CHEM 0901 Episode 6: Alkenes PDF

 WHO’S WATCHING? Dr. Gallimore Dr. Downer-Riley Mr. Denny Dr. Brown Prof. Porter  4 Home TV Shows Movies My List Browse...

 WHO’S WATCHING? Dr. Gallimore Dr. Downer-Riley Mr. Denny Dr. Brown Prof. Porter  4 Home TV Shows Movies My List Browse By Language Organic CHEM 0901 97% for you 19+ 2024 2024 This show seeks to bridge the divide between CSEC and university-level chemistry for students. Within this course, you will be exposed to 4 types of chemistry, each with rules, jargon, and theory to be understood and expose you to the main branches of chemistry (Organic, General, Inorganic & Physical). At the end of this series, if the content was successfully mastered, other levels of expertise will become available, whether it be Level 1 within this discipline or other disciplines within or beyond this faculty. Are you ready for the experience?  4 Home TV Shows Movies My List Browse By Language Season 1- Organic Chemistry (10 Episodes)  4 Home TV Shows Movies My List Browse By Language Season 1 1. Introduction to Organic Chemistry 2. Introduction to reaction mechanism 3. Alkanes 4. Alkenes 5. Alkynes Play See More New on Netflix  4 Home TV Shows Movies My List Browse By Language Season 3 1. Reaction mechanisms and methods by which they are determined. 2. Reactive Intermediates - generation, structure, stability and reactivity of carbanions and carbocations. Episodes 3. Carbanion and Organometallic Chemistry. 4. Season 3 Pericyclic Reactions - the Diels-Alder reaction. Episode 6 Alkenes Play See More Preparations and Reactions My list Episode 7 Alkynes Naming, Preparation & Reactions Episode 6 Alkenes  REDUCTION OF ALKYNES Catalytic hydrogenation – alkyne is converted to an alkane by addition of two equivalents of H2 The first addition produces a cis alkene (via syn addition) which then undergoes a second addition to yield the alkane  REDUCTION OF ALKYNES A deactivated or poisoned catalyst can be used to stop the reaction at the cis alkene, without further reduction: Lindlar’s catalyst and P-2 (Ni2B complex-Nickel Boride) are common examples of a poisoned catalysts  REDUCTION OF ALKYNES The poisoned catalyst catalyzes the first addition of H2, but not the second.  REDUCTION OF ALKYNES Dissolving metal reduction – reduces an alkyne to a trans alkene using sodium metal and ammonia This reaction is stereoselective for anti addition of H and H  REDUCTION OF ALKYNES Dissolving metal reduction – reduces an alkyne to a trans alkene using sodium metal and ammonia Solomons 12 Edition pp 321  Reduction of Alkynes - SUMMARY Know the reagents needed to reduce an alkyne to an alkane, a cis alkene, or a trans alkene. 9-14 INTRODUCTION TO ADDITION REACTIONS Addition is the C=C  bond is opposite of converted to two elimination new sigma bonds 8-15 INTRODUCTION TO ADDITION REACTIONS The  bond is an electron-pair donor 8-16  ADDITION vs. ELIMINATION Addition and elimination are equilibrating reactions: Which side is favored depends on the temperature The higher the temperature, the more important entropy becomes 8-17  ADDITION vs. ELIMINATION At lower temps, enthalpy dominates, and addition reactions are favored At higher temps, entropy dominates, and elimination reactions are favored So, we use lower temperatures when doing an addition reaction 8-18 CATALYTIC HYDROGENATION Hydrogenation - the addition of H2 across a C=C double bond Requires a metal catalyst Alkene is converted to the corresponding alkane 8-19 Catalytic Hydrogenation selectivity Hydrogenation - the addition of H2 across a C=C double bond Stereospecific – only syn addition is observed with hydrogenation 8-20 CATALYTIC HYDROGENATION Without the metal catalyst, the addition of H2 is too slow due to a very high activation energy (Ea) 8-21 CATALYTIC HYDROGENATION The metal surface binds the H2, and the alkene, which explains why H atoms are added syn across the  bond 8-22 PARTIALLY