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Alkyne combustion reaction: 2 C 2 H 2 + 5 O 2 4 CO 2 + 2 H 2 O The combustion reactions are all exothermic . . Substitution Reactions. Substitution Reactions. Reaction with chlorine :. Substitution Reactions. Reaction with chlorine : - PowerPoint PPT Presentation
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Alkyne combustion reaction: 2 C2H2 + 5 O2 4 CO2 + 2 H2O
The combustion reactions are all exothermic.
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Substitution Reactions
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Substitution Reactions
Reaction with chlorine:
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Substitution Reactions
Reaction with chlorine: CH4 + Cl2 CH3Cl + HCl chloromethane
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Substitution Reactions
Reaction with chlorine: CH4 + Cl2 CH3Cl + HCl chloromethane
CH3Cl + Cl2 CH2Cl2 + HCl dichloromethane
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CH2Cl2 + Cl2 CHCl3 + HCl trichloromethane
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CH2Cl2 + Cl2 CHCl3 + HCl trichloromethane
CHCl3 + Cl2 CCl4 + HCl tetrachloromethane
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For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine:
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For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine:
CH4 + Cl2 CH3Cl + HCl
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For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine:
heat (300 oC) CH4 + Cl2 CH3Cl + HCl
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For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine:
heat (300 oC) CH4 + Cl2 CH3Cl + HCl or uv irrad. room temp.
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Addition Reactions
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dark Cl2 + 25 oC
1,2- dichloroethane
C C HH
HHCC
HH
HH
ClCl
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CH3CCH + 2 Cl2 CH3CCl2CHCl2
propyne 1,1,2,2-tetrachloropropane
CH3CHCH2 + HBr CH3CHBrCH3
propene 2-bromopropane
It turns out that when a hydrogen halide add to an alkene, the more electronegative halogen atom always tends to end up on the carbon atom of the double bond that has fewer hydrogen atoms (Markovnikov’s rule).
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H2SO4
CH2CH2 + H2O CH3CH2OH
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Hydrogenation
The following reaction is an example of hydrogenation of an alkene, addition of H2 across a double bond.
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+ H2
ethene ethane
C C HH
HHCC
HH
HH
HH
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Functional Group Concept
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Functional Group Concept
A great many organic molecules have complex structures.
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Functional Group Concept
A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult.
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Functional Group Concept
A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult. Chemists have found it very useful to characterize certain well defined fragments of an organic molecule.
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Functional Group Concept
A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult. Chemists have found it very useful to characterize certain well defined fragments of an organic molecule. These fragments (in isolation) have well defined reactive capabilities.
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When these units are found in complex structures, predictions can be made as to the likely properties and reactions of the complex structure.
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When these units are found in complex structures, predictions can be made as to the likely properties and reactions of the complex structure. These fragment units are called functional groups.
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Some common functional groupsFunctional Name Example IUPAC Name Common Name group formula
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Some common functional groupsFunctional Name Example IUPAC Name Common Name group formula
R O H alcohol CH3OH methanol methyl alcohol
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Some common functional groupsFunctional Name Example IUPAC Name Common Name group formula
R O H alcohol CH3OH methanol methyl alcohol R C carboxylic CH3CO2H ethanoic acid acetic acid acid
O
H _O
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Some common functional groupsFunctional Name Example IUPAC Name Common Name group formula
R O H alcohol CH3OH methanol methyl alcohol R C carboxylic CH3CO2H ethanoic acid acetic acid acid R C ketone CH3COCH3 propanone acetone
O
H _OO
R
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Some common functional groupsFunctional Name Example IUPAC Name Common Name group formula
R O H alcohol CH3OH methanol methyl alcohol R C carboxylic CH3CO2H ethanoic acid acetic acid acid R C ketone CH3COCH3 propanone acetone
R and are alkyl (or more complicated groups). cannot be H. R cannot be H for the alcohol (that would be water!), nor for the
ketone (that would give an aldehyde).
