (hydroxyl) group bonded to a
tetrahedral carbon atom.
H H
:
-C-O-H
:
H-C-C-O-H
Fu nctional
group
 Ethanol
H H
Ethan ol
(an alcohol)
may also be written as a condensed
structural formula.
CH3 -CH2 -OH
or
CH3 CH2 OH
2-9
Alcohols
 Alcohols
are classified as primary (1°),
secondary (2°), or tertiary (3°) depending on the
number of carbon atoms bonded to the carbon
bearing the -OH group.
H
CH3 -C-OH
H
A 1° alcohol
H
CH3 -C-OH
CH3
A 2° alcohol
CH3
CH3 -C-OH
CH3
A 3° alcohol
2-10
Alcohols
There are two alcohols with molecular formula
C3H8O
HHH
H-C-C-C-O-H
or CH3 CH2 CH2 OH
H HH
a 1° alcohol
H
HOH
H C-C-C-H
HH H
or
OH
CH3 CHCH3
a 2° alcohol
2-11
Amines
an amino group; an sp3-hybridized
nitrogen bonded to one, two, or three carbon
atoms.
 Contain
• An amine may by 1°, 2°, or 3°.
Methylamine
(a 1° amine)
CH3 N H
CH3
Dimethylamine
(a 2° amine)
:
H
:
:
CH3 N H
CH3 N CH3
CH3
Trimethylamine
(a 3° amine)
2-12
Aldehydes and Ketones
 Contain
: O:
C
a carbonyl (C=O) group.
O
H
CH3 -C- H
Functional Acetaldehyde
(an aldehyde)
group
:O:
O
C
CH3 -C- CH3
Functional Acetone
(a ketone)
group
2-13
Carboxylic Acids
 Contain
:
Fu nctional
group
:O:
CH3 -C-O-H
:
O
C O H
a carboxyl (-COOH) group.
or CH3 COOH or CH3 CO2 H
Acetic aci d
(a carboxy li c acid )
2-14
Carboxylic Esters
 Ester:
A derivative of a carboxylic acid in which
the carboxyl hydrogen is replaced by a carbon
group.
O
C O
Functional
group
O
CH3 - C-O- CH 2 -CH3
Ethyl acetate
(an ester)
2-15
Carboxylic Amide
 Carboxylic
amide, commonly referred to as an
amide: A derivative of a carboxylic acid in
which the -OH of the -COOH group is replaced
by an amine.
O
C N
Fu nctional
group
O
CH3 -C-N-H
H
Acetamid e
(a 1° amid e)
• The six atoms of the amide functional group lie in a
plane with bond angles of approximately 120°.
2-16
Alkanes
2-17
Structure
 Shape
• tetrahedral about carbon
• all bond angles are approximately 109.5°
• sp3 hybridization
2-18
Drawing Alkanes
 Line-angle
formulas
• an abbreviated way to draw structural formulas
• each vertex and line ending represents a carbon
Ball-and stick
mod el
Line-an gle
formula
Structu ral
formu la
CH3 CH2 CH3
CH3 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH3
Propane
Butan e
Pentan e
2-19
Constitutional Isomerism
 Constitutional
isomers: compounds with the
same molecular formula but a different
connectivity of their atoms
• example: C4H10
CH3 CH2 CH 2 CH3
Butane
(bp -0.5°C)
CH3
CH3 CHCH3
2-Methylpropane
(bp -11.6°C)
2-20
Constitutional Isomerism
• do these formulas represent constitutional isomers?
