Of the 20 canonical amino acids, arginine has the most basic side chain. Below i
ID: 476443 • Letter: O
Question
Of the 20 canonical amino acids, arginine has the most basic side chain. Below is the structure of the arginine side chain before it reacts with an aqueous Which nitrogen can be protonated to give a resonance stabilized conjugate acid? Draw the resonance structure. The pKa's of arginine are 2.01, 9.04, and 12.48. Draw the structure of arginine at pH 10.5. What is the net charge of arginine at pH 1? Rank the molecules below from least acidic (1) to most acidic (4). Rank the molecules below from least basic (1) to most basic (4). Draw a curved arrow mechanism explain the reaction below.Explanation / Answer
1a) The double bonded nitrogen is the most basic nitrogen . The reosonating structures are given in scheme.
1b) The isoelectric point of Arginine is 10.76 (average of 9.04 and 12.48). Thus at pH = 10.5 , it exists nearly in zwitterionic form.
1c) At pH =1 all the basic groups are completely protonated (highly acidic solution). The the charge of argnine is +2.
2) acidity order is carboxylic acids > thiols> alcohols. The presence of strong -I groups Cl increase its acidity more than less electronegative Br.
3) The double bonded nitrogen in the 5 membered ring is more basic due to the resonance of the conjugate acid formed. Aniline is least basic, as the elecron pair is less available due to resonance with aromatic rin.
4) first a tertiary carbocation is formed which attacks internally the other double bond to give cyclic compound.
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