Organic Chemistry In Real Life

Organic Chemistry in Real Life

How does organic chemistry fit into everyday life? Well, let’s take a look at a medical case and see…

A 52-year-old woman presents to the clinic complaining of several moths of generalized weakness, cold intolerance, and weight gain. Physical examination reveals alopecia, a thick and beefy tongue, myxedema, and delayed tendon reflexes. Her heart rate is 55/min and her blood pressure is 100/70 mm Hg. She is not taking any medications.

Relevant laboratory findings:
  • Free thyroxine (T4): 4.5 pmol/L (normal is 10.3-35 pmol)
  • Thyriod-stimulating hormone (TSH): 31mU/mL (normal is 0.8-2 mU/mL)
  • Cholesterol: 230 mg/dL
DIAGNOSIS:

Primary hypothyroidism

Treatment:

Levothyroxine

When a chemist is interested in synthesizing a molecule, they come up with what is known as a retrosynthetic analysis. This is where they take the initial molecular structure of interest and come up with a way of synthesizing it in the lab. Here is an example with our prescribed drug:

Now we have two aromatic compounds to work with. The reaction we will consider to synthesize the iodo-aromatic compounds is Electrophilic Aromatic Substitution (EAS).

How do we know where the iodine will go? Let’s review the resonance structures of ortho-para directors (in this case, the OH group).

What about the other compound with an OH group AND an R group? Aren’t both ortho-para directing groups? YES!!! Good catch on your part!

The ortho-para directing group that can form resonance structures (groups with lone pairs, such as OH or NH2) are the groups that win. Therefore, the iodo groups go next to the OH group, not the R group.

(The case is taken from First Aid Cases for the USMLE Step I, Second Edition)

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