Carbohydrates - Haworth & Fischer Projections With Chair Conformations

Summary

This educational video delves into the world of carbohydrates, starting with their historical naming to their crucial role in energy storage. It explains the structure and types of monosaccharides, highlighting glucose and fructose. The video then explores disaccharides like sucrose, maltose, and lactose, before moving on to polysaccharides such as starch and cellulose. It also covers the concept of epimers, focusing on glucose and galactose, and concludes with an in-depth look at glucose's cyclic form, its anomers, and the stability of its chair conformation.

Takeaways

• 🔍 Carbohydrates are biomolecules known for their role in storing energy and are historically named for their carbon-hydrate composition, as seen in glucose's formula C6H12O6.
• 🍬 Monosaccharides are the simplest form of carbohydrates, with common examples including glucose, fructose, and galactose.
• 🔗 Disaccharides are formed by the combination of two monosaccharide units, such as sucrose (glucose + fructose), maltose (two glucose units), and lactose (glucose + galactose).
• 🌐 Polysaccharides are complex carbohydrate polymers, with starch being a storage form in animals and cellulose providing structure in plants, both composed of many glucose units.
• 🧪 Glucose is a key monosaccharide, identified as D-glucose due to the hydroxyl group's position on the chiral carbon atom furthest from the aldehyde group.
• 🔄 Fructose differs from glucose by having a ketone functional group instead of an aldehyde, making it a ketose, and it is also a D-isomer with the hydroxyl group on the right at the bottom carbon.
• 🔑 The term 'epimer' refers to molecules that are identical except for the configuration at one chiral center, exemplified by glucose and galactose differing at carbon 4.
• 🔁 Glucose predominantly exists in a cyclic form rather than a straight chain, with the cyclic form involving the reaction of the aldehyde group with a hydroxyl group to form a ring.
• 🌀 The cyclic form of glucose can exist as two interconvertible anomers, alpha and beta, determined by the orientation of the hydroxyl group on the anomeric carbon.
• 📉 The specific rotation of glucose in its beta form is 18.7 degrees, and in its alpha form is 112.2 degrees, indicating how it rotates plane polarized light.
• 🪑 The chair conformation of beta D-glucose is more stable due to the equatorial positioning of the hydroxyl groups, which minimizes 1,3-diaxial strain, making it the predominant form in nature.

Q & A

What is the origin of the name 'carbohydrates'?

The name 'carbohydrates' comes from the early chemists' view of them as 'hydrates of carbon'. This is derived from the molecular formula of glucose, C6H12O6, which simplifies to CH2O when each subscript is divided by 6, resembling carbon plus water.

What are monosaccharides and what are the most common ones?

Monosaccharides are simple sugars, and the most common ones include glucose, fructose, galactose, mannose, ribulose, and xylose. Among these, glucose and fructose are the most frequently encountered.

Define disaccharides and give some examples.

Disaccharides are carbohydrates that consist of two simple sugar units linked together. Examples include sucrose (glucose + fructose), maltose (two glucose units), and lactose (glucose + galactose).

What is a polysaccharide and what are two common examples?

A polysaccharide is a long polymer molecule made up of many monosaccharide units. Two common polysaccharides are starch, which is found in animals and used for energy storage, and cellulose, found in plants and serving a structural purpose.

How are glucose and fructose structurally different?

Glucose and fructose differ structurally by their functional groups; glucose has an aldehyde group, while fructose has a ketone group. This is the primary distinction between the two.

What is the significance of the 'D' and 'L' prefixes in the context of glucose?

The 'D' and 'L' prefixes in glucose indicate the configuration of the hydroxyl group at the chiral carbon atom farthest from the aldehyde group. 'D' glucose has the hydroxyl group on the right at this carbon, while 'L' glucose has it on the left.

What is an epimer and how does it relate to glucose and galactose?

Epimers are molecules that differ in configuration at only one chiral center. Galactose is a C4 epimer of glucose, meaning it differs from glucose only at the fourth carbon atom's chiral center.

