Where Electrons Are

What Makes A Good Nucleophile?

June 18, 2012

If you read the last post, you’ll recall that a nucleophile is a species that donates a pair of electrons to form a new covalent bond. Nucleophilicity is measured by comparing reaction rates; the faster the reaction, the better (or, “stronger”) the nucleophile. When discussing nucleophilicity we’re specifically talking about donating a pair of electrons [...]

Tagged as: base, charge, electron rich, electronegativity, leaving groups, lewis bases, nucleophiles, nucleophilicity, solvent, steric hindrance

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Nucleophiles and Electrophiles

June 5, 2012

All through the series on understanding where electrons are, and how they flow, we’ve been talking about how the basis of chemistry is that opposite charges attract and like charges repel, and that in reactions, electrons flow from “electron rich” areas to “electron poor” areas. Today, we’ll officially give a name to the types of [...]

Tagged as: acids, bases, electrophiles, electrophilicity, lewis acids, lewis bases, nucleophiles, nucleophilicity

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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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7 Factors That Stabilize Positive Charge in Organic Chemistry

March 7, 2012

Just to clarify: make sure you’re familiar with how formal charge can lie before you read this. These factors determine the stability of “true” positive charges (i.e. low electron densities), not “formal” positive charges.  After discussing 7 factors that stabilize negative charge, it would make sense to talk about 7 factors that stabilize positive charge. [...]

Tagged as: aromaticity, charge density, electronegativity, negative charge, opposite charges attract, orbitals, positive charge, resonance

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Common Mistakes: Formal Charges Can Mislead

Common Mistakes: Formal Charges Can Mislead

February 22, 2012

Formal charges have their plusses and minuses. Har har. One one hand, they’re an indispensable accounting tool. If a molecule bears a charge, it would drive us nuts (for nomenclature reasons) if we didn’t adopt some kind of system where a charge was unambiguously assigned to one atom. In many instances, the formal charge on [...]

Tagged as: curved arrows, electron densities, electronegativity, formal charge, Where Electrons Are

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The Third Most Important Question to Ask When Learning A New Reaction

February 20, 2012

When learning any new reaction, I think you always have to start with the “what”. What bonds are forming, and what bonds are breaking. After you answer “what”, then you can start asking “where” – as in , “where are the electrons of the reactants?” What areas are electron rich? What areas are electron poor? [...]

Tagged as: curved arrows, formal charge, lone pairs, mechanisms, pi bonds, sigma bonds

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How to apply electronegativity and resonance to understand reactivity

How to apply electronegativity and resonance to understand reactivity

January 17, 2012

One thing has been missing from the discussion of resonance. What’s the point? Who cares if we can write out resonance structures? What does it matter if we can figure out the two or three most stable resonance structures? So what? Here’s the point: we can apply resonance (and electronegativity) to figure out the electron [...]

Tagged as: charges, electronegativity, formal charge, opposite charges attract, resonance

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Common Mistakes: How not to draw resonance curved arrows

January 10, 2012

No discussion of resonance structures would be complete without mention of how to royally screw them up. This isn’t something to feel bad about, by the way: there isn’t a chemist alive who hasn’t made one of these mistakes at some point. Think of it as a rite of passage. The trick is to make the mistakes [...]

Tagged as: accounting, curved arrows, electrons, mistakes, resonance

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In Summary: Resonance

December 22, 2011

After all these posts about resonance, I thought it would be good to have a post summarizing what’s been discussed so far. One of the key skills in analyzing the reactivity of a molecule is to be able to figure out where the electrons are.  As I wrote here, if we’re dealing with single bonds, [...]

Tagged as: arrow pushing, charge stabilization, electron density, least charges, negative charge, pi acceptors, pi donation, positive charge, resonance

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