20'6 20'15: Reactions, Aromatics and Functional Groups

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20.6 20.15Reactions, Aromatics and Functional
Groups
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20.6 Reactions of Alkanes

• At lower temperatures, alkanes are NOT reactive
• High temperatures are needed for alkanes to react
• Called combustion reactions
• This is the reason alkanes make good fuels
• 2C4H10 13O2 ? 8CO2 10H2O

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20.6 Reactions of Alkanes

• Alkanes also undergo substitution reactions
• When one or more hydrogens on an alkane is
  replaced with different atoms
• General formula
• R H X2 ? R X HX
• X must be a halogen
• CH4 Cl2 ? CH3Cl HCl

methane
chloromethane
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20.6 Reactions of Alkanes

• Alkanes can also undergo dehydrogenation
  reactions
• When hydrogen atoms are removed and a double or
  triple bond is made
• From saturated to unsaturated
• CH3CH3 ? CH2CH2 H2

ethane
ethene
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20.7 Reactions of Alkenes

• Alekenes and alkynes are unsaturated
• Undergo addition reactions
• New atoms form single bonds with the carbon atoms
  involved in the double or triple bond
• Examples
• Hydrogenation reactions when hydrogens are added
  to the compound
• CH2CHCH3 H2 ?CH3CH2CH3
• Halogenation addition of halogen atoms
• CH2CHCH3 Br2 ? CH2BrCHBrCH3
• Polymerization when many small molecules are
  joined to form one large molecule

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20.8 Aromatic Hydrocarbons

• When mixtures of hydrocarbons from natural
  sources are separated, certain compounds that
  emerge have pleasant odors
• Called aromatic hydrocarbons
• Examples wintergreen, cinnamon, vanilin
• Contain a six-membered ring of carbon called a
  benzene ring
• Has the formula C6H6
• All bond angles are 120o

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20.8 Aromatic Hydrocarbons

• Ways to represent a benzene ring
• Lewis structure
• Shorthand notation

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20.9 Naming Aromatic Compounds

• Substituted benzene molecules are formed by
  replacing one (or more) of the H atoms with
  another atom or group of atoms

One of the Hs has been replaced with an OH
group!
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20.9 Naming Aromatic Compounds

• Monosubstituted Benzens
• Where there is only ONE H replaced on the benzene
  ring
• To name
• Use the substituent name as a prefix of benzene

Cl
CH2CH3
chlorobenzene
ethylbenzene
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20.9 Naming Aromatic Compounds

• Disubstituted Benzenes
• When two Hs on a benzene ring are replaced
• To name
• Number the carbons starting with one of the
  substituted Hs
• Use the substituent name as a prefix for benzene

1,3-dichlorobenzene
1,4-dimethlybenzene
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20.9 Naming Aromatic Compounds

• Sometimes it is more convenient to name compounds
  if we view the benzene ring as a substituent
• When the benzene ring is used as a substituent,
  it is called the phenyl group

CH3CHCHCH2
CH3CHCH2CHCH2CH3
Cl
4-chloro-2-phenylhexane
3-phenyl-1-butene
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20.10 Functional Groups

• A functional group is an atom or a group of atoms
  in hydrocarbon derivatives that contains elements
  in addition to carbon and hydrogen
• Table of Common Functional Groups
• (pg. 660 in text)

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20.11 Alcohols

• Alcohols have an OH group attached to one of the
  carbons
• To name
• Replace -e on end of name with ol
• Use a number to indicate location of alcohol
  group (if necessary)
• CH3CHCH2CH2CH3 CH3CH2CHCH2CH2CH3

OH
OH
3-hexanol
2-pentanol
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20.13 Aldehydes and Ketones

• Aldehydes and ketones contain the carbonyl group
• In ketones the group is bonded to two carbon
  atoms
• In aldehydes the group ALWAYS appears at the END
  of the carbon chain
• There is ALWAYS at least one H atom bonded to the
  carbonyl atoms

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20.15 Carboxylic Acids and Esters

• Carboxylic acids have a carboxyl group
• Short-hand COOH
• Structural Formula

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20.15 Carboxylic Acids and Esters

• Esters can be made from the reaction of a
  carboxylic acid with and alcohol
• Esters have the general formula

Called a condensation reaction ? water is a
product!