Exam 1: Chp 4 Flashcards
How are substituents assigned priority when assigning R and S configurations?
Atomic Number, lowest is lowest priority
When the lowest priority substituent is pointing into the page, what configuration is a clockwise arrangement?
R-configuration
When the lowest priority substituent is pointing into the page, what configuration is a counter-clockwise arrangement?
S- configuration
When identifying L and D stereochemistry in Fischer protection, which direction should the carboxyl group be?
Up
When identifying L and D stereochemistry in Fischer projection, which direction should the side-chain be?
Down
If the amino group is on the left in Fischer projection, is the amino acid a L or D stereoisomer?
L
If the amino group is on the right in Fischer projection, is the amino acid a L or D stereoisomer?
D
Which stereoisomer are most natural amino acids?
L
What is the typical pKa of a carboxyl group?
pKa ~ 2
What is the typical pKa of a amino group
pKa ~ 9
What is zwitterion?
An ion with a formal negative charge and a formal positive charge that sum to a charge of 0
Why is the reaction between a polypeptide between amino acids and phenylisothiocyanate (Edmund reagent) useful?
The PTH-derivative is UV active meaning it can be separated then analyzed via absorbance to determine the R group and thus the N-terminal amino acid
Process can be repeated to sequence small polypeptides
Why do peptide bonds have partial double bond character?
Resonance caused by delocalization the lone pair on Nitrogen
What are implications of the double bond character in peptide bonds?
Restricted rotation
Surrounding atoms are planar
Bond is sp2 hybridized
