The Golden Rules of Organic Chemistry

Your goal should be to understand, not memorize organic chemistry. The following 7 Golden Rules should be learned at the beginning of this semester. These simple ideas explain a very large number of things about the way organic molecules interact. Thus, understanding the 7 Golden Rules will allow you to develop an intuitive feel for organic chemistry, and things will make sense! (Warning: this means you will start thinking like a chemist, but, of course, no one needs to know if you don't want them to know.)

1. Atoms prefer filled valence shells. This rule explains why atoms make bonds, and the type of bonds created. A corollary is that centers of electron density (bonds and lone pairs of electrons) repel each other so they stay as far apart as possible. This latter rule, the basis for the so-called VSEPR model, explains 3-dimensional molecular structure.

2. The most important question in chemistry is "Where are the electrons?" The answer is that electrons are generally in higher amounts around the more electronegative atoms (e.g. F, Cl, O, N). The electronegative atoms pull electron density away from the less electronegative atoms (e.g. C, H) to which they are bonded. Thus, understanding electronegativities provides a simple method of deciding which portions of a molecule have a relatively high electron density, and which portions have a relatively low electron density.

3. Nature hates unpaired electrons. If a molecule must have an unpaired electron (a.k.a. radical), it is better to have the unpaired electron distributed over as many atoms as possible through resonance, inductive effects, and hyperconjugation.

4. Nature hates localized charges. If a molecule must have a charge, it is better to have the charge distributed over as many atoms as possible through resonance, inductive effects, and hyperconjugation. In addition, when given the choice, it is better to have more negative charge on a more electronegative atom (e.g. O), and more positive charge on a less electronegative atom (e.g. C).

5. Most reactions involve nucleophiles (molecules with a location of particularly high electron density) attacking electrophiles (molecules with a location of particularly low electron density). When in doubt, transfer a proton! Thus, simply understanding where electrons are provides you with the best way of analyzing new molecules so that you will be able to PREDICT how they will react.

6. Steric interactions (atoms bumping into each other) can prevent reactions by keeping the reactive atoms away from each other.

7. Pi electrons prefer to be delocalized over as many adjacent sp² hybridized atoms (or sp¹ hybridized atoms in some cases) as possible, and aromaticity is the most stable form of pi electron delocalization. Pi electrons cannot delocalize onto or through sp³ hybridized atoms since an sp³ atom has no 2p orbital available.

There are two Golden Subrules:

1. In mechanisms, proton transfers are generally the fastest possible reaction, so this usually happens before other possible processes such as nucleophilic attack. The exception is deprotonation of non-acidic carbon atoms such as in alkanes, these can be slow.

2. If a five or six-membered ring can be formed, intramolecular reaction will predominate if a molecule has two functional groups that can react with each other. Other rings can sometimes be formed, but when five or six-membered rings are not possible, intermolecular reactions become important competing reactions.

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