Chapter 2 Alkanes

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Chapter 2. The Nature of Organic Molecules
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• 2.1 Functional Groups
• 2.2 Alkanes and Alkyl Groups Isomers
• 2.3 Naming Branched-Chain Alkanes
• 2.4 Properties of Alkanes
• 2.5 Conformations of Ethane
• 2.6 Drawing Chemical Structures

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Functional Groups
FIGURE 2.1 The reactions of ethlene and menthene
with Br2. In both cases, Br2 reacts with the C
C functional group in exactly the same way. The
size and nature of the remainder of the molecule
are not important.

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2.1 Functional groups

• Organic compounds can be grouped into families by
  their common structural features
• A group of atoms of organic molecules that has a
  characteristic chemical behavior, regardless of
  size complexity.
• (Table 2.1)

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P.36
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P.36
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P.37
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P.37
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• Carbon-Carbon multiple bonds

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• Carbon-Electronegative atom

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• Carbon-Oxygen double bond (carbonyl)

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PROBLEM 2.1
P.39
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2.2 Alkanes Alkyl Groups Isomers

• Hydrocarbons compounds have only C H
• Saturated only single bonds
• Alkane saturated hydrocarbons (CnH2n2)
• They are also called aliphatic compounds

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• Straight-chain alkanes (normal alkane)
• Carbons connected in a row
• Names Table 2.2
• Representation
• Branched-chain alkanes
• with one or more Cs connected to 3 or 4 Cs

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2.2 Alkanes Alkyl Groups Isomers

• Isomers (P.42)
• same formula
• different chemical structures
• Constitutional isomers butane isobutane

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P.42
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• Alkyl group (Table 2.3) remove one H from an
  alkane
• Name replace -ane ending of alkane with -yl
  ending

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FIGURE 2.3 Generation of straight-chain and
branched- chain alkyl groups from alkanes.
P.43
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2.2 Alkanes Alkyl Groups Isomers

• 4 possible carbons
• Primary (1?) carbon R-CH3
• Secondary (2?) carbon R2-CH2
• Tertiary (3?) carbon R3-CH
• Quaternary (4?) carbon R4-C
• R-CH2OH?

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• Ex
• Problem 2.8

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2.3 Naming Alkane

• IUPAC (International Union of Pure Applied
  Chemistry)

Step1 Find the parent hydrocarbon Step2 Number
the atoms in the main chain Step3 identify
number the substituents Step4 write the name as a
single word
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Find the parent hydrocarbon.
STEP 1
(a)
(b)
P.45
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Number the atoms in the main chain.
STEP 2
P.46
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Identify and number the substituents.
STEP 3
P.46
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Write the name as a single word.
STEP 4
P.46
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PRACTICE PROBLEM 2.2
P.47
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PRACTICE PROBLEM 2.3
P.47
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2.3 Naming Alkane

• Some complex substituent

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2.3 Naming Alkane

• Ex

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2.3 Naming Alkane

• Common (nonsystematic) name
• Ex

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2.3 Naming Alkane

• Problem 2.9

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2.4 Properties of Alkanes

• Combustion
• CnH2n2 (3n1/2)O2 ? nCO2 (n1)H2O
• Chlorination reaction
• CH4 4Cl2 ? CCl4 4HCl
• Molecular weight m.p. b.p.
• C-C
• 1.54 ? 0.01Å
• 85 ? 5 Kcal/mol
• C-H
• 1.09 ? 0.01Å
• 95 ? 5 Kcal/mol

hn
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FIGURE 2.5 Fractional distillation separates
crude mixtures of alkanes based on differences in
boiling point. Temperature decreases in the tower
with increasing hwight, allowing condensation of
the gases and fractional collection of components.
P.49
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2.5 Conformations of Ethane

• Conformations
• Different spatial arrangements of atoms caused by
  rotation around a single bond
• Conformers
• Conformational
• isomers

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2.5 Conformations of Ethane
FIGURE 2.7 A sawhorse representation and a
Newman projection of ethane. The sawhorse
projection views the molecule from an oblique
angle, while the Newman projection views the
molecule end-on.
P.51
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2.5 Conformations of Ethane
FIGURE 2.8 Staggered and eclipsed conformations
of ethane. The staggered conformation is lower in
energy and more stable by 12.0 kj/mol.
P.52
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FIGURE 2.9 The most stable conformation of any
alkane is the one in which the bonds on adjacent
carbons are staggered and the carbon chain is
fully extended, as in this structure of decane.
P.52
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2.6 Drawing Chemical Structure
P.53
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2.7 Cycloalkane (CnH2n)

• Alkane with a ring of carbons

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2.7 Cycloalkane (CnH2n)

• Nomenclature
• Cyclo- for prefix
• Alkyl-substituted
• How to number?
• example

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2.7 Cycloalkane (CnH2n)

• Ex

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2.7 Cycloalkane (CnH2n)

• Ex

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PROBLEM 2.18
P.55
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2.8 Cis-Trans Isomerism in Cycloalkanes

• Less flexible than open-chain
• No rotation around C-C without breaking the ring
• Stereoisomers
• Cis-trans isomers

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Cyclohexane
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FIGURE 2.13 The strain-free, chair conformation
of cyclohexane. All C-C-C bond angles are close
to 109, and all neighboring C-H bonds are
staggered, as evident in the end-on view in (b).
P.58
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2.9 Conformations of cycloalkane

• Cyclohexane
• Chair conformation

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STEP 1
STEP 2
STEP 3
P.58
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2.10 Axial Equatorial Bonds
Six axial hydrogens Six equatorial hydrogens
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2.10 Axial Equatorial Bonds

• Axial Equatorial bonds

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2.11 Conformational Mobility
FIGURE 2.16 A ring-flip in chair cyclohexane
interconverts axial and equatorial positions.
P.60
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2.11 Conformational Mobility
FIGURE 2.17 Axial versus equatorial
methylcyclohexane. The 1,3-diaxial steric
interactions in axial methylcyclohexane (easier
to see in space-filling models) make the
equatorial conformation more stable by 7.6 kj/mol.
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PRACTICE PROBLEM 2.6
PROBLEM 2.26
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I N T E R L U D E
The Sources and Development of Drugs
Sources of the 1031 new potential drugs reported
between 1981 and 2002.
P.62
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Timeline for bringing drugs to the market.
P.63
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PROBLEM 2.54
PROBLEM 2.56
P.69
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PROBLEM 2.74
P.70
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PROBLEM 2.75
P.71