Chapter 26 CARBONYLS AND CARBOXYLIC ACIDS

• What type of bond do carbonyl compounds contain?

  C=O bond
• What are the 3 types of carbonyl compounds?

  Aldehydes, ketones and carboxylic acids
• Where is the double bond located in an aldehyde?

  End of the carbon chain
• Where is the double bond located in a ketone?

  Middle of the carbon chain
• Why are smaller carbonyl compounds soluble in water?

  They can form hydrogen bonds with water
• Why do carbonyls undergo nucleophilic substitution?

  Because the C=O bond is polarized by electronegative oxygen
• Which is stronger, the C=O bond or the C=C bond in alkenes?

  C=O bond
• Why do carbonyl compounds not undergo addition reactions as easily?

  Because the C=O bond is stronger than the C=C bond
• What oxidizing agent is used to oxidize aldehydes to carboxylic acids?

  Acidified potassium dichromate
• What is the result of oxidizing aldehydes using Tollens reagent?

  Aldehydes are oxidized to carboxylic acids
• What do aldehydes reduce to when treated with NaBH₄ in aqueous ethanol?

  Primary alcohols
• What do ketones reduce to when treated with NaBH₄ in aqueous ethanol?

  Secondary alcohols
• What does [H] represent in the context of reduction reactions?

  Reducing agent
• What is the source of nucleophilic hydride ions in the reduction of carbonyls?

  NaBH₄
• How can carbonyls be reduced by catalytic hydrogenation?

  Using hydrogen and a nickel catalyst under high pressure
• What does Tollen's reagent do and what does a positive result look like?


  Distinguishes between ketones and aldehydes as it only reacts with aldehydes. Positive result is formation of a silver mirror
• How is tollens reagent made?


  Silver nitrate dissolved in sodium hydroxide to form a brown precipitate which is then dissolved into solution by addition of dilute ammonia
• What does Brady's reagent (2,4-DNP) test for and what is a positive result?


  Presence of a C=O and a positive result is formation of orange precipitate
• How can Brady's reagent distinguish between aldehydes and ketones?


  The orange precipitate can be filtered off and its melting point can be identified and compared to a data base with known melting points.
• What type of mechanism is reduction of aldehydes and ketones?


  Nucleophilic addition
• What is produced when potassium cyanide reacts with carbonyls?


  Hydroxynitriles
• How is the nucleophile generated from potassium cyanide?


  KCN is dissolved in acidic solution and dissociates forming K+ ions and CN- (nucleophile)
• What are the risks of using potassium cyanide?


  Cyanide is an irritant and can cause death if inhaled/ingested. Cyanide reacts with moisture in the air forming toxic HCN gas
• What forms when asymmetrical ketones/aldehydes react with KCN?


  A mixture of enantiomers
• Why do longer carboxylic acids not dissolve in water so well?


  The longer the hydrocarbon, the less soluble because the hydrocarbon part is non-polar
• Why are carboxylic acids weak acids?


  They only partially dissociate into H+ and the carboxylate ion
• Carboxylic Acid + Bases =?


  Salt and water
• Carboxylic Acid + Metals =?

  Salt and Hydrogen
• Carboxylic Acid + Metal Oxides =?


  Salt and Water
• Carboxylic Acid + Carbonates = ?


  Salt, Water and Carbon dioxide
• How are acyl chlorides formed?


  Carboxylic acid reacts with thionyl chloride (SOCl2)
• What suffix do acyl chlorides have and what functional group?


  -oyl chloride

  -COCl group
• Acyl Chloride + Water =?


  Carboxylic acid + HCl
• Acyl Chloride + Ammonia =?


  Amide + HCl
• Acyl Chloride + Alcohol =?


  Esters + HCl
• Acyl Chlorides + Primary Amines =?


  N-Substituted amides + HCl
• What reaction mechanism do acyl chlorides undergo?


  Nucleophilic addition-elimination
• How are acid anhydrides made?


  Reacting 2 of the same carboxylic acid together
• What suffix do acid anhydrides have?

  -anhydride
• Acid Anhydride + Alcohol =?


  Esters and carboxylic acids