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7/29/2019 Hydrocarbon Compounds - By Razi
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(C4H10)
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Hydrocarbons
OBJECTIVES:
Describe the relationshipbetween number of valence
electrons and bonding incarbon.
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Hydrocarbons
OBJECTIVES:
Define and describe alkanes.
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Hydrocarbons
OBJECTIVES:
Relate thepolarity ofhydrocarbons to their
solubility.
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Organic Chemistry and
Hydrocarbons
Organic originally referred to anychemicals that came from organisms
1828 - German chemist FriedrichWohler synthesized urea in a lab
Today, organic chemistry is the
chemistry of virtually all compoundscontaining the element carbon
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Friedrich Wohler
1800 1882
Used inorganic
substances tosynthesize urea, a
carbon compound
found in urine.This re-defined
organic chemistry.
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Organic Chemistry and
Hydrocarbons Over a million organic compounds,
with a dazzling array of properties
Why so many? Carbons uniquebonding ability!
Lets start with the simplest of the
organic compounds. These are theHydrocarbons
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Organic Chemistry and
Hydrocarbons
Hydrocarbons contain only two
elements: 1) hydrogen, and 2) carbon
simplest hydrocarbons called alkanes,which contain only carbon to carbon singlecovalent bonds (CnH2n+2)
methane (CH4) with one carbon is thesimplest alkane. It is the major component
of natural gas
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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
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Straight-Chain Alkanes
Straight-chain alkanes contain anynumber of carbon atoms, one afterthe other, in a chain pattern -
meaning one linked to the next (notalways straight)
C-C-C C-C-C-C etc.
Names of alkanes always will always
end with -ane
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Straight-Chain Alkanes
Combined with the -ane ending is aprefix for the number of carbons
Table 22.1, page 695 Homologous series- a group of
compounds that have a constant
increment of change In alkanes, it is: -CH2- (methylene)
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Straight-Chain Alkanes
Many alkanes used forfuels: methane,propane, butane, octane
As the number of carbons increases, so
does the boiling and melting pt.
The first 4 are gases; #5-15 are liquids;
higher alkanes are solids Condensedstructural formulas? Note
examples on page 696
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Naming Straight-Chain Alkanes
Names recommended by IUPAC - the
International Union ofPure and Applied
Chemistry
end withane; the root part of the name
indicates the # of carbons
We sometimes still rely on common
names, some of which are well-known
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Naming Straight-Chain Alkanes
IUPAC names may be long andcumbersome
Common names may be easier ormore familiar, but usually do notdescribe the chemical structure!
Methane is natural gas or swampgas
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Branched-Chain Alkanes
Branched-chain means that otherelements besides hydrogen may beattached to the carbon
halogens, oxygen, nitrogen, sulfur,and even other carbons
any atom that takes the place of a
hydrogen on a parent hydrocarbon iscalled asubstituent, or the branched
part
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Branched-Chain Alkanes
A hydrocarbon substituent is called analkyl group or sometimes radicals
use the same prefixes to indicate the
number of carbons, but -ane ending isnow -yl such as: methyl, ethyl,
propyl, etc.
Gives much more variety to the organiccompounds
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Branched-Chain Alkanes
Rules for naminggo from right toleft - page 698
1. 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 branch5. Alphabetize branches (not prefix)
6. Use proper punctuation ( - and , )
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- Page 699
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Branched-Chain Alkanes
From the name, draw the structure, in
a right-to-left manner:
1. Find the parent, with the -ane2. Number carbons on parent
3. Identify substituent groups (givelowest number); attach
4. Add remaining hydrogens
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- Page 700
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Section 22.2
Unsaturated Hydrocarbons OBJECTIVES:
Describe the differencebetween unsaturated andsaturated hydrocarbons.
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Section 22.2
Unsaturated Hydrocarbons OBJECTIVES:
Distinguish the structures ofalkenes and alkynes.
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Alkenes
Multiple bonds can also existbetween the carbon atoms
Hydrocarbons containing carbon to
carbon double bonds are calledalkenes(CnH2n) C=C C-C=C
Called unsaturated if theycontain double or triple bonds
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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
Samples on page 702
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Alkynes
Hydrocarbons containing carbon tocarbon triple bonds are calledalkynes
(CnH2n-2) -C C- Alkynes are not plentiful in nature
Simplest is ethyne- common nameacetylene (fuel for torches)
Table 22.3, p. 703 for boiling pt.
ethyne
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Section 22.3
Isomers OBJECTIVES:
Explain why structuralisomers have different
properties.
