Chapter 11-12 Organic Chemistry: Hydrocarbons

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Chapter 11-12 Organic Chemistry Hydrocarbons

• Suggested Problems
• Chapter 11 5,10, 18, 20, 22, 28-48 even
• Chapter 12
• 3,4,5,6,8a,c, 20,21,39,52,53,73

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Organic Chemistry

• Organic chemistry is the study of the compounds
  containing carbon
• Although inorganic cyanides and carbonates are
  generally excluded from this list

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Organic Chemistry

• The term organic says nothing about the source
  or purity of a compound
• While many compounds found in living organisms
  are organic, most organic compounds do not come
  from living sources
• Most organic compounds are synthetic, but
  ultimately come from petroleum

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Structural Formulas

• In organic and biochemistry it is much more
  useful to think of molecules in terms of
  structural formulas, rather than molecular
  formulas

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Example

• Butane is the stuff in lighters, and has a
  molecular formula C4H10

a full structural formula
a condensed structural formula
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Bonding and Carbon

• Carbon always has four covalent bonds

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Functional Groups

• It is helpful to think of organic molecules as
  having two distinct parts
• A carbon backbone that is relatively inert
• One (or more) functional group(s)
• A functional group is a set of atoms bonded
  together in a specific way
• Functional groups largely define the chemical and
  physical properties of the compound

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Summary of the Functional Groups
Alkane C-C single bond Aldehyde Terminal carbonyl (CO), RCHO
Alkene CC double bond Ketone Carbonyl (CO), R2CO
Alkyne CC triple bond Carboxylic Acid Carboxyl group, RCO2H
Aromatic Benzene ring Ester Carboxylic acid alcohol, RCO2R
Alcohol Hydroxyl group, ROH Amide Carboxylic acid amine, RCONR2
Ether Oxygen bridge, ROR Amine Nitrogen, R3N
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Hydrocarbon Functional Groups

• Hydrocarbons contain only hydrogen and carbon
• The hydrocarbon functional groups include
• Alkanes
• Alkenes
• Alkynes
• Aromatics

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Alkanes

• Alkanes are the simplest functional group
• An older name for alkanes is parafins
• The functional group is the C-C single bond
• Methane and ethane are examples of alkanes

CH3CH3
CH4
ethane
methane
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Alkane Models
a space-filling model of ethane
a ball-and stick model of ethane
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Single Bonds

• There is free rotation around carbon-carbon
  single bonds
• For example both of these structures represent
  the same compound (butane)

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The Normal Alkanes
CH4 methane
CH3CH3 ethane
CH3CH2CH3 propane
CH3CH2CH2CH3 butane
CH3CH2CH2CH2CH3 pentane
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The Normal Alkanes
CH3(CH2)4CH3 hexane
CH3(CH2)5CH3 heptane
CH3(CH2)6CH3 octane
CH3(CH2)7CH3 nonane
CH3(CH2)8CH3 decane
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Alkyl Groups

• A carbon chain stuck onto a larger molecule is
  called an alkyl group
• R is the symbol for a generic alkyl group
• Think of the R group as the (relatively
  uninteresting) carbon backbone

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Some Alkyl Groups
CH3 methyl
CH3CH2 ethyl
CH3CH2CH2 propyl
CH3CHCH3 isopropyl
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Isomerism

• Isomerism is one reason there are so many organic
  compounds
• Isomers are different compounds that have the
  same molecular formula

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Example

• Draw 2 structural isomers of C4H10

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Alkane Nomenclature Rules

• Name the longest chain as the parent alkane
• Find and Name alkyl substituents
• Indicate the number of identical substituents
• di2 tri3 tetra4 penta5
• Number the parent chaine to give the lowest
  possible numbers to each substituent to indicate
  its position on the parent chain
• Alphabetize the substituents by name Prefixes
  di, tri, tetra, however the prefixes iso and
  cyclo are considered when alphabatizing

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Example
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Example
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Example