O
H _OO
R
R R
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Functional Name Example IUPAC Name Common Name group formula
R C aldehyde HCHO methanal formaldehyde
O
H
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Functional Name Example IUPAC Name Common Name group formula
R C aldehyde HCHO methanal formaldehyde R C ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate
O
O
O
H
R
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Functional Name Example IUPAC Name Common Name group formula
R C aldehyde HCHO methanal formaldehyde R C ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate R NH2 amine CH3NH2 aminomethane methylamine
O
O
O
H
R
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Functional Name Example IUPAC Name Common Name group formula
R C aldehyde HCHO methanal formaldehyde R C ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate R NH2 amine CH3NH2 aminomethane methylamine
R and are alkyl (or more complicated groups). cannot be H (that would give an acid). R cannot be H for the amine (that would be ammonia!).
O
O
O
H
R
R R
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Functional Name Example IUPAC Name Common Name group formula
R O ether CH3OCH3 methoxymethane dimethyl ether
R
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Functional Name Example IUPAC Name Common Name group formula
R O ether CH3OCH3 methoxymethane dimethyl ether
R C amide CH3CONH2 ethanamide
O
R
2NH
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Functional Name Example IUPAC Name Common Name group formula
R O ether CH3OCH3 methoxymethane dimethyl ether
R C amide CH3CONH2 ethanamide
R and are alkyl (or more complicated groups). cannot be H (that would give an alcohol). R cannot be H for the ether (that would also give an alcohol).
O
R
2NH
R R
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Summary of name endings
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Summary of name endings Functional group Parent alkane name ending
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one aldehyde change e to al
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one aldehyde change e to al amide change e to amide
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one aldehyde change e to al amide change e to amide
amine insert amino in front of alkane name
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one aldehyde change e to al amide change e to amide
amine insert amino in front of alkane name ester insert alkyl name then change e to oate
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Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one aldehyde change e to al amide change e to amide
amine insert amino in front of alkane name ester insert alkyl name then change e to oate ether change ane to oxy then add in second alkane name.
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Key comment on a functional group The carboxylic acid is a combination of two
functions groups:
O O C C plus O H
O H carboxylic acid ketone alcohol
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Key comment on a functional group The carboxylic acid is a combination of two
functions groups:
O O C C plus O H
O H carboxylic acid ketone alcohol HOWEVER, a compound such as
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CH3CH2CCH2CH2 OH O would NOT function like a carboxylic acid, but
as an alcohol in some reactions and a ketone in some other reactions.
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Comparison of some properties
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Some simple representative reactions of a few functional groups.
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Formation of an ester:
O O
CH3 C + CH3CH2OH CH3 C + H2O O H OCH2CH3
carboxylic acid alcohol ester
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Formation of an ester:
O O
CH3 C + CH3CH2OH CH3 C + H2O O H OCH2CH3
carboxylic acid alcohol ester ethanoic acid ethanol ethyl ethanoate
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Oxidation of an alcohol:
H2SO4,K2Cr2O7
CH3CH2OH alcohol warm
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Oxidation of an alcohol:
H2SO4,K2Cr2O7 OCH3CH2OH CH3 C alcohol warm H aldehyde
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Oxidation of an alcohol:
H2SO4,K2Cr2O7 OCH3CH2OH CH3 C alcohol warm H aldehyde further warming O carboxylic acid CH3 C O H
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Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given.
Here is the complete chemical equation:
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Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given.
Here is the complete chemical equation:
16 H+ + 2 Cr2O72- + 3 CH3CH2OH 4 Cr3+ +3CH3CO2H
+ 11 H2O
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Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given.
Here is the complete chemical equation:
16 H+ + 2 Cr2O72- + 3 CH3CH2OH 4 Cr3+ +3CH3CO2H
+ 11 H2O (orange) (green)
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The intermediate reaction would be:
8 H+ + Cr2O72- + 3 CH3CH2OH 2 Cr3+ + 3 CH3CHO
+ 7 H2O (orange) (green)
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Oxidation of an alcohol:
OH H2SO4,K2Cr2O7 OCH3CHCH3 CH3CCH3
alcohol or KMnO4 ketone
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Aromatic Compounds
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Aromatic Compounds
Aromatic – from aroma – a number of these compounds have strong and sometimes pleasant odors.
