9.4 Hydration The components of water (-H and –OH) are added across a C=C double bond The acid catalyst is often shown over the arrow, because it is regenerated rather than being a reactant Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-1 Klein, Organic Chemistry 2e

Given the data below, do you think the acid catalyzed hydration goes through a mechanism that involves a carbocation? 9.4 Hydration Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-2 Klein, Organic Chemistry 2e

9.4 Hydration Mechanism Why does the hydrogen add to this carbon of the alkene? Mechanism continues on next slide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-3 Klein, Organic Chemistry 2e

9.4 Hydration Mechanism Could a stronger base help promote the last step? Practice with conceptual checkpoint 9.10 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-4 Klein, Organic Chemistry 2e

9.4 Hydration Thermodynamics Similar to Hydrohalogenation, hydration reactions are also at equilibrium Explain HOW and WHY temperature could be used to shift the equilibrium to the right or left Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-5 Klein, Organic Chemistry 2e Addition Elimination

9.4 Hydration Thermodynamics How could Le Châtelier’s principle be used to shift the equilibrium to the right or left? Practice with conceptual checkpoint 9.11 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-6 Klein, Organic Chemistry 2e

9.4 Hydration Thermodynamics Similar to Hydrohalogenation, the stereochemistry of hydration reactions is controlled by the geometry of the carbocation Draw the complete mechanism for the reaction above to show WHY a racemic mixture is formed Practice with SkillBuilder 9.3 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-7 Klein, Organic Chemistry 2e

9.4 Hydrations Ethanol is mostly produced from fermentation of sugar using yeast, but industrial synthesis is also used to produce ethanol through a hydration reaction Predict the major product(s) for the reaction below Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-8 Klein, Organic Chemistry 2e

9.5 Oxymercuration- Demercuration Because rearrangements often produce a mixture of products, the synthetic utility of Markovnikov hydration reactions is somewhat limited Oxymercuration-demercuration is an alternative process that can yeild Markovnikov products without the possibility of rearrangement Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 9-9 Klein, Organic Chemistry 2e

9.5 Oxymercuration- Demercuration Oxymercuration begins with mercuric acetate How would you classify the mercuric cation? As a nucleophile or an electrophile? As a Lewis acid or Lewis base? How might an alkene react with the mercuric cation? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.5 Oxymercuration- Demercuration Similar to how we saw the alkene attack a proton previously, it can also attack the mercuric cation Resonance stabilizes the mercurinium ion and the carbocation. Draw a reasonable resonance hybrid Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.5 Oxymercuration- Demercuration The mercurinium ion is also a good electrophile, and it can easily be attacked by a nucleophile, even a weak nucleophile such as water NaBH 4 is generally used to replace the –HgOAc group with a –H group via a free radical mechanism Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation To achieve anti-Markovnikov hydration, Hydroboration- Oxidation is often used Note that the process occurs in two steps Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Hydroboration-Oxidation reactions achieve syn addition Anti addition is NOT observed To answer WHY, we must investigate the mechanism Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Let’s examine how this new set of reagents might react The BH 3 molecule is similar to a carbocation but not as reactive, because it does not carry a formal charge Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Because of their broken octet, BH 3 molecules undergo intermolecular resonance to help fulfill their octets The hybrid that results from the resonance (diborane) involves a new type of bonding called banana bonds Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation In the hydroboration reaction, BH 3 THF is used. BH 3 THF is formed when borane is stabilized with THF (tetrahydrofuran) What general role do you think BH 3 THF is likely to play in a reaction? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Let’s examine the first step of the Hydroboration mechanism on the next slide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e Hydroboration

9.6 Hydroboration-Oxidation What evidence is there for a concerted addition of the B- H bond across the C=C double bond? Use sterics and electronics to explain the regioselectivity of the reaction Practice with conceptual checkpoint 9.17 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e Oxidation

9.6 Hydroboration-Oxidation Start Here Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e Oxidation

9.6 Hydroboration-Oxidation When ONE chirality center is formed, a racemic mixture results WHY? What is the geometry of the alkene as the borane attacks? The squiggle bond above shows two products, a 50/50 mixture of the R and the S enantiomer Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation When TWO chirality centers are formed, a racemic mixture results Why aren’t the other stereoisomers formed? Practice with SkillBuilder 9.4 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e

9.6 Hydroboration-Oxidation Predict the major product(s) for the reactions below Copyright © 2015 John Wiley & Sons, Inc. All rights reserved Klein, Organic Chemistry 2e