Chapter 4 - What do organic chemists do? Synthesize organic...

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1 What do organic chemists do? Synthesize organic molecules of defined structures Mostly drugs Organic materials - polymers and monomeric precursors to polymers. Study of mechanism of organic reactions, many of which are important in chemical syntheses.
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2 What are reaction mechanisms? Defined pathways that lead from reactant A to product B Me H H I Cl O CH 3 O CH 3 Me H H Cl CH 3 H O I + + + + Each of these reactions has a defined “mechanism”
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3 Tools for Study To determine a reaction’s mechanism , look at: Equilibrium constant Free energy change Enthalpy Entropy Bond dissociation energy Kinetics Activation energy =>
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4 Chlorination of Methane Requires heat or light for initiation. The most effective wavelength is blue, which is absorbed by chlorine gas. Lots of product formed from absorption of only one photon of light (chain reaction). => C H H H H + Cl 2 heat or light C H H H Cl + HCl
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5 Free-Radical Chain Reaction Initiation generates a reactive intermediate. Propagation: the intermediate reacts with a stable molecule to produce another reactive intermediate (and a product molecule). Termination: side reactions that destroy the reactive intermediate. =>
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6 Initiation Step A chlorine molecule splits homolytically into chlorine atoms (free radicals) => Cl Cl + photon ( h ν29 Χλ + Χλ
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7 Initiation Step/Homolytic Cl Cl + photon ( h ν29 Χλ + Χλ Two electrons in bond partition between two bonded atoms to form radical.
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8 Heterolytic Cleavage Cl CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 Cl O H B + O HB + Two electron reactions - Ions result
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9 Propagation Step (1) The chlorine atom collides with a methane molecule and abstracts (removes) a H, forming another free radical and one of the products (HCl). C H H H H Cl + C H H H + H Cl =>
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10 Propagation Step (2) The methyl free radical collides with another chlorine molecule, producing the other product (methyl chloride) and regenerating the chlorine radical. C H H H + Cl Cl C H H H Cl + Cl =>
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11 Overall Reaction C H H H H Cl + C H H H + H Cl C H H H + Cl Cl C H H H Cl + Cl C H H H H + Cl Cl C H H H Cl + H Cl => Cl Cl + photon ( h ν29 Χλ + Χλ
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Termination Steps Collision of any two free radicals Combination of free radical with contaminant or collision with wall. C
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Chapter 4 - What do organic chemists do? Synthesize organic...

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