Why does glucose predominantly exist in a cyclic form rather than a straight chain form?

Glucose predominantly exists in a cyclic form because it can undergo an intramolecular reaction where the hydroxyl group on carbon five attacks the carbonyl carbon, forming a ring structure. This cyclic form is more stable and common in nature.

What are the alpha and beta anomers of glucose, and which is more prevalent?

The alpha and beta anomers of glucose refer to the orientation of the hydroxyl group on the anomeric carbon. The beta anomer, with the hydroxyl group in the equatorial position, is more prevalent, making up about 64% of glucose in solution, due to its greater stability.

Why is the beta D-glucose more stable than the alpha D-glucose?

Beta D-glucose is more stable than alpha D-glucose because in the beta form, the hydroxyl group is in the equatorial position, which minimizes 1,3-diaxial strain. This results in a more stable chair conformation, making beta D-glucose the most common form of glucose.

How does the specific rotation of glucose change when it goes from the beta form to a solution?

The specific rotation of beta D-glucose changes from 18.7 degrees to 52.7 degrees when dissolved in water, indicating a mixture of alpha and beta forms, with the beta form being more prevalent.

Outlines

00:00

🍬 Introduction to Carbohydrates

This paragraph introduces carbohydrates, explaining their historical naming as 'hydrates of carbon' due to their molecular formula resembling carbon plus water. It emphasizes the importance of carbohydrates as energy storage molecules and introduces key terms: monosaccharides (simple sugars like glucose and fructose), disaccharides (combinations of two sugar units, e.g., sucrose, maltose, and lactose), and polysaccharides (long chains of monomers, including starch and cellulose). The paragraph also discusses the significance of glucose, highlighting its structure, including aldehyde functional group and chiral centers, and differentiates between D-glucose and L-glucose based on the orientation of the OH group on the chiral carbon.

05:01

🔍 Deep Dive into Monosaccharides

This section delves deeper into monosaccharides, focusing on glucose and fructose. It contrasts glucose's aldehyde group with fructose's ketone group, which is a key difference between the two. The paragraph explains the terms 'aldose' and 'ketose' based on the functional group present, with glucose being an aldohexose and fructose a ketohexose due to their six-carbon structure. It also introduces the concept of epimers, using glucose and galactose as examples to illustrate how epimers differ in configuration at only one chiral center.

10:02

🔄 Cyclic Forms of Glucose

The paragraph discusses the cyclic forms of glucose, explaining that glucose predominantly exists in a cyclic rather than a straight-chain form. It outlines the process of forming the cyclic structure through a reaction with a mild acid to activate the aldehyde group, leading to an intramolecular reaction that forms a ring. The explanation includes the orientation of hydroxyl groups on different carbons and the concept of the anomeric carbon, which can exist in two forms: alpha and beta anomers, due to the different orientations of the OH group during the ring formation.

15:03

🌀 Stability and Conformation of Beta D-Glucose

This section focuses on the stability and chair conformation of beta D-glucose. It explains why the beta anomer is more prevalent than the alpha anomer due to the more stable equatorial position of the OH group, which minimizes 1,3-diaxial strain. The paragraph provides a step-by-step guide on drawing the chair conformation of beta D-glucose, detailing the positions of hydrogen and hydroxyl groups on each carbon. It also touches on the specific rotation values for beta D-glucose and how they change when dissolved in water, indicating the presence of both alpha and beta forms in solution.

20:05

📚 Drawing Chair Conformation of Beta D-Galactose

The final paragraph guides on how to draw the chair conformation of beta D-galactose, starting from the known structure of beta D-glucose. It emphasizes the importance of recognizing epimers and using this knowledge to modify the structure at the specific chiral center to represent galactose. The paragraph reinforces the concept of epimers and provides a practical application for drawing the chair conformation of related sugars.

