Chapter05 - 5.1 Kinds of Organic Reactions 5. An Overview...

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1 1 5. An Overview of Organic Reactions Based on McMurry’s Organic Chemistry , 6 th edition, Chapter 5 2 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 – two molecules combine ± Elimination – one molecule splits into two ± Substitution – parts from two molecules exchange ± Rearrangement – a molecule undergoes changes in the way its atoms are connected 3 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 4 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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2 5 Types of Steps in Reaction Mechanisms ± Formation of a covalent bond ± Homogenic or heterogenic ± Breaking of a covalent bond ± Homolytic or heterolytic ± Oxidation of a functional group ± Reduction of a functional group X H H X X H H X 6 Homogenic Formation of a Bond ± One electron comes from each fragment ± No electronic charges are involved ± Not common in organic chemistry 7 Heterogenic Formation of a Bond ± One fragment supplies two electrons ± One fragment supplies no electrons ± Combination can involve electronic charges ± Common in organic chemistry 8 Homolytic Breaking of Covalent Bonds ± Each product gets one electron from the bond ± Not common in organic chemistry
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3 9 Heterolytic Breaking of Covalent Bonds ± Both electrons from the bond that is broken become associated with one resulting fragment ± A common pattern in reaction mechanisms 10 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’) 11 Radicals ± Alkyl groups are abbreviate “R” for radical ± Example: Methyl iodide = CH 3 I, Ethyl iodide = CH 3 CH 2 I, Alkyl iodides (in general) = RI ± A “free radical” is an “R” group on its own: ± CH 3 is a “free radical” or simply “radical”
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Chapter05 - 5.1 Kinds of Organic Reactions 5. An Overview...

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