21.2-Carboxylic Acid Derivatives
Summary
TLDRThis video explores carboxilic acid derivatives, discussing their reactivity, naming conventions, and how they differ from carboxilic acids. It delves into the stability of leaving groups, the role of resonance in reactivity, and the mechanisms of interconversion between derivatives, emphasizing the importance of nucleophilic attack and leaving group steps in reactions.
Takeaways
- 🌟 Carboxilic acid derivatives are compounds where the OH group of a carboxylic acid is replaced with other functional groups containing oxygen, such as O, NR2, or Cl.
- 🔍 Different types of carboxylic acid derivatives include acid chlorides, anhydrides, esters, amides, and nitriles, each with varying reactivities.
- 📚 Naming conventions for these derivatives involve removing 'acid' for acid chlorides, adding 'ide' for anhydrides, and using alkyl groups for esters and amides.
- 💡 The reactivity of carboxylic acid derivatives can be understood through the stability of the leaving group, the electronegativity of the attached atom, and resonance structures.
- 🌡 Acid chlorides are the most reactive due to the stability of the chloride leaving group, while amides are the least reactive due to the least electrophilic carbon.
- 🔄 The interconversion of carboxylic acid derivatives typically involves nucleophilic attack, followed by the reformation of a carbon-oxygen double bond and a leaving group.
- 🚫 Under acidic conditions, avoid generating negatively charged intermediates, and under basic conditions, avoid positively charged intermediates.
- 🌐 Resonance structures play a significant role in determining reactivity, with the more positive charge character on carbon indicating higher reactivity.
- 💧 Hydrolysis of esters is an example of a reaction involving carboxylic acid derivatives, where water acts as a nucleophile under both acidic and basic conditions.
- 📉 The reactivity order of carboxylic acid derivatives from most to least reactive is: acid chlorides > anhydrides > esters > amides.
Q & A
What are carboxilic acid derivatives?
-Carboxilic acid derivatives are compounds that result from modifying the hydroxyl group (-OH) of a carboxilic acid. They differ in reactivity due to the change in the nature of the group attached to the carbonyl carbon, which can be an O, NR2, or Cl.
What is an acid chloride and how is it named?
-An acid chloride is a type of carboxilic acid derivative where the hydroxyl group is replaced by a chlorine atom. It is named by replacing the word 'acid' in the carboxilic acid name with 'chloride', for example, benzoic acid chloride is named benzo chloride.
What is an anhydride and how does it differ from other carboxilic acid derivatives?
-An anhydride is a carboxilic acid derivative where the hydroxyl group is replaced by an oxygen atom that forms a double bond with another carbon. It differs from other derivatives in that it contains a carbon-oxygen double bond, unlike esters, amides, or nitriles.
How are esters named in the context of carboxilic acid derivatives?
-Esters are named as alkyl alkanoates, where 'alkyl' refers to the alkyl group attached to the carboxilic acid and 'alkanoate' is derived from the carboxilic acid name, for instance, ethyl acetate from acetic acid.
What is an amide and how does its naming differ from other derivatives?
-An amide is a carboxilic acid derivative with a nitrogen containing group, where the hydroxyl group is replaced by an NR2 group. It is named by dropping the 'oic' from the carboxilic acid name and adding 'amide', such as propionic acid becoming propenamide.
How does the stability of the leaving group affect the reactivity of carboxilic acid derivatives?
-The reactivity of carboxilic acid derivatives is influenced by the stability of the leaving group. A more stable leaving group, such as chloride, results in a more reactive derivative because it can more readily depart, leaving behind a nucleophile attached to the electrophilic carbon.
What role does resonance play in determining the reactivity of carboxilic acid derivatives?
-Resonance significantly affects the reactivity by distributing the charge across the molecule. In derivatives like amides, the resonance structure contributes more to the hybrid, stabilizing the positive charge on carbon and making the amide less reactive compared to other derivatives like acid chlorides.
How can one convert an acid chloride to an ester?
-An acid chloride can be converted to an ester through nucleophilic attack by an alcohol, followed by the departure of the chloride ion as the leaving group, resulting in the formation of a new ester and a chloride ion.
What is a nucleophilic attack and why is it important in the conversion of carboxilic acid derivatives?
-Nucleophilic attack is a chemical reaction where a nucleophile, a species with a lone pair of electrons, donates its electrons to an electrophilic center, typically a carbon atom in carboxilic acid derivatives. It is important because it initiates the conversion process from one derivative to another.
