key sugar chemisty concepts and definitions Flashcards
When does a hemiacetal form?
- 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
What term can be used if the hemiacetal is a ketone?
hemiketal, but not used much anymore because its an old term
Aldose has a… while a ketose has a….
aldose has an RCHO while a ketose has a ketone
-ulose ending means
a ketose.
ex: ribulose
final chiral OH shows us what
(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.
final chiral carbon on the Left Side OH of fischer
OH on the left side of a fischer projection = L form of the sugar
final chiral carbon right side OH of fischer
OH on the right side of fischer projection = D form of the sugar
OH groups on the left vs right side of the fischer projection in chiral box
Left: will be on the top of the haworth projection
Right: will be pointing down
If the OH attacks the carbonyl carbon from above
the anomeric OH will be pointing down
if the chiral OH attacks the carbonyl carbon from below
the anomeric OH will be pointing up
chiral box
all OH’s that are chiral and not involved with the hemiacetal formation
Epimer
diastereomer in which a single chiral center is inverted
enantiomer
stereoisomers that are mirror images
diastereomers
stereoisomers that are not mirror images
How do we determine anomers, including for ketoses?
- 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)
anomers help define
helps define your anomers as either a or b and it is the previous carbonyl carbon.
anomers are a subset of
epimers which are a subset of diastereomers.
Beta-D-glucose is more or less stable than alpha anomer?
B glucose is more stable than the alpha form.
Chairform shows us that all OH groups are equitorial
reducing sugars
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
isomerization of D fructose
- 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
Is fructose a reducing sugar?
yes, even tho is has a ketone, it can be isomerized using oH that is always present in water solution
pyranose ring based on
pyran, a 6 membered heterocycle with an oxygen
furanose ring based on
furan, five membered heterocycle with an oxygen.
mutarotation
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
