Question

Need help on 6a and 6b. (Molecule 1&2, their pH and group are circled in blue)

6a. On the answer sheet, draw molecule 1 and molecule 2 (at the indicated pH) and also draw their conjugate bases. (For any molecules you do not know, look up the structure on google/wikipedia/text). Based on ionic stabilization effects, which molecule would have a lower pKa for the group listed? Explain in 2-3 sentences. b. timt-1 molecule l molecule 2 pH group phenylalanine l 0-methyl phenylalanine 7- a-amino * N-acetyl modifications are produced when an acetic acid is linked to the a-amino group : O-methyl groups are produced by adding a methyl group (as an ester) to the α-carboxylic § β-amino acids have the amino group on the β-carbon rather than the a-carbon. by an amide bond. acid group.

Answer 1

molecule - 1 - This molecule is phenylalanine which has the p^ka values of 1.83 and 9.13. Thus the structure of molecule-1 at p^H 7 is as - molecule - 2 - This molecule is O-methyl phenylalanine Thus. This molecule has one group that can be protonated which has p^ka value of 9.13 Thus the structure of molecule 2 at p^H 7 is as - At p^H 7 , molecule 1 would have a lower p^ka For amino group. This is because at p^H, group is produced and stabilities the - NH^+_3, while molecule 2 has ester group which is non-ion sable.