Download Alkenes undergo Addition Reactions Predict the product of each

Alkenes undergo Addition Reactions
Predict the product of each reaction:
Alkene Addition Reactions Make Different Functional Groups
Polar Additions:
alkene + HX --> alkyl halide
alkene + HOH ---> alcohol
Propylene
Identify functional group.
What reaction type occurs with this functional group?
At what atom(s) does this reaction type occur?
What reagent is needed for this reaction type to occur?
Isopropanol
Rubbing alcohol
Addition Reaction of HX or HOH is the REVERSE of an
Elimination Reaction
(Use this in Organic Synthesis!)
E
Progress of reaction
Which reaction requires high T? Why?
Alkene Addition of HX or HOH is a Polar Mechanism
Alkene = π bond = Nu:- reacts with E+ to form a ______
intermediate.
HX addition: E+ = H in HX
HOH addition: E+ = H in H2SO4 (H2SO4 is an acid catalyst)
The Stability of the _______ Intermediate Determines the
Product.
Once a carbocation forms, any Nu:- can react with it.
Cationic Polymerization: Styrene --> Polystyrene (Klein p. 405).
What is A and B?
(Use this reaction to make a larger molecule - lengthen carbon chain)
A Reaction Mechanism Describes How a Product is Produced
Explain how Product 1 is produced. Draw the structure of
Product 2.
Predict the product of each reaction:
Practice problems,
Klein, Ch. 9.60
ID the 2 reactions
that use HBr and
H2SO4.
Alkenes undergo Addition Reactions
Predict the product:
Alkene Addition Reactions Make Different Functional Groups
Polar Additions:
alkene
alkene
alkene
alkene
+ HX --> alkyl halide
+ HOH ---> alcohol
+ X2 ---> dihalide
+ X-OH ---> halohydrin
Identify functional group.
What reaction type occurs with this functional group?
At what atom(s) does this reaction type occur?
What reagent is needed for this reaction type to occur?
Alkene addition of X2, e.g.,Br2, forms a dihalide.
Br2 is non-polar, but at one instant in time, Br is E+
Alkene Addition of X2 is a Polar Mechanism
Alkene addition of X2 and H2O forms a halohydrin.
Why does H2O react and not Br-?
Polar mechanism
Add the alkene addition reactions to your
Organic Reaction Roadmap
Identify the reaction conditions 1 - 6.
Name 3 ways to make ethanol.
Determine the reaction conditions for each reaction:
Choices: a. H2SO4
c. HBr
e. HBr and peroxides
g. BH3/H2O2, OH-
b. H2O
d. NaOMe
f. Br2
h. H2/Pd
Reaction Conditions Determine the Product
Alkyl halide <--------- alkene ----------> Alcohol
Peroxides - radical reaction
E+ = B in BH3
Which conditions produce the Markovnikov product?
Which conditions produce the non-Markovnikov product?
Two (2) Ways to Convert an Alkene to an Alcohol:
1.  H2SO4 (acid catalyzed hydration - Markovnikov)
2. BH3/ H2O2, OH- (hydroboration - anti-Markovnikov)
What is the mechanism?
Which intermediate
is formed?
BH3 = E+
Two (2) Ways to Convert an Alkene to an Alkyl Halide:
1.  HX (hydrohalogenation - Markovnikov)
2. HX/ ROOR (hydrohalogenation - anti-Markovnikov)
What is the mechanism?
Peroxide: ROOR --> 2 RO•
HBr + RO• --> ROH + •Br
•Br + alkene --> alkyl radical
Which intermediate is formed?
+ •Br
See Ch. 11.10
Alkene Addition Forms Different Functional Groups
X-Y adds across C=C double bond
X
Y
Reaction Conditions
Product
H
X
HX (Markovnikov)
HX/ROOR (Non-
Alkyl
halide
Markovnikov)
H
OH
H2SO4 (Markovnikov)
1. BH3 2. H2O2, OH-
Alcohol
(Non-Markovnikov)
X
X
X2
Dihalide
X
OH
X2/H2O
Halohydrin
H
H
H2/Pd, Pt, Ni
Alkane
OH
OH
Peroxyacid/
H3O+
Diol
Very useful in organic synthesis
Convert an Unsaturated fat to a Saturated fat by Hydrogenation
But trans fats are also formed
Also, polyunsaturated fat ---> monounsaturated fat
Why convert an unsaturated fat to a saturated fat?
Alkene --> EPOXIDE --> Diol
Epoxides are important intermediates in organic synthesis
Which one?
Make a smaller compound from a bigger one:
Use OZONOLYSIS
What product(s) are formed?
