Aromaticity description for non-science nerds

               While the specific chemical and physical reasons as to what determines “aromaticity” or if a compound is aromatic is difficult to understand without having taken a year of college chemistry, the basic structure can be understood easily enough. Molecules must be cyclic, which is any polygon shape. There can't be a break in the shape, thus each side must touch two other sides. Next the compound must be completely conjugated which means that there is no more than one bond between each double bond. Bonds are represented by a line in a line-angle structure(see picture), and double bonds are represented by a double line. These compounds actually share those double bonds so each bond has a bond order of 1.5, thus a more accurate depiction would have a double bond on each carbon (corners of the compound), but for visual aid they are only on every other carbon. A classic example that depicts these explanations is the benzene ring (figure 1). Notice the double lines(double bonds) as well as how they are actually shared by all of the carbons(corners of the internal structure) illustrated by the bottom image.                                   

                                               (Figure 1- Benzene Resonance Structures)

             

              Finally, they must have a multiple of 4n +2 pi electrons. Each double bond contains 2 pi bonded electrons so by counting the double bonds one can determine the amount of pi electrons. For example the two dimensional structure of a benzene ring has alternating double bonds thus it has six pi electrons(see figure 2), which is a multiple of 4(n) +2=6, where n=1. In this compound, each carbon is sharing the electrons that belong to the Hydrogen (H) and each Carbon to which it is connected. This type of electron "sharing" is called covalent bonding. Pi bonds are covalent chemical bonds where two lobes of one involved electron orbital overlap two lobes of the other involved electron orbital.

                                                            (Figure 2- Benzene Orbitals)

Resource:

1. Janice Smith,Organic chemistry. 3rd. New York City: McGraw-Hill Companies, 2008. pg 616-618

2. Benzene Resonance Structures. February 24, 2011. http://en.wikipedia.org/wiki/File:Benzene_resonance_structures.png

3. Benzene Orbitals. February 24, 2011. http://en.wikipedia.org/wiki/File:Benzene_Orbitals.svg

Response to Test #1

Although the test was very challenging, after looking back over sapling I realized the percentage of problems from each section mimicked that of the test. The only problems on the test I do not believe we had experienced before were questions 18 and 20. In those, we had to write the molecular ion and any other important peaks(due to fragments or M+1, M+2) for five different compounds written in C10H14N2 form instead of in the structural form. Due to the multiple examples of determining the number of unique CNMR and HNMR signals for compounds as in problems 15 and 16 on sapling I had expected another one of those problems on the test. We did receive a HNMR question of similarity but not a CNMR question.

Going back to the molecular ion and important peak question I could have figured it out with a few more minutes of time but because of the other time consuming  questions on the test I could not. Over all I believe the difficulty of the test did not match the test restraint we were given. I barely finished writing the last question before the 50 minute time period expired and could not adequately answer them. But I do understand we are in a very advanced college science course so the difficultly is expected.