5 Organic Reactions to 5 Organic Reactions to discuss….discuss….

•Addition ReactionsAddition Reactions

•Oxidation/Reduction ReactionsOxidation/Reduction Reactions

•Substitution ReactionsSubstitution Reactions

•Esterification ReactionsEsterification Reactions

•Polymerization ReactionsPolymerization Reactions

• There are thousands of other organic reactions we There are thousands of other organic reactions we will not cover!will not cover!

1. Addition Reactions1. Addition Reactions• Must involve a double or triple bond – an alkene or alkyne!Must involve a double or triple bond – an alkene or alkyne!• As the name suggests, it involves As the name suggests, it involves addingadding a compound to the double bond a compound to the double bond

• Sometimes a catalyst is used to speed up the reaction – this will be written Sometimes a catalyst is used to speed up the reaction – this will be written over the arrow! over the arrow!

X-Y

H

C C CC

H

H H

+

H H

HH

X Y

What is the mechanism of What is the mechanism of these reactions?these reactions?

• A A mechanismmechanism visually shows the visually shows the steps that the molecules follow in steps that the molecules follow in order to complete the reaction…order to complete the reaction…

• Let’s look at a sample addition Let’s look at a sample addition reaction…..reaction…..

• This reaction is what we call This reaction is what we call stepwisestepwise – it occurs in steps!– it occurs in steps!

• H-Cl breaks into HH-Cl breaks into H+1+1 and Cl and Cl-1-1 in in solutionsolution

• It is an ionic compound with hydrogen It is an ionic compound with hydrogen acting as the metalacting as the metal

• The HThe H+1+1 attacks the double bond… attacks the double bond…• Why…..?Why…..?

H-Cl

H

C C C

Cl HC

H H

+

H

HH

H H

• The double bond is a great source of The double bond is a great source of electrons!electrons!

• Opposites attract!Opposites attract!• This causes the electrons in the This causes the electrons in the

double bond to drop out and bond double bond to drop out and bond with the hydrogen!with the hydrogen!

• This leaves the other C positive – This leaves the other C positive – why….?why….?

H

C C

H HH+1

Cl-1

H H

C C

H H

+

H

Cl-1

H

H+1

H

C C

H H

Cl-1

H 11

•This carbon is missing a bond!This carbon is missing a bond!

•The formal charge on the carbon on the right The formal charge on the carbon on the right is a +1is a +1

•This highly unstable atom is known as a This highly unstable atom is known as a carbocationcarbocation

•This atom will react immediatelyThis atom will react immediately

•Anything Anything negativenegative will attack it – in this case, will attack it – in this case, the chlorine!the chlorine!

•The new electrons for the bond come from The new electrons for the bond come from the chlorine atomthe chlorine atom

H

C C

H HH Cl

H

11

:..

..:

H

C C

H HH

Cl-1

H+

:..

..:

H

C C

H HH

Cl-1

H+

• All addition reactions occur this way…All addition reactions occur this way…• Something positive (called the electrophile) attacks the double bond….Something positive (called the electrophile) attacks the double bond….• A carbocation is formed…A carbocation is formed…• Something negative attacks the carbocation…Something negative attacks the carbocation…• The positive atom or molecule is called the electrophile because it is The positive atom or molecule is called the electrophile because it is

electron loving, or seeking! Opposites attract!electron loving, or seeking! Opposites attract!

H+1

H

C C

H H

Cl-1

H

H

C C

H HH+1

Cl-1

H

H

C C

H H

+

H

Cl-1

HH

C C

H H

+

H

Cl-1

H

H

C C

H HH Cl

H

• We can add a number of substances to double or triple bonds…We can add a number of substances to double or triple bonds…• Halogens – ClHalogens – Cl22, Br, Br22, I, I22, F, F22 can be added with a uv light catalyst… can be added with a uv light catalyst…• The mechanism follows the same pattern….The mechanism follows the same pattern….