Ozonolysis cleaves (breaks) C=C bond
to form two C=O bonds
Predict the products:
Which alkene would you use to prepare methyl ethyl ketone?
An Organic Reaction Roadmap is useful in Organic Synthesis
Identify reaction conditions 1-13
Reaction 12 - make smaller molecules (shorten carbon chain)
Reaction 13 - make larger molecules (lengthen carbon chain)
Do a reaction backwards = Synthesis!
Given a target compound (often large) and a starting
material (usually small), figure out how to make it.
Describe a synthesis of ethanol starting from appropriate alkene.
Synthesis Strategy:
Identify functional group in target compound.
How is this functional group prepared?
What reaction type is involved?
At what atom does this reaction type occur?
What reagent is needed for this reaction type to occur?
Synthesis often involves several steps.
Alkenes have π bonds and cis/trans/E/Z isomers
What functional group is used to make a π bond?
How does a π bond react? What functional group is produced?
What is the difference between cis/trans/E/Z?
Alkyl Halides have X, α-C, H bonded to β-C
What is X used for?
What type of reaction occurs at α-C?
What type of reaction occurs at H bonded to β-C?
Alcohols have OH, α-C, H bonded to β-C
What is OH used for?
What type of reaction occurs at α-C?
What type of reaction occurs at H bonded to β-C?
How do you convert an alkene to an alkyl halide to an
alcohol? And then back again?
Synthesis: Given a Product, determine the Reactant
and Reaction Conditions
1. Describe a synthesis of the following compounds starting
from appropriate alkene.
a)  Butane
b)  2-bromo-2-methylbutane
c)  Acetone
2. Starting with isopropanol, describe a synthesis of
propane.
Synthesis often involves moving a pi bond or a functional group,
e.g., X or OH.
Alkene Addition <===> Elimination (RX or ROH)
Steroids, e.g., Cholesterol, are Made From Squalene (precursor)
http://en.wikipedia.org/wiki/Squalene
http://en.wikipedia.org/wiki/Cholesterol
http://themedicalbiochemistrypage.org/cholesterol.html
20-25% of total daily cholesterol production occurs in liver
Squalene is Converted to Lanosterol by Alkene Addition
How is squalene (chain) converted to Lanosterol (rings)?
Squalene Undergoes Alkene Addition, Rearrangements,
and Elimination to form Lanosterol
CEN, 4/4/11, p. 11. Limonene (from lemons) is used to make
many products:
Ethylene and Propylene are used to make many products
petroleum
aromatics
acetylene
ethanol
Acetaldehyde
Solvents
Pharmaceutic
als
Cleaning
compounds
aliphatics
ethylene
polyethylene
Ethylene
oxide
inorganics
butylene
Ethyl
chloride
Plastics
Ethylene
Gasoline
packaging
glycol
additive
pipe
(TEL)
construction
Antifreeze
household
Synthetic fibers
items
films
propylene
polypropy
lene
Plastic
bottles
Solvents
Resins
Drugs
Dry
cleaning
fluids
Antifreeze
Detergents
Hydraulic
fluids
plasticizers
http://cen.acs.org/articles/91/i16/Hydroformylations-Diamond-Jubilee.html
4/22/13, CEN, Hydroformylation s Diamond Jubilee , p. 38
The industrial reaction to convert olefins (alkenes) to aldehydes
A primary use of industrial hydroformylation is the preparation of
butyraldehydes and their downstream products, a sampling of which is
shown.
Word Association: Write the first word or phrase that
comes to your mind when you see the following substance.
Substance
Answer
Example
BH3
Non-Markovnikov alkene addition
to ROH
1
H2SO4
2
H2
3
NaOEt
4
peroxides
5
O3
BH3, H2O2, OH-, HBr
Or HBr, NaOEt
Or HBr, ROOR, NaOEt
1. The growth hormone from the cecropia moth has the structure
shown below. Express the stereochemistry of the double bonds
according to the E-Z system.
This hormone is made from a triene. What is the structure of the
triene? What are the reaction conditions?
2. Write structural formulas for all the alkene products that could
reasonably be formed from the following compound under the
indicated reaction conditions. Where more than one alkene is
produced, specify the one that is the major product.
2,3-dimethyl-2-butanol (phosphoric acid, 120oC)
1. You have available 2,2-dimethylcyclopentanol (A) and 2bromo-1,1-dimethylcyclopentane (B) and wish to prepare 3,3dimethylcyclopentene (C). Which would you choose as the more
suitable reactant, A or B, and with what would you treat it?
