Aldehydes and Ketones

• Carbonyl Group (C=O)

  • most important functional group
• Carbonyl Group 1: Aldehydes and Ketones
• Carbonyl Group 2: Carboxylic acid and Derivatives
• Aldehyde (-H) and Ketone (-R') are not electronegative enough to stabilize negative charge and cannot serve as a leaving group
• Aldehyde and Ketones are not able to serve as leaving groups which means they do not undergo SN reactions
• C=O of Aldehyde and of Ketone behaves similarly to C=C of alkenes
• Aldehydes and Ketones undergo nucleophilic addition reaction (AN)
• As functional groups, aldehydes are always attached to terminal carbon while ketones are internal
• Cyclic structure are only possible for ketones as well
• Synthesis of Aldehydes and Ketones

  • Hydration
  • Oxidation
  • FC Acylation
• Hydration to Alkynes

  • Markovnikov's Hydration = Ketone
  • Anti-Markovnikov's Hydration = Aldehyde
• Anti-Markovnikov's Hydration

  • H2O + BH3/THF/H2O2, NaOH, H2O
• Oxidation of Alcohols

  • Primary Alcohol = Aldehyde = Carboxylic Acid
  • Secondary Alcohol = Ketone
  • Tertiary Alcohol = does not undergo
• FC Acylation of Aromatic Ring

  • Benzene + RCO-Cl/RCO-Br + AlCl3/AlBr3
• Markovnikov's Hydration

  • H2O + H2SO4/HgSO4
  • Hg(OAc)2, H2O/NaBH4
• Nucleophilic Addition Reactions

  • can take place in basic or acidic conditions and is only differentiated by the intermediate in basic conditions
• Common Nü used for AN Reactions:

  • Negatively charged Nü (basic conditions) = -OH, -H, R3C-, RO-, and -CN
  • Neutral Nü (acidic conditions) = H2O, ROH, NH3, RNH2
• Nucleophilic Addition Reactions: In basic condition

  • the Nü adds to the carbonyl group using an electron pair
  • the addition creates an alkoxide ion intermediate
  • the intermediate is protonated by an acid or a solvent forming the final product
• Nucleophilic Addition Reactions: In acidic condition

  • an acid protonates the carbonyl group which increases the electrophilic potential of the carbon atom
  • a neutral Nü attaches to the C=O group and a base deprotonates the Nü regenerating the acid catalyst
• Alcohol Formation

  • from aldehydes and ketones is done by either addition of an H- (hydride - reduction) or C- (carbanion - RMgX reaction) resulting to a type of alcohol
  • reduction reaction
• AN with Hydride reagents - Reduction

  • Aldehyde = Primary Alcohol
  • Ketone = Secondary Alcohol
  • reagents used: NaBH4, ethanol/H3O+ (mild reducing), LiAlH4/H3O+ (strong reducing)
• AN with Carbanion - using RMgX reagent

  • Formaldehyde = Primary Alcohol
  • Aldehyde except formaldehyde = Secondary Alcohol
  • Ketone = Tertiary Alcohol
  • reagents used: RMgX, ether/H3O+
• Hydrate Formation

  • from aldehydes and ketones is done by adding water to the carbonyl group resulting to a carbonyl hydrate or geminal diols
  • catalyzed in both basic and acidic conditions
• Hydrate Formation: Basic condition

  • reaction is rapid because the -OH is a better nucleophile than in water
  • resulting into an alkoxide intermediate
• Hydrate Formation: Acidic condition

  • the reaction is rapid because the protonated carbonyl is a better electrophile than in water
• Dehydration of Vicinal Diols will produce a pi bond
• Acetal Formation

  • from aldehydes and ketones is done by adding alcohol to a carbonyl group resulting to an acetal (for aldehydes) or ketal (for ketones)
  • acetals are two ether-like bonded to the same carbon
  • acetals are used to protect aldehydes/ketones in synthesis reaction
  • acid catalyzed and is reversible like hydrate formation
  • yields an -OH intermediate, hemiacetal/hemiketal and subsequent reaction with another mol of ROH yields the final product, and acetal or ketal
• Imine Formation

  • from aldehydes and ketones is done by adding amines to a carbonyl group resulting into an imine (R2C=NR')
  • by product is H2O
  • NH3 or RNH2 -> Amino Alcohol -> Imine
• Conjugates Nucleophilic Addition

  • takes place when an aldehyde or ketone have their carbon group directly attached next to a C=C, it is referred to as an alpha, beta unsaturated aldehyde or ketone