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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)
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)