Chem 313 Problem Set #6 2010 Answers
1. The synthesis of polynucleotides has been studied and refined for years. Some of
the original work in this field was carried out at UBC, by H.G. Khorana. His
lab’s methods of forming the phosphodiester backbone of polynucleotides
involved the use of dicyclohexylcarbodiimide (DCC) with 5’ phosphorylated
precursors. A potential byproduct of this reaction is the formation of 5’-3’ cyclic
phosphates. What is the mechanism of this reaction?
2. The rate of acidic hydrolysis of trityl ethers is very dependent on the substituents
on the phenyl rings. Predict (using >,< or =) the relative rate of each of the
following reactions. Provide structural evidence supporting your claim. OMe is an EDG and stabilizes NO i2 an EWG and therefore
the carbocation through resonance destabilizes the carbocation
3. Show the reagents you would use for the following transformations.
4. Upon purification of B via HPLC, you noticed it actually contains two species,
each with the expected mass for the product. Reaction of either of these
derivatives using the conditions to form C gives the same, expected product.
What is the difference in the two products observed for B?
B shows two products due to the tetrahedral nature of phosphorous. There are 2
diasteromers. Upon removal of the cyanoethyl