Why can't carbon or hydrogen act as leaving groups in the reactions of carboxilic acid derivatives?
-Carbon and hydrogen cannot act as leaving groups in reactions of carboxilic acid derivatives because they are less electronegative than nitrogen, oxygen, or chlorine and cannot stabilize a negative charge. Thus, they are too unstable to leave the molecule.
How do proton transfer steps affect the mechanism of reactions involving carboxilic acid derivatives?
-Proton transfer steps can influence the mechanism by stabilizing intermediates under certain conditions. For instance, under acidic conditions, a proton can be transferred to an oxygen to make it a better leaving group, facilitating the reaction progress.
What is the general rule for writing mechanisms involving carboxilic acid derivatives?
-The general rule for writing mechanisms involving carboxilic acid derivatives is to include nucleophilic attack and leaving group departure in every mechanism. Additionally, avoid generating negative charges under acidic conditions and positive charges under basic conditions.
Outlines
🧪 Introduction to Carboxylic Acid Derivatives
This paragraph introduces the concept of carboxylic acid derivatives, explaining how they are modifications of carboxylic acids that alter their reactivity. The focus is on the different types of derivatives, such as acid chlorides, anhydrides, esters, and amides, which are formed by changing the hydroxyl group (-OH) of a carboxylic acid to other functional groups containing oxygen or nitrogen. The paragraph also covers the basic nomenclature of these derivatives, emphasizing the importance of recognizing their structures and reactivity for understanding the mechanisms of their reactions.
🔍 Understanding Reactivity Through Stability and Resonance
The second paragraph delves into the factors that influence the reactivity of carboxylic acid derivatives. It discusses the stability of the leaving group, the electrophilicity of the carbon atom in the derivative, and the role of resonance structures in determining reactivity. The paragraph explains that acid chlorides are the most reactive due to the stability of the chloride leaving group and the electrophilic nature of the carbon atom, while amides are the least reactive due to the resonance stabilization of the positive charge on the carbon. The summary highlights the importance of these factors in predicting the outcomes of nucleophilic reactions with these derivatives.
🛠 Mechanisms of Interconversion of Carboxylic Acid Derivatives
This paragraph outlines the mechanisms by which different carboxylic acid derivatives can be interconverted. It describes the general process involving nucleophilic attack on the electrophilic carbon, followed by the departure of a leaving group to reform a carbon-oxygen double bond. The paragraph emphasizes that the nature of the leaving group and the stability of the intermediates play a crucial role in the direction of these reactions. It also touches on the potential for proton transfer steps in the mechanisms, especially under acidic or basic conditions, and stresses the importance of avoiding the formation of unstable charged intermediates.
🌡 Conditions Affecting Reaction Mechanisms and Reactivity
The final paragraph discusses the impact of reaction conditions on the mechanisms of carboxylic acid derivative reactions. It explains that under acidic conditions, negatively charged intermediates are unfavorable, and under basic conditions, positively charged intermediates are avoided. The paragraph uses the example of ester hydrolysis to illustrate how protonation can facilitate nucleophilic attack and how proton transfer can aid in the departure of leaving groups. It concludes with a summary of the reactivity order of carboxylic acid derivatives, with acid chlorides being the most reactive and amides the least, and stresses the importance of adhering to the rules of mechanism writing to avoid generating unstable charged species.
Mindmap
Keywords
💡Carboxilic Acid Derivatives
💡Acid Chlorides
💡Anhydrides
💡Esters
💡Amides
💡Reactivity
💡Nucleophilic Attack
💡Leaving Group
💡Resonance
💡Proton Transfer
💡Hydrolysis
Highlights
Introduction to carboxilic acid derivatives and their reactivity.
Modification of carboxilic acids to create different derivatives.
Explanation of how the nature of the group attached to the carbon in carboxilic acids affects reactivity.
Identification of different carboxilic acid derivatives such as acid chlorides, anhydrides, esters, amides, and nitriles.
Naming conventions for carboxilic acid derivatives, including acid chlorides, anhydrides, esters, and amides.
Discussion on the reactivity of carboxilic acid derivatives based on the stability of the leaving group.
Explanation of how electronegativity affects the reactivity of the electrophilic carbon in carboxilic acid derivatives.
Importance of resonance in determining the reactivity differences among carboxilic acid derivatives.
Mechanism of interconversion between different carboxilic acid derivatives involving nucleophilic attack and leaving group departure.