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Aromatic Compounds
Aromatic – from aroma – a number of these compounds have strong and sometimes pleasant odors.
The most important compound in this family is benzene.
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Benzene C6H6
This is a very important example in organic chemistry – an example of resonance:
C C C C C C C C C C C C
H
HH
H
H
H
HH
H
HHH
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The two resonance structures are averaged leading to the following structure:
C C C C C C
HH
H
HHH
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If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to
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If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to
CH2 CH CH CH CH CH2
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If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to
CH2 CH CH CH CH CH2
1,3,5-hexatriene
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If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to
CH2 CH CH CH CH CH2
1,3,5-hexatriene This is not the case!
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If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to
CH2 CH CH CH CH CH2
1,3,5-hexatriene This is not the case! 1,3,5-hexatriene is fairly
reactive with a variety of reagents (e.g. HBr, Cl2, etc. in the dark). These reagents react only slowly with benzene.
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Benzene is more stable than might be expected by examination of the individual resonance structures.
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Naming benzene compounds
HH
H
HHCl
CC
CCC
C
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Naming benzene compounds
chlorobenzeneHH
H
HHCl
CC
CCC
C
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1,2-dibromobenzene
HH
H
BrHBr
CC
CCC
C
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1,2-dibromobenzene 1,3-dibromobenzene
BrH
H
HHBr
CC
CCC
CHH
H
BrHBr
CC
CCC
C
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1,2-dibromobenzene 1,3-dibromobenzene
1,4-dibromobenzene
BrH
H
HHBr
CC
CCC
C
HBr
H
HHBr
CC
CCC
C
HH
H
BrHBr
CC
CCC
C
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o-dibromobenzene m-dibromobenzene p-dibromobenzene
BrH
H
HHBr
CC
CCC
C
HBr
H
HHBr
CC
CCC
C
HH
H
BrHBr
CC
CCC
C
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o-dibromobenzene m-dibromobenzene o = ortho m = meta p = para p-dibromobenzene
BrH
H
HHBr
CC
CCC
C
HBr
H
HHBr
CC
CCC
C
HH
H
BrHBr
CC
CCC
C
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Steroids
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IUPAC name
(10R, 13R)-10,13-dimethyl-17-(6-methylheptan-2-yl)-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol
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oral contraceptive
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Theobromine (replace the CH3 at the arrow by H) is the stimulant found in
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Theobromine (replace the CH3 at the arrow by H) is the stimulant found in chocolate.
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Stereochemistry
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Stereochemistry
Stereochemistry: Deals with the 3-dimensional arrangement of atoms in space for a particular chemical structure.
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Stereochemistry
Stereochemistry: Deals with the 3-dimensional arrangement of atoms in space for a particular chemical structure. It also deals with how molecules react in 3-dimensions.
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Isomers
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Isomers Two or more compounds with the same
molecular formulas but different arrangements of the atoms in space.
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Isomers Two or more compounds with the same
molecular formulas but different arrangements of the atoms in space.
Three different types of isomerism will be considered.
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Isomers Two or more compounds with the same
molecular formulas but different arrangements of the atoms in space.
Three different types of isomerism will be considered.
1. Structural isomers (constitutional isomers)
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Isomers Two or more compounds with the same
molecular formulas but different arrangements of the atoms in space.
Three different types of isomerism will be considered.
1. Structural isomers (constitutional isomers) 2. Geometric isomers
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Isomers Two or more compounds with the same
molecular formulas but different arrangements of the atoms in space.
Three different types of isomerism will be considered.
1. Structural isomers (constitutional isomers) 2. Geometric isomers 3. Optical isomers
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Structural isomers
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Structural isomers
Structural isomers (constitutional isomers): Compounds with the same molecular formulas but different arrangements of the atoms.