• 3,5-diethyl-2,2,3-trimethyldecane

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Halogens

• Name halogens as stick-on groups
• F fluoro
• Cl chloro
• Br bromo
• I iodo

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Example
Substituents are placed into the name in
alphabetical order disregarding the prefix needed
to identify the number of substituents
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Example

• 1,3,5-tribromo-2,4,6-trichloro-2-isopropylhexane

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Cycloalkanes

• Carbon chains can close on themselves to give
  cyclic structures
• Add the prefix cyclo to indicate a cyclic
  structure

cycloalkanes are sometimes drawn as geometric
shapes
cyclobutane
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Example
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Alkenes

• The functional group in an alkene is the CC
  double bond
• An older name for alkenes is olefins
• Ethene (or ethylene) is an example of an alkene

CH2 CH2
ethene common name ethylene
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Alkene Models
a space-filling model of ethene
a ball-and stick model of ethene
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Alkene Nomenclature

• Name the longest chain as the parent
• Add suffix -ene
• Give double bond lowest number
• Name and number substituents
• Rules for alkanes are followed except for the
  double bond has to have the lowest number and you
  must tell where this is in the name if there are
  multiple places possible

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Example
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Example

• 2,3-dimethyl-2-hexene

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Alkenes Bonding

• There is NO free rotation around carbon-carbon
  double bonds

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Cis-Trans Isomerism

• Since there is no rotation around the double
  bond, a special type of isomerism is possible for
  alkenes
• Cis-Trans isomerism is possible ONLY when neither
  alkene carbon (i.e. the two carbons making the
  double bond) has two identical substitutents

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Cis and Trans Isomers
cis-2-butene Hs on same side
trans-2-butene Hs on opposite sides
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Example

• Which compound exhibits cis-trans isomerism?

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Example

• trans-4-methyl-2-pentene

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Reactions of Alkenes

• Alkenes undergo addition reactions
• This reaction always costs the double bond

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Addition of Hydrogen Hydrogenation

• This is the addition of hydrogen to an alkene
• The product is an alkane
• This reaction requires a Pt catalyst

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Examples
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Unsaturation

• A saturated compound has the maximum possible
  amount of hydrogens per carbon atom
• Since alkenes react with hydrogen, they are
  called unsaturated

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Fats

• Vegetable oils have double bonds
• These oils are unsaturated
• Addition of hydrogen to unsaturated fats gives
  hydrogenated vegetable oils

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Alkynes

• The functional group in an alkyne is the CC
  triple bond
• Ethyne (or acetylene) is an example of an alkyne

H-C C-H
ethyne common name acetylene
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Alkyne Models
a space-filling model of ethyne
a ball-and stick model of ethyne
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Alkyne Nomenclature

• Name the longest chain as the parent
• Add suffix -yne
• Give triple bond lowest number
• Name and number substituents
• Rules for alkanes are followed except for the
  triple bond has to have the lowest number and you
  must tell where this is in the name if there are
  multiple places possible

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Example
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Example

• 4,4-dimethyl-2-pentyne

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Aromatic Compounds

• The functional group of aromatic compounds is the
  benzene ring
• Benzene is the archetype aromatic compound

a space-filling model of benzene
benzene
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Benzene Where are the Double Bonds?

• Benzene appears to have alternating double and
  single bonds, but this is NOT the case
• There are two identical structures for benzene
• The actual benzene molecule is a hybrid of these

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Benzene Where are the Double Bonds?

• Because the double bonds are delocalized
  equally over all six carbons, benzene is often
  drawn with a circle

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Naming Aromatic Compounds

• Name benzene as the parent and then name the
  substituents

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Examples
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Ortho, Meta and Para Isomers

• ortho 1,2 meta 1,3 para 1,4

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Example
Trinitrotoluene OK Really ?
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Benzene as an Alkyl Group

• Benzene as a stick-on group is called a phenyl
  group

When polymerized styrene will make a rigid
plastic used in the production of plastic
cutlery, license plate frames and CD Jewel cases.