On from General to Organic Chemistry
Transitioning from General to Organic Chemistry

While General Chemistry involves lots of calculations and equations, Organic Chemistry involves lots of concepts and mechanisms. This is where things get a bit sticky for many students. They are going to have to change their approach in order to achieve success and this can be a little uncomfortable. Knowing how to approach Organic can make the difference so here we pass along some ideas for how to do that.  

In the sophomore Organic Chemistry sequence you may only ever use a calculator in the lab setting to work out yield returns from synthesis experiments. In the lecture and recitation classes you will need to do a lot more thinking and linking ideas together to solve problems. If a student takes a linear "front-on" approach to this subject they could get overwhelmed early on and never recover. This is like looking a a forest from ground level and only seeing the first row of trees. The way to approach Organic is to try to take the "helicopter" approach in which you are viewing the forest, and what is in it, from above and seeing all of the roads and streams intersect. That isn't easy but it can be done if you trust that Organic is based on a fairly small number of intersecting ideas. 

Below is a listing of the main ideas that form the basis of Organic Chemistry, some of which come from General Chemistry, and some of which are new. Try to use this as a guide for how to prep for your Organic sequence. The topics highlighted in blue are ones you have seen before, the ones in red are new in Organic. Keep in mind that the vocabulary in Organic is quite complicated so anticipate learning new words and not going back and relearning terms from the first year that your should already know.


Periodic Table

The first ideas, grouped in the first column, are obviously things you have studied before and should be solid on if you have passed the General Chemistry sequence with decent grades. It is worth learning the Pauling Electronegativity Scale (H = 2.0; C = 2.5; F = 4.0, etc.) before you start Organic as those numbers will help you decide on whether bonds are polar or non-polar. Even if your Professor doesn't expressly require you to know these numbers, this will be hugely helpful in the future. Then know the common valences for the elements us early on in Organic (C = 4; H = 1; O = 2; N = 3; Br = 1, etc.) so that you know what to expect when drawing molecules. Understand that the octet rule still governs everything and that atoms with too few or too many electrons may well be reactive. It goes without saying that you should know the difference between covalent and ionic bonds and when each applies. 


While this is going to get quite complicated in Organic, the foundations for what constitutes reactive and, conversely, stable were laid early on in the first year sequence. You know that water (H2O) is stable because it is neutral while hydronium (H3O+) is reactive because it is positively charged. Similarly hydroxide (HO-) is reactive because the oxygen is negaitively charged. In Organic you will consider more closely why this is the case and then extroplate those ideas to other atoms and molecules. In water the highly electronegative oxygen has both of its lone pairs to istelf while in hydronium one lone pair had to be shared with H; O wants it back, hence the reactivity. In hydroxide the oxygen has three lone pairs packed around a fairly small atom, which is destabilizing and this leads to the observed reactivity. Knowing these simple ideas from General Chemistry will allow you to extrapolate to Organic compounds quickly, e.g. CH3OH (stable), CH3OH2+ (reactive), and CH3O- (reactive). Organic adds terms such as electron-rich and electron-poor, which should be obvious, the where charges prefer to be, based on atomic size and delocalization possibilities.

Reaction Pathways

Most organic courses start out with a review of the important General Chemistry concepts and then move into the hybridization patterns and shapes used by atoms in organic molecules. Do not ignore that material, instead make sure it checks out with what your learned before or, hopefuly, it actually cements and deepens the understanding of what went before. Once chapters on conformation (shape dynamics) and asymmetry (chirality) have been covered, it's on to chemical reactivity and how organic chemicals behave under different conditions in different environments. You should realize that this is where everything comes together and where problems often arise. Know that there are only so many things that molecules can do in reactions in terms of bonds being formed or broken. This either involves everything happening at once in concerted processes, or in stepwise sequences that involve the formation of intermediate species. Those processes are governed by steric and/or electronic factors that show up repeatedly and which dictate the viability of a transition state (kinetics) or the formation of products of different stabilities (thermodynamics). Whether reactions are reversible or irreversible will play a major role in outcomes.

Mechanism Details

Once the basics are understood, the Organic course will move to mechanism and how we establish the details of reaction pathways. This usually begins with acid-base reactions as students have familiarity with that topic. Be careful here. While the ideas are the same, the structures change constantly, which can be overwhelming. You are still trying to identify bases as being electron-rich and acids as being electron-poor and the electron-rich base will still attack the electron-poor acid. Now, however we introduce the "curved arrow" as a way to describe bonds being formed or broken and you must be comfortable with how this notation is used. Practice the arrows extensively with acid-base examples before moving on to more complex situations. Then realize that there are only so many events that can occur in polar mechanisms: proton transfer (acid-base event), nucleophilic attack (electron-rich species attacking carbon), loss of leaving group (a species stable with a lone pair breaks away from carbon), and rearrangement (a molecule reorganizes to become more stable). While that summarizes polar mechanisms the main other option for stepwise reactions for carbon is the radical chemistry, which is quite different. Again, however, there are only so many things that molecules can do, but staying on top of ideas from the beginning is how you succeed.

As may be gathered from the above introduction, Organic Chemistry certainly does build on the foundations laid in General Chemistry, however the demands of the student will change. Ideas will start to overlap and combinations of concepts will be needed to explain outcomes and to solve problems. While the Organic sequence starts slow, it always builds quickly and may overwhelm students who are not seeing the bigger picture. As shown in the graphic above, the ideas are limited in number but, like playing chess or tennis, which move/shot do you play and when do you do it? This skill should develop if you study consistently and practice the basics continually. If Organic is approached correctly it can become a very satisfying and rewarding subject.

In the next post we will discuss what to review before starting Organic 1.