Stereochemistry

Bridged Bicyclic Rings (And How To Name Them)

August 14, 2014

In the last post we started our discussion of structures with more than one ring, using decalin as our key example. We saw how much the stereochemistry at the ring junction can affect the overall shape of the molecule, as well as its stability. What we didn’t talk about is that the ring junction of decalin […]

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Fused Rings

August 5, 2014

At the beginning of this series I said that the fact that carbon can form rings leads to all kinds of interesting consequences. We’re going to see many examples of that in our post today! So far, we’ve only talked about cyclic molecules containing one ring. But, of course, molecules with multiple rings are very common […]

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Cycloalkanes – Dashes And Wedges

Cycloalkanes – Dashes And Wedges

March 20, 2014

In the last post, we mentioned that one of the consequences of the fact that carbon can form rings is that small rings (less than 8 carbons) are so rigid that they can’t be turned inside out [video]. One of the important consequences of this, as we’ll see today, is that it leads to the […]

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Partial Reduction of Alkynes

Partial Reduction of Alkynes

May 8, 2013

Alkynes bear many similarities to alkenes, but as we have already seen, their chemistry can differ in subtle and interesting ways. Today’s post is another case in point. The reduction of alkenes by hydrogen in the presence of a metal catalyst (“catalytic hydrogenation”) is a time-honoured reaction recognized by Sabatier’s receipt of the Nobel Prize for […]

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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 […]

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A Fourth Alkene Addition Pattern – Free Radical Addition

April 12, 2013

I’ve written that there are three major alkene reactivity patterns [carbocation, three membered ring, and concerted], but there are two minor pathways as well. This post discusses one of them. As discussed previously, alkenes normally react with HBr to give products of “Markovnikov” addition; the bromine ends up on the most substituted carbon of the […]

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Alkene Addition Pattern #3: The “Concerted” Pathway

April 2, 2013

In contrast to alkene addition reactions in the Carbocation Pathway and the 3-Membered Ring Pathway, we saw in the last two posts that hydroboration of alkenes is anomalous. The regioselectivity of the reaction is “anti-Markovnikov” and the stereochemistry of the addition is “syn“: We also saw that the “syn” stereochemistry is due to the concerted […]

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Bromination of Alkenes – How Does It Work?

March 6, 2013

In a previous post we went through the key reactions of the carbocation pathway. It’s a family of reactions which proceed through 1) attack of an alkene upon an acid, forming a free carbocation, and 2) attack of a nucleophile upon the carbocation. Although we saw that several key reactions of alkenes were consistent with […]

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Markovnikov’s Rule (2) – Why It Works

February 11, 2013

Understanding Why Markovnikov’s Rule Works Let’s assemble all the facts we know about the reactions of alkenes with an acid like HCl so far. Regiochemistry: as we saw in the last post, reactions of alkenes with acids like HCl follow Markovnikov’s rule: the major product formed is that where the hydrogen adds to the carbon […]

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Addition Reactions: Stereochemistry

January 30, 2013

In the last post on alkene addition reactions, we discussed one of the two key themes to look for in addition reactions: regiochemistry (in other words – what “region” of the alkene do different atoms end up forming bonds to?). This post is about the second key theme in addition reactions of alkenes: stereochemistry.  We’re going […]

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