CHEM 2081 Exam 3

Question 1

Ketone Nomenclature & Relative Reactivity

Answer 1

Suffix “-one”, Prefix “Oxo-“, needs locator

Less reactive than aldehydes

Question 2

Aldehyde Nomenclature & Relative Reactivity

Answer 2

Suffix “-al”, no locator due to occurrence at the end of a molcule

More reactive than ketones

Question 3

Hydride (H^-) Reducting Agents

Answer 3

+ Lithium Aluminum Hydride (LiAlH₄): Less electronegative Al, stronger negative hydride (2-step mechanisms), can also carry out SN2 reactions of alkyl halides and open epoxide rings

+ Sodium Borohydride (NaBH₄): More electronegative B, less negative hydride

Both add 1,2 on carbonyls, reduce ketones to 2^o alcohols and aldehydes to 1^o alcohols

Question 4

Sodium Hydride (NaH)

Answer 4

Relatively weaker reducing agent, adds through 1,4 addition

Deprotonates alkynes

Question 5

Organometallic (R^-) Reducing Agents

Answer 5

Form from alkyl halides

+ Organolithium Reagents (R-Li): Direct 1,2 addition
+ Grignard Reagents (R-MgBr): Direct 1,2 addition

Form 3^o alcohols from ketones (no stereochem) and 2^o alcohols from aldehydes, can also form imines from nitriles and carboxylic acids from CO₂ and acid

Question 6

Organocuperates (R₂-CuLi)

Answer 6

Form from alkyl halides, conjugate 1,4 addition, only adds 1 of 2 identical R groups

Question 7

Wittig Reactions

Answer 7

First form Wittig reagents from alkyl halides (R-X) + PPh₃ to form R-PPh₃

Direct 1,2 addition reduces C=O bonds to C=C bonds through oxaphsophatane (“box”) intermediate

cis/trans when it’s an asymmetric product

Question 8

Hemiacetals vs. Acetals

Answer 8

Form via nucleophilic addition of alcohols to a carbonyl in equilibrium.

Products favored by providing XS reactant or removing H₂O byproduct (Le Châtelier’s Principle), therefore hydrolysis can occur by adding H₂O to product to revert to carbonyl

Hemiacetals (OH-C-OR) are highly unstable, seek to form acetals (RO-C-OR), occurs through acid (forms activated carbonyl intermediate)/base (deprotonates weak Nu) catalysis

Question 9

Addition of Amines to Carbonyls

Answer 9

Amines add to carbonyls to form enamines (HN=R) from ammonia and 1^o amines, and imines (R₂N-C=R) from 2^o amines

No reaction will occur if 3^o amine is used

Question 10

Hydrolysis of Nitriles

Answer 10

Nitriles can be hydrolyzed with water under basic conditions to form an amide (R-(C=O)-N(H₂))

Question 11

Wolff-Kishner Reduction

Answer 11

Uses H₂NNH₂ with a mild acid to reduce C=O to CH₂

Question 12

Reductive Amination

Answer 12

Adds only 1 R group to an amine by reducing a carbonyl and adding it to 1^o or 2^o amines

Question 13

Monosaccharide Structure

Answer 13

Prefer cyclic form for stability, vary based on anomeric positions, making them diastereomers (anomers)