Week 2 Workshop Questions Key concepts: Line structures, hybridization, acidity,

Question

Week 2 Workshop Questions Key concepts: Line structures, hybridization, acidity, resonance, intermolecular forces, units of unsaturation, naming functional groups 1. Replacing carbon-hydrogen bonds with carbon-fluorine bonds to slow drug metabolism and increase potency of pharmaceutical drugs is becoming a common strategy in drug development. The C-F bond does not occur naturally in animals and therefore our bodies do not know how to metabolize this group. This slows drug metabolism, leads to high blood levels and higher drug potency. One example of a drug with a C-F bond is fluoxetine (Prozac ) developed by Lilly in the 1980s (structure below). Fluoxetine is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. The C-F bonds slovw fluoxetine metabolism in the liver and leads to greater blood levels and effacacy. The C-H bonds of drugs are oxidatively metabolized by the liver into C-OH bonds. The C-OH bonds are more polar and more water soluble, and leads to the drug being excreted from the body through the kidneys into urine. The potential energy diagram for a C-H bond is shown below. This diagram shows the C-H bond length (11.0 nm), and the bond dissociation energy (440 kJ/mol). Potential 0_ Internuclear Distance (am) Prepare a similar potential energy diagram for the C-F bond with bond energy and bond length. Your diagram should contain the following. a. axis labels b. where attractive forces are present c. where repulsive forces predominate; d. where atoms are too far apart to interact; e. where the repulsive and attractive forces are balanced f look up the bond energy and bond length for the C-F bond and label these in your diagram. propose three reasons why the C-F bond would be more difficult to metabolize in the liver than the C-H bond. g.

Explanation / Answer

This graph represents the energy changes involved in formation of bond between C and H.

Following type of interactions are present :

a) Attraction between electron of one atom to nucleus of other atom.

b) repulsion between electron of one atom to electron of another atom and nucleus of one atom to nucleus of another atom.

As atoms comes closer , attractive forces comes into play, their atomic orbital starts overlapping as bond starts to form , system attains stability so its potential energy goes on decreasing.

Energy gets minimized as overlap of atomic orbitals of C and H occurs up to maximum extent. At this point bond is formed between C and H , distance between them is called bond length. Its value is 11nm . At this point attractive forces balances the repulsive forces.

If atoms gets more closer than this distance, then repulsion starts . Repulsive forces becomes greater than attractive forces. Energy of system starts increasing due to decrease in stability.

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