Orgo Exam 3

What does a hemiacetal contain?

one -OH group and one -OR group

What does an acetal group contain?

two -OR groups

What environment does acetal formation take place in?

Acidic only 

What is the purpose of acetal hydrolysis?

to remove the protecting group

Why are acetals used as protecting groups?

They protect aldehydes/ketones from reacting while other parts of the molecule react

How are protecting groups removed?

Acid and water (acetal hydrolysis)

How do you recognize a protecting group?

Two oxygens that are each part of OR groups 

What conditions are required for imine formation?

Acidic

How do you form an imine?

Carbonyl and primary amine

What is the mechanism for imine formation?

1. Nu attack by amine 

2. Protonate

3. Deprotonate

4. Protonate to make better LG

5. Eliminate LG

6. Deprotonate 

When the nucleophile is a secondary amine, what is the product?

Enamine

When the nucleophile is a hydride (NaBH3CN), what is the product?

Reductive Amination Product (C-N bond remains, C=O replaced by C-h)

When the nucleophile is -CN, what is the product?

aminonitrile - Strecker Synthesis 

What are the conditions for an SN2 reaction?

strong nucleophile, polar aprotic solvent 

What are the favored structures for SN2?

primary > secondary > never tertiary (too much steric hinderance)

What are key features of SN2?

one step concerted reaction, backside attack, inversion of stereochemistry

What are the conditions for an E2 reaction?

strong base, heat favors elimination 

What are the favored structures for E2?

strong base

What are key features of E2?

one step concerted, beta - hydrogen bond much be anti-periplanar, forms alkene

What are the conditions required for an SN1 reaction?

weak nucleophile, polar protic solvent 

What are the favored structures for SN1?

tertiary > secondary > never primary

What are the key features of SN1?

Carbocation intermediate, racemization

What are the conditions required for E1?

weak base, heat favors elimination 

What are the favored structures for E1?

tertiary > secondary > never primary

What are key features of E1?

Carbocation intermediate, possible rearrangements

What are the protic solvents?

Water and alcohol

What are the aprotic solvents?

DMSO and acetone

What is the mechanism for these conditions - primary + strong nucleophile (no strong base)?

SN2

What is the mechanism for these conditions - primary + strong bulky base 

E2

What is the mechanism for these conditions - secondary + strong nucleophile/base

SN2 or E2 (depends on heat)

What is the mechanism for these conditions - secondary + weak nucleophile in protic solvent?

SN1 or E1 (depends on heat)

What is the mechanism for these conditions - tertiary + strong base?

E2

What is the mechanism for these conditions - tertiary + weak nucleophile?

SN1/E1

SN1 steps 

1. carbocation formation 

2. Nu attack 

3. deprotonation (if Nu was neutral)

SN2 steps 

1. Nu attack and leaving group leaves (concerted)

E1 steps

1. Leaving group leaves

2. deprotonation by base

E2 steps 

1. Proton removal via strong base (deprotonation) and leaving group leaves (concerted)

Acetal Formation Steps

1. Protonation of carbonyl

2. Nu attack by alcohol

3. Deprotonate to hemiacetal

4. Protonate hydroxyl group

5. Loss of water (elimination)

6. Nu attack using 2nd alcohol

7. Deprotonate to acetal

What is a reduction?

If the oxidation state of the C atom decreases from reactant to product 

What is oxidation?

If the oxidation state of the C atom increases from reactant to product

When H- is added to aldehydes and ketones what is produced?

Alcohols

When an aldehyde is reduced what type of alcohol is produced?

Primary

When a ketone in reduced what type of alcohol is produced?

Secondary 

What is used to oxidize an alcohol?

Jones reagent - Na2Cr2O7 + H2SO4

What is an imine?

C=N

What is an enamine?

C=C

Which are stronger bases, amines or alcohols?

Amines 

Which are stronger nucleophiles, alcohols or amines?

Amines

What is a Zwitterion?

Neutral molecule with 2 atoms having opposite formal charges

What is Zaitsev’s Rule?

In elimination of H-X from an alkyl halide, the more substituted alkene is formed as the major product (for small bases only)

NaBH4 reduces which group?

Aldehydes and ketone only

LiAlH4 reduces which groups?

Aldehydes, jetones, esters, carboxylic acids, and amides

What does PCC do to a primary alcohol?

Oxidizes it to an aldehyde

What does a Jones Reagent (Na2,Cr2,O7/H2SO4) do to a primary alcohol?

Oxidizes to a carboxylic acid

What group do acetals protect?

carbonyls (ketones and aldehydes)