Keywords

💡Carbohydrates

Carbohydrates are organic molecules that were historically thought to be hydrates of carbon, hence their name. They serve as a primary source of energy for living organisms. In the video, carbohydrates are discussed as essential biomolecules, with glucose being a key example, highlighting their importance in energy storage and biological processes.

💡Monosaccharides

Monosaccharides are simple sugars that cannot be hydrolyzed into simpler sugars. They are the building blocks of more complex carbohydrates. The video mentions glucose, fructose, and galactose as examples, emphasizing their role as the most common monosaccharides in biological systems.

💡Disaccharides

Disaccharides are carbohydrates composed of two monosaccharide units linked together. The video explains that sucrose (glucose + fructose), maltose (two glucose units), and lactose (glucose + galactose) are common disaccharides, illustrating how they form from simpler sugar units.

💡Polysaccharides

Polysaccharides are long chains of monosaccharide units, serving various functions in organisms. Starch and cellulose are highlighted in the video as examples, with starch being a storage form in animals and cellulose providing structural support in plants, showcasing their diverse roles.

💡Glucose

Glucose is a monosaccharide and an important energy source for cells. The video discusses its molecular structure, including its aldehyde group and chiral centers, and how it is the primary unit in polysaccharides like starch and cellulose, emphasizing its ubiquity and significance in biology.

💡Fructose

Fructose is a ketose, a type of sugar with a ketone functional group, differing from glucose in its functional group. The video contrasts fructose with glucose, noting its role in disaccharides like sucrose, and its importance in human nutrition and metabolism.

💡Epimers

Epimers are monosaccharides that differ in configuration at only one chiral center. Galactose is described as a C4 epimer of glucose in the video, differing only at the fourth carbon atom. This concept helps understand how slight structural differences can lead to different biochemical properties.

💡Aldose

An aldose is a type of monosaccharide with an aldehyde group. Glucose, being an aldose, is termed as such because of its aldehyde functional group. The video uses this term to classify glucose and distinguish it from ketoses like fructose.

💡Ketose

A ketose is a monosaccharide with a ketone group. Fructose is identified as a ketose in the video, highlighting the difference in its functional group compared to aldoses like glucose, which influences its reactivity and role in metabolism.

💡Anomers

Anomers are stereoisomers of a sugar that differ in the configuration around the anomeric carbon, which is the carbon involved in the hemiacetal or hemiketal linkage in the cyclic form. The video explains the alpha and beta anomers of glucose, detailing how they differ in the orientation of the hydroxyl group and their prevalence in solution.

💡Chair Conformation

The chair conformation is the most stable cyclic structure of a cyclohexane ring, as seen in the six-membered ring of glucose. The video describes the椅式构象 of beta D-glucose, explaining how the hydroxyl groups are positioned to minimize steric strain, contributing to its stability and prevalence in nature.

Highlights

Carbohydrates were historically thought of as hydrates of carbon, hence the name.

Glucose has the molecular formula C6H12O6, which simplifies to CH2O, resembling carbon plus water.

Carbohydrates are crucial for energy storage and are vital biomolecules.

Monosaccharides are simple sugars like glucose, fructose, and galactose.

Glucose and fructose are the most common monosaccharides.

Disaccharides are combinations of two simple sugar units, such as sucrose, maltose, and lactose.

Polysaccharides are long-chain polymers with many monomers, like starch and cellulose.

Starch is a storage polysaccharide in animals, while cellulose provides structure in plants.

Glucose is the primary monosaccharide unit in starch and cellulose.

Glucose has an aldehyde functional group and is a polyhydroxy aldehyde.

D-glucose is the most common form in nature, with the OH group on the right at the chiral carbon.

Fructose differs from glucose by having a ketone functional group.

Glucose is an aldohexose, while fructose is a ketohexose due to their functional groups and six carbons.

Epimers are isomers that differ at only one chiral center, like galactose being the C4 epimer of glucose.

Glucose predominantly exists in a cyclic form rather than a straight chain.

The cyclic form of glucose involves an intramolecular reaction forming a ring structure.

