chapter 19 reactions

nucleophilic addition reactions to C=O

C=O is the electrophile due to the partial positive charge. This makes it susceptible to a nucleophilic attack

hydration of C=O (NA to C=O)

addition of H2O…Addition of water (H₂O) in the presence of an acid (H⁺) or base (OH⁻) catalyst results in the formation of hydrates

• Reagents: H2​O with an acid (H+) or base (OH−) catalyst.

• Product: A hydrate (gem-diol).

• Key Fact: The reaction is reversible; aldehydes generally favor hydrate formation more than ketones

cyano hydrin formation

• Reagents: HCN (often generated from NaCN at pH 9–10 in H2​O).

• Product: Cyanohydrin.

• Key Fact: This reaction is reversible under basic conditions; the carbonyl form is typically thermodynamically favored.

election ____ groups attatched to the carbonyl carbon make additon reaction more ______. while eclectron ____ groups attached to carbon make addition reaction less favorable

• withdrawing(larger keq)

• donating (smaller keq)

bulky alkyl groups around the C=O are going to _____reactivity

decrease

acetal and hemicetal formation

• Reagents: Alcohol (ROH) and a trace acid catalyst.

• Products:

  • Hemiacetal: Formed when one equivalent of alcohol adds to the carbonyl.

  • Acetal: Formed when a large excess of alcohol is used.

• Protecting Groups: 1,2- or 1,3-diols are used to form cyclic acetals, which protect the carbonyl from strong bases or reducing agents like LiAlH4​. They are removed with dilute aqueous acid

what are the 3 nucleophilic reactions

1. hydration (addition of h2o to C=O)

2. cyanohydrin formation ( addition of HCN, NACN, ph9-10 H2O)

3. acetal and hemiacetal formation (hemiactel, both acidic and basic 1eq of OH, acetal, large excess of OH used acididc conditions only)

reactions with nitrogen nucleophiles —→ imine formation[schiff base]

• Reagents: Primary amine (R−NH2​) and an acid catalyst (optimum pH 4–6).

  +1

• Mechanism: Proceeds via a hemiaminal (carbinolamine) intermediate followed by dehydration

enamin formation

• Reagents: Secondary amine (R2​NH) and an acid catalyst.

  +1

• Mechanism: Formation of a carbinolamine, then dehydration to an iminium ion, followed by deprotonation at the α-carbon.

imines an enamine readily og tback to their corresponding aldehydes or ketones and amines in the presence of ______

aqueous acid

imine formation sequence

carbonyl —> carbinolamine—>protonated intermediate—>iminium—>imine

imine hydrolysis —> going back to carbonyl and primary NH2

imine—>protonated imine—>carbinolamine—>carbonyl

reduction reaction- hydridd reduction

• Reagents: NaBH4​ (selective, used in protic solvents like CH3​OH) or LiAlH4​ (highly reactive, requires anhydrous solvents like THF).

  +2

• Products: Aldehydes reduce to 1∘ alcohols; ketones reduce to 2∘ alcohols

what is the NaBH4 reducin agent used for

more selective because it is weaker

• aldehydes

• ketones

• imine

inbprotic solvents

LiAlh4 used for

stronnger reduicing agent

• COOH

• esters

• amides

• nitriles

The hydride ion in LiAlH4 is ______ than the hydride ion in NaBH4,and therefore, it is LiAlH4 reacts with _________lewis, but NaBH4 does not

• more basic

• more reactive

• alkyl halides, alkyl tosylates, and nitro groups

lewis acid

electron pair acceptor

lewis base

electron parin donor