– attack of the double bond by something positiveattack of the double bond by something positive– Formation of a carbocationFormation of a carbocation– Attack of the carbocation by something negativeAttack of the carbocation by something negative– Uv light acts as a catalyst to form two chlorine ions – one positive, one negativeUv light acts as a catalyst to form two chlorine ions – one positive, one negative

Cl-Cl

H

C C

H H

+

uvH

H

C C

H H

Cl+1 Cl-1

H

H

C C

H H

H

C C

H H

+

Cl

Cl-1Cl+1 Cl-1

H H

• Eventually, both halogens add to the Eventually, both halogens add to the double bond…double bond…

• This serves to This serves to increase increase the boiling point of the boiling point of the compound….the compound….

• Why…?Why…?• This is useful for solidifying This is useful for solidifying

hydrocarbons…hydrocarbons…• PVC is made this way…PVC is made this way…

H

C C

H HCl Cl

H

Addition of bromine….Addition of bromine….

• Alcohols can be made from water Alcohols can be made from water and an alkene or alkyne!and an alkene or alkyne!

H+1H

C C

H H

+ HOH

H H+1H

C C

H H

+ HOH

H

• Water can be forced to break into HWater can be forced to break into H+1+1 and OH and OH-1-1 by the by the double bond….double bond….

• The HThe H+1+1 attacks first… attacks first…• The carbocation forms, and the OHThe carbocation forms, and the OH-1-1 attacks the attacks the

carbocation…carbocation…• The overall effect is to create an alcohol!The overall effect is to create an alcohol!

H+1

H

C C

H H

OH-1

HOH

H

H+1 OH-1

H

C C

H H

H

C C

HH

H OH

H H

+

Catalytic Hydrogenation…Catalytic Hydrogenation…• The addition of hydrogen using a catalyst..The addition of hydrogen using a catalyst..• This breaks the double bond, adding two This breaks the double bond, adding two

hydrogens…hydrogens…• This has the effect of raising the boiling point..This has the effect of raising the boiling point..• This is how margarine and other fats are created This is how margarine and other fats are created

from vegetable oil…from vegetable oil…

H

C C

H H

Pt

+ H-H

H H

C C

H H

Pt

+ H-H

H

• The platinum atom holds the HThe platinum atom holds the H22 into place into place • The hydrogens then split and attack the double bond in a The hydrogens then split and attack the double bond in a

similar manner as the other addition reactionssimilar manner as the other addition reactions• Oils and fats have Oils and fats have many many double and triple bondsdouble and triple bonds• SomeSome of these are broken, which is called partially of these are broken, which is called partially

hydrogenatedhydrogenated• This has the effect of raising the boiling point slightly, This has the effect of raising the boiling point slightly,

changing the substance from a liquid to a thicker liquid or changing the substance from a liquid to a thicker liquid or even a solideven a solid

• The physical state is based on the amount of hydrogenationThe physical state is based on the amount of hydrogenation

H

C C

H H

Pt

H-H

H

H+1

H

C C

H HH-1

H

C C

HH

H H

HH

++

•Partial hydrogenation involves breaking some of these double or triple bonds

•This changes the texture of the fat, and creates trans-fatty acids

•These fats are unhealthy!

Alkynes can undergo Alkynes can undergo addition…addition…

H-HH C C H +

H

C C

H H

H

H

C C

H H

HH-H+ C C

H

H

HH

H

H

In summary – an addition reaction In summary – an addition reaction eliminates eliminates double or double or triple bonds, and triple bonds, and addsadds compounds or elements! compounds or elements!

PtPt

PtPt

Does it Does it mattermatter what carbon the what carbon the positive atom attacks…?positive atom attacks…?

• The molecule in all previous The molecule in all previous examples, ethene, is examples, ethene, is symmetrical!symmetrical!

• It doesn’t matter, because both It doesn’t matter, because both carbons are carbons are identical!identical!

