Unsaturated Hydrocarbons

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Unsaturated Hydrocarbons
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Saturated and Unsaturated Hydrocarbons

• Saturated compound - to contain carbon-carbon
  single bonds i.e. alkanes and cycloalkanes
• Unsaturated compound - to contain at least one
  multiple bond
• Multiple bond - a double or triple bond

RCCR
RC?CR
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• Alkenes
• Alkynes
• Aromatics

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Unsaturated Hydrocarbons
1. Alkene to have one or more C-C double
bonds H2CCH2 2. Alkyne to have one or more
C-C triple bonds HC?CH
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Unsaturated Hydrocarbons
3. Arenes- aromatic and delocalized bonding
Benzene
(chemically unreactive) Arenes
are found in proteins, nucleic acids, and
pharmaceuticals like aspirin
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Alkenes and Cycloalkenes

• Carbon-carbon double bonds
• Names end in ene
• CnH2n (alkenes)
• CnH2n-2 (cycloalkenes)
• May contain multiple double bonds i.e. dienes,
  trienes, etc.
• H2CCH2 H2CCH-CH3

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Shapes of Alkenes
VSEPR predicts 120o for bond angles in the
following examples (trigonal planar) H2CCH2
H2CCH-CH3 ?
121.7 ? 124.7 The actual ? for these
molecules are close to the predicted however, in
other alkenes the predicted angles will have a
larger deviation from that predicted in the
VESPR model due to limited rotation around a
double bond
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Naming Alkenes

• Use the suffix ene instead of ane with the
  usual stem names
• The parent chain must contain both carbons of the
  double bond
• Start numbering the parent from the end nearest
  to the double bond
• --if the double bond is equal from both ends,
  start numbering at the end closest to the first
  substituent

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Naming Alkenes

• The location number for the double bond is a
  single number (the lowest of the 2 location
  numbers) and it is placed before the parent with
  a hyphen
• If multiple double bonds are present use the
  suffix diene (2),
• -triene (3), -tetrene (4), etc. instead of -ene

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Examples
CH2CHCH2CH3 CH3CHCHCH3
CH3

CH2CCHCH2
CH3 CH3CHCH2CHCH2

• CH2
• CH3CH2CCH2CH2CH2CH3

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Naming Cycloalkenes

• No location number for the double bond is written
  in unsubstituted cycloalkenes with one double
  bond it is assumed that the two carbons of the
  double bond are at positions 1 and 2
• For substituted cycloalkenes with one double
  bond, the carbons of the double bond are assumed
  to be 1 and 2 in the direction that will give the
  first substituent the lowest location number
• If multiple double bonds are present, number one
  as carbons 1-2 and give the other the lowest
  number possible

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Examples
F
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Learning Check UH1

• Write the IUPAC name for each of the following
  unsaturated compounds
• CH3
• A. CH3CCHCH3 B.

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Solutions UH1

• Write the IUPAC name for each of the following
  unsaturated compounds
• CH3
• A. CH3CCHCH3 B.
• 2-methyl-2-butene 3-methylcyclopentene

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Isomers of Alkenes
Positional Isomer constitutional isomer with
the same C-C arrangement but different hydrogen
(H) atom arrangements - is due to different
location of the functional group Skeletal
Isomer constitutional isomer with different
C-C arrangements and H arrangements - Cis/trans
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Examples
Which set (a or b) are skeletal and positional
isomers?
A. CH2CHCH2CH3
CH3CHCHCH3
B.
CH3 CH3CHCHCH3 CH2CCH3
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Cis-Trans Isomers

• Is possible if each of the 2 carbons in CC has 2
  different groups attached to it
• Cis same side
• Trans opposite sides
• Does not exist if 1 of the carbons has 2
  identical groups
• Possible to have multiple cis-trans sections in
  one molecule if multiple CC are present

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Cis-Trans Isomers
trans-2-butene

