curved arrows

Curved Arrows (2): Initial Tails and Final Heads

February 29, 2012

Here’s a handy little trick for accounting for charges when you draw curved arrows. You know by now that curved arrows are our accounting system for showing how electrons move, from the tail (electron donor, source of electrons) to the head (electron accepting, destination of electrons). There are only three moves you can do: lone pair [...]

Tagged as: curved arrows, drawing, electron accounting, formal charge, how electrons move, mechanisms, Reaction Mechanisms

Read the full article →
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

Read the full article →

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

Read the full article →

Curved Arrows (for reactions)

February 15, 2012

If you think of electrons as the currency of chemistry, reactions are transactions of electrons between atoms. Just like double entry book keeping was developed to formalize how financial transactions  are recorded, chemists have developed their own convention for showing transactions of electrons between atoms. It’s called the curved arrow formalism. Previously I covered how [...]

Tagged as: curved arrows, drawing mechanisms, electron accounting, electron flow, formal charge

Read the full article →

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

Read the full article →

Exploring Resonance: Pi-Donation

December 15, 2011

You’d think after five or six posts on resonance, that would be enough. But NO, friends, it just keeps going. I promise that today’s post is actually useful, although to be honest it’s probably most applicable if you’re in (or going into) org 2, since the chemistry of the functional groups discussed here  don’t really [...]

Tagged as: curved arrows, electron density, electron pushing, enamines, enols, pi donation, resonance

Read the full article →

Evaluating Resonance Forms (3): Where to put the negative charge?

December 13, 2011

So far in discussing resonance forms I’ve mentioned two important principles: 1. Minimize charges: the resonance form with the fewest charges will be the most stable. 2. How to break π bonds. If you absolutely must break a  π bond to make a resonance form, do it in a way so that the pair of [...]

Tagged as: basicity, curved arrows, hybridization, minimize charges, negative charge, opposite charges attract, pi bonds, polarizability, resonance

Read the full article →
Evaluating Resonance Forms (1) – The Rule of Least Charges

Evaluating Resonance Forms (1) – The Rule of Least Charges

December 8, 2011

So far I’ve talked about resonance, and introduced the curved arrow formalism to show the movement of electrons. Importantly, we’ve talked about how the “true” picture of a molecule is a hybrid of its resonance forms (and not an equilibrium between forms). Here’s a recap of the different “moves” we can perform on a molecule [...]

Tagged as: cations, charge stability, charges, curved arrows, electron flow, formal charge, resonance

Read the full article →

Introduction to Resonance (2) : Curved Arrows!!

November 30, 2011

So last time I talked about resonance forms as being two (or more) different ways to draw the same molecule, which differ only in their distribution of electrons. Let’s look a little more closely at these resonance forms and ask, “what’s different?”, and be as specific as possible. In both cases the resonance form on the [...]

Tagged as: accounting, curved arrows, electron density, electronegativity, formal charge, negative charges, positive charges, resonance

Read the full article →

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

November 9, 2011

So once you can recognize the key bonds that are forming and breaking in a chemical reaction, the second most important question to ask yourself when learning a new reaction is “how do the electrons move?” I have a friendly disagreement with a lot of instructors on this point, since it’s common to claim that [...]

Tagged as: accounting, arrow pushing, curved arrows, electron densities, electron flow, electronegativity, opposite charges attract

Read the full article →