• A Russian scientist named A Russian scientist named Markovnikov found that with other Markovnikov found that with other alkenes and alkynes that are alkenes and alkynes that are notnot symmetrical, it does matter!symmetrical, it does matter!

• An addition reaction will occur…An addition reaction will occur…• Will the HWill the H+1+1 attack carbon 1 or carbon attack carbon 1 or carbon

2?2?• It matters…It matters…• Markovnikov’s Rule states that the Markovnikov’s Rule states that the

carbocation will form on the carbocation will form on the more more substitutedsubstituted carbon… carbon…

• What does that mean…?What does that mean…?• Let’s look at the two possible Let’s look at the two possible

carbocations that can form!carbocations that can form!

CH2CH CH2 CH2 CH3CH2 H-I+C H

2CH CH2 CH2 CH3CH2 H-I+

•Which will form….?Which will form….?

•The one that can be most stabilized will form!The one that can be most stabilized will form!

•Carbocations are Carbocations are unstableunstable and must be stabilized by…. and must be stabilized by….

•Electrons!Electrons!

•Nearby C-H bonds that have electrons in them will flow over to Nearby C-H bonds that have electrons in them will flow over to stabilize the carbocation..stabilize the carbocation..

•This is called This is called hyperconjugation!hyperconjugation!

CH2CH CH2 CH2 CH3CH2

H

I-1

+

CH2CH CH2 CH2 CH3CH2

H

I-1

+

CH2CH CH2 CH2 CH3CH2

H

I-1

+CH2CH CH2 CH2 CH3CH2

H

I-1

+

CH2C C CH2 CH3C

H+

I-1

H

H

H

H

H

Less hyperconjugation Less hyperconjugation for stability…for stability…

More More hyperconjugation for hyperconjugation for stability…stability…

CH2CH C CH2 CH3C

H

I-1

H

H

H

H+

C H

2CH C CH2 CH3C

H

I-1

H

H

H

H+

The carbocation (positive carbon) will form on the The carbocation (positive carbon) will form on the atom that has more attached carbons, and atom that has more attached carbons, and therefore more hyperconjugation for stability…therefore more hyperconjugation for stability…This is called This is called Markovnikov’s Rule….Markovnikov’s Rule….

The negative ion then attacks the carbocation…The negative ion then attacks the carbocation…

minorminor

CH2CH C CH2 CH3C

H

I-1

H

H

H

H+

C H

2CH C CH2 CH3C

H

I-1

H

H

H

H+ CH2CH C CH2 CH3C

H

H

H

H

HI

CH2CH C CH2 CH3C

H

H

H

H

HI

How about this reaction….?How about this reaction….?

Would you expect this….Why….?Would you expect this….Why….?

CH CH2

CH3

C

CH3

CH3 H-Cl+C H C H

2

CH3

C

CH3

CH3 H-Cl+

CH CH2

CH3

C

CH3

CH3

HCl

CH CH2

CH3

C

CH3

CH3

HCl

This forms instead! Why…..?This forms instead! Why…..?

The entire molecule rearranges to form a The entire molecule rearranges to form a more stable carbocation! This is called more stable carbocation! This is called rearrangement of the carbocation….rearrangement of the carbocation….

CH CH2

CH3

C

CH3

CH3

HCl

CH CH2

CH3

C

CH3

CH3

HCl

CH CH2

CH3

C

CH3

CH3

H

Cl-1

CH CH2

CH3

C

CH3

CH3

H

Cl-1

+

+CH CH2

CH3

C

CH3

CH3

H

Cl-1

CH CH2

CH3

C

CH3

CH3

H

Cl-1

+

+

The chlorine then attaches at The chlorine then attaches at carbon 2, not carbon 3!carbon 2, not carbon 3!

