Carbohydrates - Haworth & Fischer Projections With Chair Conformations
Summary
TLDRThis 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
🍬 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.
🔍 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.
🔄 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.
🌀 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.
📚 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.
Mindmap
Keywords
💡Carbohydrates
💡Monosaccharides
💡Disaccharides
💡Polysaccharides
💡Glucose
💡Fructose
💡Epimers
💡Aldose
💡Ketose
💡Anomers
💡Chair Conformation
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
Ver Más Videos Relacionados
Carbohydrates
Carbohydrates | Organic Chemistry | Chemistry | FuseSchool
Carbohydrates | Biological Molecules Simplified #1
Monomers, Polymers and Monosaccharides- A-level biology Biological Molecules topic
Dehydration synthesis or a condensation reaction | Biology | Khan Academy
Hydrolysis | Macromolecules | Biology | Khan Academy
5.0 / 5 (0 votes)