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Section 22.3
Isomers OBJECTIVES:
Identify optical isomers.
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Structural Isomers
Compounds that have the samemolecular formula, but differentmolecular structures, are calledstructural isomers
Butane and 2-methylpropane (made bybreaking carbon off the end, andmaking it a branch in the middle)
Also have different properties, such asb.p., m.p., and reactivity
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Structural Isomers of Butane, C4H10
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Stereoisomers
Dont forget that these structures are
really 3-dimensional
stereoisomers- molecules of the samemolecular structure that differ only in
the arrangement of the atoms in space.
Two types are a) geometric and b)
optical
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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 doublebond
2. cisconfiguration - same side
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Substituted
groups are on
opposite sidesof the double
bond (in this
case, one is
above, the other
is below)
Substituted
groups are on
the same sideof the double
bond (in this
case, both are
above)
Geometric Isomers
Trans-2-butene
Cis-2-butene
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Geometric Isomers
Trans-2-butene and Cis-2-butene shown
on page 705
differ in the geometry of the substitutedgroups (to double bond)
like other structural isomers, have
different physical and chemical properties( note page 705-middle)
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Optical Isomers
Asymmetric carbon? C with 4
different groups attached. Conceptual
Problem 22.4, p.706 Molecules containing asymmetric
carbons have handedness, and exist
as stereoisomers.
Figure 22.9, page 705
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Optical Isomers, and these will each show an
asymetric carbon (4 different branches attached)
The asymetric carbon
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Section 22.4
Hydrocarbon Rings OBJECTIVES:
Describe bonding in benzene.
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Cyclic Hydrocarbons
The two ends of the carbon chain are
attached in a ringin a cyclic
hydrocarbon sample drawings on page 709
named as cyclo-____
hydrocarbon compounds that do NOTcontain rings are known as aliphaticcompounds
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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
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Aromatic Hydrocarbons
Benzene is a six-carbon ring, withalternating double and single
bonds
exhibits resonance, due to location of
the double and single bonds-p.710
Benzene derivatives possible:
methylbenzene, 3-phenylhexane,
ethylbenzene (top page 711)
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Aromatic Hydrocarbons One derivative of Benzene is
called phenylethene, or commonlynamed STYRENE.
Foamed styrene is trademarked byDow Chemical as styrofoam
Other manufacturers items usuallyjust called foam cups
CHCH2
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Aromatic Hydrocarbons
Benzene derivatives can have two or
more substitutents:
1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene
Can use ortho for 1,2; meta for 1,3; and
para for 1,4 (page 711)
C
C
CC
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Section 22.5
Hydrocarbons From EarthsCrust
OBJECTIVES:
Identify three important fossilfuels and describe their
origins.
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Section 22.5
Hydrocarbons From EarthsCrust
OBJECTIVES:
Describe the composition ofnatural gas, petroleum, andcoal.
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Section 22.5
Hydrocarbons From EarthsCrust
OBJECTIVES:
Describe what happens whenpetroleum is refined.
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Natural Gas
Fossil fuels provide much of the worldsenergy
Natural gas and petroleum contain mostly
the aliphatic (or straight-chain)hydrocarbonsformed from marine life
buried in sediment of the oceans
Natural gas is an important source of
alkanes of low molecular mass
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Natural Gas
Natural gas is typically:80% methane, 10% ethane, 4%
propane, and 2% butane with the
remainder being nitrogen and highermolar mass hydrocarbons
also contains a small amount of He,
and is one of its major sources
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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, aswell as making carbon monoxide
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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
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Petroleum
It is separated by distillation into
fractions, according to boiling pt.
Fractions containing higher molar masscan be cracked into more useful
shorter chain components, such as
gasoline and kerosene involves catalyst and heat
starts materials for plastics and paints
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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 watercontent. After drying will make a low-
cost, smoky fuel
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Coal
2. Lignite- peat left in the ground longer,
loses its 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 aftermore time; lower water content, higher
C content (70-80%)
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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
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