Name the following functional groups!
Define Bronsted and Lewis acids and bases!
Bronsted acids: H+ donors
Bronsted bases: H+ acceptors
Lewis acids: e- pair acceptor
Lewis bases: e- pair donor
Lewis concept includes Bronsted bases and acids but expands definition to, e.g., metals.
What are the pKa values of the following species:
carboxylic acid
5
imidazolium ion
7
thiol
10
alkylammonium ion
11
water
16
alcohol
ketone
19 (more acidic than ester and thioester because they have more resonance)
thioester
21
ester
25 (C- and O-orbitals are more similar than S- and C-orbitals, therefore more efficient resonance)
hydrocarbon
60
Describe the mechanism of electrophilic addition of acid-catalyzed hydration of 2-methylpropene!
Markownikow product
inductive effect of the carbon substituents
hyperconjugation
Compare the two major nucleophilic substitution reactions regarding formed intermediates and the type of substrates!
Sn1:
2 steps
carbocation intermediate
tertiary/allylic substrates preferred (sterics & stability)
Sn2:
1 step
no intermediate, only transition state
primary substrates preferred
inversion of chiral molecules
Name the two major groups of compounds bearing a carbonyl group and compare their reactivities!
Carboxylic acids and derivatives:
alpha-position (heteroatom) can stabilize negative charge
can act as a leaving group
—> nucleophilic substitution
Aldehydes and ketones:
alpha-position (C/H) cannot stabilize negative charge
typically no leaving group
—> nucleophilic addition
Order the following compounds according to their reactivity starting with the most reactive species: thioester, amide, acyl phosphate and ester! Draw the functional group for each compound!
(the better the leaving group, the more reactive in nucleophilic substitution)
Name three mechanisms of elimination reactions and draw one of those explicitly
Which proteinogenic amino acids exhibit predominantly a charged side-chain at pH 7?
arginine
histidine
lysine
aspartic acid
glutamic acid
Which amino acids occurs most frequently in the active site of enzymes? Rationalize why this might be the case.
Cys
formation of disulfide bonds
covalent synthesis because S- is strong nucleophile
more than O- because it is less affected by the charge of the nucleus
Lys
interacts with negatively charged compounds
Schiff-base formation with carbonyls
His
imidazol: at pH7 His can be protonated or deprotonated
Asp
Glu
Pro
Arg
Mostly charged amino acids; uncharged are often only stabilizing.
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