310-38 - Organic Organic Lecture Series CH 310 N LECTURE 38...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Organic Organic Lecture Series CH 310 N LECTURE 38 Textbook Assignment: Chapter 25- Carbohydrates Homework (for credit): POW 12 (Due 4/25) Today’s Topics: Carbohydrates-structure; chirality; nomenclature. Notice & Announcements: XM3: Grading in Progress Selected Topics from Chapters 25, 26 & 27 for the rest of the course. Use lecture notes for topics. Med Seminar Today: 1 Organic Lecture Series Carbohydrates Chapter 24 2 Carbohydrates Organic Organic Lecture Series Carbohydrate: a polyhydroxyaldehyde, a polyhydroxyketone, polyhydroxyketone, or a compound that gives either of these compounds after hydrolysis 3 Carbohydrates Organic Lecture Series Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate – they have the general formula CnH2nOn; Cn(H2O)n where n varies from 3 to 8. – will use –ose in the suffix – aldose: a monosaccharide containing an aldehyde group – ketose: a monosaccharide containing a ketone group 4 Organic Organic Lecture Series Monosaccharides • Monosaccharides are classified by their number of carbon atoms N ame Trios e Tetros e Pen tos e Hexose Heptose Octose Formula C3 H6 O3 C4 H8 O4 C5 H1 0 O5 C6 H1 2 O6 C7 H1 4 O7 C8 H1 6 O8 5 Organic Lecture Series Monosaccharides • There are only two trioses CH O CH O H CH2 O H Glyceraldehyde (an aldotriose) CH2 OH C= O CH2 OH D ihydroxyacetone (a ketotriose) H2C HC H2C OH OH OH Glycerol 1,2,3-Propanetriol 6 Monosaccharides CHO CHOH CH 2 OH Glyceraldehyde (an aldotriose) CH 2 OH C= O CH 2 OH D ihydroxyacetone (a ketotriose) Organic Organic Lecture Series • Often the designations aldo- and keto- are omitted and these compounds are referred to simply as trioses, tetroses, and so forth – although these designations do not tell the nature of the carbonyl group, they at least tell the number of carbons 7 Organic Lecture Series Monosaccharides • Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers CHO HO C H CHO H C OH CH2 OH (R )-Glycerald ehyde CH2 OH (S)-Glyceraldeh yd e 8 Organic Organic Lecture Series Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers: CHO H C OH HO CH2 OH (R )-Glycerald ehyde CHO C H CH2 OH (S)-Glyceraldeh yd e HO CHO CH2OH OHC OH CH2OH 9 Organic Lecture Series • Fischer projection: a two dimensional representation for showing the configuration of configuration carbohydrates – horizontal lines represent bonds projecting forward – vertical lines represent bonds projecting to the rear – the only atom in the plane of the paper is the stereocenter stereocenter CHO H C OH convert to a Fisch er p rojection CHO H . OH CH2 OH (R )-Glycerald ehyde (three-dimensional represen tation ) CH2 OH (R)-Glyceraldeh yd e (Fis cher projection) 10 Organic Organic Lecture Series D,L Monosaccharides In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde (aldehyde is C1-at the top). CHO H OH CH2 OH D -Glyceraldehyde 25 [α ]D = +13.5 -OH to Right CHO HO H CH2 OH L-Glyceraldehyde 25 [α ]D = -13.5 -OH to Left 11 Organic Lecture Series According to the conventions proposed by Fischer: – D-monosaccharide: a monosaccharide that has the same configuration at its penultimate carbon as D-glyceraldehyde; that is, its -OH is on the right when written as a Fischer projection projection – L-monosaccharide: a monosaccharide that has the same configuration at its penultimate carbon as L-glyceraldehyde; that is, its -OH is on the left when written as a Fischer projection 12 12 Organic Organic Lecture Series D,L Monosaccharides • Here are the two most abundant D-aldotetroses and the two most abundant D-aldopentoses • The configuration is assigned at the next to last C in the chain CHO CHO H H OH OH CH 2 OH D-Erythrose HO H CHO H OH CH 2 OH D-Threose H H H OH OH OH CH 2 OH D-Ribose H H H CHO H OH OH CH 2 OH 2-Deoxy-Dribose 13 Organic Lecture Series And the three most abundant hexoses: CHO H HO H H OH H OH OH CH2 O H D - G l u co se H HO HO H CH O OH H H OH CH 2O H D - G a l a ct o se HO H H CH2 O H C O H OH OH CH2 O H D -F r u ct o se 14 Organic Organic Lecture Series Amino Sugars • Amino sugar: a sugar that contains an -NH2 group in place of an -OH group – only three amino sugars are common in nature – N-acetyl-D-glucosamine is a derivative of Dglucosamine CHO O CHO H2 N H H NHCCH3 H NH2 HO HO HO H HO H 4 H H H OH HO H H H H OH H OH CH2 OH CH2 OH D -Glu cosamine D -Mannosamine D -Galactosamine N-Acetyl-D glucos amin e 2 CHO NH2 H OH OH CH2 OH CHO H H OH OH CH2 OH 15 Physical Properties Organic Lecture Series • Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol – sweetness relative to sucrose (table sugar): S w eetness Relative to Carbo hy drate S ucro s e Fructos e 1.74 In vert su gar 1.25 Sucrose (tab le sugar) 1.00 Hon ey 0.97 Glucose 0.74 Maltos e 0.33 Galactose 0.32 Lactose (milk s ugar) 0.16 S w eetness Relative to Artificial S w e e te n e r S ucro s e Saccharin 450 Aces ulfame-K 200 Asp artame 160 16 Organic Organic Lecture Series Cyclic Structure • Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and sixmembered cyclic hemiacetals – anomeric carbon: the new stereocenter created as a result of cyclic hemiacetal formation – anomers: carbohydrates that differ in configuration at their anomeric carbons 17 17 Organic Lecture Series Haworth Projections Haworth projections CH2OH – five- and sixOH H membered O OH hemiacetals are Anomeric Carbon H represented as planar H pentagons or OH hexagons, viewed OH H through the edge – they are most H commonly written with HOH2C O Anomeric Carbon H H the anomeric carbon on the right and the H OH OH OH hemiacetal oxygen to the back right 18 Organic Organic Lecture Series α-D-Glucopyranose 6 α-D-Glucose CH2OH H 4 5 OH OH 3 O H 2 H 1 Anomeric Carbon OH α H OH 19 Organic Lecture Series α-D-Ribofuranose α-D-Ribose 5 CH2OH 4 H H 3 O H H 2 1 Anomeric Carbon OH OH α OH 20 Organic Organic Lecture Series • Haworth projections the designation βmeans that the OH on the anomeric carbon is cis to the terminal terminal -CH2OH; α- means that it is trans to the terminal -CH2OH CH2OH H OH OH H OH O H H Anomeric Carbon OH α CH2OH H OH OH H OH O H OH β Anomeric Carbon H 21 Haworth Projections CHO H OH HO H H H 5 1 Organic Lecture Series red raw to sh ow th e -OH on carbon-5 close to the aldeh yd e on carbon-1 Groups on the right side go down on the Haworth. OH OH CH2 OH CH2 OH OH O H C OH H 1H HO H5 H anomeric carbon OH anomeric carb on D -Glucose CH2 OH O OH( β) H H OH H HO H H OH β -D -Glucopyranose (β-D -Glucose) CH2 OH OH H H + OH H HO OH( α ) H OH α-D -Glucopyranose ( α-D -Glucos e ) 22 Organic Organic Lecture Series Haworth Projections – six-membered hemiacetal rings are shown by the infix -pyran pyran– five-membered hemiacetal rings are shown by the infix -furan furan- O O Furan Pyran 23 Organic Lecture Series – five-membered rings are close to being planar that Haworth projections are adequate to represent furanoses HOCH2 H H O H H H HOCH2 H O H H OH ( β) Conformational Formulas OH ( α) OH OH α -D -Rib ofuranose (α -D -Ribose) OH H β -2-D eoxy-D -ribofu ran os e (β -2-D eoxy-D -ribose) 24 Organic Organic Lecture Series Conformational Formulas – for pyranoses, the six-membered ring is more accurately represented as a chair conformation H OH HO HO H HO H OH H OH HO HO H H H OH H OH O OH H rotate about C-1 to C-2 bond H OH HO HO H H H OH OH H O H OH HO HO H HO H H OH OH β-D -G l u co py ran os e (β -D -Glucos e) α -D -Glucop yranose (α-D -Glu cose) 25 Conformational Formulas Organic Lecture Series – compare the orientations of groups on carbons 1-5 in the Haworth and chair projections of β-D-glucopyranose, in each case they are up-down-up-down-up respectively 6 CH OH 2 6 All Groups axial H 4 5 O H H OH 3 OH( β ) 1 4 CH2 OH O 5 3 2 HO HO HO H H 2 OH( β) OH 1 OH β -D -Glucopyranose (Haw orth projection) β -D -Glu copyran os e (chair conformation ) 26 Organic Organic Lecture Series Mutarotation: the change in specific rotation that occurs when an α or β form of a carbohydrate is converted to an equilibrium mixture of the two Mon os accharide α -D -glu cose β-D -glucos e α -D -galactos e β-D -galactose [α ] after % Present at Mutarotation Equ ilib riu m 36 +52.7 +112.0 +18.7 +52.7 64 [α ] +150.7 +52.8 +80.2 +80.2 28 72 Slight preference for equatorial HO HO CH2 OH O OH ( β ) HO HO CH2 OH O OH β-D -Glu cop yranose 25 [ α ] D + 18.7 OH ( α ) α -D -Glucopyranose [ α ] D 25 + 112 HO 27 ...
View Full Document

Ask a homework question - tutors are online