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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.