Organic Reactions

Point #13 basic kinds of reactions

A) Addition Reactions (like synthesis reactions)• Hydrogenation

– saturating an unsaturated carbon chain– alkene/yne to alkane

• Hydration– alkene to alcohol

• Halogenation/Hydrohalogenation– alkane to haloalkane– alkene to haloalkane

B) Elimination Reactions (like synthesis reactions because they result in larger compounds)

• Condensation– Esterification– Formation of alkene– Formation of amide (peptide bond)

C) Substitution Reactions (like single or double replacement reactions where one atom/ion/functional group is replaced by another)

• SN1

• SN2

Point #2 Basic process of organic reactions is through attraction of

positively (electrophile) and negatively (nucleophile) charged parts of

molecules

Electrophiles Nucleophiles “loves electrons” =

attracted to negative charge

“loves nuclei” = attracted to positive charge

maybe positively charged or have deficit of electrons b/c atom is attached to very electronegative atom

often negatively charged or

lone pairs high electronegativity

carbon of carbonyl group acids

alkenes Hydroxide –OH Chloride –Cl Ammonia – NH3

– many organic reactions happen through the attraction of electrophiles for nucleophiles

– in reaction mechanisms, curly arrows show how electrons move – generally electrons from nucleophile move to electrophile

Point #3 Alkanes/Alkenes are relatively inert compared to other functional

groups A) Alkenes have pi bonds in which electrons are

easily accessible b/c they aren’t trapped between two nuclei as sigma bonding electrons are.

B) Other functional groups have highly electronegative atoms like O, N or halogens

The table below gives the characteristic reactions for several functional groups

Functional Group

Addition Elimination Substitution

Alkane Halogenation (haloalkanes)

Alkene Hydrohalogenation (mono-haloalkanes,)

Hydration (alcohols)

Halogenation (di-haloalkanes)

Hydrogenation (alkanes)

Oxidation (-OH, C=O, COOH)

Alcohol Condensation w/ COOH to (ester)w/ conc. acid or catalyst (alkene)

Oxidation (aldehyde, ketone, COOH)

Carboxylic Acid Condensation with –OH (ester)

Amine Condensation w/ COOH (amide)

ReactionsExample #1-Halogenation of alkane

– Alkane + halogen gas haloalkane– Need ultraviolet light for rxn to occur– Depending on time and amount of reactants,

more than one halogen can added to the alkane

H

H

H

H+ Cl Cl

hCl

HH

HClCl

H

HClCl

H

Cl

ClCl

Cl

Clchloromethane dichloromethane chloroform tetrachloromethanemethane

also: trichloromethane also: carbontetrachloride

h h h

• Free radical is a element or molecule with an unpaired electron

• Homolytic fission vs Heterolytic fission:

– Fission means splitting apart

– Heterolytic means that one atom takes both electrons in the bond and two ions are formed.

– Homolytic means the bond is split in half – each side takes 1 electron and 2 free radicals are formed

-Reaction occurs through homolytic fission to form a free radical

Formation of free radicals often results in chain reactions –

reaction keeps occurring until all reactant is used up. See

polymerization notes form mechanism.

Example #2-Hydrohalogenation

– Alkene + acid halide monohaloalkane

– Halide ion adds to larger side (more substituted side of alkene) if there is one

H

H H

H

+HH

H

HH

ClH Cl

Hydrohalogenation of ethene

Hydrohalogenation of 1-propene

H

H CH3

H

+CH3

H

H

HH

ClH Cl

H Cl+ C+

CH3H

H

H H

+ Cl-

CH3

Cl

H

H

H H

CH3H

H H

Example #3-Hydration

– Alkene + water in acidic solution alcohol

– Acid acts as catalyst in rxn– –OH group adds to larger

side (more substituted side) of alkene

– Uses: hydration is used for commercial manufacture of ethanol

Hydration of etheneH

H H

H

+ OHH

a c idO

H

H

H H

H

H

Hydration of 1-propeneH

H CH3

H

+ OHH

a c id

CH3

O

H

HH

H

H

Example #4 -Halogenation

– Alkene + halogen gas 1,2-dihaloalkane– Diatomic gas has two atoms – both add to opposite sides

of the double bond (and opposite sides of the molecule)– Uses: Chlorine + ethane 1,2-dichloroethane: used as

starting material for PVC– Uses: Br2 dissolved in dichloromethane is used to

distinguish between alkenes and alkanes. If reddish-brown color of Br2 disappears when added to unknown, the unknown has alkenes in it.H

H H

H

+HH

Cl

HH

ClCl Cl

Example #5 Hydrogenation

– Alkene + Hydrogen gas (with catalyst) alkane– Hydrogenation is saturating an unsaturated hydrocarbon – Addition Reaction– Heterogeneous Catalyst: Pd or PtO2 (rxn occurs on a metal

surface)– Uses: unsaturated vegetable oils are saturated to produce

saturated fats (more solid at room temp than unsaturated) for margarines

H

H H

H

+HH

H

HH

HH H

P tO 2 /P d

Example #6 Esterification– Carboxylic acid + alcohol ester + water– Reaction conditions: acidic solution– The OH group on the carboxylic acid is replaced by the alcohols

O-R group– Condensation reaction: produces water– Uses: flavouring agents, plasticizers, as solvents in perfume,

polyesters

OH

O+ OH

O

Oac id

acetic acid propan-1-ol ethyl acetate

OH

O

OH O

O

propionic acid

propan-1-olpropyl propionate

+a c id

+

+

OH2

OH2

Examples #7 Amide formation

– Carboxylic acid + amine amide + water – Reaction condition: difficult to conduct in simple steps– The OH group on the carboxylic acid is replaced by the amine (NH-R)– Condensation rxn: produces water– Uses: peptide bond formation, polymerization reactions to make

nylons

H3C OH

ONH2 CH3+

O

H3C NHCH3acetic acid methanamine

N-methylacetamidealso: ethanoic acid

OH

ONHCH3

CH3+

O

NCH3

CH3

N-methylmethanaminebutyric acid

N,N-dimethylbutanamidealso: butanoic acid

Example #8 Oxidation of alcohol

– Alcohol + oxidizing agent COOH (1, complete) /Aldehyde (1, partial)/Ketone (2)

– Obviously an Oxidation reaction

– Reaction condition: aqueous, acidic solution. The carboxylic acid and the aldehyde can be obtained through different experimental set-ups

• Distill to get aldehyde• Heat under reflux to get COOH

Oxidation of alcohol (continued)

– Complete Oxidation: primary alcohol + oxidizing agent carboxylic acid

+OHa c id

K 2C r 2O 7

O

OHpropan-1-olpropanoic acid

Oxidation of alcohol (continued)

• Partial Oxidation: primary alcohol + oxidizing agent aldehyde

+OHa c id

K 2C r 2O 7

O

Hpropan-1-ol1-propanal

Oxidation of alcohol (continued)

• Secondary alcohol + oxidizing agent ketone

+OHa c id

K 2C r 2O 7

O

butan-2-ol butan-2-one

Example #9 Condensation of alcohol

– Condensation of alcohol alkene– Reaction conditions:

• 170 and concentrated sulfuric acid or• H3PO4 and a catalyst or Al2O3 and a catalyst

H3C

CH

H3C

OHC

C

H3C

OH

H

HHH

HO

H

CH2

CHH3C