Alcohols

Summary: Alkene Reaction Pathways

April 25, 2013

In this post we’ll do a final review of alkene addition reactions and sum up the three major pathways (and two minor classes of reactions worth paying attention to). Reaction Pathway #1 – The Carbocation Pathway In the Carbocation Pathway, the alkene acts as a nucleophile and attacks an electrophile, resulting in the formation of [...]

Tagged as: alkenes, bromination, carbocation, hydroboration, markovnikoff, markovnikov, patterns, stereochemistry

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Hydroboration of Alkenes

March 22, 2013

So far in this series on alkenes, we’ve gone through two families of mechanism pathways. In the carbocation pathway, we saw reactions that proceed with “Markovnikov” regioselectivity, a mixture of “syn” and “anti” stereochemistry, and can be accompanied by rearrangements.  In the 3 membered ring pathway, the regiochemistry is also “Markovnikov”, the stereochemistry is trans [...]

Tagged as: addition reactions, anti, anti-markovnikoff, anti-markovnikov, borane, hydroboration, reduction, syn

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Alkene Addition Pattern #2: The “Three-Membered Ring” Pathway

Alkene Addition Pattern #2: The “Three-Membered Ring” Pathway

March 20, 2013

The “Three-Membered Ring” pathway In the last post we walked through a proposal for how the bromination of alkenes works and showed that it adequately explains many of the experimental observations made for this reaction. Namely, the reaction proceeds with anti addition of substituents across the alkene, and (where relevant) the reaction proceeds with “Markovnikov“ [...]

Tagged as: addition, alkenes, anti, br2, bromination, bromonium, chlorination, Cl2, i2, iodination, markovnikoff, markovnikov, oxymercuration, syn

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Comparing the E1 and SN1 Reactions

November 8, 2012

Imagine you’re starting with the alcohol on the left and you’d like to get to the alkene on the right. What bonds are formed and broken here? We’re forming C-C (π), we’re breaking C-H, and we’re breaking C-OH. It’s an elimination reaction. Notice a problem here? We need to have HO(-) as a leaving group. [...]

Tagged as: base, conjugate acid, e1, e2, elimination, leaving groups, nucleophile

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Khan Academy Videos for Organic Chemistry, Part 6

October 30, 2012

In this post (the 6th of 6) we finish up going through all the Khan Academy videos for organic chemistry [videos 65-73]. For previous posts in this series, see [1 2 3 4 5] Video #65 – Keto-Enol Tautomerism Length: 8:03 Summary: 3-methyl 2-butanone is drawn, and the mechanism for its conversion into its enol [...]

Tagged as: khan academy, videos

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Rearrangement Reactions (1) – Hydride Shifts

August 15, 2012

For nucleophilic substitution, the pattern of bonds that form and break is pretty straightforward. You break C-(leaving group) and you form C-(nucleophile). A straight swap. But every once in awhile you might see a “weird” substitution reaction. If you look closely at the pattern of bonds formed and bonds broken in the second reaction below, there’s [...]

Tagged as: 1, 2-shift, carbocation, hydride shift, nucleophilic substitution, rearrangement, resonance, sn1, SN2, wagner-meerwein shift

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Comparing the SN1 and SN2 Reactions

August 8, 2012

Since we’ve gone through the different factors that impact the SN1 and SN2 reactions, it’s worthwhile to review and summarize  the different factors behind each of these two reactions. But first – have you ever heard of the Hobo on the bench? You’re in a park on a lovely summer day and you want to [...]

Tagged as: backside attack, carbocation stability, leaving groups, nucleophiles, sn1, SN2, steric hindrance, substitution

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The Conjugate Acid Is A Better Leaving Group

August 7, 2012

One of the key factors that determines whether a nucleophilic substitution reaction will happen or not is the identity of the leaving group. Previously, we’ve seen that good leaving groups are weak bases. That means that if you see a halogen (Cl, Br, or I) or a tosylate (OTs) or mesylate (OMs) on your molecule, [...]

Tagged as: carbocations, conjugate acid, conjugate base, leaving groups, nucleophiles, nucleophilic substitution reactions, sn1, SN2

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Walkthrough of Substitution Reactions (1) – Introduction

May 31, 2012

Today starts a new series of posts on walking through one of the key classes of reaction in organic chemistry: substitution reactions. The goal of this series is to teach you:  How to recognize substitution reactions when they are presented to you What the key components of a substitution reaction are (substrate, nucleophile, and leaving [...]

Tagged as: acids, bases, electrophile, introduction, nucleophile, sn1, SN2, substitution, walkthrough

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Acid Base Reactions: What’s the Point?

May 30, 2012

One thing has been missing from our discussion of acid-base reactions. Who cares? What does it matter that we understand acid base reactions? Why is it important? Today, I hope to show that it matters a lot, not only for its own sake, but for topics that concern the rest of the course. Let’s review [...]

Tagged as: acid, base, conjugate acid, conjugate base, electrophiles, nucleophiles

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