Glucose's cyclic form can exist as alpha or beta anomers, determined by the orientation of the OH group on the anomeric carbon.

Beta D-glucose is more prevalent due to its chair conformation's stability, minimizing 1,3-diaxial strain.

The specific rotation of beta D-glucose is 18.7 degrees, indicating its interaction with plane polarized light.

In aqueous solution, glucose's specific rotation stabilizes at 52.7, reflecting a mixture of alpha and beta forms.

The chair conformation of beta D-glucose is the most stable form due to the equatorial positions of its hydroxyl groups.

Drawing the chair conformation of beta D-galactose starts with the structure of beta D-glucose and altering the C4 chiral center.

Transcripts

in this video we're going to talk about

carbohydrates

so what exactly is a carbohydrate

well early chemists thought of them as

hydrates of carbon

so consider the molecular formula of

glucose c6h12o

if you divide every subscript by 6

you'll get c1

h2o1 or ch2o and so that looks like

carbon plus water thus we have the name

carbohydrates

and carbohydrates they're used to store

energy and so it's very useful it's a

very important biomolecule

now the first term you need to be

familiar with are the monosaccharides

so these are the simple sugars

like

glucose

fructose

galactose

mannose

ribulose xylose and things like that but

the most common

monosaccharides that you will encounter

is uh are these two glucose and fructose

now the next term you need to be

familiar with

is a disaccharide a disaccharide is

basically the combination of two simple

sugar units for example sucrose

is a disaccharide sucrose is

the combination of glucose

and fructose

another disaccharide that you need to

know is maltose

maltose is the combination of

two units of glucose

and then we have

lactose which is

glucose plus

galactose

now the next term that we're going to

talk about

is a polysaccharide

a polysaccharide is basically

a polymer and a polymer is a long

molecule with

many monomers or units

two common polysaccharides that you need

to be familiar with are starch

and cellulose

starch is found in animals it's used to

store energy

and cellulose is found in plants

it serves a structural purpose

now

both of these

polysaccharides

they contain thousands

of glucose monomers

so glucose

is the main monosaccharide or the main

unit

that comprise

these two polysaccharides

so since glucose is so important

let's draw the fischer projection of it

so glucose

has an aldehyde functional group you can

see the c atrial at the top

and it's basically

a poly hydroxy aldehyde

it has many hydroxyl groups

and it also has many

chiral centers

so this is called d glucose

now if you see the word d

what it means is that

at the chirocarbon at the bottom that is

away from the aldehyde function group

the oh group is on the right

now let's say if we drew the same

structure but if

the o h group was on the left then this

would be the less common

l glucose

so if the o h group is on the left

you get the l isomer but if it's on the

right you get the d isomer the d isomer

is the one that's most commonly found in

nature

now let's draw the structure of fructose

there's going to be some similarities

and some

differences

the biggest difference is the functional

group

fructose

has

a ketone functional group

whereas glucose has an aldehyde

functional group

and so that's the

biggest difference that you want to

pay attention to

you don't want to get that wrong when

it's s

so this is the structure of

d fructose on the right

and you can see why it's d because once

again we have the o h group

on the right side

at the bottom cairo carbon

so

glucose

is an aldos

when you hear the word os

that means that it's a sugar glucose

fructose ribulose xylose they all end in

ose and then the aldi or aldehyde part

or the ald i was trying to say it tells

us that we have an aldehyde functional

group

so it's an aldos

can you guess what fructose is

well since we have a ketone functional

group fructose

is a type of ketose

now

because we have a total of six carbons

think of six as hexane

glucose is called an aldo hexose it has

an aldehyde functional group

it has six carbons hexane and then os is

a sugar

so it's a