Role of proton transfer steps in mechanisms under acidic or basic conditions.
Guidelines for writing proper mechanisms, emphasizing the avoidance of positively charged intermediates in basic conditions and negatively charged intermediates in acidic conditions.
Conversion of an acid chloride to an ester through nucleophilic attack and leaving group departure.
Hydrolysis of an ester and the role of water as a nucleophile.
Proton transfer steps in the hydrolysis mechanism of an ester under acidic conditions.
Reactivity order of carboxilic acid derivatives from most to least reactive: acid chlorides, anhydrides, esters, amides.
Summary of the key points for understanding the reactivity and interconversion of carboxilic acid derivatives.
Transcripts
in this video we're going to talk about
carboxilic acid derivatives in the last
one we introduced carboxilic acids and
their reactivity um but you can modify
carboxilic acids to make lots of
different derivatives that differ in
their reactivities that's what we're
going to talk about in this video first
talk about what the derivatives are how
they differ in reactivity and then how
we draw mechanisms for their inner
conversion so uh what is a carboxilic
acid derivative so a carboxilic acid
remember is a carbon oxygen double bond
bonded to an O group if we change the
nature of this group to something else
that contains an oxygen like an o or an
nr2 or a chlorine these are going to be
different derivatives so Z in this case
can either be an o or nr2 or chlorine
and these are going to be different
carboxilic acid derivatives notice that
there's no oxidation or reduction here
it's
just um um um inter conversion between
carbon and the same oxidation state
so what are the different carboxilic
acid derivatives that we're going to
talk about if you if you have a chlorine
here this type of derivative is called
an acid
chloride um and those are the only kinds
of acid halides that we're going to talk
about so this is called an acid
chloride
if the R Group is O with another carbon
oxygen double bond that's called an
anhydride if it's an o r and that R is
not does not contain this carbon oxygen
double bond we know that's called an
Esther nitrogen containing groups are
called amids and a carbon nitrogen
triple bond which differs a little bit
where because we don't even have a
carbon oxygen double bond anymore is
going to be called a nitr and we'll talk
about those and why we consider those
carboxilic acid derivatives um towards
in the last
video okay so quickly I'm going just
going to go over how you name these
things because you might see these names
periodically cropping up acid chlorides
are going to be called aleno chlorides
so this is called benzoic acid it's
carboxilic or it's acid chloride is
called benzo chloride in a simpler
example right this molecule is called
propanoic
acid and so the acid chloride would be
called
propano
chloride simil Sly this carboxilic acid
is called acetic acid so we just remove
the word acid at anhydride is called
acetic and hydride so a three
carbon or an anhydride derived from
propenoic Acid would just be called
propanoic and
hydride um
Esters uh one Esther that we're
intimately familiar with from the lab is
is ethyl acetate these are named as
alkal alkanoates and you want to divide
the molecule up into two pieces this
came from the carboxylic acid and this
is an alkal group tacked on to the end
of the carboxilic acid for example if we
go
back to this example that's propenoic
acid if we put a methyl on the end
that's called
methyl
propanoate if we put an ethyl on
there that would
be ethyl propanoate or if we put a
propyl on there it' be propyl propanoate
or butal propanoate notice that what
we're doing is we're just naming these
things as if we added an alkal group to
the end of a carboxilic
acid and
similarly um for an amid like if we had
a three carbon
amid
this would be
called
propen amid so you just drop the e it's
a three propanoic acid it just be called
propen amid you see gra you drop the OIC
acid and you add the word amid I'm not
going to make you name these things but
it might be useful to recognize the
names and how especially for Esters and
the thing that's confusing about these
amids is that we can have different
alkal groups on the nitrogen so we name
those as n methyl acetamin meaning that
we have a methyl group on the nitrogen
or NN dimethyl acetamide Etc okay so for
the rest of the video what we're going
to talk about is the reactivity and how
these carboxilic acid derivatives differ
in their reactivity so it's going to be
really important that you know how to
immediately identify what kind of
carboxilic acid derivative that you have
and then how react active is that
carboxilic acid derivative and we can
understand the reactivity of these
different derivatives in several
different ways so one way would be the
stability of the leaving group kind of
like the more acidic something is more
acidic if it has a more stable conjugate
base right and if we react an acid
chloride what ends up happening is CL
minus leaves here acetate leaves here an
alkoxide leaves here a negatively
charged nitrogen leaves right so notice
that the chloride is the most stable
it's a conjugate base of a very strong
acid hydrochloric acid so that's a weak
base is pretty stable acetate is
resonant stabilized so that would be
more stable than a negative charge on
oxygen negative charge on nitrogen would
