Chapter 3 Alkanes

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Chapter 3 Alkanes
Hydrocarbons - contain only C, H saturated - no
CC or C?C unsaturated - contains one or more CC
or C?C
Saturated hydrocarbons - molecular formula
CnH2n2
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• Nomenclature
• 1. n-alkane names n normal - straight chains
• CnH2n2 or CH3-(CH2)n-2-CH3

• n name structure bp (C)
• methane CH4 -164
• ethane CH3CH3 -89
• propane CH3CH2CH3 -42
• butane CH3CH2CH2CH3 0
• pentane CH3(CH2)3CH3 36
• hexane CH3(CH2)4CH3 69
• heptane CH3(CH2)5CH3 98
• octane CH3(CH2)6CH3 126
• nonane CH3(CH2)7CH3 151
• 10 decane CH3(CH2)8CH3 174

memorize these
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2. group names
memorize these
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3. alkyl group names - alkane CH3(CH2)nCH3
alkyl
CH3(CH2)nCH2-
CH3-
methyl
CH3CH2-
ethyl
n - propyl (n normal)
CH3CH2CH2-
i - propyl (i iso)
memorize these
CH3CH2CH2CH2-
n - butyl (n normal)
s - butyl (s sec or secondary)
i - butyl (i iso)
neo - pentyl
t- butyl (t tertiary)
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4. IUPAC Rules

• Find the longest continual chain of carbons - if
  two exist use
• the one with the largest number of groups
  (substituents).

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b. Number the chain so the substituent positions
are as low as possible and name each substiuent
by its position number on the main chain.
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c. When there are two or more substituents name
them in alpha order and/or use the following,
prefixes if they are the same
di -2 tri - 3 tetra - 4 penta - 5 hexa - 6, etc.
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B. Structures and conformations 1. structures of
alkanes - all very similar
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2. Newman Diagrams
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3. Rotation around C-C bonds

• ethane - staggered energy minimum
• eclipsed energy maximum

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b. propane - the barrier is raised a bit
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c. butane - there are two different C-C bonds to
rotate around
same as in propane a little more complicated
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steric strain
van der Waals surfaces
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C. Cycloalkanes CnH2n
1. nomenclature

• n name n name
• cyclopropane 7 cycloheptane
• cyclobutane 8 cyclooctane
• cyclopentane 9 cyclononane
• 6 cyclohexane 10 cyclodecane

nomenclature examples
2-cyclobutylpentane
2-chloro-1,1-dimethyl-4-ethylcyclohexane
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cis- 1-chloro-3-methylcyclopentane
trans-1,2-dimethylcyclopropane
2. stability - ring strain needs to be
minimized a. get all angles as close to the
ideal 109.5 as possible b. avoid eclipsing C-C
and C-H bonds
heat of combustion - gives relative energies
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3. cyclopropane
Pyrethin I - insecticide chrysanthemums
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4. cyclobutane
Grandisol boll weevil sex attractant
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5. cyclopentane
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6. cyclohexane a near strain-free structure
a. structure
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chair conformation
boat conformation
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1-aminoadamantane
rim antadine
blocks association of influenza A with host
cells hallucinations turning upside down
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tetrodoxin - liver and ovaries of puffer
fish neurotoxin - death in 200lb human 0.001 gm.
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b. axial-equatorial hydrogens
c. axial/equatorial exchange - ring flipping
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d. monosubstituted cyclohexanes
Why is there an energy difference?
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e. di-substituted cyclohexanes
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• D. Summary
• Alkane - cycloalkane nomenclature
• Structure of alkanes - staggered, eclipsed,
  gauche,
• Newman diagrams
• Structure of cycloalkanes
• cyclohexane - axial versus equatorial, ring flips
• mono and disubstituted cyclohexanes
• Draw, draw, draw...