let's see if i can fit that in

an aldo hexose

fructose is a keto hexose

it has the ketone functional group it

has six carbons

and so

it's a keto

hexose

now the next thing that we need to talk

about

is a term called

epimers

what do you think epimers are

to illustrate this concept i'm going to

redraw glucose

and an isomer of glucose

which is uh galactose there's many

isomers of glucose but i'm going to

focus on

galactose

so on the left this is

as we said before d glucose

now galactose

has a very similar structure

to d

glucose in fact everything

is the same

except

one part of the molecule

and do you see where it is where

the difference occurs

so this is d

galactose

and both of these are the d isomers

because as you can see the o h group is

on the right

now

notice that the only difference between

glucose and galactose

is the configuration

at these two carbon atoms

notice that the oh group is on the right

and for galactose is on the left and so

therefore these two molecules are known

as

epimers

apomers are disturbers

that differ only at one chiral center

now

in order to have disturbers the two

molecules has to differ at at least one

chiral center or more but not all of

them but in the case of an epimer

they can only differ exactly at one

chiral center

now this is carbon one two three four

five and six

and so galactose is known as the c4

epimer

of glucose

because at carbon 4

that's where galactose differs from

glucose so make sure you understand the

term epimere

now it turns out that only a small

amount of glucose exists

in the straight chain form

the majority of it exists

in a cyclic form

and so what we're going to do is

we're going to draw the cyclic form of

glucose

so the first thing i'm going to do is

react it with

a mild acid

to activate the aldehyde

and so we're going to get a structure

that looks like this

so here's the carbon

with the aldehyde functional group

let me draw this way

and right now it has a hydrogen on it

a positive charge

and a lone pair

and let's draw everything else

so the o h group on carbon five

so that is this carbon here

is going to

attack

the aldehyde carbon or the carbonyl

group breaking this pi bond turn it into

an o h group

and so

whenever a molecule

reacts with itself it forms a ring

but before we form the ring

let's do this one step at a time

in order for the o h group

to attack

carbonyl carbon

the molecule has to bend

into the right form

and so let's draw it this way first

so this oxygen still has a positive

charge

at this moment

now

this is going to be carbon 1

and here we have carbon 2

3

4

5 and 6.

now carbon 2 has the o h group on the

right side

so when converting that into its cyclic

form

you need to put the o h group

in the downward direction which means h

is going up

now for carbon 3 the o h group is on the

left side

so in this case

it needs to be facing upward in the

cyclic structure

now for carbon 4 it's on the right side

so therefore it has to be going in the

downward direction

and that carbon 5 the oh is on

the right side so it's also in the

downward direction

so this is what we initially have

now in order for the oh group to

basically attack the carbonyl carbon it

has to be in the right position

it has to be in this position

so we need to replace these two groups

so what we're going to do is we're going

to rotate

this portion of the molecule

in

a counterclockwise direction

so the oh group

is going to be here

and then the ch2oh group will be here

and the hydrogen will be there

so let's get rid of a few things

so now the hydrogen is going to be

in this position

the ch2oh group is facing the top now

and now here is the o h group

this explains why the hydrogen is in the

downward direction because typically

if we look at this here the o h is on

the right

and so that should be on the downward

direction but here

the h is on the left

and so

that should be up instead of down

however

when you rotate it

in order to put the oh in the right

position this h is now in the downward

position

because if you look at this structure

you would think that it should be in the

upper position because everything on the

left side tends to face up like the oh

group on carbon 3.

