The cyclic forms of D-(+)-Glucose are hemiacetals formed by an intramolecular reaction of the -oH group at C-5 with the aldehyde group HH OHH H 6 CH,OH HOH,C-C-C-C-C-C=O OH CHO OHOH H OH (plane projection formula when a model of this is H OH made. it will coil follows If the group attached to C-4 is pivoted as the arrows indicate
The cyclic forms of D-(+)-Glucose are hemiacetals formed by an intramolecular reaction of the –OH group at C-5 with the aldehyde group. C C H OH C C OH H C H OH H OH HOH2C O H 5 4 3 2 1 6 CHO H CH2OH OH H H OH OH H OH 1 2 3 4 5 6 (plane projection formula) when a model of this is made. it will coil as follows If the group attached to C-4 is pivoted as the arrows indicate
his-oh group adds accross the O to close a ring make a cyclic hemiacetal 6.OH 6 CH,OH H 6 CH,OH H * Oh H OH 4K OH H CH=O OH OH H OH OH a-D-(+)-Glucopyranose Open-chain form of D-glucose B-D-(+)-Glucopyranose (α-D-(+)-吡喃(型)葡萄糖) (开链型υ-葡萄糖) (βD-(+)-吡喃型)葡萄糖) (start -OH is the hemiacetal (start-OH is the hemiacetal OH. which in a-glucose is OH. which in B-glucose is on the oppsite side of the on the same side of the ring from the-CH2OH ring as the-CH,OH group group at C-5) at C-5) Notes:
CH H O OH H H OH OH CH2OH H 1 2 3 4 5 6 H O C H O OH H H OH OH CH2OH H 1 2 3 4 5 6 OH H * C H O OH H H OH OH CH2OH H 1 2 3 4 5 6 H * OH this -OH group adds accross the to close a ring make a cyclic hemiacetal O α-D-(+)-Glucopyranose (α-D-(+)-吡喃(型)葡萄糖) β-D-(+)-Glucopyranose (β-D-(+)-吡喃(型)葡萄糖) Open-chain form of D-glucose (开 链 型 D-葡 萄 糖 ） (start -OH is the hemiacetal OH. which in α-glucose is on the oppsite side of the ring from the -CH2OH group at C-5 ) (start -OH is the hemiacetal OH. which in β-glucose is on the same side of the ring as the -CH2OH group at C-5 ) Notes:
(1) These two cyclic forms are diastereomers that differ only in the configuration of c-1 (2)In carbohydrate chemistry diastereomers of this type are called anomers. and the hemiacetal carbon atom is called the anomeric Carbon atom (3)In the orientation shown the aanomer has the -oh down and the Banomer has the -oh up (4)The actual conformations of the rings are the chair forms. In the B anomer of D-glucose, all of the large substituents,-OH,or ch2oh, are equatorial In the a anomer, the only bulky axial substituent is the -oh atc-1
(2) In carbohydrate chemistry diastereomers of this type are called anomers, and the hemiacetal carbon atom is called the anomeric Carbon atom ( 3) In the orientation shown the αanomer has the –OH down and the βanomer has the –OH up. (4) The actual conformations of the rings are the chair forms. In the β anomer of D-glucose, all of the large substituents, -OH, or –CH2OH , are equatorial. In the α anomer, the only bulky axial substituent is the -OH at C-1 (1) These two cyclic forms are diastereomers that differ only in the configuration of C-1
22.3 MUTAROTATION The optical rotations of aand forms are found to be significantly different, but when an aqueous solution of either form is allowed to stand, its rotation changed Mutarotation the change in rotation towards an equilibrium value CHO OH H,C H OH H2C HO H HO HH OH HO OH OH OH OH CH2OH a-D-(+)-Glucopyranose Open-chain form β-D-(+ -glucopyranose (α-D-(+)-吡喃(型)葡萄糖) of D-glucose (β-D-(+}吡喃(型)葡萄糖) (mp,146℃alb23=+112)(开链型D-葡萄糖)(mp,l0℃ab232=+187
22.3 MUTAROTATION The optical rotations of αand βforms are found to be significantly different,but when an aqueous solution of either form is allowed to stand, its rotation changed. Mutarotation: the change in rotation towards an equilibrium value. O HO H2 C OH HO OH OH O HO H2 C OH HO OH OH CHO H OH HO H H OH H OH CH2OH α-D-(+)-Glucopyranose (α-D-(+)-吡喃(型)葡萄糖) (mp, 146℃ [a]D 25 = +112 0 ) β-D-(+)-Glucopyranose (β-D-(+)-吡喃(型)葡萄糖) (mp, 150℃ [a]D 25 = +18.7 0 ) Open-chain form of D-glucose (开 链 型 D-葡 萄 糖 ）
Ordinary D-(+)-glucose has the a configuration at the anomeric carbon atom and that higher melting form has the bconfiguration The percentage of the a andBanomers present at equilibrium OH HO HO HO HO OH OH OH OH a-D(+)-Glucopyranose B-D-(+)-Glucopyranose (α-D-(+)-吡喃(型)葡萄糖) (βD-(+)-吡喃(型)葡萄糖) (6% at equilibrium (64% at equilibrium)
Ordinary D-(+)-glucose has the α configuration at the anomeric carbon atom and that higher melting form has the βconfiguration. The percentage of the α andβanomers present at equilibrium. O HO H2 C OH HO OH OH O HO H2 C OH HO OH OH α-D-(+)-Glucopyranose (α-D-(+)-吡喃(型)葡萄糖) (36% at equilibrium ) β-D-(+)-Glucopyranose (β-D-(+)-吡喃(型)葡萄糖) (64% at equilibrium)