Chemistry of Cooking and Oxidation Higher Supported Study Week 3 – Part 2

Chemistry of Cooking – Key Areas Shapes of Proteins Denaturing of Proteins Flavour and Aroma Molecules Aldehydes and Ketones Tests to differentiate between Aldehydes and Ketones Effect of functional groups and properties

Shapes of Proteins Spirals, Sheets, complicated shapes Held in these shapes by intermolecular bonding

Heating Proteins (Cooking) Intermolecular bonds are broken allowing the proteins to change shape (denature). These changes alter the texture of foods. New intermolecular forces form

Flavour and Aroma Molecules Many flavour and aroma molecules are ALDEHYDES

Aldehydes Functional Group  Carbonyl (C=O) END OF MOLECULE - al endings

Naming Aldehydes

Ketones Functional Group  Carbonyl (C=O) Ketone  C=O found in middle of molecule -one ending

Aldehydes and Ketones Can be named from structural formulae. Structural formulae can be drawn from names Molecular formulae can be written from names Isomers can be drawn

Aldehyde Tests Three possible tests to determine if substance is aldehyde or ketone Oxidising Agents 1)Fehling’s Solution ( Blue  brick red precipitate) 2)Acidified potassium dichromate (orange  green) 3)Tollen’s Reagent (colourless  a silver mirror) Must be warmed in a water bath

Aldehydes Oxidise (Ketones don’t)

Intermolecular Forces

Properties High boiling points STRONG INTERMOLECULAR FORCES High Volatility (how easily it evaporates) WEAK INTERMOELCULAR FORCES SMALL MOLECULAR SIZE SOLUBILITY LIKE DISSOLVES LIKE

32.C 7 H 6 O 2 → C 7 H 8 O Which line in the table is correct for the above conversion? Reaction typeH:O ratio Areductionincreases Breductiondecreases Coxidationincreases Doxidationdecreases

27.The compound with the structure CH 2 CHCH 2 CHO is Aa saturated ketone Ba saturated aldehyde Can unsaturated ketone Dan unsaturated aldehyde.

6. The molecules shown below are isomers a)Name each of the isomers. b)Which isomer can be oxidised using Tollens’ reagent and what would be observed? AB A - butanalB – butanone Isomer A (butanal) is oxidised using Tollens’ reagent A silver mirror forms (since the silver ions are reduced to silver atoms)

8. Which type of bond is broken when a protein is denatured? A Ionic B Polar covalent C Hydrogen D Non-polar covalent C

Oxidation of Food Naming branched chain alcohols Primary, secondary and tertiary alcohols Isomeric alcohols Hydrogen bonding of alcohols Diols and Triols Oxidation of alcohols Naming branched chain carboxylic acids Reactions of carboxylic acids. Antioxidants in foods. From an ion-electron equation recognise that a substance is acting as an antioxidant.

Naming branched chain alcohols Functional Group (hydroxyl) always gets first priority when numbering longest carbon chain

What SQA expect you to be able to do: Can be named from structural formulae Structural formulae can be drawn from names Molecular formulae can be written from names

Primary, secondary and tertiary alcohols Primary – Carbon to which hydroxyl group attached is bonded to 2 or more hydrogens or is bonded to 1 carbon

Primary, secondary and tertiary alcohols Secondary – Carbon to which hydroxyl group attached is bonded to 1 hydrogen or is bonded to 2 carbons

Primary, secondary and tertiary alcohols Tertiary – Carbon to which hydroxyl group attached is bonded to 0 hydrogen or is bonded to 3 carbons

10.a) Name the following alcohols and decide whether they are primary, secondary or tertiary alcohols.

Pentan-2-ol2ry Pentan-3-ol2ry 2-methylbutan-2-ol3ry 2,2-dimethylpropan-1-ol1ry Note: These alcohols are all ISOMERS

Isomers Draw the structural formula for, and name isomeric alcohols, including primary secondary and tertiary alcohols

Question Name each of these alcohols. State for each whether it is Primary, secondary or tertiary Which type of chemical reaction could be used to distinguish which was which?

Diols and Triols The more hydroxyl groups The Stronger the H-Bonding The Higher the Boiling Point The Lower the volatility (doesn’t evaporate easily) The Higher the Viscosity(the thicker the liquid appears) More Viscous – less likely to dissolve in H 2 O (immiscible)

11. The alcohols shown below have similar molecular mass, considering their structure comment on the viscosity and boiling point of the molecules pentan-1-olbutane-2,3-diol propane-1,2,3-triol Increasing the level of hydrogen bonding will make the molecule have a higher boiling point and more viscous. Propane-1,2,3-triol will have the highest boiling point and greatest viscosity, then butane-2,3-diol and lastly pentan-1-ol.

Oxidation of alcohols

Aldehydes Oxidise (Ketones don’t)

27.Which of the following would not react with acidified potassium dichromate solution? AMethanol BMethanal CButanone DButan-2-ol

Naming branched chain carboxylic acids

Reactions of carboxylic acids. reduction in terms of products and effect on the oxygen to hydrogen ratio reactions with bases to form salts reaction with alcohols to form esters

Reduction of Carboxylic Acids

Reactions with bases to form salts Bases include Metal Oxides Metal Hydroxides Metal Carbonates

12. (i) Name the functional group circled below. carboxyl (ii) Draw a structural formula for the organic compound formed when the above compound reacts with NaOH(aq). (zero)

Antioxidants in foods Oxygen reacts with edible oils giving the food a rancid flavour. Antioxidants are molecules which will prevent these oxidation reactions taking place.

Making Food Last Longer Potatoes are typically fried under an atmosphere of steam and packaged under nitrogen.

15. Vitamin C, C 6 H 8 O 6 is an antioxidant. (i)What is the purpose of adding antioxidants to food? To increase shelf life (stop it going off) (ii) Complete the ion-electron equation for the oxidation of vitamin C. C 6 H 8 O 6 (aq)  C 6 H 6 O 6 (aq) +2H + + 2e -