Organic Reactions

Mr. Montjoy, guest lecturer

3 Basic Kinds of Organic Reactions

Addition Reactions

1. Hydrogenation• Saturating an unsaturated carbon

chain• Alkene/yne to alkane/ene

2. Hydration• Alkene to alcohol

3. Halogenation/Hydrohalogenation• Alkane to haloalkane• Alkene to haloalkane

3 Basic Kinds of Organic Reactions

Elimination Reactions

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

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

• SN1

• SN2

Electrophiles & NucleophilesThe basic process of organic reactions occurs through attraction of positively and negatively charged parts of molecules

Positively and Negatively Charged Parts of Organic Molecules

Electrophiles Nucleophiles

• “loves electrons” – attracted to negative charge

• “loves nuclei” – attracted to positive charge

• may be positively charged or have deficit or electrons because 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

Organic chemistry has special names for positively and negatively chargedParts of a molecule

Positively and Negatively Charged Parts of Organic Molecules

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

• in reaction mechanisms, generally electrons from nucleophile move to electrophile

Alkanes are relatively inert compared to other functional groups

• Alkenes have pi bonds in which electrons are easily accessible because they aren’t trapped between two nuclei as sigma bonding electrons are.

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

Characteristic reactions for several functional groups reactions to recognize in bold, products indicated in ()

Functional Group Addition Elimination Substitution

Alkane Halogenation (haloalkanes)

Alkene • Hydrohalogenation (monohaloalkanes)

• Hydration (di-haloalkanes)

• Hydrogenation (alkanes)• Oxidation (-OH, C=O,

COOH)

Alcohol Condensation• w/ COOH (ester)• w/ conc. Acid or

catalist (alkene)

Oxidation (aldehyde, ketone, COOH)

Carboxylic Acid Condensation with –OH (ester)

Amine Condensation w/ COOH (amide)

REACTIONS

Halogenation of an alkane (substitution)

• Alkane + halogen gas haloalkane• Need ultraviolet light for reaction to occur• Depending on time and amount of reactants, more than

one halogen can be added to the alkane

Hydrohalogenation (addition)

• Alkene + acid halide monohaloalkane• Halide ion adds to larger side (more substituted side of

alkene)• Hydrohalogenation of ethene

• Hydrohalogenation of propene: notice that the chlorine adds to the larger side of the alkene

Hydration (addition)

• Alkene + water in acidic solution alcohol• Acid acts as catalyst in reaction• -OH group adds to larger side (more substituted side) of

alkene• Uses: hydration is used for commercial manufacture of

ethanol• Hydration of ethene

• Hydration of propene

Halogenation (addition)

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

sides of the double bond (and opposite sides of the molecule)

• Uses: Chlorine + ethene 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.

Hydrogenation (addition)

• Alkene + hydrogen gas (with catalyst) alkane• Hydrogenation is saturating an unsaturated hydrocarbon• Also called reduction• 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

Esterification (elimination)

• Carboxylic acid + alcohol ester + water• Reaction conditions: acidic solution• The OH group on the alcohol is replaced by the OOC-R

group of the carboxylic acid• Condensation reaction: produces water• Uses: flavoring agents, plasticizers, as solvents in

perfume, polyesters

Amide formation (elimination)

• Carboxylic acid + amine amide + water• Reaction condition: difficult to conduct in simple steps

since amine (a base) and acid basically neutralize each other. To form amide, other reactions that “protect” important function groups are required

• The OH group on the carboxylic acid is replaced by the amine (NH—R)

• Condensation reaction: produces water• Uses: peptide bond formation, polymerization reactions

to make nylons

video

Condensation of alcohol (elimination)

• Condensation of alcohol alkene• Reaction conditions:

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

• Al2O3 and a catalyst

• Condensation reaction: produces water

Polymerization

• Polyethylene• Reaction: n CH2=CH2 (-CH2-CH2-)n

• Three kinds of polyethylene• HDPE = gallon milk cartons (more rigid)• LDPE = plastic bags, squeeze bottles (more

flexible)• cPE = milk crates (very strong and rigid)

Polymerization occurs when a molecule has two functional groups

• Polymers formed are copolymers because they are made of two different monomers

• Polymers are formed in a step-growth method rather than a chain-growth method• In other words, molecules with 2 functional groups

can grow from both ends instead of just one end as in polyethylene

• Formation of a

nylon (a poly-

amide)

Formation of a polypeptide

• Polypeptide is a chain of amino acids, each amino acid has one carboxylic acid and one amine group

• Note that the polymerization here occurs because there are two different groups on the same molecule

• Polypeptides are not, technically, polymers since they don’t have repeating units (R group is different)

• Peptide bond between alanine and cysteine:

Summary

Functional Group Addition Elimination Substitution

Alkane Halogenation (haloalkanes)

Alkene • Hydrohalogenation (monohaloalkanes)

• Hydration (di-haloalkanes)

• Hydrogenation (alkanes)• Oxidation (-OH, C=O,

COOH)

Alcohol Condensation• w/ COOH (ester)• w/ conc. Acid or

catalist (alkene)

Oxidation (aldehyde, ketone, COOH)

Carboxylic Acid Condensation with –OH (ester)

Amine Condensation w/ COOH (amide)