Transcript Hydrocarbons

“Hydrocarbon Compounds”
(C4H10)
Hydrocarbons
 OBJECTIVES:
–Describe the relationship
between number of
valence electrons and
bonding in carbon.
Hydrocarbons
 OBJECTIVES:
–Define and describe
alkanes.
Hydrocarbons
 OBJECTIVES:
–Relate the polarity of
hydrocarbons to their
solubility.
Organic Chemistry and
Hydrocarbons
 “Organic”
originally referred to any
chemicals that came from
organisms
 1828 - German chemist Friedrich
Wohler synthesized urea in a lab
 Today, organic chemistry is the
chemistry of virtually all compounds
containing the element carbon
Friedrich Wohler
1800 – 1882
Used inorganic
substances to
synthesize urea, a
carbon compound
found in urine.
This re-defined
organic chemistry.
Organic Chemistry and
Hydrocarbons
 Over
a million organic
compounds, with a dazzling array
of properties
 Why so many? Carbon’s unique
bonding ability!
 Let’s start with the simplest of the
organic compounds. These are
the Hydrocarbons
Organic Chemistry and
Hydrocarbons
 Hydrocarbons
contain only two
elements: 1) hydrogen, and 2) carbon
– simplest hydrocarbons called “alkanes”,
which contain only carbon to carbon
single covalent bonds (CnH2n+2)
– methane (CH4) with one carbon is the
simplest alkane. It is the major
component of natural gas
Organic Chemistry and
Hydrocarbons
 Review
structural formulas - p.694
 Carbon has 4 valence electrons,
thus forms 4 covalent bonds
– not only with other elements, but also
forms bonds WITH ITSELF (nonpolar)
 Ethane
(C2H6) is the simplest alkane
with a carbon to carbon bond
Straight-Chain Alkanes
 Straight-chain
alkanes contain
any number of carbon atoms, one
after the other, in a chain pattern meaning one linked to the next
(not always straight)
C-C-C
C-C-C-C etc.
 Names of alkanes always will
always end with -ane
Straight-Chain Alkanes
 Combined
with the -ane ending is a
prefix for the number of carbons
 Homologous series- a group of
compounds that have a constant
increment of change
 In alkanes, it is: -CH2- (methylene)
Straight-Chain Alkanes
alkanes used for fuels:
methane, propane, butane, octane
 As the number of carbons increases,
so does the boiling and melting pt.
 Many
– The first 4 are gases; #5-15 are liquids;
higher alkanes are solids
 Condensed
structural formulas?
Naming Straight-Chain
Alkanes
 Names
recommended by IUPAC - the
International Union of Pure and
Applied Chemistry
end with –ane; the root part of the name
indicates the # of carbons
 We
sometimes still rely on common
names, some of which are well-known
Naming Straight-Chain
Alkanes
 IUPAC
names may be long and
cumbersome
 Common names may be easier or
more familiar, but usually do not
describe the chemical structure!
–Methane is natural gas or
swamp gas
Branched-Chain Alkanes
 Branched-chain
means that other
elements besides hydrogen may be
attached to the carbon
–halogens, oxygen, nitrogen,
sulfur, and even other carbons
–any atom that takes the place of a
hydrogen on a parent
hydrocarbon is called a
substituent, or the branched part
Branched-Chain Alkanes
A
hydrocarbon substituent is called
an alkyl group or sometimes
radicals
–use the same prefixes to indicate
the number of carbons, but -ane
ending is now -yl such as:
methyl, ethyl, propyl, etc.
 Gives much more variety to the
organic compounds
Branched-Chain Alkanes
 Rules
 1.
for naming
Longest C-C chain is parent
2. Number so branches have lowest #
3. Give position number to branch
4. Prefix (di, tri) more than one branch
5. Alphabetize branches (not prefix)
6. Use proper punctuation ( - and , )
Branched-Chain Alkanes
 From
the name, draw the
structure, in a right-to-left manner:
1. Find the parent, with the -ane
2. Number carbons on parent
3. Identify substituent groups (give
lowest number); attach
4. Add remaining hydrogens
- Page 700
Alkanes
 Draw
3-ethylpentane
 Draw 2,3,4-trimethylhexane
 Since the electrons are shared
