Food Chem 3402 Carbohydrates

What is specific rotation (ad), and its equation?

(ad)= a/(l(dm)XC(g/mol)) at 589nm Specific rotation(ad) Observed rotation(a) Path length(l)(decimeter 1dm-10cm) Sample Concentration (C)(g/mol)

What are the 5 reactions of monosaccharides?

1. Mutarotation 2. Oxidation 3. Reaction with Alcohols(glycoside formation) 4. Reduction 5. Reducing Sugars

What does it mean when a molecule has a stereogenic center? What other names does this go by? What does it mean if there is only one?

A carbon with 4 different groups attached is a sterogenic center? It is also called a chiral center or asymmetric center. A molecule with a single one of this centers is chiral.

What is the visual difference between chiral and achiral molecules?

A chiral molecules mirror images are not superimposable, and achrials are superimposable.

What is a meso compound?

A meso compound is a molecule that possesses stereocenters (chiral) but has a plane of symmetry. It is achiral and therefore optically inactive.

What is an enantiomer?

A pair of non-superimposable mirror images. They must have opposite configurations at chiral centers. They have the same boiling point, solubility, meltiing point.

What is a reducing sugar?

A reducing sugar is any monosaccharide with a free hydroxyl group at the anomeric C. They react with Tollens and Fehlings solutions acting as a reducing agent, this called reducing sugars.

Discuss lactose.

A reducing sugar with a hemiacetal group. Made up of galactose/glucose. 1,4 Linkage B anomeric carbon

How can you visually identify monosaccharides that are aldehyde or ketone?

Aldehydes have the double bonded O at the end (carbon 1) and ketones have it on carbon 2.

How are chair conformations formed from haworth?

By moving 2 carbons. The anomeric C atom is lowered below the plane of the ring The C4 atom is raised above the plane of the ring.

How is plane-polarized light produced?

By passing normal light through a polarizer such as a polarized lens or Nicol prism.

Discuss cellobiose.

Can exist as a a or b anomer. Exhibits mutarotation. Is a reducing sugar. Humans cannot digest. Can be hydrolyzed to glucose by acid or emulsion. Difference between cellobiose and maltose is glycosidic linkage 1,4 linkage B anomeric

What is mutarotation?

Change in optical activity as sugar reaches equilibrium between the a and b anomers. Occurs when the -OH group at the C1 switches between a and b. Thsi happens because in a solution a Carb can open up its aldehyde form. The carb must be hemiacetal or hemiketal.

What are the names of the 2 directions plane-polarized light can rotate?

Dextrorotatory (+) - Clockwise Levorotatory (-) - counter clockwise

How does fructose reduce benedicts reagent?

Fructose does not oxidize directly. In the presence of alkali, fructose is converted into 2 forms, through different steps. Glucose and Mannose. These 2 compounds are capable of reducing benedicts.

What are isomers and what are the two types?

Isomers are different compounds with the same molecular formula. The two types are: Constitutional Isomers - Different connections between atoms. Stereoisomers - Same connections but different 3D geometry.

What happens when plane-polarized light passes through a solution of CHIRAL molecules? Why?

It emerges with its direction changed. There is no mirror image to cancel out the rotation.

What are the 2 types of stereoisomers?

No chrial center - Cis-trans Chiral center - Enantiomers and Diastereoisomers.

What is plane-polarized light?

Normal light is made of electromagnetic waves that oscillate in all planes perpendicular to its direction. PPL oscillates in only one direction.

Discuss mild oxidation.(eg. bromine water)

Oxidizes aldehyde, but not ketone or alcohol. Forms aldonic acid Tollens test uses silver nitrate to find free silver. Fehlight test goes from deep blue to red precipitate. both tests are mild oxidizing agents and give aldonic acid.

Discuss vigorous oxidization. (eg nitric acid)

Oxidizes aldhehyde and terminal alcohol. Forms aldaric acid.

What are diastereoisomers?

Stereoisomers that are not mirror images of each other. Epimers are an example.

What is a non-reducing diasaccharide?

Sucrose Most abundnat in nature No hemiacetal linkage, thus non reducing, no positive reaction from benedicts, does not undergo mutarotation. made up of glucose and fructose. 1,2 linkage a or b anomeric carbons

What are epimers?

Sugars that differ only in their configuration at one chiral center. They are not mirror images.

What does a polarimeter measure?

The amount of light that an optically active compound rotates. Amount of rotation depends on the wavelength of the light used.

What is observed rotation (a)?

The extent of rotation, measured in degrees. This represents the difference between an inactive sample and an active sample.

What are the two types of cyclic monosaccharides and what are the formed from?

The hydroxyl group attacks the caronyl group in a nucleophilic reaction. If the carbonyl is an aldehyde a hemiacetal is formed, if it is a ketone, a hemiketal is formed. The carbon of the carbonyl becomes the anomeric carbon (C1).

What happens when plane-polarized light passes through a solution of ACHIRAL molecules? Why?

The light emerges from the solution with its direction of polarization unchanged. This is becuase for every molecule that causes the light to rotate there will be a mirror of that molecule (achiral is its own mirror) that makes it rotate in the opposite direction. no net change.

What happens when plane-polarized light passes through a molecule?

The molecule rotates the plane of light as a result of the interaction of the photons of light with the electrons in the molecule.

What is D and L? (D-Glucose, L-Glucose)

This refers to the orientation of the OH group attached to the highest number chiral carbon. (C5 on glucose) If that OH in on the right it is D, if it is on the left it is L.

How is maltose produced?

When the enzyme Amylase hydrolyzes down a starch. made up of glucose a 1,4 linkage