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Structural isomers
Structural isomers (constitutional isomers): Compounds with the same molecular formulas but different arrangements of the atoms.
Example: Draw the structural isomers for C4H10
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CH3CH2CH2CH3 butane
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CH3CH2CH2CH3 butane
CH3CHCH3 2-methylpropane CH3 (the 2 is redundant in this name)
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Example: Draw the structural isomers for C5H12
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Example: Draw the structural isomers for C5H12
CH3CH2CH2CH2CH3 pentane
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Example: Draw the structural isomers for C5H12
CH3CH2CH2CH2CH3 pentane
CH3CH2CHCH3 2-methylbutane CH3 (2 is redundant)
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Example: Draw the structural isomers for C5H12
CH3CH2CH2CH2CH3 pentane
CH3CH2CHCH3 2-methylbutane CH3 (2 is redundant) CH3
CH3CCH3 2,2-dimethylpropane CH3 (each 2 is redundant)
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Example: Draw the structural isomers for C2H6O
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Example: Draw the structural isomers for C2H6O
CH3CH2OH ethanol
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Example: Draw the structural isomers for C2H6O
CH3CH2OH ethanol
CH3OCH3 methoxymethane (dimethyl ether)
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Exercise: Draw and name all the structural isomers for C6H14 (Answer there are 5).
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Exercise: Draw and name all the structural isomers for C6H14 (Answer there are 5).
The number of structural isomers increases significantly as the number of carbon atoms increases. For example, C20H42 has 366,319 isomers.
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Number of carbons Number of isomers for alkanes
1 1 2 1 3 1 4 2 5 3 6 5 7 9 8 18 9 35 10 75 20 366,319 30 4,111,846,763 40 62,491,178,805,831
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Stereoisomerism
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Stereoisomerism Stereoisomerism: Isomers having the same
molecular formula and the same atom-to-atom bonding, but the atoms differ in their arrangement in space.
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Stereoisomerism Stereoisomerism: Isomers having the same
molecular formula and the same atom-to-atom bonding, but the atoms differ in their arrangement in space.
Geometric isomers: Isomers having the same atom-to-atom bonding, but the atoms differ in their arrangement in space.
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Examples: The trans and cis isomers of 1,2-dichloroethene.
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Examples: The trans and cis isomers of 1,2-dichloroethene.
trans- 1,2-dichloroethene.
CCClH
HCl
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Examples: The trans and cis isomers of 1,2-dichloroethene.
trans- 1,2-dichloroethene.
cis- 1,2-dichloroethene.
CCClH
HCl
CCHH
ClCl
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Examples: The trans and cis isomers of 1,2-dichloroethene.
trans- 1,2-dichloroethene. (b.p. 48 oC , m.p. -50 oC)
cis- 1,2-dichloroethene. (b.p. 60 oC , m.p. -80 oC)
CCClH
HCl
CCHH
ClCl
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An example from inorganic chemistry.
NH3 Cl NH3 Cl Pt Pt NH3 Cl Cl NH3
cis isomer trans isomer
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An example from inorganic chemistry.
NH3 Cl NH3 Cl Pt Pt NH3 Cl Cl NH3
cis isomer trans isomer common name: cisplatin
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An example from inorganic chemistry.
NH3 Cl NH3 Cl Pt Pt NH3 Cl Cl NH3
cis isomer trans isomer common name: cisplatin Only the cis isomer is an effective chemotherapy
agent.
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Optical Isomers - Chirality
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Optical Isomers - Chirality
Polarized Light: Plane polarized light consists of electromagnetic waves with the electric component vibrating in one direction.
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Optical Isomer: An isomer that causes rotation of the plane of polarization of light when passed through the substance.
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Chiral (sounds like ki ral): An object that cannot be superimposed on its mirror image is called chiral.
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CCCl
HH
ClCl ClCl Cl
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mirror plane
CCCl
HH
ClCl ClCl Cl
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mirror plane
Can superimpose these two molecules; trichloromethane is achiral.
