Alkanes

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Alkanes
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Required
background Thermodynamics from general
chemistry Lewis structures Molecular geometry
Essential
for 1. Naming organic compounds 2. Recognizing
functional groups 3. Stereochemistry 4. Role of
alkanes in the economy
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• 
  Outline
• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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1.
Carbon Chains 2. Functional Groups and Classes of
Organic Compounds 3. Isomerism and Nomenclature
of Alkanes 4. Physical Properties of Alkanes 5.
Conformations 6. Cycloalkanes 7. Polycyclic
compounds
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The idea of carbon chains was introduced in
1858-1860 by Kekule, Couper, Butlerov. The
compound with the largest known carbon Chain was
described by Bidd and Wittig in 1985
CH3(CH2)388CH3 There are significantly more
substances with an even number of carbons, than
with an odd number. Nature, 1996, 384,
320 Reasons 1. Nature utilizes acetate
(CH3COO-) as a building block for synthesis. 2.
Chemical industry utilizes mostly ethylene (C2H4)
as a building block.
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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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Presentation
of structural formulas
Hexane
Homologuos formula of alkanes CnH2n2
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Branched alkanes
Combustion CnH2n2
(3n1)/2 O2 nCO2 (n1)H2O More branched
alkanes are slightly more stable, than
unbranched alkanes. They have a little smaller
heat of combustion.
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• Nubmer of carbons Number of isomers
• 1
• 1
• 3 1
• 4 2
  
• 5 3
• 7 9
• 10 75
• 20
  366,319
• Consequence Problem of nomenclature

The first set of IUPAC (International Union of
Pure and Applied Chemistry) rules was made in
1892 in Geneva. The list of rules takes several
book volumes and is updated every few years, so
we will not learn the rules in detail. We will
consider just some basic principles, which are
unlikely to change.
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IUPAC Principles of Nomenclature
1. Name unbranched alkanes by the number of
carbons. 2. For branched alkanes, pick the
longest chain of carbons (principal chain)
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3. If there is a choice, choose the chain with
the greatest number of substituents
4. Number carbons in the principal chain to
assign the lower number to the first
substituent. Do not number carbons in the
substituents.
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5. Name each substituent
6. Construct the chemical name
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7. For compounds with multiple substituents, each
substituents receives its own number.
Each substituent has own numbers. Number of
substituents 2(di-), 3(tri-), 4(tetra-),
5(penta-) etc.
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8. Substituents are cited in the alphabetical
order regardless of their position
9. If the numbering is not resolved by other
rules, the first-cited substituent receives the
lowest number.
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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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Methane ? butane gases (at 25 oC). Pentane ?
C12-C15 liquids Each carbon increases the b.p.
by approximately 20-30 oC. More symmetrical
molecules generally melt higher. The higher the
molecular surface, the large the Van-der-Waals
forces of attraction, the higher the boiling
point. Consequences 1. Alkanes with larger
molecules boil higher, than alkanes with smaller
molecules. 2. Alkanes with unbranched molecules
boil higher, than alkanes with branched
molecules. 3. Alkanes can be separated by
distillation. They are produced in industry by
fractional distillation of petroleum and natural
gas.
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Refine petroleum--fractional distillation
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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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Conformations of ethane
Newman projections
Wedge projections
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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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• Carbon Chains
• 2. Functional Groups and Classes of Organic
  Compounds
• 3. Isomerism and Nomenclature of Alkanes
• 4. Physical Properties of Alkanes
• 5. Conformations
• 6. Cycloalkanes
• 7. Polycyclic compounds

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