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ALDEHYDES AND KETONES

This learning objective focuses on understanding the structure of the carbonyl group, naming and writing structures for aldehydes and ketones, and knowing their reactions and properties. It also covers oxidation and reduction reactions, nucleophilic addition reactions, and the role of acylation in organic synthesis.

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ALDEHYDES AND KETONES

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  1. ALDEHYDES AND KETONES LEARNING OBJECTIVES (LO) - know and understand the structure of the carbonyl group - recognise and be able to name, write structures for carbonyl compounds - know the reaction of Tollens reagent and Fehlings/ Benedicts reagent with aldehydes and ketones and understand their use for testing  - know the products of oxidation and reduction of aldehydes and ketones - understand and know nucleophilic addition reactions of aldehydes and ketones - recognise carboxylic acids as weak acids and know their reaction with carbonates - know the esterification reaction and the hydrolysis reaction, recognise these as equilibria and determine appropriate conditions using equilibrium considerations - know some uses of esters, including natural esters, soaps and biodiesel - recognise acid chlorides and acid anhydrides - know their reactions and understand their importance in organic synthesis - recognise acylation and acylation and its uses - know and be able to use the mechanism of acylation reactions - understand the role of acylation in the manufacture of aspirin

  2. aldehydes and ketonesL.O. Know and understand the structure of the carbonyl group Aldehydes and ketones have the same functional group. What is the molecular formula of the aldehyde and ketone below? an aldehyde a ketone Both have the molecular formula C3H6O

  3. Nomenclature Aldehydes L.O. Be able to name and write structures for carbonyl compounds Both IUPAC and common names are used for aldehydes and ketones. [1] Find the longest chain containing the CHOgroup, and change the -eending of the parent alkane to the suffix -al. [2] Number the chain or ring to put the CHOgroup at C1 Some common names of aldehydes Benzyaldehyde

  4. Example: Give the IUPAC name for the compound:

  5. Naming aldehydes Try and NAME these Ethanal Acetaldehyde propanal 2-methylbutanal

  6. Nomenclature for aldehydes Propanal 4-Methylpentanal 2-Ethylpentanal 4-hydroxy-2-methylbenzaldehyde 4-bromobenzaldehyde

  7. Naming Ketones in the IUPAC System Ketones are named using the suffix –one. Name both. hexan-3-one Propanone (acetone) Like alkenes, ketones with four or more carbon atoms display positional isomerism because the carbonyl group may appear between different carbon atoms. In these cases, a number is used before the –one to indicate the first carbon involved.

  8. Naming Ketones in the IUPAC System L.O. recognise and name, write structures for carbonyl compounds

  9. Let us go through This example

  10. Natural aldehydes and ketones • biologically relevant molecules possess aldehyde and/or ketone functional groups:

  11. Naming KetonesPractice (answers next slide)

  12. Answers

  13. aldehydes and ketones Aldehydes and ketones are therefore represented here with the displayed formula. Next try to name them THEN try to write structural formulae CH3CHO ethanal CH3CH2CH2CHO butanal CH3COCH2CH3 2-butanone CH3CH2COCH2CH3 3-pentanone

  14. CARBONYL COMPOUNDS - FORMULAE Aldehyde Ketone H O H H H H H C C C H H C C C O H H H H CH3 C2H5 C = O C = O CH3 H O O MolecularC3H6O Both have the molecular formulaC3H6O Structural C2H5CHO CH3COCH3 Displayed Skeletal

  15. CARBONYL COMPOUNDS – NOMENCLATURE You Try AldehydesC2H5CHO propanal KetonesCH3COCH3 propanone CH3CH2COCH3 butanone CH3COCH2CH2CH3 pentan-2-one CH3CH2COCH2CH3 pentan-3-one C6H5COCH3 phenylethanone L.O.- recognise and name, write structures for carbonyl compounds

  16. Boiling points and forces The general increase in boiling points from alkanes to aldehydes/ketones and alcohols is due to the intermolecular forces • Alkanes are only held together by London Dispersion • Ketones and Aldehydes polar carbonyl means they have (LD and DD) • Alcoholshave all 3 LD, DD, and HB Note: Carboxylic acids have 2x the due to the intermolecular hydrogen bonding, sometimes giving dimers

  17. Physical properties of aldehydes and ketones and alcohols and carboxylic Acids Carboxylic Acid Dimer

  18. Physical Properties of aldehydes and ketones δ+ δ- Small aldehydes and ketones are soluble in water As size increases, solubility decreases due to HYDROPHOBIC tails Alcohols more soluble and CA too, BUT the problem after 4 carbons is the tail.