be the least stable right because
nitrogen is the least electr negative
right so that's one way to understand it
another way to understand the reactivity
of these things has to do with the fact
that in each case
right this carbon is the one that's
being attacked by nucle nucleophile as
we're going to see here so this is the
electrophilic carbon in each case right
chlorine is the most electronegative
atom it's pulling electrons away so this
would be the this would be the
most
reactive or the most electrophilic
carbon nitrogen is not very Electro
negative so this would be the least
electronegative carbon and it would make
sense that nucleophiles would want to
attack that the
least but the most important argument
the one that we're going to spend the
most time talking about is resonance
resonance really accounts resonance is
the best explanation for the reactivity
differences
here so again electr negativity just is
explained by saying the more Electro
negative the atom is the more
electrophilic this carbon is the more
likely that it is to be attacked by a
nucleophile in resonance though remember
that every carbon oxygen Pi bond has a
resonance structure right or we can take
these two
electrons and we can make those an
additional lone pair on oxygen now we
have a positive charge on carbon and a
negative charge on oxygen so the more
positive charge character this carbon
has the more electrophilic it is or the
more reactive the overall carboxilic
acid derivative is chlorine is not very
Electro negative so while we can draw
this resonance structure it doesn't
contribute very much to the overall
resonance hybrid because chlorine is
reluctant to donate a lone pair of
electrons it's very electronegative it
doesn't want to give up those electrons
whereas we can draw the same resonance
structure in an amid but nitrogen is the
least electr negative of the elements
that we're going to discuss in these
derivatives so it's very likely to
donate that pair of electrons so this is
going to signif significantly contribute
to the resonance hybrid and thus we're
stabilizing that positive charge on
carbon making this less
reactive Okay so
now what we're going to do is talk about
inner conversion of different carboxilic
acid derivatives right we can change
this nature of whatever this thing is z
whether it is a chlorine let's say it is
let's just let's just say this is a
chlorine so we have an acid chloride and
we want to convert it to a different
carboxilic acid derivative one way we
can do this is by nucleophilic attack
followed by leaving group leaving so
regardless of what our nucleophile is
it's going to have a lone pair of
electrons and it's going to attack this
carbon right that and in order to form
this Bond we have to break a bond and
the weakest bond is that carbon oxygen
Pi
Bond so we get an O minus here and a
chlorine and whatever our nucleophile
was is going to be bonded we're going to
call this our tetrahedral
intermediate right but then what's going
to happen is this molecule is going to
want to get rid of this negative charge
and it can do that by reforming a carbon
oxygen double bond but to reform that
carbon oxygen double bond you got to
kick out something and it has a choice
it can kick out chlorine or it can kick
out the nucleophile that we just added
or it can kick out R and by far the
thing that's going to be the most stable
with the negative charge is going to be
chlorine and so what happens is we end
up with what looks like a substitution
reaction where we our leaving group is
chlorine except it's not an ESS two
reaction it's an addition followed by
leaving group leaving to give us the net
result of a substitution reaction all
the mech all the mechanisms are going to
involve nucleophilic attack followed by
Reformation of a carbon oxygen double
bond and a leaving group leaving there
might be some proton transfer steps in
there depending on if you're under
acidic or basic solution and that's what
we're going to talk about for the rest
of this
video so what can be a leaving group and
again this is kind of confusing because
when we talked about sn2 reactions we
only talked about good leaving groups
now we're going to look at anything
that's an acceptable leaving group and
in some cases can be a leaving group in
these reactions anything that has a CL
minus or even an O minus or an N minus
we're going to see can be a leaving
group what can't be a leaving group
anything with a c minus or an H minus
you're never going to see these things
leaving these are just too unstable
carbon and hydrogen have about equal
electro negativity and they're less
electronegative than nitrogen oxygen or
chlorine so while these are stable
enough to leave these guys can never
leave and that's the theme that we're
going to keep coming back to over and
over
again okay so let's say that we want to
convert an acid chloride to an Esther
right here we have an acid chloride we
treat it with a strong nucleophile right
methoxide attacks the
carbon just like we said said before we
break our carbon oxygen double bond that
gives us our tetrahedral intermediate
now what happens is we want to get rid
of that negative charge so these two
electrons come down and when these
electrons come down
right then it has a choice it can kick
out methoxide or it can kick out
chloride but it can't kick out carbon
with a negative charge and cl minus is
much more stable than om so CL minus
leaves we break this Bond
and what we get is a new
