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What is hydrolysis?
Breaking a bond by adding H2O.
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Amide hydrolysis
- Amide to carboxylic acid and amine.
- Downhill NAC with tetrahedral intermediate.
- Can be catalyzed by either acidic or basic conditions.
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Explain base catalyzed amide hydrolysis
- OH group’s O attacks C as double bonded Os electrons shift up.
- The bond attached to NR2 takes away H on O and leaves. H transfers electron to O. Double bonded Os electrons shift down.
- Final result is C double bonded to O and an O -. Also and NR2H group.
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Why can amide hydrolysis be catalyzed by the addition of either acid or base?
- Amino acids contain both acidic and basic groups.
- The specific 3D orientation of amino acid side chains change in relation to the subtrate.
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Explain acid catalyzed (H+) amide hydrolysis
- Double bonded O bonds to H and becomes +. Due to resonance, the C the positive O is bonded to is also electrophilic.
- Double bonded Os electrons shift up as a water attacks the electrophilic C.
- Lone groups on N steal H from bonded water. (Which now is a positive O)
- Double bonded O (now OH) shifts electrons down as NR2H leaves. Double bonded O is now positive.
- H leaves double bonded O by transferring electrons to it.
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How does folding of proteins catalyze a reaction?
- Stabilize a transition state. (lowers activation energy)
- Destabilize (Raise energy of) ground state of substrates,
- Provide an alternative reaction pathway. (eg. temporarily covalently bond to substrate)
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Explain chymotrypsin protease process
- N grabs H on serine while NAC occurs (Double bonded O shifts electrons up, O attacks C)
- Tetrahedral intermediate: Double bonded O shifts electrons down while NH group grabs H bonded to N and leaves.
- H2O attacks C, double bonded O shifts electrons up. His-N attacks H on the H2O
- Tetrahedral intermediate; C bonded to O, OH (H2O) and serine. His -N bonded to H. O shifts down electrons, serine O bond grabs H on His-N.
- Finally, NH2R, carboxylate, serine and his are separate.
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What are lipids?
- Not a functional group definition.
- Defined by a physical characteristic (solubility)
- Gunk that can be extracted from an organism with non-polar solvent.
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What are waxes?
- Esters of a long chain carboxylic acid and a long chain alcohol.
- Even number of Cs on left side (16-36)
- Even number of Cs on right side (24-36)
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What are fats and oils?
- Triglycerides
- Triesters of glycerol and long chain carboxylic acid.
- E ve ucunda OH var.
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What is saturated?
No double bonds in the long chain
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What is unsaturated?
Some double bonds
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What is polyunsaturated?
A lot of double bonds.
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Why are saturated fats solid at room temperature?
Dense packing with no branching, london dispersion forces
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What is Omega 3?
Double bond that starts from the 3rd carbon at the end
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What is soap?
- Salt of fatty acid used for cleaning
- H on OH leaves, leaving behind O-. This then forms a salt with some cation.
- The O- side is hydrophilic, the carbon-hydrogen chain is hydrophobic.
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What is detergent?
Surfactant or mixture of surfactants with cleaning properties in dilute solutions.
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Soap and detergent are both
Amphiphilic
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How do soap and detergent work?
Hydrophobic tail bonds to oil/fat dirt and coats it, hydrophilic tail dissolves it in water.
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Explain saponification
- Saponification is base catalyzed hydrolysis of an ester
- Double bonded O shifts electrons up as carbonyl is attacked by OH.
- There is tetrahedral intermediate. OR group leaves as double bonded O shifts down electrons. OR group is now negative since O is only bonded to R
- OR group steals off H from OH group bonded to carbonyl. The result is H being gone!
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Why is the alpha carbon to a carbonyl nucleophilic?
Because its protons are acidic.
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Explain base catalyzed keto-enol tautomerization
- Base grabs one alpha H. H transfers electrons to alpha carbon.
- Alpha carbon is now negative. Resonance structure is where O is negative and there is a double bond on alpha carbon.
- Negative O grabs H from BH.
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Explain acid catalyzed keto-enol tautomerization
- Double bonded O grabs H from H-A. H transfers electrons to A.
- Resonance form with negative O with three bonds. Resonance is positive C.
- A grabs one H from alpha carbon. Electrons of H is transferred to central C as double bond.
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In the equilibrium between keto and enol forms, which dominates?
The keto form dominates.
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When does the enol form dominate keto form?
- When there is stabilization due to H bonds or conjugation.
- An example of this is when there are two ketos bonded together. The enol form with one double bonded O and another OH. H is stabilized through H-bond with O on the other side.
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Describe the mechanism of acid catalyzed Br addition to acyl group.
- Double bonded O grabs H from Acid and becomes positive with three bonds.
- Double bonded O shifts electrons up as alpha proton’s electrons shift to form double bond.
- O shifts electrons back down as one of the double bonds grab a bromine.
- The other bromine (now negative) grabs H from positive OH. H shifts electrons to O so that it is neutral.
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What happens if we use a really strong base in keto-enol tautumerization?
