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Chemistry 102 Week 3 lecture 1 (Mon)

Chemistry 102 Week 3 lecture 1 (Mon). Start chapter 17 Organic and Biochemistry for the Allied Health Fields Dr Mark Deming. Chapter 17 Aldehydes and ketones. Next few chapters compounds with OXYGEN. Alcohols Ethers Aldehydes Ketones

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Chemistry 102 Week 3 lecture 1 (Mon)

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  1. Chemistry 102Week 3 lecture 1 (Mon) • Start chapter 17 • Organic and Biochemistry for the Allied Health Fields • Dr Mark Deming

  2. Chapter 17 Aldehydes and ketones

  3. Next few chapterscompounds with OXYGEN Alcohols Ethers Aldehydes Ketones Carboxylic acids Esters 1 CH 14 2 Connections to O CH 17 More oxidized CH 18,19 3 4

  4. Aldehydes and Ketones The carbonyl group Aldehydes have at least one hydrogen attached to the carbonyl group. Ketones have two carbons attached to the carbonyl group.

  5. methanal propanone Fig. 14-1, p.447

  6. Naming Aldehydes Find the longest carbon chain that contains the aldehyde group. Note: it will always be at the end and it will always be carbon #1 Change ending of the root alkane name by dropping –e and adding –al. All other branches and groups are named and located using standard IUPAC system.

  7. Why aren’t these 1-butanals ? butanal Examples: 3-bromobutanal

  8. Naming Ketones Find the longest chain that contains C=O. Using the root alkane name, drop the –e ending and change to –one. Number the longest carbon chain so the C=O group has the lowest number. Name and number other substituents (side groups) as before.

  9. Examples:

  10. Physical Properties of aldehydes and ketones Three physical properties of these molecules • Melting Point, Boiling Point (focus on BP) • Relative to each other The more major atoms, the higher the boiling point • Relative to other functional groups of the same size Alkanes~ethers<adehydes~ketones<alcohols<acids<salts • Solubility in water alkanes<ethers<aldehydes~ketones~alcohols<acids<salts • Smell (fragrance if good, odor if bad)

  11. can take 2 H-bonds CANT GIVE H- BONDS More polar than alcohol or ether Physical Properties The carbonyl group is moderately polar, but it doesn’t have any hydrogens attached, so it cannot hydrogen bond between molecules. Increasing polarity Ether alcohol aldehyde/ketone water No give 1 no give 2H-bond H-bond H-bond H-bond

  12. Intermolecular Forces (between molecules) Ionicmust be an ionic compound (made of full charges)starts with metal or ammonium Super H-bondingH-bonding + polar + partially ionizescarboxylic acid COOH H-bonding from a O-H > N-H to a lone pair on O: > N:Amide (with H) > alcohol (OH) > amine (NH) Dipolar net polar moleculeester > amide (no H) > aldehyde > ketone > ether London Dispersion Forces (LDF)Non polar molecule (all molecules) aromatic > -ynes > -enes > -anes (only C,H) Same force higher mass  higher mp, higher bp, lower vapor pressure Same approx. mass higher force  higher mp, higher bp, lower vapor pressure = Energy of Attraction (additive) Energy of Disruption High TEMP(higher velocity) gas bp Low Mass (MW) High Vibration High Velocity Starts with at given temp.(same force)High Mass (MW) Low Vibration Low Velocity Has OH or NH liquid Increase Energy of Attraction Increase Energy of Disruption mp Has O or N solid Low TEMP(lower velocity)

  13. Physical Properties of aldehydes and ketones Boiling point True to all organic molecules: the bigger the molecule of the same type, the higher the boiling point (and melting point) In a pure liquid the function group C=O will interact with each other. The polarity of the C=O group is actually greater than the polarity of the OH group but because of H-bonding the alcohol still has a stronger connection. This makes the boiling point of aldehydes and ketones higher than alkanes and ethers, but lower than alcohols.

  14. Big atomsC,O,N 7 6 5 4 Fig. 14-2, p.451

  15. Table 14-2, p.450

  16. Physical Properties of aldehydes and ketones Solubiliy in water: The C=O group can hydrogen bond with water molecules. This makes low molecular weight aldehydes and ketones water soluble (they have small hydrophobic sections).

  17. Fragrant Aldehydes

  18. Fragrant Ketones

  19. Some steroids are ketones

  20. excess O2 CO2 + H2O Aldehyde or Ketone  Combustion  limited O2 C + H2O or CO + H2O React with H2, Pt React with first alcohol Reactwith [O] Reduction, [H]Hydrogenation (adding H2 ) Oxidation, [O] [O]=oxidizing agent Hemi formation If aldehyde If ketone If aldehyde If ketone If aldehyde If ketone Hemiacetal Hemiketal Primaryalcohol Secondary alcohol Carboxylic Acid ----No---- Reaction React with second alcohol Acetal Ketal

  21. CombustionOxidation [O] Hemi-formation Aldehyde or Ketone Reduction, [H]Hydrogenation adding H2 (as H2 or as H-, H+ combo) [H] – 2nd Way(more practical to do in lab or in cells) Two Step1. add H- (hydride)2. add H+ (acid) [H] - 1st Way(easiest to think about) One Stepadd H2 with catalyst Ketone (middle) Aldehyde (end) [H] [H] Secondary alcohol Primary alcohol Example aldehyde Example ketone

  22. How we may write Reductions Add two H’s across the CO double bond to get the alcohol • We need to know the basic reaction • Though the reaction may be written in various ways to show how it is actually done. One stepadd H2 Two stepsH-,H+ combo

  23. Reduction, add H2 • The carbonyl group of an aldehyde or ketone is reduced to an -CHOH or -CH2OH group by hydrogen in the presence of a transition-metal catalyst (like platinum, Pt): • Reduction of an aldehyde gives a primary alcohol. • Reduction of a ketone gives a secondary alcohol.

