acidsBases - L TOPIC 5. ORGANIC REACTIONS: ACIDS AND BASES...

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CHEM 2311 B Topic 5 slide 1 TOPIC 5. ORGANIC REACTIONS: ACIDS AND BASES (Chapter 3) L CHEM 2311 B Topic 5 slide 2 OBJECTIVES 1. Classify types of reaction: -Addition, Substitution, Elimination, Rearrangement 2. Define the concept of “Mechanism” 3. Discuss the thermodynamics (equilibrium) and kinetics (rate) of organic reactions 4. Describe acid-base reactions 5. Develop relationships between structure and acidity/basicity 6. Take a first look at acid-promoted reactions
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CHEM 2311 B Topic 5 slide 3 CLASSIFYING REACTIONS Reactions are conveniently classified as substitutions, additions, eliminations and rearrangements. These terms describe the overall process, simply comparing the structure of starting materials and products. They do not indicate anything about the pathway (“mechanism”) by which the reaction proceeds. Substitutions Additions Eliminations Rearrangements (often in combination with another type of reaction) S:3.1 CHEM 2311 B Topic 5 slide 4 Substitution CH 3 CH 2 Br O C Cl H 3 C acetone (solvent) pyridine (solvent) Na I CH 3 OH + +
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CHEM 2311 B Topic 5 slide 5 Addition CC H 2 H 2 O H 2 SO 4 H 3 C H O H 2 O H 2 SO 4 CHEM 2311 B Topic 5 slide 6 Elimination C H 3 C H 2 SO 4 CH 3 HO H
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CHEM 2311 B Topic 5 slide 7 Rearrangement C CC H 3 C H 3 C CH 3 H H H H 3 PO 4 CHEM 2311 B Topic 5 slide 8 H Br H OH H H Subst n Subst n Elim n E li m n A dd Subst n Subst n Add su b st itu t io s substit u tions a d i o A Preview of Reactivity
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Topic 5 slide 9 Practical Aspects of Running a Reaction Starting material (“substrate”) Reagents Catalysis (lowers activation energy) Solvent (allows for mixing) Mode of addition BEGINNING Product Byproducts Unreacted reactants Catalyst Solvent SEPARATION PURIFICATION IDENTIFICATION END Time Temperature (heating/cooling) Environment (avoid O 2 , H 2 O?) Stirring % yield = moles of product moles of limiting reactant x 100 CHEM 2311 B Topic 5 slide 10 Reactant(s) Product(s) Substrate (organic starting material) Product ( + byproduct(s) ) reagent(s) catalyst(s) solvent(s) +H 2 H 2 ,Pt EtOH H 2 O H 2 SO 4 OH Substrate (organic starting material) reagent Representations of reactions ...more commonly written as….
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CHEM 2311 B Topic 5 slide 11 WHAT IS A MECHANISM? A mechanism is a proposal for a step-by-step pathway by which a reaction proceeds. Each step involves bond making and/or breaking. The mechanism takes into account all currently available evidence (kinetics, formation of byproducts, effect of structure on reactivity). Any new data collected must be consistent with the proposed mechanism, or the mechanism itself must be modified to account for the new finding. An understanding of common mechanistic steps can be applied to new combinations of reagents to predict the outcome of a new reaction. As such, development of an understanding of mechanisms will save you from memorizing a huge amount of material.
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acidsBases - L TOPIC 5. ORGANIC REACTIONS: ACIDS AND BASES...

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