CCCl
HH
ClCl ClCl Cl
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mirror plane
CCF
HH
FCl ClBr Br
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mirror plane
Cannot superimpose these two molecules; bromochlorofluoromethane is chiral.
CCF
HH
FCl ClBr Br
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Enantiomers: A chiral molecule and its non-superimposable mirror image are called enantiomers.
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Enantiomers: A chiral molecule and its non-superimposable mirror image are called enantiomers.
The simplest case is a tetrahedral carbon bonded to four different groups.
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Enantiomers: A chiral molecule and its non-superimposable mirror image are called enantiomers.
The simplest case is a tetrahedral carbon bonded to four different groups.
Chiral molecules lack molecular symmetry.
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Lactic acid has optical isomers.
CCHOOC
HH
COOHOH HO3CH
3CH
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One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left.
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One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left. The symbols + for rotation to the right and - rotation to the left, are also fairly commonly used.
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One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left. The symbols + for rotation to the right and - rotation to the left, are also fairly commonly used.
The lactic acid from muscle tissue is D-lactic acid or (+)-lactic acid.
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A 50:50 mixture of the + and – isomers of the same compound is called a racemic mixture. There is no rotation of the plane of polarization for a racemic mixture.
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Polymers
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Polymer: (Greek: poly meros many parts)
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Polymer: (Greek: poly meros many parts) Very large molecules with molar masses
ranging from thousands to millions.
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Polymer: (Greek: poly meros many parts) Very large molecules with molar masses
ranging from thousands to millions.
Applications: clothes, food packaging, appliances with plastic components, etc., etc., ….
Plastics are polymers.
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Two basic types of polymer:
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Two basic types of polymer:1. Thermoplastics: When heated these soften
and flow, when cooled, they harden again. This process can be repeated.
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Two basic types of polymer:1. Thermoplastics: When heated these soften
and flow, when cooled, they harden again. This process can be repeated.
Examples: polyethylene and polystyrene
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Two basic types of polymer:1. Thermoplastics: When heated these soften
and flow, when cooled, they harden again. This process can be repeated.
Examples: polyethylene and polystyrene
2. Thermosetting plastics: When first heated they are plastic, but further heating forms a highly cross-linked structure. Cannot be softened by reheating.
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Two basic types of polymer:1. Thermoplastics: When heated these soften
and flow, when cooled, they harden again. This process can be repeated.
Examples: polyethylene and polystyrene
2. Thermosetting plastics: When first heated they are plastic, but further heating forms a highly cross-linked structure. Cannot be softened by reheating. Example: formica.
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Monomers: The small (low molar mass) molecules used to synthesize polymers.
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Synthetic Polymers
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Synthetic Polymers Two principal reaction types: Addition and
condensation.
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Synthetic Polymers Two principal reaction types: Addition and
condensation.
Addition Polymers: Made by monomer units directly joining together.
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Synthetic Polymers Two principal reaction types: Addition and
condensation.
Addition Polymers: Made by monomer units directly joining together.
Condensation Polymers: Made by monomer units combining so that a small molecule, usually water, is split out.
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Addition Polymers
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Addition Polymers
The monomer for addition polymers normally contains one or more double bonds.
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Addition Polymers
The monomer for addition polymers normally contains one or more double bonds.
The polymerization reaction is initiated using an organic peroxide.
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Addition Polymers
The monomer for addition polymers normally contains one or more double bonds.
The polymerization reaction is initiated using an organic peroxide.
R O O R R O. + .O R
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Addition Polymers
The monomer for addition polymers normally contains one or more double bonds.
The polymerization reaction is initiated using an organic peroxide.
R O O R R O. + .O R organic peroxide free radicals
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Initiation step:
+ .OR . CCHH
HHCC
HH
HHOR
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Initiation step:
+ .OR . CCHH
HHCC
HH
HHOR
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Then
CCHH
HHCC
HH
HH
CCHH
HH
OR.
. CH
HOR
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Etcetera:
where n would typically range from 1000 to 50,000.
CCHH
HH
n)(
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Different experimental conditions give different polymers.