HYDROGENATED OILS Partially hydrogenated oils do have issues There is much evidence that the catalysts present during the hydrogenation process can often isomerize some of the double bonds, producing trans double bonds: These so-called trans fats are believed to cause an increase in LDL (low-density lipoprotein) cholesterol levels, which leads to an increased rate of cardiovascular disease. In response, the food industry has been making efforts to minimize or completely remove the trans fats in food products. Current food labels often boast: “0 grams of trans fats.” HALOGENATION Halogenation – addition of two halogen atoms across a C=C double bond Halogenation is a key step in the production of PVC 8-24 HALOGENATION Halogenation only practical with Cl2 and Br2 halogenation with I2 is poor; halogenation with F2 is too violent Regioselectivity – halogenation occurs with anti addition 8-25 HALOGENATION Br2 is nonpolar, but polarizable. Approach of a nucleophile will induce a dipole Think of Br2 as a bromine atom bonded to a good leaving group The alkene acts as the nucleophile 8-26 HALOGENATION - stereoselectivity Only anti addition is observed, so the mechanism is not consistent with a true carbocation intermediate Syn addition doesn’t occur  HALOGENATION - mechanism The formation of a bromomium ion intermediate is consistent with anti addition This intermediate is similar to the mercurinium ion Copyright © 2017 John Wiley & Sons, Inc. All 8-28 rights reserved. Klein, Organic Chemistry 3e Halogenation - mechanism The formation of a bromomium ion intermediate is consistent with anti addition Br- attacks backside (anti) to the bromonium ion 8-29 HYDROHALOGENATION Hydrohalogenation: addition of H-X to an alkene can use HCl, HBr, or HI If the alkene is not symmetrical, then two regioisomers are possible, depending on which carbon gets the “H” and the “X” 8-30 Hydrohalogenation - Regioselectivity Hydrohalogenation is regioselective for Markovnikov addition In 1869, Markovnikov observed the H atoms tend to add to the carbon already bearing more H atoms The halogen is generally installed at the more substituted carbon 8-31 Hydrohalogenation - Regioselectivity Hydrohalogenation is regioselective for Markovnikov addition The halogen is generally installed at the more substituted carbon Explain the difference in energy for secondary and tertiary carbocations 8-32 Hydrohalogenation - Regioselectivity When peroxides are used with HBr, the opposite regioselectivity is observed. The reaction mechanism must be different, when peroxides are present. 8-33 Hydrohalogenation - Regioselectivity Mechanism 8-34 Hydrohalogenation - Regioselectivity The important lesson here is that the regioselectivity of HBr addition can be controlled: 8-35 Hydrohalogenation - Regioselectivity Draw the expected major product for the following reactions 8-36  Hydrohalogenation - Regioselectivity – Draw the expected major product for the following reactions Copyright © 2017 John Wiley & Sons, 8-37 Inc. All rights reserved. Klein, Organic Chemistry 3e  Hydrohalogenation - Regioselectivity – Draw the expected major product for the following reactions Copyright © 2017 John Wiley & Sons, 8-38 Inc. All rights reserved. Klein, Organic Chemistry 3e  Acid-catalyzed Hydration The components of water (H and OH) are added across the  bond Acid-catalyzed hydration follows Markovnikov regeioselectivity Sulfuric acid is typically the acid catalyst used 8-39 Klein, Organic Chemistry 3e  Acid-catalyzed Hydration The OH is added to the more substituted carbon of the alkene The more substituted the carbon atom is, the faster the reaction This data is consistent with a mechanism that proceeds through a carbocation intermediate Klein, Organic Chemistry 3e Hydration - Mechanism 8-41 Solomons –Organic Chemistry 12e Summary Hydrogenation via different routes Summary Hydrohalogenation Halogenation Hydration Next Episode Next Episode