Resonance Tutorial



The ideas behind electron delocalization are presented here with examples of how molecules are able to stabilize electron clouds through spreading electron density over several atoms.


Resonance Structures

This video introduces the ideas of electron delocalization and the use of resonance structures to describe the overall structure of molecules in which atoms share electron density.

It's important to remember that resonance structures are not different molecules, they are conributors to the overall structure of the molecule.

There are some basic rules to learn about what constitutes a viable resonance structure and these are collected in Table 1.6 in the textbook.

Since this is an important idea that will show up again and again over the two semesters, it is essential that you come to terms with it as soon as possible. 



Curved Arrow Notation 

As we start to discuss chemical reactions we will go into a lot of detail about how reactants convert to products and the bonds that are formed and broken in doing so. This idea of reaction mechanism requires the use of the "curved arrow" notation to describe bond-forming and bond-breaking events and essentially follows the fate of electron pairs (in most mechanisms) that are between atoms (i.e. bond pairs) or associated with one atom (i.e. lone pairs). It is these pairs of electrons that will be used to form and break bonds on the way to reaction products. The following animation shows the use of a lone pair on the blue atom to form a bond with the red atom while the bond between red and green is broken with the bond pair becoming a lone pair. Overall this is a bimolecular process in which the new bond (blue-red) is being formed as the old bond (red-green) is being broken; this is described as a concerted process. (Note that the animation does not attempt to take into account any changes in charge on any of the atoms).



Obviously we don't have the ability or the time to make animations for each mechanism that we study so we need a fast and convenient method for describing these events as reactants convert to products. Below you can see the use of curved arrows (orange) to show how the lone pair from blue is used to form a bond to red while at the same time the bond pair between red and green is becoming a lone pair on green. As you practice with the arrows you should remember that they start at electrons and go somewhere else, not the other way around. 

 The same animation is found here as a browser-based flash file.


That Adobe ID Thing...


So we finally figured out why some of you had problems posting the results from your quiz in recitation; the Adobe ID registration process is somewhat flawed. After registering, some people received a verification link by email which they clicked and they were good to go. Others received a welcome email with no verification link - hey, thanks for the welcome but my quiz won't post. Caleb, our resident expert in all things technical, worked out how to get the verification email sent (or resent) - well played Caleb! 

All is explained in this handy video. ​

​Hopefully this will solve the problems and we will be set up for a fun semester of online quizzing. 

(If you are still struggling, stop by my office and I can help you fix this).​


Who is taking Chemistry 3719?

Wordle: class2

This is a "wordle" that is formed by taking the majors present in the Chemistry 3719 class and presenting them based on the number of each major in the class; the bigger the word, the more of those majors present. By far the largest contigent is those with an interest in Biology, with pre-Professionals, Engineers, Educators, and Clinical or Forensic Scientists making up the rest of the class.

This is interesting since Chemistry underpins each of these other subjects yet these other subjects are not required for Chemistry. For example, Biology majors need 2 years of Chemistry (General and Organic) and probably should have three (Biochemistry), however a Chemistry major requires zero (0) classes in Biology (or Engineering, etc.) for their degree. 

We have an interesting challenge here in getting you to know enough Chemistry to be able to get the most out of your major classes. It's always somewhat baffling when a pre-Pharmacy major or Biology student claims to hate/fear/loathe Chemistry when those subjects rely so heavily on Chemical ideas.

So there are a wide variety of majors present and each person has their own goals beyond Chemistry 3719 and 3720. With such a diverse audience the task here is to get each student to a place where they genuinely understand what is happening in Organic (and then Biochemical) systems. For these classes you are not Biologists, Engineers, pre-Professionals, etc. you are Chemistry students hoping to learn as much as possible about an important subject.