Chapter 22

1
Chapter 22 Hydrocarbon Compounds
(C4H10)

• Pre-AP Chemistry
• Charles Page High School
• Stephen L. Cotton

2
Section 22.1Hydrocarbons

• OBJECTIVES
• Describe the relationship between number of
  valence electrons and bonding in carbon.

3
Section 22.1Hydrocarbons

• OBJECTIVES
• Define and describe alkanes.

4
Section 22.1Hydrocarbons

• OBJECTIVES
• Relate the polarity of hydrocarbons to their
  solubility.

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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

6

• Friedrich Wohler
• 1800 1882
• Used inorganic substances to synthesize 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 unique bonding ability!
• Lets start with the simplest of the organic
  compounds. These are the Hydrocarbons

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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 single covalent
  bonds (CnH2n2)
• methane (CH4) with one carbon is the simplest
  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 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

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Straight-Chain Alkanes

• Combined with the -ane ending is a prefix 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 for fuels 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
• Condensed structural formulas? Note examples on
  page 696

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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

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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

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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

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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

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Branched-Chain Alkanes

• Rules for naming go from right to left - 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 branch
• 5. 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 -ane
• 2. Number carbons on parent
• 3. Identify substituent groups (give lowest
  number) attach
• 4. Add remaining hydrogens

20
- Page 700
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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

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Section 22.2Unsaturated Hydrocarbons

• OBJECTIVES
• Describe the difference between unsaturated and
  saturated hydrocarbons.

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Section 22.2Unsaturated Hydrocarbons

• OBJECTIVES
• Distinguish the structures of alkenes and alkynes.

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Alkenes

• Multiple bonds can also exist between the carbon
  atoms
• Hydrocarbons containing carbon to carbon double
  bonds are called alkenes (CnH2n) CC
  C-CC
• Called unsaturated if they contain 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 to carbon triple
  bonds are called alkynes
• (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.

ethyne
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Section 22.3Isomers

• OBJECTIVES
• Explain why structural isomers have different
  properties.

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Section 22.3Isomers

• OBJECTIVES
• Describe the conditions under which geometric
  isomers are possible.

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Section 22.3Isomers

• OBJECTIVES
• Identify optical isomers.

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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

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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 same molecular
  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 double bond
• 2. cis configuration - same side

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Geometric Isomers
Substituted groups are on opposite sides of the
double bond (in this case, one is above, the
other is below)
Trans-2-butene
Substituted groups are on the same side of the
double bond (in this case, both are above)
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 substituted groups
  (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 22.4Hydrocarbon Rings

• OBJECTIVES
• Identify cyclic ring structures.

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Section 22.4Hydrocarbon Rings

• OBJECTIVES
• Describe bonding in benzene.

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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

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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

42
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-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 commonly named STYRENE.
• Foamed styrene is trademarked by Dow Chemical as
  styrofoam
• Other manufacturers items usually just called
  foam cups

CH
CH2
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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
C
C
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Section 22.5Hydrocarbons From Earths Crust

• OBJECTIVES
• Identify three important fossil fuels and
  describe their origins.

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Section 22.5Hydrocarbons From Earths Crust

• OBJECTIVES
• Describe the composition of natural gas,
  petroleum, and coal.

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Section 22.5Hydrocarbons From Earths Crust

• OBJECTIVES
• Describe what happens when petroleum is refined.

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Natural Gas

• Fossil fuels provide much of the worlds 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

49
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
  its major sources

50
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

51
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

52
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

53
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

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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 after more
  time lower water content, higher C content
  (70-80)

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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

56
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.
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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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End of Chapter 22