Esther and chloride ion and notice
chloride ion is more stable than
methoxide so from a thermodynamic
perspective we're going from something
that's less stable a strong base strong
nucleophile to something that's more
stable weak base weaker
nucleophile every single mechanism in
this chapter is g to have a nucleophilic
attack step and a leaving group leaving
step but like I said there could be some
proton transfer steps thrown in as
well so how do you know when you're
going to have a proton transfer step and
how do you know if you have a formal
charge whether or not it's going to be
appropriate there's a very easy way to
figure this out you can never ever ever
have positively charged intermediates if
you have basic conditions and you can
never have negatively charged
intermediates under acidic condition so
if you have an acid Catalyst you want to
you want to avoid negatively charged
intermediates if you have um a base
Catalyst you want to avoid positively
charged intermediates so let's say um
we're going to talk about this reaction
in the chapter this is called hydrolysis
of an Esther so you have an Esther water
is your nucleophile so you get a
carboxilic acid and an alcohol as a
product right there's lots of possible
ways that we can draw this mechanism and
based on
the slide that I just showed you right
what one thing that could happen would
be the nucleophile would attack to break
the carbon oxygen double bond but that
doesn't happen under acidic conditions
right because that would generate a
negatively charged intermediate so let's
look at another
possibility instead of water attacking
directly to create a negatively charged
intermediate this is going to be very
unlikely under acidic conditions mostly
because we went from two things that
don't have any charges to a molecule
that Sim multaneously has a negative and
a positive charge generating a negative
charge results in a h a new negative
charge generates a huge increase in
energy in the molecule which is going to
be unlikely but if you're already under
acidic conditions right then you already
have protons available so what you want
to do first is protonate the oxygen so
you're going to start
with a neutral molecule but since you're
under acidic conditions this can pick up
a proton perhaps from
hydronium ion and you have a positive
charge to start with so the net increase
in activation energy is not going to be
that high you have a net positive charge
here and you have a net positive charge
here and you have a net positive charge
here so once we've added a hydrogen to
our oxygen now this carbon is activated
towards nucleophilic attack we attack
that with a water molecule everybody's
happy to get this tetrahedral
intermediate which is much more likely
under acidic conditions
under basic conditions though we already
have a negatively charged species right
so the negatively charged species can
directly attack the carbon to break the
carbon oxygen double bond to give us
this tetrahedral intermediate right
because hydroxide is so much higher in
energy than water we start off higher in
energy so the potential energy barrier
that we have to overcome is smaller
notice that here is our tetrahedral
intermediate and I said before like in
the sn2 chapter we said you can can
never have a negatively charged oxygen
as a leaving group so why would it be
okay in this case well the reason is
because we already have a negatively
negative charge on oxygen right so we
have a negative charge on oxygen in our
reactants we have a negative charge on
oxygen in our products so the stability
of these two sides of the equilibrium is
fairly similar right so the equilibrium
constant for something like this is
going to be around one right because we
have a negatively charged oxygen here
negatively charged oxygen here these
have about equal stability meaning that
the equilibrium is going to exist or
there's going to be significant
concentrations of each species under
equilibrium conditions the last thing I
want to talk about is in the last step
when you have a leaving group leaving
sometimes you need to transfer a proton
to it to leave again this is another
example of our hydrolysis mechanism of
an Esther which we're going to talk
about more in future videos but
sometimes people are tempted to just
show
the oxygen leaving with a negative
charge right but right now we're under
acidic conditions so under acidic
conditions methoxide is not a good
leaving group and in order to induce
this oxygen to leave we need to transfer
a proton to it which makes it into a
much better leaving group
now this thing can leave and it's
neutrally charged so everybody's
happy okay so to summarize acid
chlorides are the most reactive then
anhydrides then Esters amids are the
least reactive carboxilic acid
derivatives we'll talk about how we
interconvert these and the reactions
that these different um carboxilic acid
derivatives undergo in future
videos okay make sure you know the
different carboxilic acid derivatives
and review these and keep these rules
for writing proper mechanisms in mind
when you're writing any mechanism that
we talk about in this chapter all
mechanisms are going to include
nucleophilic attack and leaving group
leaving but most reactions also contain
other proton transfer steps never
generate negative charges under acidic
conditions never generate positive
charges under basic conditions
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