  19. C=O Bond Bondingthe carbon is sp2 hybridised with 3 sigma (s) planar bonds the unhybridised 2p orbital of carbon is at 90° to these. when it hybridizes it overlaps with a 2p orbital of oxygen to form p bond BASICALLY, PI BONDS ALLOW FOR A LOT OF REACTIONS. P ORBITAL ORBITAL OVERLAP PLANAR WITH BOND ANGLES OF 120° NEW ORBITAL

  20. Ketone/Aldehyde Oxidation Prep How to make them L.O. know the products of oxidation and reduction of aldehydes and ketones

  21. 2 Reactions Types of aldehydes and ketones: • Oxidation: Increase Oxygen or Loss H • Oxidation: Primary OH Aldehydes Carboxylic Acids (C.A.) • but Secondary OH Ketones • Reduction: Aldehydes  10 Alcohols and Ketone  2o Alcohols • Reduction: Increase Hydrogen. Also called Nucleophilic addition: NaBH4 NaBH4

  22. 1° 2° H H R C O + [O]R C O + H2O H H H H R C O + [O]R C O + H2O RR R H R C O + [O] R 3° OXIDATION OF ALCOHOLS Why 1° and 2°alcohols are easily oxidised and 3° alcohols are not For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms. Reduction is the removal of H or adding of O This is possible in 1° and 2°alcoholsbut not in 3° alcohols.

  23. OXIDATION OF PRIMARY ALCOHOLS Aldehydes have no hydrogen bonding - they distil off immediately. if it didn’t distil off it would be oxidised to the equivalent carboxylic acid compound formula intermolecular bonding boiling point ETHANOL C2H5OH HYDROGEN BONDING 78°C ETHANAL CH3CHO DIPOLE-DIPOLE 23°C ETHANOIC ACID CH3COOH HYDROGEN BONDING 118°C What pattern do you see? OXIDATION TO ALDEHYDES DRAW DISTILLATION PROCESS OXIDATION TO CARBOXYLIC ACIDS REFLUX, What is the process? Aldehyde has a lower boiling point so distils off before being oxidised further Aldehyde condenses back into the mixture and gets oxidised to the acid

  24. 2,4-DINITROPHENYLHYDRAZINE Usereacts with carbonyl compounds (aldehydes and ketones) used as a simple test for aldehydes and ketones ESTERS, and Carboxylic Acids, Ketones And Aldehydes ALL have C=O (carbonyl). Only aldehydes and ketones go reed in DNPH or ( Brady's reagent) C6H3(NO2)2NHNH2

  25. SUMMARY OF PROCEDURE LO. Tollen’s reagent and Fehling’s/ Benedict’s reagent with aldehydes and ketones, know the tests

  26. SUMMARY OF IDENTIFICATION L.O.: know the reaction of Tollen’s reagent and Fehling’s/ Benedict’s reagent with aldehydes and ketones and understand their use in testing

  27. SUMMARY OF IDENTIFICATION L.O.: know the reaction of Tollen’s reagent and Fehling’s/ Benedict’s reagent with aldehydes and ketones and understand their use in testing

  28. CARBONYL COMPOUNDS - IDENTIFICATION L.O. know the reaction of Tollens reagent and Fehlings/ Benedicts reagent with aldehydes and ketones Tollen’sammoniacal silver nitrate (THE SILVER MIRROR TEST) mild oxidising agent which will oxidise aldehydes but not ketones contains the diammine silver(I) ion - [Ag(NH3)2 ]+ the silver(I) ion is reduced to silver Ag+(aq) + e¯ ——> Ag(s) Fehling’scontains a copper(II) complex ion giving a blue solution on warming, it will oxidise aldehydes (not with aromatic aldehydes) the copper(II) is blue and it is reduced to copper(I) red ppt Cu2O The silver mirror test is the better alternative as it works with all aldehydes Ketones do not react with Tollen’s Reagent or Fehling’s Solution

  29. : Nu Addition This is reduction, and the reducing agent is: A) H2/Pt (Electrophilic Addition) or B) NaBH4 (Nucleophilic Addition)

  30. Electrophilicity of Aldehydes and Ketones Why are aldehydes more reactive? Look at the pics, find 2 reasons 1) More alkyl groups (ketone) stabilize inductively 2) The aldehyde is less sterically crowded and lower in energy for an approaching :Nucleophile like :H-

  31. : Nu and C=O Reactivity The chemical properties of aldehydes and ketones result from the polar nature of the C=O bond. δ+ δ- The positive charge on the carbon atom is attacked by nucleophiles:CN- CYNAIDE IS DEADLY So we use KCN or NaCN , Acidified, instead of HCN ADDING ACROSS A DOUBLE BOND. THE :Nu adds to one side of The Double Bond, a hydrogen to the other

  32. NUCLEOPHILIC ADDITION CH3CHO + HCN ——> CH3CH(OH)CN 2-hydroxypropanenitrile STEP 1 STEP 2 δ + Step 1: CN¯ acts as a nucleophile, & attacks Carbon. One of the C=O bonds breaks; a pair of electrons goes onto the O Step 2: A pair of electrons is used to form a bond with H+. Overall, there has been addition of HCN