CH3
CH3
CH3
CH3 CHCH2 CH and CH3 CH2 CHCHCH3
CH3
CH3
(each is C7 H 16)
• find the longest carbon chain
• number each chain from the end nearest the first
branch
• compare chain lengths as well the identity and location
of branches
CH3 5 CH3
4
CH3 CHCH2 CH
1
2 3
CH3
1
2
3
4
and
5
CH3
CH3 CH2 CHCHCH3
2 1
CH3
5
4
3
5
4
3
2
2-21
1
Constitutional Isomerism
Molecular
Formula
CH4
Cons titutional
Isomers
C5 H1 2
1
3
C1 0 H2 2
75
C1 5 H3 2
4,347
C2 5 H5 2
36,797,588
C3 0 H6 2
4,111,846,763
World population
is about
6,000,000,000
2-22
Nomenclature - IUPAC
 Suffix
-ane specifies an alkane
 Prefix tells the number of carbon atoms
Prefix Carbons
meth1
eth2
prop3
but4
pent5
hex6
7
heptoct8
non9
dec10
Carbons
Prefix
undec11
dodec12
tridec13
tetradec14
pentadec15
hexadec16
heptadec17
octadec18
nonadec19
eicos 20
2-23
Nomenclature - IUPAC
 Parent
name: the longest carbon chain
 Substituent: a group bonded to the parent chain
• alkyl group: a substituent derived by removal of a
hydrogen from an alkane; given the symbol RAlkane
Name
Alkyl group
Name
CH4
Methane
CH3 -
Methyl group
CH3 CH3
Ethane
CH3 CH2 -
Ethyl group
2-24
Nomenclature - IUPAC
1.The name of a saturated hydrocarbon with an
unbranched chain consists of a prefix and suffix
2. The parent chain is the longest chain of carbon atoms
3. Each substituent is given a name and a number
CH3
CH3 CHCH3
1
2
3
2-Methylprop ane
4. If there is one substituent, number the chain from the
end that gives it the lower number
CH3
CH3 CH2 CH2 CHCH3
4
5
32
1
2-Methylpentane
2
1
34
5
(not 4-methylpentane)
2-25
Nomenclature - IUPAC
5. If there are two or more identical substituents, number
the chain from the end that gives the lower number to
the substituent encountered first
• indicate the number of times the substituent appears
by a prefix di-, tri-, tetra-, etc.
• use commas to separate position numbers
6
5
4
2
3
1
1
2
3
5
4
6
2,4-Dimethylhexan e (n ot 3,5-d imethylhexan e)
2-26
Nomenclature - I UPAC
6. If there are two or more different substituents,
• list them in alphabetical order
• number from the end of the chain that gives the
substituent encountered first the lower number
1
2
3
4
5
6
7
3-Ethyl-5-methylh eptane
7
6
5
4
3
2
1
(n ot 3-methyl-5-ethylheptane)
2-27
Nomenclature - IUPAC
7. The prefixes di-, tri-, tetra-, etc. are not included in
alphabetization
• alphabetize the names of substituents first and then
insert these prefixes
1
2
3
4
5
6
4-Ethyl-2,2-dimethylh exane
(not 2,2-dimethyl-4-eth ylh exane)
2-28
Nomenclature - IUPAC
 Alkyl
groups
Name
Condens ed
Structural Formula
butyl
- CH 2 CH2 CH2 CH 3
Name
methyl
Condens ed
Structural Formula
- CH 3
2-methylpropyl
(isobutyl)
- CH 2 CHCH3
ethyl
- CH 2 CH3
propyl
- CH 2 CH2 CH3
1-methylpropyl
(sec- butyl)
- CH CH 2 CH3
1-methylethyl
(isopropyl)
- CH CH 3
CH3
CH3
CH3
CH3
1,1-dimethylethyl
(tert- butyl)
- CCH3
CH3
2-29
Nomenclature - Common
 The
number of carbons in the alkane determines
the name
• all alkanes with four carbons are butanes, those with
five carbons are pentanes, etc.
