CHE 350 Lecture Notes - Lecture 12: Condensation Reaction, Hexose, Deoxy Sugar
Chapter 8 – Carbohydrates
Carbs = saccharides (sugar)
Formula (C*H2O)n n>= 3
1 | Monosaccharides
They’re either aldoses or ketoses
# of stereoisomers = 2^#ofchiralcenters
D vs L
oD has the OH before the CH2OH on the right always
oL has the OH before the CH2OH on the left
oMirror images of each other
o
Epimers = sugars that differ only by the configuration around one C-atom
Monosaccharides vary in configuration and conformation
o6-membered ring = pyranose
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o5-membered ring = furanose
Cyclic Sugars have 2 Anomeric Forms
oCarbonyl carbon becomes chiral with 2 possible configurations after cyclization
oPair of stereoisomers that differ in configuration at the anomeric carbon =
anomers
Alpha anomer (α) OH is DOWN
Beta anomer (β) OH is UP
Diff optical rotations, properties etc
oAnomers freely interconvert in aqueous solution
Called mutarotation
At equilibrium d-glucose is a mix of beta anomer and alpha anomer
Linear form normally present in minute amounts
Hexose and larger sugars can form huge rings (7+) but they don’t because of the stability
of 5/6 membered rings
Internal strain of ¾ membered rings makes then less stable than their linear forms
Furanose and pyranose rings are NOT planar
oSp3 hybridizatoion
oEquatorial 4 bulky, axial 4 nonbulky = stable
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Document Summary
D vs l: d has the oh before the ch2oh on the right always, l has the oh before the ch2oh on the left, mirror images of each other o. Epimers = sugars that differ only by the configuration around one c-atom. Monosaccharides vary in configuration and conformation: 6-membered ring = pyranose, 5-membered ring = furanose. Cyclic sugars have 2 anomeric forms: carbonyl carbon becomes chiral with 2 possible configurations after cyclization, pair of stereoisomers that differ in configuration at the anomeric carbon = anomers. Diff optical rotations, properties etc: anomers freely interconvert in aqueous solution. At equilibrium d-glucose is a mix of beta anomer and alpha anomer. Linear form normally present in minute amounts. Hexose and larger sugars can form huge rings (7+) but they don"t because of the stability of 5/6 membered rings. Internal strain of membered rings makes then less stable than their linear forms.
