lecture 05 - 5. An Overview of Organic Reactions Based on...

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5. An Overview of Organic Reactions Based on McMurry’s Organic Chemistry , 7 th edition
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2 Why this chapter? To understand organic and/or biochemistry, it is necessary to know: -What occurs -Why and how chemical reactions take place We will see how a reaction can be described
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3 5.1 Kinds of Organic Reactions In general, we look at what occurs and try to learn how it happens Common patterns describe the changes Addition reactions – two molecules combine Elimination reactions – one molecule splits into two
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4 Substitution – parts from two molecules exchange
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5 Rearrangement reactions – a molecule undergoes changes in the way its atoms are connected
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6 5.2 How Organic Reactions Occur: Mechanisms In a clock the hands move but the mechanism behind the face is what causes the movement In an organic reaction, we see the transformation that has occurred. The mechanism describes the steps behind the changes that we can observe Reactions occur in defined steps that lead from reactant to product
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7 Steps in Mechanisms We classify the types of steps in a sequence A step involves either the formation or breaking of a covalent bond Steps can occur in individually or in combination with other steps When several steps occur at the same time they are said to be concerted
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8 Types of Steps in Reaction Mechanisms Bond formation or breakage can be symmetrical or unsymetrical Symmetrical- homolytic Unsymmetrical- heterolytic
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9 Indicating Steps in Mechanisms Curved arrows indicate breaking and forming of bonds Arrowheads with a “half” head (“fish-hook”) indicate homolytic and homogenic steps (called ‘radical processes’) Arrowheads with a complete head indicate heterolytic and heterogenic steps (called ‘polar processes’)
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10 5.3 Radical Reactions Not as common as polar reactions Radicals react to complete electron octet of valence shell A radical can break a bond in another molecule and abstract a partner with an electron, giving substitution in the original molecule A radical can add to an alkene to give a new radical, causing an addition reaction
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lecture 05 - 5. An Overview of Organic Reactions Based on...

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