Preparing for Organic 2
Successful completion of the first term of Organic Chemistry means you should have a basic handle on what structures are possible, what constitutes reactivity and stability, and which pathways are open to organic molecules when they react. The second semester continues the discussion of the important functional groups while expanding the toolbox of useful synthetic transformations and the scope of mechanistic possibilities. To be successful in the second term it is essential that the student knows the basics from the first semester. Below is a series of the most important mechanisms studied previously, the features of which show up repeatedly in the second half of the course.
The analysis below gives us an idea of the main topics that need to be understood before beginning Organic 2. The first image details a typical course structure with the main ideas of structure, electronic stabilization, and mechanism being studied in parallel with the chemical reactions that are useful in synthesis. In the second semester, those ideas are coupled with analytical techniques such as NMR, IR and MS to complete the survey of chemistry and techniques required in the sophomore Organic sequence. The second image shows how each of the second semester chemical (i.e non-spectroscopic) topics all rely on a fairly compact number of topics from Organic 1. Delocalization of electrons (resonance structures) are involved in a lot of the second semester mechanisms. Acid-base reactions (proton transfers) are a key component of many of the reactions studied so a thorough understanding of pH and pKa is crucial. Further, the second semester will mechanisms will mostly involve combinations of basic first semester mechanisms so being confident with the mechanics of Substitution, Elimination, and Addition pathways will make the new mechanisms easier to digest.
Since there are so many mechanisms in Organic 2, the student must be conversant with how curly arrows are used to describe breaking and formation of bonds. There are no new arrows in the second semester, so reaction pathways will involve either the double-headed (2-electron) arrows or the single-headed (1-electron) version. The former are by far more common and found in the mostly polar pathways, while the latter feature in only a few processes. Being able to decide which type of arrow to use, and the directions in which they need to be pushed, is essential. It is important therefore to practice arrow pushing before the semester begins with the video on acid-base arrows (below) being a good place to start.
From the charts above, Resonance (or electron delocalization) is a key topic that appears often throughout Organic 2. Being able to predict when delocalization will apply, and then being able to construct the individual resonance structures and a detailed resonance hybrid, will be essential for success. The following video reviews the basics of how to create delocalization patterns for allyl anions, allyl carbocations, heteroatom-stabilized carbocations, and allylic radicals. Be sure to review these ideas before the second semester begins.
A review of the main topics from Organic 1 is also advised before the first week of Organic 2 begins. This will include the details of shapes of molecules, hybridization patterns, electron districutions, modes of reactivity, and reaction basics. Successful completion of Organic 1 as a pre-requisite for Organic 2 means that you should be conversant with mechanistic ideas and be able to spot what will happen to organic molecules under different conditions. The video below is a review of those essential topics.