Mechanism%20Guide - Understanding (as opposed to...

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Understanding (as opposed to memorizing) mechanisms is critical to mastering organic chemistry. Although the mechanisms you encounter throughout the course may seem entirely different, they are actually related in fundamental ways. In fact, almost all of the organic reaction mechanisms you will learn are composed of only a few different individual elements (steps) that are put together in various combinations. Your job is to learn these individual mechanism elements, and then understand how to assemble them into the steps of the correct mechanism for the reactions you will see. The KEY idea is that each mechanism step should be thought of as a MULTIPLE CHOICE situation in which you evaluate the structures and reactivities of the molecules involved then rule out inappropriate elements on the way to deducing the appropriate element for each step of the mechanism. Polar Reaction Mechanisms: Polar reactions are most of what you will see in organic chemistry, amounting to greater than 95% of cases we will discuss. There are only a few different mechanistic elements that combine to make up the different steps of almost all the mechanisms you saw in CH310M. Better yet, in CH310N the following four mechanistic elements are pretty much all you need to think about until we get to electrophilic aromatic substitution near the end of the semester. 1. Make a new bond between a nucleophile (source for an arrow) and an electrophile (sink for an arrow). Use this element when there is a nucleophile present in the solution as well as an electrophile suitable for reaction to occur. CH 3 CHCH 3 CHCH 3 O CH 3 Isopropyl cation intermediate (an electrophile) Oxomium ion intermediate O H H Water (a nucleophile) H H 2. Break a bond so that relatively stable molecules or ions are created Use this element when there is no suitable nucleophile-electrophile or proton transfer reaction, but breaking a bond can create neutral molecules or relatively stable ions, or both. CCH 3 Br CH 3 2-Bromo-2-methylpropane CH 3 Br Bromide ion (relatively stable anion) CCH 3 CH 3 CH 3 tert -Butyl cation intermediate (stabilized by inductive and hyperconjugation effects. See Section 6.3A)
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3. Add a proton Use this element when there is no suitable nucleophile-electrophile reaction, but the molecule has a strongly basic functional group or there is a strong acid present. 4.
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Mechanism%20Guide - Understanding (as opposed to...

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