• cis-2-butene

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Learning Check 2

• Draw the structures for the following compounds
• cis-6-methyl-3-heptene

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Alkynes

• Carbon-carbon triple bonds
• Names end in yne
• CnH2n-2
• Use the same naming rules as previously discussed
• No cis-trans isomers
• Constitutional isomers (skeletal and positional)
  possible
• HC?CH HC?C-CH3

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Shapes of Alkynes
VSEPR predicts 180o for bond angles in ethyne H
C?C H ethyne ? 180
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Learning Check 3

• Write the IUPAC name for each of the following
  unsaturated compounds
• CH3CH2C?CCH3

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Learning Check 4

• Write the IUPAC name for each of the following
  unsaturated compounds
• CH3CH2C?CCH3
• CH3C?CCH2CH2CH3
• CH3C?CCH2CH2C?CCH2CH3

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Solutions Learning Check 4

• Write the IUPAC name for each of the following
  unsaturated compounds
• CH3CH2C?CCH3 2-Pentyne
• CH3C?CCH2CH2CH3 2-Hexyne
• CH3C?CCH2CH2C?CCH2CH3 2,6- Nondiyne

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Alkynes

• Name the following compounds
• CH3CH2C CCHCH3
• CH2CH3
• CH3CH2C CCl

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Alkynes

• Draw the following alkynes.
• 4-chloro-2-pentyne
• 3-propyl-1-hexyne

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Physical Properties

• alkenes and alkynes are nonpolar compounds
• alkenes and alkynes are insoluble in water but
  soluble in one another and in nonpolar organic
  liquids
• alkenes and alkynes tend to be less dense than
  water

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Reactions of Alkenes Alkynes

• More reactive than alkanes or aromatics, why?
• Generally undergo addition reactions
• Presence of easily accessible ? electrons
• Unsaturated can fit more atoms around the carbons

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Reaction of Alkenes

• Addition reaction to add an atom or substituent
  to each carbon of the multiple bond
• - can be either symmetrical or unsymmetrical
• H H H H
• H C CH X-Y HCCH
• X Y

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Hydrogenation

• Adds a hydrogen atom to each carbon atom of a
  double bond
• H H H H
• Ni
• HCCH H2 HCCH
• heat
• H H
• ethene
  ethane
• Reacts with H2 in the presence of transition
• metal catalyst (Pd, Pt, Ru, Ni)

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Products of Hydrogenation

• Adding H2 to vegetable oils produces compounds
  with higher melting points
• Margarines
• Soft margarines
• Shortenings (solid)

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Trans Fats

• In vegetable oils, the unsaturated fats usually
  contain cis double bonds.
• During hydrogenation, some cis double bonds are
  converted to trans double bonds (more stable)
  causing a change in the fatty acid structure
• If a label states partially or fully
  hydrogenated, the fats contain trans fatty
  acids.

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Learning Check 5

• What is the product of adding H2 (Ni catalyst)
  to 1-butene?

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Solution 5

• What is the product of adding H2 (Ni catalyst)
  to 1-butene?
• Ni
• CH2CHCH2CH3 H2
• CH3CH2CH2CH3

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Halogenation

• Adds a halogen to each carbon atom of a double
  bond
• H H H H
• HCCH X2 HCCH
• X X
• ethene
  1,2-dihaloethane
• -use of Cl2 and Br2 is most common

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Addition of Bromine

• Br2 (in CCl4) is added to an unknown liquid
• The unknown is saturated b/c Br2 does not lose
  its red color.
• The unknown was unsaturated. The deep red color
  of Br2 is
• decolorized as it reacts with the double
  bond.