CHRCH 22 2CH _
2CH _ C _ _CH _2
H
H
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Different experimental conditions give different polymers.
CHRCH 22 2CH _
2CH _ C _ _CH _2
H
H
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Different experimental conditions give different polymers.
+
CHRCH 22 2CH _
2CH _ C _ _CH _2
H
HCH _
2CH _2CH _
2CH
2CHR
H
_CH _2
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Different experimental conditions give different polymers.
+ branched polymer chain
CHRCH 22 2CH _
2CH _ C _ _CH _2
H
HCH _
2CH _2CH _
2CH
2CHR
H
_CH _2
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Cross linked polymers are formed in the following manner:
2CH _2CH _ CH _ _CH _
2H
R RO
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Cross linked polymers are formed in the following manner:
2CH _2CH _ CH _ _CH _
2H
R RO
HC _ _CH _
22CH _2CH _
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Cross linked polymers are formed in the following manner:
2CH _2CH _ CH _ _CH _
2H
R RO
HC _ _CH _
22CH _2CH _
CCHH
HH
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Cross linked polymers are formed in the following manner:
2CH _2CH _ CH _ _CH _
2H
R RO
HC _ _CH _
22CH _2CH _
CCHH
HH
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Cross linked polymers are formed in the following manner:
2CH _2CH _ CH _ _CH _
2H
R RO
HC _ _CH _
22CH _2CH _
CH _2CH _
2CH _
2CH
2HC
CCHH
HH
_CH _2
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CH _2CH _
2CH _
2CH
2HC
_CH _2
HC _ 2CH _
2CH _ _CH _2
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CH _2CH _
2CH _
2CH
2HC
_CH _2
HC _ 2CH _
2CH _ _CH _2
CH _2CH _
2CH _
2CH
2CH
_CH _2
2CH _2CH _ _CH _
2CH _
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cross linked polymer
CH _2CH _
2CH _
2CH
2HC
_CH _2
HC _ 2CH _
2CH _ _CH _2
CH _2CH _
2CH _
2CH
2CH
_CH _2
2CH _2CH _ _CH _
2CH _
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Polyethylene is the most widely used polymer.
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Polyethylene is the most widely used polymer.
The long linear chain version is called high density polyethylene (HDPE) (d = 0.97 g/ml).
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Polyethylene is the most widely used polymer.
The long linear chain version is called high density polyethylene (HDPE) (d = 0.97 g/ml).
It is hard, tough, and rigid. Used for milk and detergent containers.
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The branched chain version is called low density polyethylene (LDPE) (d=0.92 g/ml). The branched chains of polyethylene prevent close packing – hence the density is lower.
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The branched chain version is called low density polyethylene (LDPE) (d=0.92 g/ml). The branched chains of polyethylene prevent close packing – hence the density is lower.
This polymer is soft and flexible. Used for grocery bags, bread bags, etc.
195
The cross linked polymer is called cross-linked polyethylene (CLPE). This is a very tough material. Used for plastic caps on soft drink bottles.
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Condensation Polymers
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Condensation Polymers
A condensation reaction occurs when two molecules react by splitting out or eliminating a small molecule such as water.
Ester formation reaction:
CH3CO2H + CH3CH2OH CH3CO2CH2CH3 + H2Oacetic acid ethanol ethyl acetate
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Polyesters
OH
OC C
O
HH_O_CH_CH_O_H 22
O
OOH
OC C
OO
H
_O_CH_CH_O _22 C C
O
CH2
CH2
O
terephthalic acid ethylene glycol
+22
+2 H2O
201
Polyesters
OH
OC C
O
HH_O_CH_CH_O_H 22
O
OOH
OC C
OO
H
_O_CH_CH_O _22 C C
O
CH2
CH2
O
terephthalic acid ethylene glycol
+22
+2 H2O
Now consider another terephthalic acid molecule reacting with the indicated alcohol functional group.
202
O
OC C
O
_O_CH_CH_O _22
n
This is an example of the repeat unit for a polyester. In this case it is poly(ethylene terephthalate) called PET.