equally, the molecule is nonpolar
–thus, not attracted to water
–oil (a hydrocarbon) not soluble in
H2O
–“like dissolves like”
Section 22.2
Unsaturated Hydrocarbons
 OBJECTIVES:
–Describe the difference
between unsaturated
and saturated
hydrocarbons.
Section 22.2
Unsaturated Hydrocarbons
 OBJECTIVES:
–Distinguish the
structures of alkenes and
alkynes.
Alkenes
 Multiple bonds can also exist
between the carbon atoms
 Hydrocarbons containing
carbon to carbon double bonds
are called alkenes (CnH2n)
C=C
C-C=C
 Called “unsaturated” if they
contain double or triple bonds
Naming Alkenes
 Find
longest parent that has the
double bond in it
 New ending: -ene
 Number the chain, so that the
double bond gets the lower number
 Name and number the substituents
Alkynes
 Hydrocarbons
containing carbon
to carbon triple bonds are called
alkynes
ethyne
(CnH2n-2)
-C C Alkynes are not plentiful in nature
 Simplest is ethyne- common
name acetylene (fuel for torches)
 Table 22.3, p. 703 for boiling pt.
Section 22.3
Isomers
 OBJECTIVES:
–Explain why structural
isomers have different
properties.
Section 22.3
Isomers
 OBJECTIVES:
–Describe the conditions
under which geometric
isomers are possible.
Section 22.3
Isomers
 OBJECTIVES:
–Identify optical isomers.
Structural Isomers
 Compounds
that have the same
molecular formula, but different
molecular structures, are called
structural isomers
 Butane and 2-methylpropane (made
by breaking carbon off the end, and
making it a branch in the middle)
 Also have different properties, such
as b.p., m.p., and reactivity
Structural Isomers of Butane, C4H10
Stereoisomers
 Don’t
forget that these structures
are really 3-dimensional
 stereoisomers- molecules of the
same molecular structure that
differ only in the arrangement of
the atoms in space. Two types
are a) geometric and b) optical
Geometric Isomers
 There
is a lack of rotation around a
carbon to carbon multiple bond
– has an important structural implication
– Two possible arrangements:
1. trans configuration - substituted
groups on opposite sides of double
bond
2. cis configuration - same side
Geometric Isomers
Trans-2-butene
Substituted
groups are on
the same side
of the double
bond (in this
case, both are
above)
Substituted
groups are on
opposite sides
of the double
bond (in this
case, one is
above, the other
is below)
Cis-2-butene
Geometric Isomers
 Trans-2-butene
and Cis-2-butene
differ in the geometry of the
substituted groups (to double bond)
 like other structural isomers, have
different physical and chemical
properties
Optical Isomers
 Asymmetric
carbon? C with 4
different groups attached.
 Molecules containing asymmetric
carbons have “handedness”, and
exist as stereoisomers.
Optical Isomers, and these will each show an
asymetric carbon (4 different branches attached)
The asymetric carbon
Section 22.4
Hydrocarbon Rings
 OBJECTIVES:
–Identify cyclic ring
structures.
Section 22.4
Hydrocarbon Rings
 OBJECTIVES:
–Describe bonding in
benzene.
Cyclic Hydrocarbons
 The
two ends of the carbon chain
are attached in a ring in a cyclic
hydrocarbon
– sample drawings on page 709
– named as “cyclo- ____”
 hydrocarbon
compounds that do
NOT contain rings are known as
aliphatic compounds
Aromatic Hydrocarbons
A
special group of unsaturated cyclic
hydrocarbons is known as arenes
– contain single rings, or groups of rings
– also called “aromatic hydrocarbons”,
because of pleasant odor
– simplest aromatic is benzene (C6H6)
– Term “aromatic” applies to materials with
bonding like that of benzene
Aromatic Hydrocarbons

Benzene is a six-carbon ring,
with alternating double and
single bonds
– exhibits resonance, due to
location of the double and single
bonds-Benzene derivatives
possible:
– methylbenzene, 3-phenylhexane,
ethylbenzene
Aromatic Hydrocarbons

One derivative of Benzene is
called phenylethene, or
commonly named STYRENE.

