Transcript Organic Reactions

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 & Nucleophiles
The basic process of organic reactions occurs
through attraction of positively and negatively
charged parts of molecules
Positively and Negatively Charged Parts of
Organic Molecules
Organic chemistry has special names for positively and negatively charged
Parts of a molecule
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
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•
•
•
alkenes
hydroxide –OH
chloride –Cl
ammonia – NH3
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
Alkane
Alkene
Substitution
Halogenation
(haloalkanes)
•
•
•
•
Hydrohalogenation
(monohaloalkanes)
Hydration (dihaloalkanes)
Hydrogenation (alkanes)
Oxidation (-OH, C=O,
COOH)
Alcohol
Condensation
• w/ COOH (ester)
• w/ conc. Acid or
catalist (alkene)
Carboxylic Acid
Condensation with –
OH (ester)
Amine
Condensation w/
COOH (amide)
Oxidation (aldehyde,
ketone, COOH)
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 reddishbrown 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 polyamide)
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
Alkane
Alkene
Substitution
Halogenation
(haloalkanes)
•
•
•
•
Hydrohalogenation
(monohaloalkanes)
Hydration (dihaloalkanes)
Hydrogenation (alkanes)
Oxidation (-OH, C=O,
COOH)
Alcohol
Condensation
• w/ COOH (ester)
• w/ conc. Acid or
catalist (alkene)
Carboxylic Acid
Condensation with –
OH (ester)
Amine
Condensation w/
COOH (amide)
Oxidation (aldehyde,
ketone, COOH)