Tutor profile: Elliot S.
Subject: Organic Chemistry
Explain the components and the mechanism of the Wittig Reaction.
The Wittig Reaction is a chemical reaction that is often used to convert Aldehydes and Ketones (Carbonyls) into Alkenes. The components of the Wittig Reaction include the Carbonyl compound (aldehyde or ketone, but not an ester), and the Phosphonium Ylide. A Ylide is a compound that has opposite charges positioned on adjacent atoms. The Phosphonium Ylide can be drawn with a double bond between the PPh3 and the CH2 or with a single bond and a positive charge on the PPh3 and a negative charge on the CH2 due to resonance. The first step in the Wittig reaction is the nucleophilic attack of the Ylide carbon on the Carbonyl carbon located at the base of the Carbonyl. This results in a single bond being formed between the two carbons involved. Additionally, this results in a negatively charged Oxygen atom joined to the carbonyl carbon by a single bond. Next, one of the lone pairs on the oxygen attack the adjacent, positively charged PPh3 group and a bond is formed between the two groups. The result is a brief, unstable, four membered ring that breaks down quite quickly. I like to imagine this step as a box snapping shut and pancaking on the ground in four layers (two newly formed double bonds). The technical name for this is Reverse Cycloaddition. Basically, the electrons from the single bonds between the Oxygen and the carbon join the O-PPh3 bond and the electrons from the phosphonium Ylide bond join the Carbon-Carbon bond. The resultant product is an oxygen double bonded to PPh3 and a new Carbon=Carbon double bond joining the two carbon chains present at the beginning of the reaction. A short cut to solving this problem is to envision the starting materials and sever both double bonds (the carbonyl and the Ylide) in your mind. Then, join the carbon chains by a double bond at the same carbons that used to be connected to the oxygen and the PPh3.
Subject: Biomedical Science
Describe the difference between Orthosteric and Allosteric drugs and describe positive and negative allosteric modulators.
Orthosteric drugs are drugs that bind to the primary agonist site on the receptor. Allosteric drugs are drugs that bind to the secondary, allosteric site on the receptor to positively or negatively regulate agonist binding and efficacy. Positive Allosteric Modulators cause greater signaling by increasing the affinity and efficacy of the Othersteric agonist. Negative Allosteric Modulators cause diminished signaling by dampening affinity and efficacy of the Othersteric site.
During a cranial nerve clinical exam, a patient complains of weakened tongue mobility. When asked to protrude the tongue, the patient attempts to stick the tongue straight out but his tongue deviates toward one side. What is the innervation of the muscle that protrudes the tongue?
Cranial Nerve XII (Hypoglossal nerve). Cranial nerve XII is the cranial nerve that provides motor function to the Genioglossus muscle. Therefore, a student must understand that the Genioglossus muscle protrudes the tongue and that it receives innervation from CN XII. This muscle is bilateral, therefore, if one side of the Hypoglossal nerve is damaged, that side of the tongue will not be able to protrude. During a cranial nerve exam, patients will be asked to protrude their tongue. If they try to stick their tongue straight out, but it deviates to one side, the medical professional should know that the Hypoglossal nerve is damaged on the effected side. Since the unaffected side is still functional, the Genioglossus muscle on the unaffected side will push the tongue over to the effected side.
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