Granny's Rendition of Aromatic Compounds

   Aromaticity is a chemical property that compounds are listed as if they qualify for the four criteria that are listed such as it must be cyclic, planar, completely conjugated and have 4n + 2 pi electrons.All aromatic compounds are based off of the basic benzene ring which is a ring with six sides and six carbons and six hydrogens.  The first criterion is that the molecule must be cyclic which means that it must be shaped like a ring or in a circle to be an aromatic compound.  The second criterion is that the molecule must be planar which means that the compound needs to be flat like a piece of paper to be aromatic.  For example, if the structure of the compound is shaped as a tub with some parts higher than others then it is not planar. 
   The third criterion is that a molecule must be completely conjugated which means that these compounds must have a p orbital on every atom.  For example, if you have a 6-sided ring, you will need three double bonds with the double and single bond followed by another double bond and so on.  The last criterion is that a molecule must satisfy Huckel’s rule and contain a particular number of pi electrons.  The particular number of pi electrons must meet the 4n + 2 pi electron rule.  For instance, if you use something like pencils you can have 2, 6, 10, etc. because n equals 0, 1 and 2.  Hope this helps clear up how to distinguish aromatic compounds from nonaromatic ones.

Exam Uno Questions

After taking the first Organic Chemistry exam, I wondered why there was not a question that required us to label and count the number of ¹H NMR signals for different compounds.  After working hard and completing the Sapling homework I fully understood and knew I was able to answer these questions.  On Sapling, there were a few questions that covered this portion of Organic Chemistry.  When the exam was handed out I was confused on why there wasnt any of these choices of questions on there.  The correct way to answer these types of questions is to make sure to understand that the number of NMR signals equals the number of different types of protons in a compound.  The main principle of finding the number of signals is that protons in different environments give different NMR signals.  The same NMR signals are given by protons being equivalent to each other.  For example, a compound such as CH₃OCH₃ has only one ¹H NMR signal.  The reasoning for this is that each methyl group CH₃ is bonded to the same group which makes both methyl groups have the same signal.  However, for a compound such as CH₃CH₂Cl there are two different signals because the hydrogens are two carbons away from the chlorine for one signal and for the other signal the hydrogens are located one carbon away.  After working on the sapling problems and reading over this section in the book I was confident that I would be able to complete a question on the number of ¹H NMR signals.  However, since there was not a question on the exam containing this subject I was a little confused but this is still a great part of Organic Chemistry that needs to be understood.