CH2 CH2

CH3

C

CH3

CH3

H

Cl-1

+CH2 CH2

CH3

C

CH3

CH3

H+

Cl-1

CH2 CH2

CH3

C

CH3

CH3

HCl

2. Oxidation/Reduction Reactions2. Oxidation/Reduction Reactions•Oxidation, by definition, can mean three things:Oxidation, by definition, can mean three things:

•Gaining oxygenGaining oxygen

•Losing hydrogen (dehydrogenation) and adding Losing hydrogen (dehydrogenation) and adding double or triple bondsdouble or triple bonds

•Losing electronsLosing electrons

•Reduction, by definition, can mean three things:Reduction, by definition, can mean three things:

•Losing oxygenLosing oxygen

•Gaining hydrogen (hydrogenation – as in the Gaining hydrogen (hydrogenation – as in the addition reaction mentioned before!) and removing addition reaction mentioned before!) and removing double or triple bondsdouble or triple bonds

•Gaining electronsGaining electrons

H-HH C C H +

H

C C

H H

H

H

C C

H H

HH-H+ C C

H

H

HH

H

H

Yes, this is an addition reaction – it Yes, this is an addition reaction – it is also a is also a reductionreduction reaction, because reaction, because it involves it involves addingadding hydrogens, and hydrogens, and removing double and triple removing double and triple bonds….hydrogenation…bonds….hydrogenation…

H-H

H C C H

+

H

C C

H H

H

H

C C

H H

HH-H+

C C

H

H

HH

H

H

K2Cr2O7

K2Cr2O7

Yes, this is the reverse of an Yes, this is the reverse of an addition reaction – it is an addition reaction – it is an oxidationoxidation reaction, because it reaction, because it involves involves removingremoving hydrogens, and adding hydrogens, and adding double and triple bonds…double and triple bonds…dehydrogenation….dehydrogenation….

Notice the Notice the chemical written chemical written over the arrow – over the arrow – this is known as this is known as a a catalyst…catalyst…

PtPt

PtPt

• Oxidation reactions require a catalyst….Oxidation reactions require a catalyst….• Look for common catalysts in oxidation reactions:Look for common catalysts in oxidation reactions:

– KK22CrCr22OO77

– HH22SOSO44

– KMnOKMnO44

• Hydrocarbons follow a Hydrocarbons follow a predictable predictable pattern when oxidized…pattern when oxidized…• An alcohol is produced – then an aldehyde – then a carboxylic An alcohol is produced – then an aldehyde – then a carboxylic

acid – and eventually water and carbon dioxideacid – and eventually water and carbon dioxide

H2O

CH

H

H

H

K2Cr2O7

CH

OH

H

H

K2Cr2O7

CH

O

H

K2Cr2O7

CH

O

H CH

O

OHK2Cr2O7

C OO

• A substitution reaction involves one molecule A substitution reaction involves one molecule or atom or atom substitutingsubstituting another in a another in a hydrocarbon!hydrocarbon!

• It has the general form:It has the general form:

3.3. Substitution reactions….Substitution reactions….

C

H

Nu-1

H

H Y+ C

H

Nu

H

HY-1 +

• NuNu-1-1 is called a is called a nucleophilenucleophile…. It means nucleus …. It means nucleus loving, or seeking! They like positive charge… loving, or seeking! They like positive charge… because they are negative!because they are negative!

• Carbon atoms have a tetrahedral Carbon atoms have a tetrahedral shape around them…shape around them…

• This is crucial in determining the type This is crucial in determining the type of substitution reaction you will of substitution reaction you will have…have…

• Two types:Two types:– SN1 substitutionSN1 substitution– SN2 substitutionSN2 substitution

• Let’s look at SN2 substitution first…Let’s look at SN2 substitution first…

•What motivates the leaving group to What motivates the leaving group to actually actually leave….?leave….?

•The incoming nucleophile!The incoming nucleophile!

•The carbon, if it is going to bond to The carbon, if it is going to bond to something new, has to eject something…something new, has to eject something…

•That something is called the That something is called the leaving group!leaving group!