Foamed styrene is trademarked
by Dow Chemical as
CH2
“styrofoam”
CH

Other manufacturers items
usually just called “foam cups”
Aromatic Hydrocarbons
 Benzene
derivatives can have two
C
or more substitutents:
– 1,2-dimethylbenzene
– 1,3-dimethylbenzene
– 1,4-dimethylbenzene
C
C
 Can
C
use ortho for 1,2; meta for 1,3;
and para for 1,4
Section 22.5
Hydrocarbons From Earth’s Crust
 OBJECTIVES:
–Identify three important
fossil fuels and describe
their origins.
Section 22.5
Hydrocarbons From Earth’s Crust
 OBJECTIVES:
–Describe the
composition of natural
gas, petroleum, and
coal.
Section 22.5
Hydrocarbons From Earth’s Crust
 OBJECTIVES:
–Describe what happens
when petroleum is
refined.
Natural Gas
 Fossil
fuels provide much of the
world’s energy
 Natural gas and petroleum contain
mostly the aliphatic (or straight-chain)
hydrocarbons – formed from marine
life buried in sediment of the oceans
 Natural gas is an important source of
alkanes of low molecular mass
Natural Gas
 Natural
gas is typically:
–80% methane, 10% ethane, 4%
propane, and 2% butane with the
remainder being nitrogen and
higher molar mass hydrocarbons
–also contains a small amount of
He, and is one of it’s major
sources
Natural Gas
 Natural
gas is prized for
combustion, because with
adequate oxygen, it burns with a
hot, clean blue flame:
– CH4 + 2O2  CO2 + 2H2O + heat
 Incomplete
burning has a yellow
flame, due to glowing carbon parts,
as well as making carbon monoxide
Petroleum
 The
compounds found in petroleum
(or crude oil) are more complex
than those in natural gas
 Usually straight-chain and
branched-chain alkanes, with some
aromatic compounds also
 Crude oil must be refined
(separated) before being used
Petroleum
 It
is separated by distillation into
fractions, according to boiling pt.
 Fractions containing higher molar
mass can be “cracked” into more
useful shorter chain components,
such as gasoline and kerosene
– involves catalyst and heat
– starts materials for plastics and paints
Coal
 From
huge fern trees and mosses
decaying millions of years ago
under great pressure of rocks / soil.
 Stages in coal formation:
1. Peat- soft, fibrous material much
like decayed garden refuse; high
water content. After drying will
make a low-cost, smoky fuel
Coal
2. Lignite- peat left in the ground
longer, loses it’s fibrous texture,
and is also called brown coal
– harder than peat; higher C content
(50%); still has high water content
3. Bituminous, or soft coal- formed
after more time; lower water
content, higher C content (70-80%)
Coal
4. Anthracite, or hard coal
– carbon content exceeding 80%,
making it an excellent fuel source
 Coal
may be found close to the
surface (strip-mined), or deep
within the earth
 Pollutants from coal are common;
soot and sulfur problems
BIG BRUTUS
Dragline used to
remove the
overburden of a
strip mining coal
field near West
Mineral, Kansas.
Note the size of
the man standing
next to it.
Coal

Coal may be distilled for many products
– coal gas, coal tar, coke, and
ammonia
– further distilled into benzene, toluene,
naphthalene, phenol- the aromatics
– Coke is almost pure carbon;
produces intense heat and little or no
smoke, thus used in industrial
processes