Addition Reactions of Alkenes In previous series, we’ve discussed acid-base reactions, nucleophilic substitution reactions, and elimination reactions. These represent three of the four most important reaction types in a typical Org 1 course. What each of these reactions have had in common so far is that each of them begin with a Lewis base (which we call a “base” or “nucleophile” depending on whether it is attacking hydrogen or carbon) donating a lone pair to an electrophile (either hydrogen or carbon). In this series of posts we’ll cover the fourth major class of reactions, addition reactions ..read more

Alkene Stability (And Instability) What factors affect alkene stability? If you’ve studied elimination reactions, no doubt you’ve learned about Zaitsev’s Rule – about how elimination reactions generally favor the “more substituted” alkene. In this post we explore how increasing substitution at carbon increases the stability of alkenes, as well as the effects of conjugation and strain. Table of Contents Heat Of Hydrogenation As A Measure Of Alkene Stability Stability of Alkenes Increases With Increasing Substitution Heats Of Hydrogenation For Some Monosubstituted Alkenes The Relative Stabilit ..read more

What Bonds Form, What Bonds Break? About a month or so ago I had a big revelation as an instructor. Something that I’d been taking for granted, that was right under my nose. I was spending so much time focusing on the why and how of chemical reactions, that I had neglected to make sure that students understood the what  – in detail.  I was assuming that the vast majority of students could look at a reaction and quickly see which bonds were being formed and which were broken.  I was assuming this because I’d always ask “do you have any questions about this?” and they’d say “no ..read more

No doubt you’ve got some important exams coming up. With that in mind, here’s three simple tactics you can use during exams. 1. Draw partial charges If you get complete brain-lock during a question, try drawing out the partial charges. Ask yourself what the most electronegative atoms in the molecule are. The most electronegative atoms (e.g. oxygen, nitrogen, chlorine) are generally going to have partial negative charges on them, while carbons that they’re bonded to will have partial positive charges. This will help in identifying potential nucleophiles and electrophiles. And sin ..read more

Nucleophilic Acyl Substitution (With Negatively Charged Nucleophiles) Yes, there are a lot of reactions of carboxylic acid derivatives to learn!  In this article we’ll explore what is hands-down the most important pathway: nucleophilic acyl substitution. There is good news, though: with negatively charged nucleophiles nucleophilic acyl substitution tends to follow a simple two-step mechanism (addition-elimination) furthermore, for all intents and purposes, NAS reactions behave a lot like acid-base reactions. If you recall that “stronger acid plus stronger base gives weaker acid plus weak ..read more

No doubt you’ve got some important exams coming up. With that in mind, here’s three simple tactics you can use during exams. 1. Draw partial charges If you get complete brain-lock during a question, try drawing out the partial charges. Ask yourself what the most electronegative atoms in the molecule are. The most electronegative atoms (e.g. oxygen, nitrogen, chlorine) are generally going to have partial negative charges on them, while carbons that they’re bonded to will have partial positive charges. This will help in identifying potential nucleophiles and electrophiles. And sin ..read more

Now that pretty much the entire course has been covered, maybe it’s helpful to go back and highlight some of the key skills you should have in your toolbox as you finish up. As I tell my students, there’s an infinite number of things to learn, but a finite number of important things to learn. Here’s my top 10. Be able to identify the electron-rich and electron poor atoms in a molecule, using electronegativity and resonance. Be able to draw resonance structures, using the “three legal moves“. Be able to draw curved reaction arrows Recognize when molecules are aromatic (and when they’re not) Be ..read more

Now that pretty much the entire course has been covered, maybe it’s helpful to go back and highlight some of the key skills you should have in your toolbox as you finish up. As I tell my students, there’s an infinite number of things to learn, but a finite number of important things to learn. Here’s my top 10. Be able to identify the electron-rich and electron poor atoms in a molecule, using electronegativity and resonance. Be able to draw resonance structures, using the “three legal moves“. Be able to draw curved reaction arrows Recognize when molecules are aromatic (and when they’re not) Be ..read more

I have a lot of students ask me about how to do synthesis. Today, I’ll share with you  a 3-step method I suggest to them, and today we’ll start to go through it. It goes like this: Analyze the starting material and the product – ask yourself, what bonds are formed and what bonds are broken? When you’ve made your list, ask yourself – what reactions do I know that will form/break these bonds? In what order do I do these reactions? As an illustration, let’s use this synthesis question for alkynes. Part 1. Asking “what’s new” ?  A lot of students expect that they’ll be able to look at ..read more

Part 1 – Synthesis Let’s start talking about synthesis. Guess where I’m going to start? You might think,  “what bonds form, and what bonds break?”. Well… yes, but first, let’s start with arithmetic. Back in first grade, your teacher might have given you questions like this: 4+ 2 = ? 3 + 5 = ? And you got more and more comfortable with answering those questions. But then, one day, your teacher threw you a curveball. 3 + ? = 9 The first time you saw this it might have looked weird. But then you learned that you could solve them by moving the 3 over to the right hand part of the equation (ma ..read more