•What type of atoms would leave?What type of atoms would leave?

•Ones that are highly electronegative, and Ones that are highly electronegative, and would want to leave, pulling electrons off would want to leave, pulling electrons off with it!with it!

•In this case, the chlorine!In this case, the chlorine!

•Why is the nucleophile attacking from the Why is the nucleophile attacking from the backback..?..?

•The chlorine is in the way in the front!The chlorine is in the way in the front!The nucleophile can’t attack from the front!The nucleophile can’t attack from the front!

C

HOH-1:

H

HCl

SN2 substitution….SN2 substitution….

C

H

OH-1:

H

HCl

•The leaving group takes the electrons with The leaving group takes the electrons with it…it…

•The incoming group The incoming group repelsrepels the electrons the electrons that are being shared with the hydrogens on that are being shared with the hydrogens on the carbon – the carbon –

•Like charges repel!Like charges repel!

•This causes the atoms to This causes the atoms to reverse reverse direction, direction, or invert shape!or invert shape!

•This is called This is called inversion of configuration….inversion of configuration….

•This whole process happens all at once, This whole process happens all at once, because the only thing that would promote because the only thing that would promote the Cl leaving would be something coming the Cl leaving would be something coming in from the other side to bond with the in from the other side to bond with the carbon!carbon!

•This is called a This is called a concertedconcerted reaction – reaction – meaning, all at once!meaning, all at once!

C

HOH-1:

H

HCl

C

HOH-1:

H

HCl

C

H

OH

H

H Cl-1+

C

HOH-1:

H

HCl

•This reaction also occurs with This reaction also occurs with backside attack, backside attack, meaning that the meaning that the nucleophile attacks from the backside nucleophile attacks from the backside of the molecule!of the molecule!

•It is called SN2 because two It is called SN2 because two molecules must collide to promote the molecules must collide to promote the reaction!reaction!

•In summary, SN2 reactions occur:In summary, SN2 reactions occur:

•Backside attackBackside attack

•ConcertedConcerted

•Inversion of configurationInversion of configuration

SN1 substitution…SN1 substitution…• This occurs when backside attack is not possible…This occurs when backside attack is not possible…• Why would backside attack not be possible…?Why would backside attack not be possible…?• Too many carbons in the way!Too many carbons in the way!• This only occurs when you have a tertiaryThis only occurs when you have a tertiary carbon – a carbon carbon – a carbon

that is attached to three other carbons! ONLY THREE that is attached to three other carbons! ONLY THREE CARBONS CAN EFFECTIVELY BLOCK BACKSIDE ATTACK – CARBONS CAN EFFECTIVELY BLOCK BACKSIDE ATTACK – BACKSIDE ATTACK CAN OCCUR WITH ONE OR TWO BACKSIDE ATTACK CAN OCCUR WITH ONE OR TWO CARBONS ATTACHED!CARBONS ATTACHED!

• Backside attack is still possible with a secondary carbon – Backside attack is still possible with a secondary carbon – meaning, a carbon with two other carbon groups attached to it!meaning, a carbon with two other carbon groups attached to it!

C

CH3OH-1:

ClCH3

CH3

Tertiary carbonTertiary carbon

Not possible!Not possible!

SN1 substitution…SN1 substitution…• So could frontside attack take place…?So could frontside attack take place…?• NO!NO!• There is a chlorine in the front in the way!There is a chlorine in the front in the way!• So we have to remove the chlorine…So we have to remove the chlorine…

C

CH3OH-1:

ClCH3

CH3Must use Must use something to something to remove the remove the chlorine….chlorine….

SN1 substitution…SN1 substitution…• Normally, a Normally, a solventsolvent is is

used to remove the used to remove the chlorine…chlorine…

• AgAg+1+1 works well to pull off works well to pull off the chlorine…the chlorine…

• The molecule now has a The molecule now has a trigonal planar trigonal planar geometry geometry around it, allowing the OHaround it, allowing the OH--

11 to attack from either side…!

