EXPERIMENT 4: Properties of Carbohydrates (Part 1)

Cn(H2O)n

General molecular formula for carbohydrates:

Carbohydrates

Were once considered hydrates of carbon

Carbohydrates

Cn(H2O)n

hydrates of carbon

Carbohydrates were once considered what?

inaccurate

Examination of the structures of carbohydrates readily reveals that this view is (accurate/inaccurate), but use of the term persists.

monosaccharides

Simplest carbohydrates

polyhydroxy aldehydes
polyhydroxy ketones

The simplest carbohydrates are monosaccharides, which can either be?

polyhydroxy aldehydes

Have the general structure A

polyhydroxy aldehydes

Are referred to as aldoses

polyhydroxy ketones

Have the general structure B

polyhydroxy ketones

Referred to as ketoses

A; aldoses

Polyhydroxy aldehydes, which have the general structure ___ and are referred to as ____

B; ketoses

Polyhydroxy ketones, which have the general structure ___ and referred to as ____.

3-6 carbons

A monosaccharide usually consists of how many carbons?

monosaccharide

Usually consists of 3-6 carbons

number of carbons

The _______ in a monosaccharide can also be used as a way classifying them, specifically trioses (3C), tetroses (4C), pentoses (5C), and hexoses (6C).

trioses

3C

tetroses

4C

pentoses

5C

hexoses

6C

ribose, glucose, and fructose

Examples of monosaccharides:

monosaccharides

Ribose, glucose, and fructose are?

cyclic form

In solution, most monosaccharides exist in what form?

aldehyde or ketone group

In solution, most monosaccharides exist in a cyclic form - the _______ reacts with one of the -OH groups on the other end of the same molecule to form a cyclic hemiacetal.

-OH groups

In solution, most monosaccharides exist in a cyclic form - the aldehyde or ketone group reacts with one of the ____ on the other end of the same molecule to form a cyclic hemiacetal.

cyclic hemiacetal

In solution, most monosaccharides exist in a cyclic form - the aldehyde or ketone group reacts with one of the -OH groups on the other end of the same molecule to form a _____.

a-D-glucose and B-D-glucose

Two possibilities of D-glucose (Different anomers of glucose):

a-D-glucose

B-D-glucose

different anomers of glucose

a-D-glucose and B-D-glucose are called the?

cyclic form; open chain or free aldehyde form

In solution, there is equilibrium between the ____ and the _____.

inter-converted

The rings are constantly opening and closing again. In this way, the a and ẞ forms can be ____.

Two monosaccharides; loss of one molecule of water

______ may be combined with the ______ to form a disaccharide.

disaccharide

Two monosaccharides combined with the loss of one molecule of water

glycosidic bond

The bond that connects 2 monosaccharide units in a disaccharide is known as?

2 monosaccharide units

The glycosidic bond connects how many monosaccharide units in a disaccharide?

sucrose and lactose

Examples of disaccharides:

Sucrose

table dugar

Lactose

milk sugar

disaccharides

Sucrose and lactose are examples of?

polysaccharide

Consists of many monosaccharides linked together.

Starch, pectin, glycogen, and cellulose

Examples of polysaccharides:

polysaccharides

Starch, pectin, glycogen, and cellulose are examples of what?

Molisch's Test

Qualitative detection of carbohydrates in solution is usually done in the laboratory using the _______.

Molisch's Test

Is a qualitative detection of carbohhydrates

Molisch's Test

Is named after Czech-Austrian botanist Hans Molisch.

Hans Molisch

Molisch's Test is named after Czech-Austrian botanist _____.

Molisch's reagent; concentrated sulfuric acid (H2SO4)

Molisch's test involves the addition of _____ to the analyte and the subsequent addition of a few drops of ____ to the mixture.

analyte; mixture

Molisch's test involves the addition of Molisch's reagent to the _____ and the subsequent addition of a few drops of concentrated sulfuric acid (H2SO4) to the ____.

formation of purple or purplish-red ring

This confirms the presence of carbohydrates in the analyte

tetroses and trioses

A positive reaction for Molisch's test is given by almost all carbohydrates; exceptions include?.

Molisch's Test

General test for the presence of carbohydrates:

Benedict's Test
Picric Test
Moore's Test

Tests for Reducing Sugar:

Benedict's Test
Picric Test
Moore's Test
Barfoed's Test for Monosaccharides
Seliwanoff's Test for Ketoses
Bial's Test for Pentoses
Iodine Test for Polysaccharides

Classification Tests for Carbohydrates:

reducing sugar

Is a carbohydrate that is oxidized by a weak oxidizing agent in basic aqueous solutions.

non-reducing sugar

A sugar which cannot serve as a reducing agent and is not oxidized.

True

Ali aldoses are the true reducing sugars. (True or False)

aldehyde functional group

All aldoses are the true reducing sugars because they contain the _____.

Ketoses

_____ do not contain aldehyde (they contain ketone); however, as you will later find out, they also show reducing properties

ketone

Ketoses do not contain aldehyde (they contain _____); however, as you will later find out, they also show reducing properties

False

Ketoses contains aldehydes (True or False)

Yes

Do ketoses show reducing properties, yes or no?

keto-enol tautomerization

Ketoses also show reducing properties because ketoses, when in basic aqueous solutions, undergo _____ converting them to mixture of aldoses.

basic

Ketoses also show reducing properties because ketoses, when in (acidic/neutral/basic) aqueous solutions, undergo keto-enol tautomerization converting them to mixture of aldoses.

mixture of aldoses

Ketoses also show reducing properties because ketoses, when in basic aqueous solutions, undergo keto-enol tautomerization converting them to _____.

True

All monosaccharides are reducing sugars. (True or False)

free anomeric carbon

The only disaccharides that are reducing are those that contain ______ because a ______ has the capacity to open and expose the aldehyde group.

free anomeric carbon

Has the capacity to open and expose the aldehyde group.

True

All polysaccharides are non-reducing. (True or False)

Benedict's reagent
Fehling's reagent
Tollen's reagent
Nylander's reagent
picric acid with sodium carbonate solution

There are several weak oxidizing agents that can be used to determine whether a carbohydrate is reducing or not, such as:

They are all in basic conditions (pH > 7).

Benedict's reagent Fehling's reagent Tollen's reagent, Nylander's reagent, and picric acid with sodium carbonate solution.

What is common to all these reagents?

a-naphthol in Ethanol 99% and concentrated sulfuric acid (H2SO4)

Molisch’s reagent:

Copper sulfate pentahydrate, sodium citrate and sodium carbonate

Benedict’s Reagent