key sugar chemisty concepts and definitions

Question 1

When does a hemiacetal form?

Answer 1

• a hemiacetal forms when a sugar cyclizes, regardless of if its RCHO or ketone.
• sugars exist in water solutions in a cyclic form because it is more stable
• literally just the cyclized form of a sugar such as glucose or fructose

Question 1

What term can be used if the hemiacetal is a ketone?

Answer 1

hemiketal, but not used much anymore because its an old term

Question 2

Aldose has a… while a ketose has a….

Answer 2

aldose has an RCHO while a ketose has a ketone

Question 3

-ulose ending means

Answer 3

a ketose.
ex: ribulose

Question 4

final chiral OH shows us what

Answer 4

(NOT THE CH2OH carbon)
in glucose is carbon 5.
- tells us if it is D or L sugar depending on the orientation of the OH.

Question 5

final chiral carbon on the Left Side OH of fischer

Answer 5

OH on the left side of a fischer projection = L form of the sugar

Question 6

final chiral carbon right side OH of fischer

Answer 6

OH on the right side of fischer projection = D form of the sugar

Question 7

OH groups on the left vs right side of the fischer projection in chiral box

Answer 7

Left: will be on the top of the haworth projection
Right: will be pointing down

Question 8

If the OH attacks the carbonyl carbon from above

Answer 8

the anomeric OH will be pointing down

Question 9

if the chiral OH attacks the carbonyl carbon from below

Answer 9

the anomeric OH will be pointing up

Question 10

chiral box

Answer 10

all OH’s that are chiral and not involved with the hemiacetal formation

Question 11

Epimer

Answer 11

diastereomer in which a single chiral center is inverted

Question 12

enantiomer

Answer 12

stereoisomers that are mirror images

Question 13

diastereomers

Answer 13

stereoisomers that are not mirror images

Question 14

How do we determine anomers, including for ketoses?

Answer 14

• new chiral center created when forming hemiacetal, the OH can either go up or down. (above vs below attack)
• if anomeric C and CH2OH (D/L sugar) are on opposite sides, it is alpha
• if on same side, they are beta (beta and same have 4 letters)

Question 15

anomers help define

Answer 15

helps define your anomers as either a or b and it is the previous carbonyl carbon.

Question 16

anomers are a subset of

Answer 16

epimers which are a subset of diastereomers.

Question 17

Beta-D-glucose is more or less stable than alpha anomer?

Answer 17

B glucose is more stable than the alpha form.
Chairform shows us that all OH groups are equitorial

Question 18

reducing sugars

Answer 18

sugars that will reduce a metal solution (benedicts is an example)
- must have at least one hemiacetal whose open chain form ( linear form, some of which is always present) is an aldehyde or can be isomerized to one

Question 19

isomerization of D fructose

Answer 19

• D-fructose, in the presence of a small amount of base ( can be the amount of base in distilled water solution [ autoionization of water]) can be isomerized to the enolate ion.
• then, the enolate C=C bond can be moved and become enediol
• then enediol can become enediolate
• then enediolate become aldehyde D glucose

Question 20

Is fructose a reducing sugar?

Answer 20

yes, even tho is has a ketone, it can be isomerized using oH that is always present in water solution

Question 21

pyranose ring based on

Answer 21

pyran, a 6 membered heterocycle with an oxygen

Question 22

furanose ring based on

Answer 22

furan, five membered heterocycle with an oxygen.

Question 23

mutarotation

Answer 23

If you take pure alpha or b sugar and measure their optical rotation in water, the optical rotation will change over time.
- this is the concept of mutarotation, an observed change in the optical rotation of the a- and b- anomers of glucose upon dissolution in solvent. These will change until they converge on an intermediate value

• The intermediate value reflects an equilibrium mixture of the a and b anomers which can interconvert through the intermediate open-chain form

Question 24

ratio of a to b when in equilibrium in water

Answer 24

37:63

Question 25

intermediate open-chain form of the ring chain tautomerism can do what?

Answer 25

• act as a reducing sugars due to the presence of the aldehyde at C 1.

Question 26

Aldonic acids

Answer 26

aldehyde functional group is oxidized to a carboxylic acid

Question 27

uronic acid

Answer 27

CH2OH at bottom of fischer projection is oxidized to carboxylic acid.

Question 28

lactone

Answer 28

cyclic ester

Question 29

glycosides

Answer 29

acetals frequently used to link sugar units

Question 30

hemiacetal vs acetal

Answer 30

hemi - C directly attached to two O, one O is attached to C other one is attached to H

acetal - C directly attached to two O, both O attached to C

Question 31

which carbon comes first when naming?

Answer 31

the anomeric carbon (C1) is named first.

Question 32

which anomeric carbon do you use to determine if the molecule is a or b when there are two sugar rings?

Answer 32

Use the sugar with an anomeric carbon that is involved in the bonding.

Question 33

why is sucrose weird?

Answer 33

have to list multiple requirements. look into this more!