Hydrocarbons

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Hydrocarbons
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Straight Chain Alkanes arent Straight
C C bonds are sp3 hybridized
Butane, C4H10
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Structural Shorthand
Explicit hydrogens (those required to complete
carbons valence) are usually left off of
drawings of hydrocarbons
C1
C2
C3
C4
C1
C3
C4
C2
Line intersections represent carbon atoms
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Structural Isomers
Isomers are molecules with the same chemical
formula, but different organization of atoms
(different bonding)
n-Pentane, C5H12
Isopentane, C5H12
Neopentane, C5H12
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Cyclic Alkanes
Cyclopropane, C3H6
Cyclobutane, C4H8
Cyclopentane, C5H10
Cyclohexane, C6H12
Cycloheptane, C7H14
Remember, explicit hydrogens are left out
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Rules for Naming Alkanes (Nomenclature)

• For a branched hydrocarbon, the longest
  continuous chain
• of carbon atoms gives the root name for the
  hydrocarbon

1
2
3
4
4 carbon chain butane
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Rules for Naming Alkanes (Nomenclature)

• When alkane groups appear as substituents, they
• are named by dropping the -ane and adding -yl.

CH3 Methyl
CH2CH3 Ethyl
CH2CH2CH3 Propyl
CH2CH2CH2CH3 Butyl
Methyl
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Rules for Naming Alkanes (Nomenclature)

• The positions of substituent groups are specified
• by numbering the longest chain of carbon atoms
• sequentially, starting at the end closest to the
• branching.

1
2
3
4
Methyl
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Rules for Naming Alkanes (Nomenclature)

• The location and name of each substituent are
• followed by the root alkane name. The
  substituents
• are listed in alphabetical order (irrespective of
  any
• prefix), and the prefixes di-, tri-, etc. are
  used to
• indicate multiple identical substituents.

1
2
3
4
Name
2-methylbutane
Methyl
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Nomenclature Practice
Name this compound
1
9 carbons nonane
2
4
3
5
6
7
8
9

• Step 1 For a branched hydrocarbon, the longest
  continuous chain of carbon atoms gives the root
  name for the hydrocarbon

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Nomenclature Practice
Name this compound
9 carbons nonane
1
2
4
3
5
6
CH3 methyl
7
chlorine chloro
8
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Step 2 When alkane groups appear as
substituents, they are named by dropping the -ane
and adding -yl.
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Nomenclature Practice
Name this compound
9 carbons nonane
1
2
4
3
5
6
CH3 methyl
7
chlorine chloro
8
9
1
9
NOT
9
1

• Step 3 The positions of substituent groups are
  specified by numbering the longest chain of
  carbon atoms sequentially, starting at the end
  closest to the branching.

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Nomenclature Practice
Name this compound
9 carbons nonane
1
2
4
3
5
6
CH3 methyl
7
chlorine chloro
8
9
2-chloro-3,6-dimethylnonane

• Step 4 The location and name of each
  substituent are followed by the root alkane name.
  The substituents are listed in alphabetical order
  (irrespective of any prefix), and the prefixes
  di-, tri-, etc. are used to indicate multiple
  identical substituents.

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Properties of Hydrocarbons

• Made up of mostly C and H
• Relatively nonpolar
• Low solubility in polar solvents (e.g. water)
• Good solvents for other nonpolar molecules
• Mostly london-dispersion forces (weak)
• Low boiling and melting points

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Reactions of Hydrocarbons

• Combustion
• Hydrocarbons burn readily in air to produce
  carbon dioxide and water.

C3H8(g) 5 O2(g) --gt 3CO2(g) H2O(g)
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Reactivity of Hydrocarbons

• Alkanes are generally less reactive than alkenes
  or alkynes
• Aromatic compounds are more reactive than
  alkanes, but less reactive than alkenes and
  alkynes.

Alkanes lt aromatics lt alkenes lt alkynes
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Reactions of Alkanes

• Single bonds between carbon atoms are difficult
  to break. (This is why alkanes are relatively
  unreactive)
• Can undergo combustion reactions

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Reactions of Alkanes

• Substitution Reactions
• Hydrogen atoms may be substituted by a halogen.
• The product is a halogenated alkane (alkyl
  halides)

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Reactions of Alkenes and Alkynes

• Addition Reactions
• Reactions in which a molecule is added to a
  double or triple bond.
• No loss of hydrogen atoms from the hydrocarbon

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Hydrogenation
Halogenation
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Hydrohalogenation
Hydration
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Markovnikovs Rule

• When molecules with two identical atoms (e.g. H2)
  are added to a double bond, only one possible
  product is formed.
• When molecules of nonidentical atoms (e.g. HBr)
  are added, two different products are
  theoretically possible

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Markovnikovs Rule

• However, experiments show that only one main
  product is formed.
• This product can be predicted by Markovnikovs
  rule
• The rich get richer
• When a hydrogen halide is added to an alkene or
  alkyne, the hydrogen atom bonds to the carbon
  atom that already has more hydrogen atoms.

Carbon 1 has 2 Hs
Carbon 2 has 1 H
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Benzene Ring

• Does not act as 3 single bonds and 3 double bonds
• Its 6 identical bonds of intermediate length
• Due to hybridization (delocalized, shared
  electrons)

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Reactions of Aromatic Hydrocarbons

• Less reactive than alkenes and do not undergo
  addition reactions unless under conditions of
  extreme temperature or pressure
• Do undergo substitution reactions (more reactive
  than alkanes)

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