Part of running an unbiased and feature driven Organic Chemistry education service is recommending students to outside websites for alternative stimulating content. The Chemistry Cascade is a WordPress blog site that highlights interesting recent developments in synthetic and mechanistic Organic Chemistry. The brief articles encapsulating novel chemical research are abstracted from major American Chemical Society journals, and are well presented.
Long ago I learned a simple rule in Organic Chemistry. Practically every synthetic organic transformation and corresponding reaction mechanism can be described in entirety as a series of attacks of nucleophiles (Nu) on electrophiles (E). This simple rule was so etched into my psyche that it became unconscious. This article is dedicated to my current students who are voluntarily, and quite eagerly, undergoing my facilitated “reorganization” of their thought patterns in their endeavor to learn the logic of Organic Chemistry.
Whereas the SN2 reaction is a concerted process, the SN1 reaction (substitution, nucleophilic, unimolecular) proceeds via a stepwise mechanism. The rate determining step for the SN1 reaction involves formation of a stable (trigonal planar) carbocation intermediate. Carbocations, in general, are high energy intermediates, and hence the term “stable” is relative, not absolute.
One of the first things new students in Organic Chemistry are astounded by once the class begins is the absence of mathematics. A sigh of relief is breathed as they are introduced to qualitative topics such as nomenclature and alkanes. Soon a feeling of comfort sets in. Stereoisomerism is introduced and then wham! Nucleophilic substitution (SN1 / SN2 reaction) and elimination appear to come from nowhere.
With each new student I meet I deliver the same message. The most challenging exam of the first half of the course will be SN1, SN2, E1, E2. The seemingly new concept of chemical reactions coupled with reaction mechanisms influenced by reagents, solvent and temperature all too frequently lead to confusion and even intimidation. This doesn’t have to happen. Continue reading