Thermodynamics and Kinetics

The E2 Mechanism

September 27, 2012

Having gone through the E1 mechanism for elimination reactions, we’ve accounted for one way in which elimination reactions can occur. However, there’s still another set of data that describes some elimination reactions that we haven’t adequately explained yet. Here’s an example of the reaction I’m talking about: What’s interesting about this reaction is that it [...]

Tagged as: anti, base, e2, elimination, kinetics, stereochemistry, zaitsev's rule

Read the full article →

Elimination Reactions Are Favored By Heat

September 10, 2012

A few posts back we saw how elimination reactions are often in competition with substitution reactions. ow do we know when one reaction pathway is going to be preferred over another? As we’ll see, there are going to be several components to answering this question fully, but today we’ll talk about one simple rule of [...]

Tagged as: activation energy, base, competing reactions, elimination, gibbs energy, nucleophile, rate constants, substitution

Read the full article →

The SN2 Mechanism

July 4, 2012

Having gone through the two different types of substitution reactions, and talked about nucleophiles and electrophiles, we’re finally in a position to reveal the mechanism for one of the most important reactions in organic chemistry. It’s called the SN2 reaction, and it’s going to be super useful for us going forward. Let’s look at the [...]

Tagged as: backside attack, inversion, leaving groups, nucleophiles, nucleophilic substitution, SN2, stereochemistry, substitution

Read the full article →

Two Types of Substitution Reactions

June 27, 2012

Chemistry is an experimental science. There is no great Ramanujan of our discipline, who, starting with a simple set of premises, could derive and predict all of the depth and variety of modern chemistry. No, it is much messier than that. Chemists have to actively interrogate Nature to learn her secrets. We add substances together [...]

Tagged as: alkyl halide, leaving group, nucleophile, primary, rate law, sn1, SN2, substitution, tertiary

Read the full article →

Acid Base Reactions Are Fast

May 21, 2012

Common dilemma in organic chemistry as you move through the latter parts of Org 1 and then into Org 2: When more than one reaction is possible, how do you know which one will happen? In a steel cage match between an acid base reaction and other types of reactions, which wins? Here’s a good [...]

Tagged as: acidity, basicity, conjugate acid, conjugate base, nucleophile, nucleophilicity, pka, trick questions

Read the full article →

A Handy Rule of Thumb for Acid-Base Reactions

May 17, 2012

Last time I talked about pKa and how it’s the closest thing we have to a universal measurement of  the strengths of all kinds of different acids and bases.  I also referred to a post on how to use a pKa table (key lesson: stronger acid plus stronger base gives weaker acid and weaker base). [...]

Tagged as: acids, bases, conjugate acid, conjugate base, equilibrium, pka

Read the full article →
Walkthrough of Acid-Base reactions (4) – pKa

Walkthrough of Acid-Base reactions (4) – pKa

May 9, 2012

So last time we went through all the different trends that affect acidity. The bottom line is that any factor which stabilizes the conjugate base will result in increased acidity.  Now it’s fine to know trends – it’s extremely important, in fact – but what do you do when you want to compare the acidity [...]

Tagged as: acid strength, acidity, acids, bases, basicity, electron flow, equilibria, pka, trends

Read the full article →

Hammond’s Postulate

September 28, 2011

Last week Diana left this comment: I recently had my first orgo exam and one of the concepts that I have trouble visceralizing is Hammond’s Postulate. I can follow the explanation in my textbook (L.G. Wade, Jr. 7th edition), but I don’t really grasp it. Is there an alternative intuitive explanation? The official explanation of [...]

Tagged as: endothermic, exothermic, Hammond's postulate, reaction coordinate, transition state

Read the full article →

What To Expect In Organic Chemistry 2

January 19, 2011

A large part of organic chemistry 1 is devoted to laying the foundations: introducing structural concepts such as bonding, geometry, stereochemistry, conformations, resonance, and steric effects, while introducing concepts in chemical reactivity such as nucleophilicity, electrophilicity, acidity, basicity and so on. While there are several important new concepts introduced in Org 2 (especially in the [...]

Tagged as: aromaticity, conjugation, cycloaddition, diels alder, org 2, resonance, thermodynamic and kinetic

Read the full article →

What’s a Transition State?

November 3, 2010

Here’s a question that comes up a lot: What’s a transition state? In the Harry Potter series, Remus Lupin changed to his werewolf form when the moon was full. But he didn’t go from human to werewolf just by snapping his fingers:  the fangs and hair had to grow, the spine curled, the hands became [...]

Tagged as: endothermic, exothermic, Hammond's postulate, intermediates, kinetics, reaction diagrams, reaction rate, transition states

Read the full article →