• iso- indicates the chain terminates in -CH(CH3)2; neothat it terminates in -C(CH3)3
CH3
CH3 CH2 CH2 CH3
Butane
CH3 CHCH3
Is ob utane
CH3
CH3 CH2 CH2 CH2 CH3 CH3 CH2 CHCH3
Pentan e
Is op entane
CH3
CH3 CCH3
CH3
N eopentan e
2-30
Classification of C & H
 Primary
(1°) C: a carbon bonded to one other
carbon
• 1° H: a hydrogen bonded to a 1° carbon
 Secondary
(2°) C: a carbon bonded to two other
carbons
• 2° H: a hydrogen bonded to a 2° carbon
 Tertiary
(3°) C: a carbon bonded to three other
carbons
• 3° H: a hydrogen bonded to a 3° carbon
 Quaternary
(4°) C: a carbon bonded to four other
carbons
2-31
Cycloalkanes
 General
formula CnH2n
• five- and six-membered rings are the most common
 Structure
and nomenclature
• to name, prefix the name of the corresponding openchain alkane with cyclo-, and name each substituent
on the ring
• if only one substituent, no need to give it a number
• if two substituents, number from the substituent of
lower alphabetical order
• if three or more substituents, number to give them the
lowest set of numbers and then list substituents in
alphabetical order
2-32
Cycloalkanes
 Line-angle
drawings
• each line represents a C-C bond
• each vertex and line ending represents a C
C
C
C
C
C C
C
C
H2 C
H2 C
CH2
CH3
CH CH
CH2
CH3
C8 H1 6
2-33
Cycloalkanes

Example: name these cycloalkanes
(a)
(b)
(c)
(d)
2-34
IUPAC - General
 prefix-infix-suffix
• prefix tells the number of carbon atoms in the parent
• infix tells the nature of the carbon-carbon bonds
• suffix tells the class of compound
Infix
-an-en-yn-
Nature of Carbon-Carbon
Bonds in the Parent Chain
Suffix
Class
hydrocarbon
all single bonds
-e
-ol
alcohol
-al
aldehyde
-amine
amine
-one
ketone
-oic acid carboxylic acid
one or more double bonds
one or more triple bonds
2-35
IUPAC - General
prop-en-e = propene
CH3 CH=CH 2
eth-an-ol = ethanol
OH
but-an-one = butanone
HC CH
but-an-al = butanal
pent-an-oic acid = pentanoic acid CH3 CH2 NH 2
cyclohex-an-ol = cyclohexanol
O
eth-yn-e = ethyne
CH3 CH2 CH2 CH
eth-an-amine = ethanamine
O
O
CH3 CCH2 CH 3
CH3 CH2 OH
CH3 CH2 CH2 CH2 COH
2-36
Conformations
 Conformation:
any three-dimensional
arrangement of atoms in a molecule that results
from rotation about a single bond
 Newman projection: a way to view a molecule by
looking along a carbon-carbon single bond
2-37
Conformations
 Staggered
conformation: a conformation about a
carbon-carbon single bond in which the atoms or
groups on one carbon are as far apart as
possible from the atoms or groups on an
adjacent carbon
H
H
H
H
H
H
2-38
Conformations
 Eclipsed
conformation: a conformation about a
carbon-carbon single bond in which the atoms or
groups of atoms on one carbon are as close as
possible to the atoms or groups of atoms on an
adjacent carbon
H
H
H
H
HH
2-39
Conformations
 Torsional
strain
• also called eclipsed interaction strain
• strain that arises when nonbonded atoms separated by
three bonds are forced from a staggered conformation
to an eclipsed conformation
• the torsional strain between eclipsed and staggered
ethane is approximately 12.6 kJ (3.0 kcal)/mol
+12.6 kJ/mol
2-40
Conformations
angle (Q): the angle created by two
intersecting planes
 Dihedral
2-41
Conformations
 Steric
strain (nonbonded interaction strain):
• the strain that arises when atoms separated by four or
more bonds are forced closer to each other than their
atomic (contact) radii will allow
 Angle
strain:
• strain that arises when a bond angle is either
compressed or expanded compared to its optimal
value
2-42
Cyclopropane
• angle strain: the C-C-C bond angles are compressed
from 109.5° to 60°
• torsional strain: there are 6 sets of eclipsed hydrogen
interactions
• strain energy is about 116 kJ (27.7 kcal)/mol
H
H
H
H
H
H
2-43
Cyclohexane
 Chair
conformation: the most stable puckered
