6 Pilares de quimica organik

In the Classroom

Six Pillars of Organic Chemistry
Joseph J. Mullins Department of Chemistry and Physics, Le Moyne College, Syracuse, NY 13214; mullinjj@lemoyne.edu

A conceptual framework for the presentation of organic chemistry that I call “the six pillars of organic chemistry” has led to greater student comprehension and enjoyment of the subject matter. Organic chemistry is a course ofstudy pursued by a variety of majors (in addition to chemistry), particularly those in the pre-health studies. The course often represents a hurdle, or rite of passage, to be overcome en route to a career in another profession. Great apprehension is experienced about the difficulty of the subject matter, the volume of material to be mastered, and the grades required for admission to professionalschools. A variety of articles on the topic of the organic chemistry lecture course have appeared in this Journal (1). The objectives of the six pillar approach are (i) building knowledge of organic chemistry upon a strong foundation of fundamental concepts; (ii) explaining and predicting a wide variety of chemical, physical, and biological properties of molecules; (iii) conceptually unitingimportant features of general, organic, and biochemistry; and (iv) the early introduction and frequent reinforcement of concepts in a memorable way. This approach is not intended to represent all the concepts required for second-year organic chemistry or to define precisely which concepts should be included. Rather, I intend to promote a teaching methodology of a general formula that appeals to studentsand appears to be in harmony with many ideas concerning the instruction of chemistry. For example, Taber has reported, “...the unfamiliar has to be made familiar in manageable chunks if we are to learn it effectively. New concepts have to be appreciated and integrated into our knowledge systems before they can be used as a secure foundation for developing super-ordinate concepts—no matter howlogical and clear the teacher’s exposition” (2). Many instructors and textbooks of organic chemistry appreciate the importance of a conceptual approach. For example, McMurry, in his popular text states, “...organic chemistry is a beautifully logical subject that is unified by a few broad themes. When these themes are understood, learning organic chemistry becomes much easier and rote memorization isminimized” (3). But, it is tempered by the initial reliance of students on memorization, “...the what of chemistry is easier for most students to grasp than the why” (3). My focus is in the details of a framework that I have applied and in the emphasis of such throughout the school year. The idea is to provide a structural foundation upon which organic chemistry may be learned; to de-mystify andsimplify, in the minds of students, the apparently overwhelming avalanche of facts that intimidates organic chemistry students; and to persuade general chemistry instructors of the importance of emphasis on key concepts of chemistry, which are often reviewed in the initial weeks of an organic chemistry course. The six pillars are listed below, with brief definitions.
1. Electronegativity: thetendency of an atom in a covalent bond to attract electron density to itself 2. Polar covalent bonding: generally, a bond between atoms of different electronegativity

3. Steric effects: the usual tendency of atoms or groups of atoms to repel one another and to occupy space 4. Inductive effects: through sigma-bond electron-density donation or withdrawal 5. Resonance: electron delocalization involvingelectrons in p orbitals 6. Aromaticity: the unique stability of electrons in p orbitals in certain cyclic systems

One could coalesce these into fewer concepts, which would focus upon electron or charge delocalization. One might alternatively suggest many more, particularly when advanced organic chemistry is considered. Why six? These suffice, individually or in combination, for many of the...