LEC 6: Amino Acids II Flashcards
What are some factors influencing acidity (pKa) (4)
- Resonance
- Periodic trend
- Inductive effect
- Orbitals
Values of pKa depend on what (4)
- Temperature
- Ionic strength
- Ionizable groups
- Microenvironment
What are the characteristics of the resonance effect (2)
- Acidity of the molecule relates to the stability of the CB
- Stability of the CB depends on how well it can accommodate its new pair of electrons
Define what the resonance effect is
Negative charge on the CB is delocalized through resonance over multiple atoms which increases stability of the base and increases the acidity
What are the characteristics of the periodic trend when acidity increases? (2)
- EN of atom bonded to proteon
2. Atom size of X of atom bonded to proton
What is the difference between Electron withdrawing groups vs Electron donating groups
EWG: EN elements take electron density FROM C and strengthens the acidity
EX: F,Cl,Br..
EDG: Donate electron density TO C and decreases markedly with distance
EX: Alkyl groups
What are the characteristics of the orbital effect (3)
- Represent the most likely location of an electron around an atom
- Electrons in s orbital are closer to the nucleus
- Acidity increase with increasing the s character of the orbitals
Define what the Isoelectric point is
pH at which the Aa carries no net charge
the average charge on all the Aa molecules sums to 0
pH = pI
Neutral moleucle
pH < pI
Positive molecule
pH > pI
Negative molecule
What are titration curves show
Shows the changing ionic state of an Aa as pH increases
What does resonance do to influence the acidity
Acidity increases with resonance structure
What does the periodic trend do to influence the acidity
Acidity increases with EN and size of atom
What does the inductive effect do to influence the acidity
Acidity increases with nearby electrons withdrawing groups
