a. Provide the reagents necessary to complete the following transformations ( or

Question

a. Provide the reagents necessary to complete the following transformations ( or more steps may be required for each arrow). Pay attention to stereochemistry. H OH H S + enantiomer molecule A molecule B b. Imagine you ran the FIRST reaction in the lab (molecule A to molecule B). Fill in the table below to indicate which peaks you would look for in the IR and NMR for evidence of the presence of molecules A and B. Molecule B 1 peak Molecule A Wavenumber of the interesting peak(s) in the IR (cm). Indicate which specific bond is responsible for each peak. 2 peaks Chemical shift of the interesting peak in the NMR (ppm)

Explanation / Answer

Organic chemistry

a. Reagents for the transformation,

molecule A ---> molecule B

1. BH3,THF

2. H2O2,OH-

This is hydroboration reaction which gives least substituted alcohol product.

molecule B ---> molecule C

1. TsCl, pyridine

2. 2-cyclopentylthiol

this is Sn2 substitution reaction which occurs with inversion of configuration at the carbon center.

b. If the first reaction has occured. The changes we would observe spectroscopically are,

molecule A

IR

peak at 3020 cm-1 for sp2 =C-H stretch

peak at 1640 cm-1 for C=C stretch

NMR

13C NMR would show typical peaks at 115 ppm and 125 ppm for alkenic carbons

1H NMR peaks at 5.5 ppm and 5.9 ppm for alkenic protons

Molecule B

IR

3300 cm-1 broad peak for O-H stretch

NMR

13C NMR

peak at 66 ppm for carbon having -OH group

1H NMR

peak at 3.7 ppm for proton attached to carbon having -OH group

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