• However, a carbocation However, a carbocation forms….!forms….!

• But aren’t carbocations But aren’t carbocations UNSTABLE…?UNSTABLE…?

C

CH3OH-1:

ClCH3

CH3

Ag+1

C

CH3OH-1:

Cl-1CH3

CH3

Ag+1++

C

CH3

OH-1:

Cl-1

CH3 CH3

Ag+1

++ OH-1:

•There are nearby carbon-There are nearby carbon-hydrogen bonds to stabilize hydrogen bonds to stabilize the carbon…!the carbon…!

•This is why the carbocation This is why the carbocation can form…can form…

•What would have happened if What would have happened if we had a primary (meaning no we had a primary (meaning no or one carbon attached) or one carbon attached) carbon?carbon?

•There is no stabilization!There is no stabilization!

•The molecule would go back The molecule would go back to square one…to square one…

•No reaction….No reaction….No stabilization! No stabilization!

C

CH3

Cl-1CH3 CH3Ag+1

++ OH-1OH-1

C

H

++

H

H

Cl-1 Ag+1

•This is why primary carbons won’t occur frontside This is why primary carbons won’t occur frontside attack…attack…

•The solvent would pull off the leaving group, but there The solvent would pull off the leaving group, but there wouldn’t be enough nearby carbons to stabilize the wouldn’t be enough nearby carbons to stabilize the carbocation…carbocation…

•Only secondary (2 carbons attached to the Only secondary (2 carbons attached to the carbocation) or tertiary carbons can occur SN1….carbocation) or tertiary carbons can occur SN1….

•And you HAVE TO HAVE A SOLVENT TO PULL And you HAVE TO HAVE A SOLVENT TO PULL OF THE LEAVING GROUP!OF THE LEAVING GROUP!

C

CH3

OH-1:

Cl-1

CH3 CH3

Ag+1

++ OH-1:

C

CH3

OH

Cl-1

CH3

CH3

Ag+1

CCH3

CH3

CH3

OH

•Both products are formed in an SN1 substitution…Both products are formed in an SN1 substitution…

•Both frontside and backside attack can take place…Both frontside and backside attack can take place…

•This can either invert the shape (if backside occurs) or This can either invert the shape (if backside occurs) or retain the shape (if frontside occurs)retain the shape (if frontside occurs)

•The reaction occurs in steps, or The reaction occurs in steps, or stepwise,stepwise,where SN2 where SN2 occurs occurs all at once, all at once, or concertedor concerted

•Both products are produced 50-50!Both products are produced 50-50!

This reaction is called This reaction is called SN1 because the speed of SN1 because the speed of the reaction is dependent the reaction is dependent on only on only oneone step! step!

SN1 versus SN2 substitution…SN1 versus SN2 substitution…

http://www.colby.edu/chemistry/OChem/http://www.colby.edu/chemistry/OChem/DEMOS/Substitution.htmlDEMOS/Substitution.html

SN1 Substitution:SN1 Substitution:

•Must have a solvent to pull Must have a solvent to pull off leaving groupoff leaving group

•Must have a secondary or Must have a secondary or tertiary carbon to stabilize tertiary carbon to stabilize the carbocationthe carbocation

•Can occur frontside or Can occur frontside or backside attackbackside attack

•Can retain or invert Can retain or invert configurationconfiguration

•Occurs stepwiseOccurs stepwise

SN2 Substitution:SN2 Substitution:

•Occurs with primary or Occurs with primary or secondary carbonssecondary carbons

•Only occurs backside Only occurs backside attackattack

•Always inverts Always inverts configurationconfiguration

•Always occurs concertedlyAlways occurs concertedly

SN1 versus SN2 substitution…SN1 versus SN2 substitution…

http://www.colby.edu/chemistry/OChem/http://www.colby.edu/chemistry/OChem/DEMOS/Substitution.htmlDEMOS/Substitution.html