Presentation is loading. Please wait.

Presentation is loading. Please wait.

Food Chemistry Chapter 17 in Green / Damjii. Homework Read F9– Texture pp. 488-490 Do Qs 43-50 on p 494 F.9: Texture.

Similar presentations


Presentation on theme: "Food Chemistry Chapter 17 in Green / Damjii. Homework Read F9– Texture pp. 488-490 Do Qs 43-50 on p 494 F.9: Texture."— Presentation transcript:

1 Food Chemistry Chapter 17 in Green / Damjii

2 Homework Read F9– Texture pp Do Qs on p 494 F.9: Texture

3 F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

4 Types of Isomerism – II cont. Stereoisomers – Enantiomers (aka Optical Isomers) Requires a molecule with a chiral center – An atom (usu C) with four different groups attached to it – aka an asymmetric carbon atom Two forms are mirror images of one another that cannot be superimposed on each other (like gloves)

5 24.2 achiralchiral

6

7 Types of Isomerism – II cont. Stereoisomers – Enantiomers Common example are amino acids – only glycine does not have an enantiomeric form

8 Types of Isomerism – II cont. Stereoisomers – Enantiomers Common example are amino acids – only glycine does not have an enantiomeric form - why?

9

10 Types of Isomerism – II cont. Thalidomide a drug once prescribed to counteract pregnancy-related morning sickness, is an effective sedative as the R enantiomer (left side), but the S enantiomer (right side) is a potent teratogen (it causes birth defects). Source -

11 Types of Isomerism – II cont. Stereoisomers – Enantiomers have different effects on polarised light said to be optically active in a polarimeter if a mixture has both enantiomers it is said to be a racemic mixture and is not optically active

12

13 CONVENTION 1: – dextrorotary [ + or (d) ] – clockwise rotating enantiomer; positive specific rotation value – laevorotatory [ - or (l) ] – counter clockwise rotating enantiomer; negative specific rotation value Does differentiate between the 2 enantiomers… but does NOT indicate absolute configuration (spatial arrangement). F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

14 CONVENTION 2: D, L (no relation to d and l ) – older convention… used mostly for sugars and amino acids – Most naturally occurring sugars are in the D-form ! (and taste sweet) – Most amino acids are in the L-form ! (and are tasteless) – Enantiomers that don’t occur naturally are typically NOT metabolized by our bodies. F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

15 CONVENTION 2: D, L (no relation to d and l ) – For sugars… absolute configuration related to glyceraldehyde Locate chiral center Orient aldehyde group away from you If OH is on right, the sugar is D- If OH is on left, the sugar is L- – Most naturally occurring sugars are in the D-form ! (and taste sweet) F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

16 CONVENTION 2: D, L (no relation to d and l ) – For amino acids… use “CORN” rule Locate chiral center and orient C-H bond away from you If the groups COOH, R, NH2 are arranged clockwise around the chiral carbon the amino acid is the D-form If the groups COOH, R, NH2 are arranged counterclockwise around the chiral carbon the amino acid is the L-form – Most amino acids are in the L-form ! (and are tasteless) F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

17 CONVENTION 3: R, S – Newer convention… used for most other compounds – aka CIP system – named after originators: Cahn, Ingold, and Prelog F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

18 SYSTEM 3: R,S  Locate chiral center  Rank atoms bonded to the chiral carbon in order of increasing atomic number. (One through four, one being the group of highest priority… highest atomic number).  H < C < N < O < F < Cl < Br  If there are two or more atoms with same atomic number the second atoms are used to rank the substituents… then the third… etc.  Orient the molecule so that the lowest ranking (4) substituent points away from you.  If the other three substituents decrease in a clockwise direction, it is the R-enantiomer  If the other three substituents decrease in a counterclockwise direction, it is the S-enantiomer F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.

19  Orient the molecule so that the lowest ranking substituent points away from you.  If the other three substituents decrease in a clockwise direction, it is the R- enantiomer  If the other three substituents decrease in a counterclockwise direction, it is the S-enantiomer

20 F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.  Orient the molecule so that the lowest ranking substituent points away from you.  If the other three substituents decrease in a clockwise direction, it is the R- enantiomer  If the other three substituents decrease in a counterclockwise direction, it is the S-enantiomer

21 F.9.1: Explain the three different conventions used for naming the different enantiomeric forms. (S)-(+)-lactic acid (left) and (R)-(–)-lactic acid (right)lactic acid

22 F.9.1: Explain the three different conventions used for naming the different enantiomeric forms. Enantiomers of citalopram (anti- depressant). citalopram The top is (S)- citalopram(S)- citalopram The bottom is (R)- citalopram

23 F.9.1: Explain the three different conventions used for naming the different enantiomeric forms.  Enantiomers of mecoprop, 2-(4-chloro-2-methylphenoxy)propanoic acid – a herbicidemecoprop This molecule (on left side) needs to be re- oriented so the C-H bond is facing away from us

24 Natural flavors tend to be pure enatiomers – biosynthesis is stereospecific Synthetic flavors tend to be racemic mixtures Alpha-ionone (found in raspberries) Natural = R-alpha-ionone F.9.2: Distinguish between the properties of the different enantiomeric forms of stereoisomers found in food.

25 Stereoisomers – Enantiomers Usually have similar physical properties – except when they interact with other optically active substances – which happens often in the human body Usually have similar chemical properties – except when they interact with other optically active substances – which happens often in the human body – general, only one enantiomer of a drug, agrochemical (herbicide, pesticide), flavoring agent, or other molecule (when asymmetric) has the desired biological effect, while the other enantiomer has very different effects or, at least, places a metabolic burden on the body.

26 Types of Isomerism – II cont. amino acid asparagine - taste one form tastes bitter, the other tastes sweet each of the two enantiomers binds differently to chemoreceptors in the tongue. Source -

27 Carvone forms two mirror image forms or enantiomers: R-(–)-carvone smells like spearmint (happens to be laevorotary) S-(+)-carvone, smells like caraway seeds. – each of the two enantiomers binds differently to chemoreceptors in the nose

28 Limone forms two mirror image forms or enantiomers: R + (d) enantiomer - smells like orange S – (l) enantiomer - smells like lemon

29 (R)-(+)-(E)-alpha-ionone violet-like fruity raspberry-like flowery ( Yamamoto et al., 2009) (S)-(-)-(E)-alpha-ionone – woody cedar wood like fresh juicy greenish flavor(aroma) ( Yamamoto et al., 2009)


Download ppt "Food Chemistry Chapter 17 in Green / Damjii. Homework Read F9– Texture pp. 488-490 Do Qs 43-50 on p 494 F.9: Texture."

Similar presentations


Ads by Google