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Learning Check 6

• Write the product of the following addition
  reactions
• CH3CHCHCH3 H2

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Solution 6

• Write the product of the following addition
  reactions
• CH3CHCHCH3 H2 CH3CH2CH2CH3

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Orientation of Addition

• Both alkene reagent are symmetric one possible
  product
• One is symmetric and the other is asymmetric one
  possible product
• Both alkene reagent are asymmetric
• two possible products

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Markovinkovs Rule

• When an unsymmetrical reactant of the type H-Y
  adds to an unsymmetrical alkene, the H adds to
  the multiple bond carbon with the greater number
  of hydrogens on it
• Used to predict the major product of many alkene
  addition reactions

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Markovinkovs Rule
Try This !!!
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Hydrohalogenation

• Adds a H and X to each carbon atom of a double
  bond
• H H H H
• HCCH HX HCC H
• H X
• ethene haloethane
• Occurs with HCl, HBr, HI

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Addition of Hydrogen Halides

• Markovnikovs rule when unsymmetrical reagent
  adds to an unsymmetrical carbon, the carbon with
  the greater of hydrogens gets more H
• 
  Cl
• CH3CCH2 HCl CH3CCH3
• CH3
  CH3

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Learning Check 7

• CH3CHCH2 HI
• HBr
• CH2 HBr

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Solution 7
I

• CH3CHCH2 HI
• HBr
• CH2 HCl

CH3CHCH3
H
Br
I
CH3
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Question 3

• What is the major product of the following
  reaction?

HBr
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Hydration

• Addition of water in the form as H and OH
• is acid catalyzed, most commonly by H2SO4

H

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(No Transcript)
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Alkene Addition
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Reactions of Alkynes

• Follow the same mechanism and reactions as
  alkenes for hydrohalogenation, halogenation, and
  hydrogenation
• Only difference is an alkyne needs two
  equivalents of reagent to form an alkane

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Reactions of Alkynes

• Halogens also add to the triple bond of an
  alkyne.

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Polymerization

• 100s to 1000s of alkene molecules can join
  together to make one large molecule
• Polymer large molecule composed of smaller
  repeating units
• Monomer the smaller repeating units of a
  polymer
• Polymerization the chemical reaction were
  monomers combine to form a polymer
• Addition polymer polymer where the monomers add
  together and no other products result

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Polymerization

• From the perspective of the organic chemical
  industry, the single most important reaction of
  alkenes is polymerization
• polymer Greek poly, many and meros, part
• monomer Greek mono, single and meros, part

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Polymerization

• Types of polymers
• Alkenes
• Substituted alkenes
• Butadienes
• Co-polymers polymer where two different types
  of monomers are used

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Polymerization
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Polymers
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Codes for Plastics
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Pheromones

• Compounds used by insects and animals to send
  messages to members of the same species
• Are either alkenes or alkene derivatives
• Cis/trans arrangement determines biological
  activity

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Terpenes

• Terpene a compound whose carbon skeleton
  consists of multiple five-carbon isoprene units
• Refer to Figure 13.5

C
1
2
3
4
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Aromatic Hydrocarbons

• Is a unsaturated cyclic hydrocarbon
• Undergoes substitution, not addition reactions
• Is delocalized the electrons of the covalent
  bond are shared between multiple atoms
• Aromatic a highly unsaturated carbon ring
  system where both localized and delocalized bonds
  occur (a functional group)

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Naming Aromatics

• Monosubstitution (1 substituent)
• - the name of the substituent is followed with
  benzene
• - if the substituent is too complex it becomes
  the parent and the benzene is named as a phenyl
  group

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Naming Aromatics

• Disubstitution (2 substituents)
• - 3 isomers possible (ortho, meta, para)
• - if a common name is possible, it is used as
  the parent name
• - if no common name is possible, put the
  substituents in ABC order and use benzene as the
  parent

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Naming Aromatics

• Trisubstitution (3 substituents)
• - denote the substituent positions with location
  numbers such that you use the lowest numbers
  possible
• - if 2 equal numbering systems are possible, use
  ABC order when numbering the substituents

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Properties of Aromatics

• Nonpolar molecules (insoluble in water)
• Less dense than water

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Aromatic Reactions

• Alkylation

catalyst
aromatic alkyl halide
alkylated aromatic
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Aromatic Reactions

• Halogenation

catalyst
aromatic X2 halogenated
aromatic
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Fused Aromatics

• Fused aromatic hydrocarbon whose structure has
  multiple rings that are fused together