- Base grabs one alpha proton. Electrons from alpha proton form double bond. Double bonded O shifts electrons up.
- We form an enolate as the MINOR resonance structure. (conjugate base of enol.) C on the tip is negative and a really good nucleophile.
- Reprotonation to enol or keto form is disfavored.
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Is enolate minor or major?
It is the minor resonance structure.
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What is LDA?
An example of a really strong base that generates enolates.
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What types of reactions to enolates take part in?
They act as nucleophiles in SN2 reactions
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Explain SN2 with enolate as nucleophile
Attacks electrophilic carbon. In the same step, the leaving group leaves in one step. Draw this as a single line connecting electrophilic carbon and nucleophilic carbon.
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What are aldol reactions?
- Enolate can attack an acyl copy of itself, since the c bonded to double bonded o is somewhat electrophilic.
- Only happen with weaker bases, where both forms of the enolate can exist in the pot.
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Explain steps of aldol reactions?
- Base removes an alpha proton. Electrons from alpha proton are transferred as double bond. Double bonded O shifts electrons up.
- Minor resonance from of enolate attacks carbon on itself as the prior self shifts electrons up.
- Negative O grabs an H and forms an OH.
- The result is a beta-hydroxy carbonyl.
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What is the result of aldol reactions?
Beta-hydroxy carbonyl.
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What happens when we add heat and water to beta hydroxy carbonyls?
- They turn to alpha beta unsaturated carbonyls.
- This is because they are thermodynamically favored.
- OH group leaves. There is a double bond between alpha and beta.
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Explain how beta hydroxy carbonyls convert to alpha beta unsaturated carbonyls with base catalysis.
- Base grabs H from alpha carbon. Electrons transfer to from double bond. Double bonded O shifts electrons up.
- O shifts electrons down. Double bond shifts to beta carbon. OH group leaves.
- Result is alpha beta unsaturated carbonyl.
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Explain how beta hydroxy carbonyls convert to alpha beta unsaturated carbonyls convert to alpha beta unsaturated carbonyls with acid catalysis.
- Double bonded O grabs an H and becomes positive.
- H2O grabs one alpha proton. Electrons from alpha proton shift to become double bond. O shifts electrons up to become neutral.
- O shifts electrons down. Double bond shifts places. OH leaves.
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Explain aldol reactions with esters?
- Nucleophile grabs alpha proton. Alpha proton shifts electrons to form double bond. O shifts electrons up.
- Minor resonance structure is enolate. Enolate attacks a copy of itself.
- Tetrahedral intermediate. Ester group leaves beta carbon.
- The result is a beta keto ester
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What results from aldol reactions with ester?
Beta keto, ester
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What is the general rule of decarboxylations?
If the pair of electrons left behind by the departure of CO2 can be stabilized by resonance, decarboxylation can occur.
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Why does equilibrium for decarboxylations lie on the right?
CO2 is incredibly low in energy.
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Explain decarboxylation in beta keto acid
O to H bond becomes double bond. Bond between CO2 and everything else is transferred to a carbon, which becomes negative. (Although resonance stabilized)
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What undergoes decarboxylation?
Beta keto carboxylation.
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Explain mechanism of carboxylation
- Base grabs an alpha proton. H transfers electrons to alpha carbon, making it negative.
- Negative then grabs a C on CO2 and bonds to CO (double bond) and Oi. O- grabs H back from base.
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What is oxidation?
- Decrease in number of CH bonds
- Increase in number of C heteroatom bonds (particularly C-O bonds)
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What is reduction?
- Increase in number of C-H bonds
- Decrease in number of C heteroatom bonds
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Explain energy and redox?
- Oxidation results in energy being released.
- Reduction requires energy input.
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Explain mechanism of carbonyl reduction
- NEGATIVE H (nucleophile) attacks carbonyl. O shifts electrons up.
- Tetrahedral intermediate. Negative O grabs H, resulting in OH.
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What is the source of H- in the lab?
NaBH4, LiAlH4
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What is the source of H- in biology?
NADH, NADPH, FADH2
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Explain NADH and NAD
- NAD is H- donor, reducing agent
- NADH is H- acceptor, oxidizing agent
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How does NADH reduce?
H- is not generated at any point. It shifts directly from NADH to carbonyl.
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How does NAD oxidize?
- H- is never generated.
- Base grabs H from OH, O shifts electrons from its bond to H to form double bond.
- At the same time H- acts as a leaving group and attached to NAD.
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How does aldehyde dehydrogenase work?
- It oxidizes acetaldehyde to acetic acid.
- S-ALDH attacks carbonyl. O shifts electrons up. As O shifts electrons down, H acts as a leaving group and reduces NAD to NADH.
- Water then attacks carbonyl, resulting in the loss of S and ALDH.
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Explain reduction of NADH
- Electrons from H directly bond to carbonyl
- Lone pairs on N transfer to left as double bond. The other double bond moves to the right
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Explain keto-enol tautomerization from enol to keto
- OH loses H to B.
- Resonance structure with double bonded O and negative H. C gets H.
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