2. Write the structure of the major organic product formed in the
reaction of 2-methyl-2-butene with each of the following:
a.  Hydrogen iodide
b. Dilute sulfuric acid
c. Hydrogen bromide in the presence of peroxides
1. Predict the product of each reaction:
2. Suggest a sequence of reactions suitable for preparing the
following compound from the indicated starting material. You
may use any necessary organic or inorganic reagents.
1-bromopropane from 2-bromopropane
3. Klein, Ch. 9 problems
1. Identify the reagents you would use for each transformation.
2. Suggest an efficient
synthesis for the following
transformation:
Organic Reaction Review:
Given reactants and reaction conditions, Predict Product
1.  Draw structure
2.  ID functional group(s) ==> ID reaction types
alkanes: halogenation using light (substitute X for H)
alkenes: addition across C=C bond
alcohols: subsitution and elimination, acid-base
alkyl halides: subsitution and elimination
Many Biologically Active Molecules Are Chiral
E.g., most amino acids are L
Most sugars are D
Enzymes distinguish between two enantiomers of a chiral
substrate
D amino acids tend to taste sweet; L amino acids are usually
tasteless.
Olfactory (smell) receptors contain chiral molecules:
Spearmint leaves contain R-(-)-carvone
Caraway seeds contain S-(+)-carvone
Stereochemistry in Reactions:
Optical Activity Has To Come From Somewhere
Optically inactive starting materials can give optically active
products only if they are treated with an optically active reagent
or if the reaction is catalyzed by an optically active
substance. (Carey, Organic Chemistry , 8th ed., p. 298)
or
1.  How is chirality related to optical activity?
An optically active compound has a chirality center.
2. What is a racemic mixture?
A racemic mixture is a 50:50 mixture of the R and S
enantiomers ==> optically inactive.
3. How would you experimentally determine whether a mixture
is racemic?
Measure optical activity (how much plane polarized light is
rotated) with a polarimeter.
An Achiral (Optically Inactive) Reactant Can Produce a Chiral
Product … but in a Racemic Mixture
Why is the product racemic? See reaction intermediate.
What is the shape at C-2?
On which side does Cl2
react with the radical?
Addition of Br2 to Alkene Produces a Chiral, Racemic Product
Determine the configuration (R/S) at each chirality center.
Explain why the product is racemic.
Does Br2 + trans-2-butene give a racemic product?
Lab: see Br2 addition to trans-cinnamic acid.
C&EN, 10/10/11 Chemoenzymatic Path Yields Chiral Amides
α-Substituted amides are important building blocks in medicinal
chemistry for the synthesis of antibiotics and peptide-based
enzyme inhibitors.
What type of reaction is the 2nd step?
What is the mechanism type?
1. For the following reactions, predict the product(s) and
stereochemistry. Is/are the product(s) optically active?
2. For each reaction, is the product optically active or optically
inactive? Give reasons.
a. 1-pentene + HBr -->
b. 3-methyl-1-pentene + HBr --> optically active product mixture
c. 3-methyl-3-hexanol + HBr ! Is product optically active?
1. Identify the relationship in each of the following pairs. Do the
drawings represent constitutional isomers or stereoisomers, or
they just different ways of drawing the same compound? If they
are stereoisomers, are they enantiomers or diastereomers?
2. Write the organic products of the following reaction. If two
stereoisomers are formed, show both. Label all chirality centers R or
S as appropriate.
1-butene and hydrogen iodide
http://cen.acs.org/articles/91/i13/Elimination-Reaction-Cooks-Chiral-Allenes.html
4/1/13, CEN, p. 38 Elimination Reaction Cooks Up Chiral
Allenes
Something is wrong with the structure of the product. What is
wrong?
What is the reaction type?
Locate the chirality center in the ligand.
Why is the product chiral?
http://cen.acs.org/articles/91/i22/Power-Two.html
6/3/13, CEN, The Power Of Two: Organic Synthesis: Dual
catalysis creates stereochemical complexity , p. 9
Depending on which chiral catalysts they choose, chemists can make any
one of four possible stereoisomers.
How many chirality centers are in each reactant?
What is the configuration at each chirality center in each product?
1. Write the structure of the principal organic product from
the reaction of 1-bromopropane with sodium acetate
(CH3COONa) in acetic acid.
2. Outline an efficient synthesis of the following compound
from the indicated starting material and any necessary
organic or inorganic reagents:
cyclopentyl cyanide from cyclopentanol
3. Solvolysis of 2-bromo-2-methylbutane in acetic acid
containing potassium acetate gave three products. Identify
them.