so that's why the hydrogen of carbon 5

is in a downward direction

so now that the oh group is in the right

position it's going to attack the

carbonyl carbon that's close in the ring

and then the solution will take away

this hydrogen

so now we're going to get this structure

initially we're going to have a hydrogen

here

but

we can use water in a solution

to take away this hydrogen so i'm not

going to show that hydrogen in the final

structure

but just keep that in mind

now on carbon 2 we had the oh group

facing the downward direction

and on carbon 3

the oh group was facing upward and on

carbon 4 it was facing downward

and then on carbon 5 we have the ch2oh

group

facing upward and h

facing downward

now on carbon 1

we can get two different forms the oh

group

can be in the upward direction

like this

or

it can be in the downward direction

and so because

we can get both forms

this carbon is known as the anomeric

carbon

and these two forms are insert

convertible

the oh group when it attacks the

carbonyl carbon

depends on how it attacks it either from

the top or from the bottom

you can get these two different products

but because they're interconvertible

they're still considered glucose

so whenever you have the oh group

face in the upward direction

this is the beta

anomer and whenever you have the oh

group

facing the downward direction this is

the alpha anomer

the beta anomer

is more predominant than the alpha

anomer about 64 percent

of glucose in the solution is going to

be in the beta form and the other 36

percent

is going to be in the alpha form

and a very small amount is in

the straight chain form

less than one percent like point zero

something

but the majority of it will be in the

beta form

now there are some other things that you

need to know

the specific rotation of beta d glucose

is

18.7 degrees

and that's how much it rotates

plane polarized light

and for alpha d glucose

the specific rotation

is 112.2

and

let's say if you take

uh pure beta d-glucose and you dissolve

in water

the specific rotation will change from

18.7

and it's going to go up to

52.7

likewise

if you dissolve alpha d-glucose it's

going to decrease from 112.2 and it's

going to stop at 52.7

and that tells us that

in water

both of these two forms exists

because

the specific rotation of the mixture

is between these two numbers but it's

closer to 18.7 and so we're going to

have more of the beta anomer and less of

the alpha anomer

now let's talk about the chair

conformation

of beta d-glucose

let's see if we can draw it

so let me get rid of

a few things here

so how can we convert this

into the chair conformation

so let's start by drawing the chair with

an oxygen on the inside

it helps if you label

the carbon atoms

so this is going to be carbon five

four

three

two and one

so at carbon two

we have an h

in the upward direction

so it's going to be in the actual

position

and the oh in the downward direction so

it's in the equatorial position

which is slightly down and on carbon 3

the h is going to be in the downward

axle position and the oh will be

slightly up in the equity position

for carbon four

h is in the oxy position the oh is in

the downward equatorial position and for

carbon five we have h in the downward

axis position

and

we have

the ch2oh group

in the slightly up

equatorial position

now in order to draw

the beta isomer we need to put

the oh group in the upward position

which will be in the equator position

so this is the the beta anomer

of glucose

in its chair conformation

if you want to draw the alpha anomer

all you need to do is put the o h group

in the axial position

and the h in the equatorial position

so this would be the alpha anomer

but let's keep the beta enemy

so why is

the beta anamer more prevalent than the

alpha hammer

is it better to put the oh group in the

equator position

or in the axial position

we know that the equatorial position of

the chair conformation is always more

stable because you minimize

one three diaxial strain

and this is why beta d-glucose is more

favored at equilibrium than alpha

d-glucose

it's because putting the o-h group

on the equatorial position it makes the

whole molecule more stable

and not only that but

notice that

the ch2oh group and all of the other

hydroxyl groups

they are all

on the equatorial position

thus the glucose is the most stable aldo

hexose

and that's why beta d-glucose is so

common

is because of the stability of the chair

conformation that it forms and so

glucose is the most common aldo hexose

now

given beta d-glucose how would you draw

the chair conformation

of

beta d galactose

because let's say if you're given a

question

and you need to draw

the chair confirmation

of another type of sugar

how can you do it

now remember galactose

is

the c4 epimer

of glucose

so all we need to do

is simply

change the chiral center at carbon four

everything else

we need to keep it the same

now we also need to take into account

uh what type of animal we're dealing

with

since we're dealing with the beta anomer

this is going to stay the same but

if we wanted to draw the alpha anomer we

also have to change

that section as well but let's draw the

beta anomer

this might take a while but

i'll get it done soon

so now the oh group has to be facing in

the upward direction and the hydrogen

has to face in the downward direction so

this is the only part

that we

really need to change

and so that's how you can quickly draw

beta d

galactose

so if you know what type of epimer

you're dealing with

then starting from glucose you can draw

a beta d galactose

so make sure you really know the

structure of glucose and fructose and

from those two structures

you can draw other

isomers of those two molecules thanks

for watching

you