conformation of a cyclohexane ring
• all bond C-C-C bond angles are 110.9°
• all bonds on adjacent carbons are staggered
2-44
Cyclohexane
 In
a chair conformation, six H are equatorial and
six are axial
2-45
Cyclohexane
 For
cyclohexane, there are two equivalent chair
conformations
• all C-H bonds equatorial in one chair are axial in the
alternative chair, and vice versa
2-46
Cyclohexane
 Boat
conformation: a puckered conformation of a
cyclohexane ring in which carbons 1 and 4 are
bent toward each other
• there are four sets of eclipsed C-H interactions and
one flagpole interaction
• a boat conformation is less stable than a chair
conformation by 27 kJ (6.5 kcal)/mol
2-47
Cyclohexane
 Twist-boat
conformation
• approximately 41.8 kJ (5.5 kcal)/mol less stable than a
chair conformation
• approximately 6.3 kJ (1.5 kcal)/mol more stable than a
boat conformation
2-48
Methylcyclohexane
 Equatorial
and axial methyl conformations
CH3
+7.28 kJ/mol
CH3
2-49
Cis,Trans Isomerism
 Stereoisomers:
compounds that have
• the same molecular formula
• the same connectivity
• a different orientation of their atoms in space
 Cis,trans
isomers
• stereoisomers that are the result of the presence of
either a ring (this chapter) or a carbon-carbon double
bond (Chapter 5)
2-50
Cis,Trans Isomers
 1,2-Dimethylcyclopentane
H
H
H
H
H H H
H
H
CH3
H3 C
CH3
CH3
cis-1,2-D imeth ylcyclop entane
H
H
H HH3 C
H
H
CH3
H3 C
H
CH3
trans-1,2-D imethylcyclop entane
2-51
Cis,Trans Isomerism
 1,4-Dimethylcyclohexane
H
H3 C
CH3
H
H
H3 C
CH3
H3 C
t rans-1,4-D imethylcyclohexane
H
CH3
CH3
H3 C
cis-1,4-D imethylcycloh exane
2-52
Cis,Trans Isomerism
 trans-1,4-Dimethylcyclohexane
• the diequatorial-methyl chair conformation is more
stable by approximately 2 x (7.28) = 14.56 kJ/mol
CH3
H
H
H3 C
H
CH3
CH3
(less s table)
H
(more s table)
2-53
Cis,Trans Isomerism
 cis-1,4-Dimethylcyclohexane
H
H
CH3
H3 C
H
H
CH3
conformation s are of equal s tability
CH3
2-54
Physical Properties
 Low-molecular-weight
alkanes
(methane....butane) are gases at room
temperature
 Higher molecular-weight alkanes (pentane,
decane, gasoline, kerosene) are liquids at room
temperature
 High-molecular-weight alkanes (paraffin wax) are
semisolids or solids at room temperature
2-55
Physical Properties
 Constitutional
isomers have different physical
properties
Name
mp
(°C)
bp
(°C)
Density
(g/mL)
hexane
2-methylpentane
3-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
-95
-154
-118
-129
-98
68.7
60.3
63.3
58.0
49.7
0.659
0.653
0.664
0.661
0.649
2-56
Preparation and
Reactions of
Alkanes
2-57
Preparation of Alkanes via Reduction
1)
Hydrogenation of Alkenes
Hydrogenation of Alkynes
R
R'
C C
R
R
H 2 /Pt
R'
C C R'
R
R'
CH
CH
R
H 2 /Pt
R'
H H
R
C C
R'
H H
2-58
2. Reduction of an alkyl halide
a) hydrolysis of a Grignard reagent (two steps)
i) R—X + Mg  RMgX
(Grignard reagent)
ii) RMgX + H2O  RH + Mg(OH)X
SB
SA
WA
WB
CH3CH2CH2-Br + Mg  CH3CH2CH2-MgBr
n-propyl bromide
n-propyl magnesium bromide
CH3CH2CH2-MgBr + H2O  CH3CH2CH3 +
Mg(OH)Br
propane
2-59
CH3
CH3
CH3CH-Br + Mg  CH3CH-MgBr
isopropyl bromide
isopropyl magnesium bromide
CH3
CH3CH-MgBr + H2O  CH3CH2CH3
propane
CH3CH2CH2-MgBr + D2O  CH3CH2CH2D
heavy water
CH3
CH3
CH3CH-MgBr + D2O  CH3CHD
2-60
b) with an active metal and an acid
R—X + metal/acid  RH
active metals = Sn, Zn, Fe, etc.
acid = HCl, etc. (H+)
CH3CH2CHCH3 + Sn/HCl  CH3CH2CH2CH3 +
Cl
sec-butyl chloride
SnCl2
n-butane
CH3
CH3
CH3CCH3 + Zn/H+  CH3CHCH3 + ZnBr2
Br
tert-butyl bromide
isobutane
2-61
Reactions of alkanes:
alkane + H2SO4  no reaction (NR)
alkane + NaOH  NR
alkane + Na  NR
alkane + KMnO4  NR
alkane + H2,Ni  NR
alkane + Br2  NR
alkane + H2O  NR
(Alkanes are typically non-reactive. They don’t react
with acids, bases, active metals, oxidizing agents,
reducing agents, halogens, etc.)
