Alkyne combustion reaction: 2 C 2 H 2 + 5 O 2 4 CO 2 + 2 H 2 O

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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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Reaction with chlorine:

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Reaction with chlorine: CH4 + Cl2 CH3Cl + HCl chloromethane

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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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CH4 + Cl2 CH3Cl + HCl

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heat (300 oC) CH4 + Cl2 CH3Cl + HCl

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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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A great many organic molecules have complex structures.

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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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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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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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R O H alcohol CH3OH methanol methyl alcohol

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R O H alcohol CH3OH methanol methyl alcohol R C carboxylic CH3CO2H ethanoic acid acetic acid acid

O

H _O

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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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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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R C aldehyde HCHO methanal formaldehyde R C ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate

O

O

O

H

R

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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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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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R O ether CH3OCH3 methoxymethane dimethyl ether

R

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R C amide CH3CONH2 ethanamide

O

R

2NH

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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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amine insert amino in front of alkane name

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amine insert amino in front of alkane name ester insert alkyl name then change e to oate

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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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H2SO4,K2Cr2O7 OCH3CH2OH CH3 C alcohol warm H aldehyde

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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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16 H+ + 2 Cr2O72- + 3 CH3CH2OH 4 Cr3+ +3CH3CO2H

+ 11 H2O

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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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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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CH2 CH CH CH CH CH2

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CH2 CH CH CH CH CH2

1,3,5-hexatriene

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CH2 CH CH CH CH CH2

1,3,5-hexatriene This is not the case!

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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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Three different types of isomerism will be considered.

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1. Structural isomers (constitutional isomers)

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1. Structural isomers (constitutional isomers) 2. Geometric isomers

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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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CH3CH2CH2CH2CH3 pentane

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CH3CH2CHCH3 2-methylbutane CH3 (2 is redundant)

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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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CH3CH2OH ethanol

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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

125

Stereoisomerism Stereoisomerism: Isomers having the same

molecular formula and the same atom-to-atom bonding, but the atoms differ in their arrangement in space.

126

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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trans- 1,2-dichloroethene.

CCClH

HCl

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trans- 1,2-dichloroethene.

cis- 1,2-dichloroethene.

CCClH

HCl

CCHH

ClCl

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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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cis isomer trans isomer common name: cisplatin

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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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The simplest case is a tetrahedral carbon bonded to four different groups.

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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.

152

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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Examples: polyethylene and polystyrene

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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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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

166

Synthetic Polymers Two principal reaction types: Addition and

condensation.

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condensation.

Addition Polymers: Made by monomer units directly joining together.

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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 polymerization reaction is initiated using an organic peroxide.

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Addition Polymers



R O O R R O. + .O R

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Addition Polymers



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

177

Etcetera:

where n would typically range from 1000 to 50,000.

CCHH

HH

n)(

178

Different experimental conditions give different polymers.

CHRCH 22 2CH _

2CH _ C _ _CH _2

H

H

179


CHRCH 22 2CH _

2CH _ C _ _CH _2

H

H

180


+

CHRCH 22 2CH _

2CH _ C _ _CH _2

H

HCH _

2CH _2CH _

2CH

2CHR

H

_CH _2

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+ 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

183


2CH _2CH _ CH _ _CH _

2H

R RO

HC _ _CH _

22CH _2CH _

184


2CH _2CH _ CH _ _CH _

2H

R RO

HC _ _CH _

22CH _2CH _

CCHH

HH

185


2CH _2CH _ CH _ _CH _

2H

R RO

HC _ _CH _

22CH _2CH _

CCHH

HH

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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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The long linear chain version is called high density polyethylene (HDPE) (d = 0.97 g/ml).

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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.

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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

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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

Now consider another terephthalic acid molecule reacting with the indicated alcohol functional group.

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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.

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Alkyne combustion reaction: 2 C 2 H 2 + 5 O 2 4 CO 2 + 2 H 2 O

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