Cyclic Structures and Anomeric (异头的)Forms Although Fischer projections are useful for presenting the structures of particular monosaccharides and their stereoisomers they ignore one of the most interesting facets 面)of sugar structure-—the ability to form cyclic structures with formation ofan additional asymmetric center,Alcohols react readily with aldehydes to form hemiacetals
Although Fischer projections are useful for presenting the structures of particular monosaccharides and their stereoisomers , they ignore one of the most interesting facets（方 面） of sugar structure—the ability to form cyclic structures with formation of an additional asymmetric center. Alcohols react readily with aldehydes to form hemiacetals Cyclic Structures and Anomeric（异头的） Forms
Cyclization sugars from formation of hemiacetal or hemiketal HO OR' +HOR' H R H Aldehyde Alcohol Hemiacetal HO OR" +HOR” R R Ketone Alcohol Hemiketal
Cyclization sugars from formation of hemiacetal or hemiketal
OH HO-R3 OR3 +HO-RR0-OR R-C-OR2+H2O H HO-R3 H Aldehyde Alcohol Hemiacetal Acetal OH HO-R1 OR4 R2C=0+HO-R3、R2C-OR、 R2C-OR+H20 R E HO-R Ketone Alcohol Hemiketal Ketal
H 0 HC-OH HO C-H n-Glucoee HC-OH HC-OH “cH0H CH.OH H OH H H OH OH 4 CH.OH CHOH H H 0 OH 4C OH 4 mutarotation OH HO OH HO C Anomeric Forms OH OH a-D-Glucopyranose B-D-Glucopyranose
Anomeric Forms
Cyclization of Glucose-Anomers CH2OH OH H OHH〉 HO OH CH2OH H OH OH OH a-D-Glucopyranose HO H H-C H/ H OH OH HO H OH H OH CH2OH O OH CH2OH OH H/ D-Glucose HO H (open-chain form) H OH B-D-Glucopyranose
Cyclization of Glucose - Anomers