2-62
Alkane, reactions:
1. Halogenation
2. Combustion (oxidation)
3. Pyrolysis (cracking)
2-63
1. Halogenation
R-H + X2, heat or hv  R-X + HX
a) heat or light required for reaction.
b) X2: Cl2 > Br2  I2
c) yields mixtures 
d) H: 3o > 2o > 1o > CH4
e) bromine is more selective
2-64
CH3CH3 + Cl2, hv  CH3CH2-Cl + HCl
ethane
ethyl chloride
CH3CH2CH3 + Cl2, hv  CH3CH2CH2-Cl + CH3CHCH3
propane
n-propyl chloride
Cl
45%
isopropyl chloride
55%
possible
gives a mixture of both the
alkyl halides! 
2-65
CH3CH2CH2CH3 + Cl2, hv  CH3CH2CH2CH2-Cl
n-butane
n-butyl chloride 28%
+
CH3CH2CHCH3
Cl
72%
sec-butyl chloride
CH3
CH3
CH3CHCH3 + Cl2, hv  CH3CHCH2-Cl
isobutane
64%
isobutyl chloride
+
CH3
CH3CCH3
Cl
36%
tert-butyl chloride
2-66
chlorination of propane, mechanism:
1) abstraction of 1o hydrogen:
Cl• + CH3CH2CH3  CH3CH2CH2• + HCl
or abstraction of 2o hydrogen:
Cl• + CH3CH2CH3  CH3CHCH3
•
+ HCl
2)CH3CH2CH2• + Cl2  CH3CH2CH2Cl + Cl•
or CH3CHCH3 + Cl2  CH3CHCH3 + Cl•
•
Cl
plus terminating steps
3) Cl—Cl  2 Cl•
2-67
2.Oxidation of Alkanes ( combustion )
 Oxidation
is the basis for their use as energy
sources for heat and power
• heat of combustion: heat released when one mole of a
substance in its standard state is oxidized to carbon
dioxide and water
H 0
kJ(k cal)/mol
CH4 + 2 O2
Methan e
CH3 CH2 CH3 + 5 O2
Propane
CO2 + 2 H2 O
-890.4 (-212.8)
3 CO2 + 4 H2 O
-2220 (-530.6)
2-68
Sources of Alkanes
 Natural
gas
• 90-95% methane
 Petroleum
•
•
•
•
•
•
gases (bp below 20°C)
naphthas, including gasoline (bp 20 - 200°C)
kerosene (bp 175 - 275°C)
fuel oil (bp 250 - 400°C)
lubricating oils (bp above 350°C)
asphalt (residue after distillation)
 Coal
2-69
Gasoline
 Octane
rating: the percent 2,2,4-trimethylpentane
(isooctane) in a mixture of isooctane and heptane that
has equivalent antiknock properties
Hep tane
(octane rating 0)
2,2,4-Trimeth ylp entane
(octane rating 100)
2-70
Synthesis Gas
A
mixture of carbon monoxide and hydrogen in
varying proportions which depend on the means
by which it is produced
C +
Coal
CH4 +
Methane
H2 O
1
O2
2
heat
catalyst
CO + H2
CO + 2 H2
2-71
Synthesis Gas
 Synthesis
gas is a feedstock for the industrial
production of methanol and acetic acid
CO + 2 H2
catalyst
CH3 OH
Methanol
CH3 OH + CO
Methanol
catalyst
O
CH3 COH
Acetic acid
• it is likely that industrial routes to other organic
chemicals from coal via methanol will also be
developed
2-72
Alkanes and
Cycloalkanes
End Chapter 2
2-73