Organic Chemistry

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Organic Chemistry

• Alkenes / Dienes
• Alkynes

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Alkenes

• The Alkenes form another homologous hydrocarbon
  series
• Each member contains one double covalent bond
  between two C atoms.
• So alkenes are said to be unsaturated.
• Only 3 atoms joined to each C, not 4
• General formula CnH2n
• What was the general formula for the Alkanes?

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Saturated vs Unsaturated
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Saturation vs. Unsaturation

• Simply put, a saturated hydrocarbon has no double
  bonds between the Carbon atoms (ex. alkanes)
• Unsaturated has one or more double or triple
  bonds between carbons (alkenes, alkynes)

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Physical properties of the Alkenes

• Very similar to the alkanes
• Insoluble in water
• very soluble in organic solvents
• Less dense than water
• B.P. and M.P increase with increasing carbon
• As with alkanes B.P rises about 20-30 C per
  carbon
• Hexane b.p. 69 C 1-Hexene b.p. 63.5 C
• Heptane b.p. 98 C 1-Heptene b.p. 93 C

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Naming Alkenes

• Names are derived from the name of the alkane
  chain with the same number of C atoms.
• Replace the ane ending of the alkane name with
  ene.

1st member is C2H4, ethene. H H CC H
H
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Alkene Homologous Series(C1-C2 double bond)

• Ethene
• Propene
• 1-Butene
• 1-Pentene
• 1-Hexene
• 1-Heptene
• 1-Octene
• 1-Nonene
• 1-Decene

• CC
• C-CC
• C-C-CC
• C-C-C-CC
• C-C-C-C-CC
• C-C-C-C-C-CC
• C-C-C-C-C-C-CC
• C-C-C-C-C-C-C-CC
• C-C-C-C-C-C-C-C-CC

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Naming Alkenes

• Location of double bond is specified by numbering
  C atoms in backbone. Give bond the lowest
  possible number.

1-butene (not 4)
2-butene
H H H CCCCH H H H H
H H H H HCCCCH H H
Structural Formula Chemical formula Condensed
Structural formula
C4H8 CH2CHCH2CH3
C4H8 CH3CHCHCH3
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Naming Alkenes

• Once double bond is numbered specify substituents
  alphabetically by number
• Use di, tri and tetra for multiple substituents
  of the same group

2,3-dimethyl-1-butene
CCCC C C

Structural Formula (w/o the H) Chemical
formula Condensed Structural formula
C6H12 CH2C(CH3)CH(CH3)CH3
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Problems

• Draw the following alkenes
• 2-Butene
• 2methylpropene
• 4Methyl2-pentene
• 3,3-Dimethyl-1-butene

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Name this Compound
4-ethyl-5-methyl-4-octene
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Dienes

• Alkenes 1 double bond
• Dienes have 2 double bonds
• End in -diene
• Location still denoted by numbers
• Determine which way to number the C backbone by
  assigning the lowest possible number to one of
  the double bonds

• Example 1,3 pentadiene
• cc-cc-c
• Not 2,4-pentadiene
• Substituents are named first
• Numbers are separated by commas and the s are
• Separated from the name by a dash

Double bonds must all be in the backbone.
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Name this compound CC-C-C-CC-C C
5-methyl-1,5-heptadiene
Draw 2-methyl-1,3-heptadiene
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Alkynes

• Homologous series of unsaturated hydrocarbons
  that contain one triple bond.
• Each member contains one triple carbon-carbon
  bond.
• Alkynes are unsaturated.
• General formula CnH2n-2

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Alkyne Homologous Series(C1-C2 triple bond)

• Ethyne
• Propyne
• 1-Butyne
• 1-Pentyne
• 1-Hexyne
• 1-Heptyne
• 1-Octyne
• 1-Nonyne
• 1-Decyne

• C C
• C-C C
• C-C-C C
• C-C-C-C C
• C-C-C-C-C C
• C-C-C-C-C-C C
• C-C-C-C-C-C-C C
• C-C-C-C-C-C-C-C C
• C-C-C-C-C-C-C-C-C C

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Ethene
(Common name)
A common use of one of the alkynes The Acetylene
torch
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Hydrocarbon Table
Notice that each Of the hydrocarbon Families
differs From the next By 2 hydrogen Alkanes
share 1pr e- Alkenes share 2pr e- Alkynes share
3pr e- Can you explain how The above
comments Are related?
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Naming Alkynes

• Use the corresponding name from the alkane series
  and change the ane to yne.
• If necessary, number the carbon atom at which the
  triple bond occurs with the lowest number.
• Use the same naming process you used for naming
  Alkenes

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Structural Chemical Name
Condensed Formula Formula
Structural
formula
HC?CH C2H2 ethyne CHCH
H HC?CCH C3H4 propyne CHCCH3
H
H H HC?CCCH C4H6 1-butyne CHCC
H2CH3 H H
H H HCC?CCH C4H6 2-butyne C
H3CCCH3 H H
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Can you name this compound?
3-ethyl-1-pentyne