21.2-Carboxylic Acid Derivatives

Summary

This 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

00:00

🧪 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.

05:00

🔍 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.

10:02

🛠 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.

15:03

🌡 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.

Keywords

💡Carboxilic Acid Derivatives

Carboxilic acid derivatives are compounds that are modified from carboxilic acids by changing the nature of the group attached to the carbonyl carbon. In the video, these derivatives are discussed in terms of their reactivity and how they differ from each other. Examples include acid chlorides, anhydrides, esters, and amides. The video emphasizes that these derivatives are crucial for understanding the reactivity and mechanisms of reactions involving carboxilic acids.

💡Acid Chlorides

Acid chlorides are a type of carboxilic acid derivative where the hydroxyl group (-OH) of the carboxilic acid is replaced by a chlorine atom. They are mentioned in the script as being the most reactive among the carboxilic acid derivatives. The video explains that acid chlorides are formed by the substitution of the hydroxyl group with chlorine, and they are used to illustrate the concept of reactivity in carboxilic acid derivatives.

💡Anhydrides

Anhydrides are carboxilic acid derivatives where two carboxilic acid molecules are linked by a carbonyl group, forming a cyclic structure. The video discusses anhydrides as intermediates in terms of reactivity, less reactive than acid chlorides but more reactive than esters. An example given in the script is propanoic anhydride, derived from propenoic acid.

💡Esters

Esters are formed when a carboxilic acid reacts with an alcohol, resulting in the formation of an ester linkage. In the video, esters are described as being less reactive than anhydrides. They are named by combining the alkyl group from the alcohol with the name of the acid, such as ethyl acetate. The video script uses the example of methyl propanoate to illustrate the naming convention.

💡Amides

Amides are carboxilic acid derivatives where the hydroxyl group is replaced by an amine (-NH2). They are the least reactive among the carboxilic acid derivatives discussed in the video. Amides are named by dropping the 'ic' from the acid name and adding 'amide', such as propenamide from propanoic acid. The video script also mentions nitrogen-containing groups in amides, which can affect the reactivity.

💡Reactivity

Reactivity in the context of the video refers to how readily a compound will undergo a chemical reaction. The video script discusses the reactivity of different carboxilic acid derivatives, explaining that acid chlorides are the most reactive and amides are the least. Reactivity is crucial for understanding how these derivatives will behave in various chemical reactions.

💡Nucleophilic Attack

Nucleophilic attack is a fundamental concept in organic chemistry where a nucleophile (a species with a lone pair of electrons) attacks an electrophilic center. In the video, nucleophilic attack is a key step in the mechanisms of reactions involving carboxilic acid derivatives, leading to the formation of a tetrahedral intermediate. The video script uses this concept to explain the reactivity differences among the derivatives.

💡Leaving Group

A leaving group is a part of a molecule that departs during a chemical reaction, often carrying a negative charge. The video script discusses the importance of leaving groups in the mechanisms of reactions involving carboxilic acid derivatives. It explains that the stability of the leaving group affects the reactivity of the derivative, with chloride being the most stable and thus the most reactive.

💡Resonance

Resonance is a concept in chemistry that describes the delocalization of electrons within a molecule, leading to a more stable structure. The video script uses resonance to explain the reactivity differences among carboxilic acid derivatives. It explains that the more a carbon atom in a derivative has positive charge character, the more electrophilic and reactive it is.

💡Proton Transfer

Proton transfer is the movement of a proton (H+) from one molecule to another, often occurring in acid-base reactions. In the video, proton transfer is mentioned in the context of reaction mechanisms involving carboxilic acid derivatives, particularly under acidic or basic conditions. The script explains that proton transfer can affect the reactivity and the formation of intermediates in these reactions.

💡Hydrolysis

Hydrolysis is a chemical reaction where a molecule of water breaks a bond in another molecule, typically resulting in the formation of a hydroxyl group and another product. In the video script, hydrolysis of an ester is discussed as an example of a reaction involving carboxilic acid derivatives. The reaction mechanism involves nucleophilic attack by water, followed by the departure of a leaving group.

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