  33. Stereoisomers NUCLEOPHILIC ADDITION Watch out for the possibility of optical isomerism. What is charity? CN¯ attacks from above A chiral molecule/ion is non-superimposable on its mirror image, with 4 different attachments to the center. CN¯ attacks from below

  34. Dangers of HCN HCN(aq)H+(aq) + CN-(aq) Hydrogen cyanide (HCN) is highly volatile liquid (boiling point 26 °C), which has a faint bitter almond smell. In solution, hydrogen cyanide partially dissociates: Hydrogen cyanide is highly toxic because it inhibits a mitochondrial enzyme that is essential for respiration. Being so volatile and flammable, it is difficult to handle safely. A safer alternative is KCN, which is a solid at room temperature and is therefore easier to handle. An acidified solution contains both the H+ and CN- ions.

  35. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION ANIMATED MECHANISM

  36. Video CLIP Frankly Chem https://www.youtube.com/watch?v=Csaczjeoblc

  37. Nitriles, RCN • Closely related to carboxylic acids named by adding -nitrileas a suffix to the alkane name, with the • nitrile carbon numbered C #1 CH3CN ethanenitrile

  38. Do you remember that [O] was the loss of Hydrogen's? • So what is reduction, terms of hydrogen? • Reduction( :NU Addition of Hydrogen) • To alcohols ALDEHYDE  1O Alcohol • KETONE  2o Alcohol

  39. CARBONYL COMPOUNDS - REDUCTION WITH NaBH4 Our source of hydrogen as a :Nu is sodium borohydride, NaBH4 , Why? Recall the BH3 Lewis dot diagram How did NaBH4 come to be? Dative or coordinate covalent bond. Nucleophilic addition (also reduction as it is addition of H¯) using :H¯ (hydride ion is :Nu) Water is added or alcohol for the OTHER H+ Aldehyde Primary alcohol

  40. CARBONYL COMPOUNDS - REDUCTION WITH NaBH4 ANIMATED MECHANISM

  41. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION BOTH have a DOUBLE BOND Mechanismoccurs with both aldehydes and ketones involves addition to the C=O double bond C=O are attacked by nucleophiles at alkenes are non-polar and are attacked by electrophiles It is still addition but electrophilic addition, no δ+ C δ+ C Group Bond Polarity Attacking species Result ALKENES C=C NON-POLAR ELECTROPHILES ADDITION CARBONYLS C=O POLAR NUCLEOPHILES ADDITION SAME RESULT, DIFFERENT MECHANISMS

  42. CARBONYL COMPOUNDS - REDUCTION Functional groups containing multiple bonds can be reduced 2 ways C=C is reduced to CH-CH by electrophilic addition of H2 and Pt C=O is reduced to CH-OH by :Nu or nucleophilic addition of :H- using NaBH4 Tale of 2 Hydrogen's H2 H: H+ (electrophile) H¯ (nucleophile) ReactionsHydrogen reduces BOTH double Bonds C=C and C=O bonds CH2= CHCHO + 4[H] ——> CH3CH2CH2OH H¯ from borotetrahydride BH4 - acidified (H+)reduces ONLY C=O bonds CH2 = CHCHO + 2[H] ——> CH2=CHCH2OH ExplanationC=O is polar so is attacked by the nucleophilic H¯ C=C is non-polar so is attacked by an electrophile not a nucleophile H¯

  43. Electrophilic H2 Addition (reduction rx) with Pt Pt

  44. Examples:

  45. :Nu Addition Across a DB with Hydrogen and :H- (Hydride

  46. CARBONYL COMPOUNDS – REDUCTION or :Nu Addition ExampleWhat are the products when Compound X is reduced? COMPOUND X Pt/H2 NaBH4 C=O is polar so is attacked by the nucleophilicH¯ C=C is non-polar so is not attacked by the nucleophilicH¯ We need H2 and Pt to do a totally full job

  47. CARBONYL COMPOUNDS - IDENTIFICATION Method 1strong peak around 1400-1600 cm-1 in the infra red spectrum Method 2Tollen’s Test (silver mirror) and Fehling’s Test ( Red ppt of Copper)

  48. Remember the fun times O–H bond of the carboxyl group gives a very broad absorption 2500 to 3300 cm1 • Commonly encountered carboxyl groups absorb in a broad band centered around 1710 cm1

  49. REACTION REVIEW 10 alcohol 20 alcohol oxidation Cr2O72-, H+ reduction :H-or H2/Pt Oxidation Cr2O72-, H+, Distillation reduction, :H- or H2/Pt ketone aldehyde Oxidation Cr2O72-, H+, or Tollen’s, or Fehling’s Reflux carboxylic acid

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