  24. Reduction, add H2 (cont.) The addition of H2 in the presence of catalysts.

  25. Reduction, add H2 (cont.) Examples:

  26. Reduction, [H] (H- then H+ combo) • The most common laboratory reagent for the reduction of an aldehyde or ketone is sodium borohydride, NaBH4which is easy to weigh out. • This reagent contains hydrogen in the form of the very reactive hydride ion, H-. • In a hydride ion, hydrogen has two valence electrons and bears a negative charge. • In a reduction by sodium borohydride, hydride ion adds to the partially positive carbonyl carbon which leaves a negative charge on the carbonyl oxygen. • Reaction of this intermediate with aqueous acid (shown as H+ or H3O+) gives the alcohol.

  27. Reduction, [H] (H- then H+ combo)(don’t worry about this, only know [H] • Reduction by NaBH4 does not affect a carbon-carbon double bond or an aromatic ring.

  28. Reduction [H], (H- then H+ combo) Biological with NADH • In biological systems, the agent for the reduction of aldehydes and ketones is the reduced form of nicotinamide adenine dinucleotide, abbreviated NADH (Section 26.3) • This reducing agent, like NaBH4, delivers a hydride ion to the carbonyl carbon of the aldehyde or ketone. • Reduction of pyruvate, the end product of glycolysis, by NADH gives lactate.

  29. CombustionReduction [H]Hemi-formation Aldehyde or Ketone Oxidation Increase # of oxygen connections [O]=oxidizing agent (end) (middle) aldehyde ketone [O] [O] Carboxylic Acid ----No---- Reaction New O connection Example aldehyde Note: [O] can be in reaction or written on top of arrow Example ketone

  30. Aldehyde and Ketone Reactions Recall the oxidation of alcohols to produce aldehydes and ketones.

  31. Oxidation Reactions • Aldehydes are oxidized to carboxylic acids by a variety of oxidizing agents, including potassium dichromate. • Liquid aldehydes are so sensitive to oxidation by O2 of the air that they must be protected from contact with air during storage. [O]

  32. Oxidation Reactions (cont.) The ease with which aldehydes are oxidized allows us to test for the presence of aldehydes with Tollens’ reagent or Benedict’s reagent (these are weaker oxidizing agents). In general, ketones fail to react with these reagents.

  33. Oxidation Reactions (cont.) In the presence of aldehydes, Benedict’s reagent, an Oxidizing Agent, [O] produces a red precipitate. Acid , H+ or H3O+

  34. CombustionReduction [H]Oxidation [O] Aldehyde or Ketone Hemi formation(addition of alcohols) (end) (middle) aldehyde ketone R”OH R”OH Add first alcohol Hemiacetal Hemiketal Add second alcohol R”OH R”OH Acetal Ketal

  35. aldehyde Hemiacetal Acetal ketone Ketal Hemiketal

  36. Acetal Formation Reactions, cont. The addition of alcohols to aldehydes produces an unstable hemiacetal intermediate. Addition of a second alcohol makes an acetal

  37. Acetal Formation (cont.)

  38. Ketal Formation Reactions, cont. The addition of alcohol to ketones produces an unstable hemiketalintermediate. Addition of a second alcohol results in a ketal

  39. Ketal Formation (cont.) Specific Example:

  40. Hemiacetals, Hemiketals in Rings O O CH2CH2CH2CCH3 CH2CH2CH2CH2CH OH ketone OH aldehyde Reactions, cont. Cyclical hemiacetals and hemiketals are more stable than open chains and are important in carbohydrate chemistry. an internal Hemiketal (Cyclic ketone/alcohol) an internal Hemacetal(Cyclic aldehyde/alcohol)

  41. Acetal and Ketal reactions (cont.) Acetals and ketals are stable, but may be converted back to aldehydes and ketones through acid catalyzed hydrolysis. Hydrolysis is where water (H2O) gets incorporated into the structure of the molecule typically as an H and an OH separately. (This is different than hydration which has waters loosely attached to the outside of a molecule but is still water.)

  42. Add =O, and H’sBreak C—O bonds Get final molecule Reactions, cont. Acetal hydrolysis: Ketal hydrolysis:

  43. Specific Exampleof a ketal hydrolysis:

  44. * * * Important Aldehydes and Ketones Formaldehyde (methanal) Gas at room temperature Formalin – 37% aqueous solution Sterilizer Embalming fluid Formaldehyde is starting material for plastics such as Formica and Bakelite. * Need to know

  45. Important Aldehydes and Ketones, cont. Acetone (propanone) * Important organic solvent used in such things as nail polish remover. * Miscible (easily mixes) with water.

  46. * * Important Aldehydes and Ketones, cont. Progesterone and testosterone(female and male sex hormones) are ketones. Some aldehydes and ketones are very fragrant and are used in flavorings. Vanillin (vanilla) Cinnamaldehyde (cinnamon) Citral (citrus flavoring) Camphor (medicinal odor)

  47. End of chapter 17

  48. Neutralize with acid Reactions, cont. In the presence of aldehydes, Tollens’ reagent produces a silver coating on glass. Oxidize aldehyde to carboxylic acid

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