CH 16: Carbohydrates

What is the general formula for carbohydrates?

• C_n(H₂O)_n

  • For every carbon, there is one water molecule.

What are carbohydrates made of?

polymers of sugar molecules

What are polymers?

large molecules made of repeating subunits (called monomers)

What are monomers?

small, basic units that combine to form polymers

How do plants synthesize carbohydrates?

starts from an open chain (fischer projection) to form a 6-membered ring via photosynthesis

What do you call a carbohydrate that has an aldehyde?

aldose

What do you call a carbohydrate that has a ketone?

ketose

How do you name carbohydrates?

1) Name the carbonyl group

1a) If it is a ketone, then the carbohydrate is called a ketose.

1b) If it is an aldehyde, then the carbohydrate is called an aldose.

2) Number the carbon atoms starting from the carbonyl carbon.

3) Uses prefixes for the total number of carbons followed by -ose.

4) Combine the terms in which it places the prefix before -ose.

Ex) Aldotriose

How is stereochemistry assigned for carbohydrates?

Using the Fischer projection, the orientation of the highest numbered chiral carbon is used to determine the stereochemistry.

What configuration do most carbohydrates naturally occur in?

D-configuration

How do you figure out the stereochemistry of the carbohydrate?

1) Number the carbon chain from top to bottom.

2) Identify your highest numbered chiral carbon.

3) Determine the configuration based on the biggest group.

3a) If the group is on the right side, then the cabohydrate is in the D-configuration.

3b) If the group is on the left side, then the carbohydrate is in the L-configuration.

What formation do carbohydrates undergo? Why?

Carbohydrates undergo intramolecular hemiacetal formation because they have both an alcohol and cabonyl group.

How do carbohydrates form into a mixed acetal (glycoside)?

Carbohydrates form mixed acetals (glycosides) when they react with an alcohol in the presence of an acid catalyst.

In terms of ring size, how big is a pyranose? How big is a furnose?

• pyranose: 6-membered ring

• furnose: 5-membered ring

What does cyclization of carbohydrates to hemiacetal newly create?

chiral center

What is the hemiacetal carbon of the cyclic form of carbohydrates called?

anomeric carbon

What are carbohydrate isomers that differ only in stereochemistry of the anomeric carbon called?

anomers

What is mutarotation?

α- and ß-anomer are in equilibrium and interconvert through open form

How are pure anomers isolated?

crystalization

What process happens when pure anomers are dissolved in water?

mutarotation