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The Organic acids

Teacher’s guide

The Organic acids

Learner’s guide

You can draw a correct structure for a organic acids. The functional groups in a molecule help to define its reactivity.

The Organic acids

Learner’s activates

IntroductionIntroduction

Acidity of theoriesAcidity of theories

Acidity of organic acidsAcidity of organic acids

Examples of interactionsExamples of interactions

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Organic chemistry is one branch from chemical, it is care to study the carbon compounds and their derivatives.

Definitions acidities of compounds :

In organic chemistry we are frequently concerned with the acidities of compounds that do not turn litmus red or neutralize aqueous bases, yet have a tendency- even though small- to lose a hydrogen ion.

In first, to define the acids according to the properties general to those compounds,…………

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Definitions acids.

Strong Acid donates H+ easily. Weak Acid has more difficulty donating H+.

Examples.

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CH3CO2H + H2O= CH3CO2¯ + H3O+

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The Definition of an acidic Solution

We define an acidic Solution as one where the [H+] in the solution is greater than the [H+] in pure water.

Acidic solution [H+] > 1.0 x 10-7 mole/L at 298.2 K.

Acid Strength and Equilibrium Constant

For the following weak acid according to the Law of Chemical Equilibrium:

HA + H2O = H3O+ + A-

Ionization constant = Ka = [H3O+] [A-] / [HA]

The larger the value of Ka the more Hydronium ion will be in the

solution for a given initial concentration of the acid since the value of Ka must equal the ionization expression on the right side of the

above equation and the Hydronium ion concentration is in the top portion of that expression. The percentage of ionizations will therefore be larger. Strong acids have Ka's that approach infinity in

value. Therefore the percentage of ionization would approach 100% for strong acids.

 

 

 

 

 

Lewis TheoryLewis Theory

Bronsted-Lowry theoryBronsted-Lowry theory

Arrhenious theory Arrhenious theory

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Lewis acid is an electron-pair acceptor.

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Lewise Theory

One advantage of the Lewis theory is the way it complements the model of oxidation-reduction reactions. Oxidation-reduction reactions involve a transfer of electrons from one atom to another, with a net change in the oxidation number of one or more atoms.

acidBasic

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Examples: the subject to interaction base and acids according to this theory:

1- Equal compound with ion negative interaction:

BF3 + F: = BF4

2- Ion negative with ion positive interaction:

H++ (aq) + OH: (aq) = H2O

The Lewis theory suggests that acids react with bases to share a pair of electrons, with no change in the oxidation numbers of any atoms.

Which of the following compounds can be Lewise acids? 3

1-AlCl3

correct

2-NH3

3-Cl-

Bronsted-Lowry theory

Acids donate H+ ions to another ion or molecule, which acts as a base.

There are two ways of naming the H+ ion. Some chemists call it a hydrogen ion; others call it a proton. As a result, Brønsted acids are known as either hydrogen-ion donors or proton donors.

Examples.

HCl + H2O CH3O+ + Cl¯

1

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+

CH3COOH +H2O=CH3COO¯ +H+

2

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The Acid Strength according to this theory, depend to ability to lose the protons, thence the acid strong to change at interaction to attendant base, the opposite is right.

Which of the following compounds can be Brønsted acids?

a) H2O

(b) NH3

(c) HSO4-

(d) OH-

Conclusion.

The Lowry-Bronsted definition is quite adequate for the chemistry of acids and bases in aqueous solution. The Lewis definition is useful because it allows us to classify so many substances as acids or bases, and because it provides an understanding of the details of many chemical reactions.

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Arrhenious theory

Arrhenious: acids are ionization in water to produce hydrogen aqueous atom [H+ [aq]].

Although, after that has been found that hydrogen defiant with water molecule to formed another ion to call hydronium ion {H3O

+ [aq]}

HCl + H2O H3O+ [aq] + Cl¯[aq]

Therefore, the substances, which to applied the Arrhenious’ role:

1-     Contain the hydrogen element [H].

2-     Dissolve in water [H2O] and their solution aqueous ability to

reach electricity by different degree.

Questions

Fill in space:

Lewis was said acids are an electron pair acceptor.

Acids are Proton donor, the Scientist told that……………………….

1-Arrhenious 2-Bronsted 3- Lewis

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Acidity of Organic acids

Alkane and Alkyne and AlkeneAlkane and Alkyne and Alkene

Alcohol and PhenolAlcohol and Phenol

Aldehydes and KetonesAldehydes and Ketones

Carboxylic acidsCarboxylic acids

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Organic acids

The organic acids are weak in the sense that this ionisation is very incomplete. At any one time, most of the acid will be present in the solution as un-ionised molecules. For example, in the case of dilute ethanoic acid, the solution contains about 99% of ethanoic acid molecules - at any instant, only about 1% have actually ionised. The strengths of weak acids are measured on the pKa scale. The

smaller the number on this scale, the stronger the acid is.

Acidities of Aliphatic Hydrocarbons

The acidity of the aliphatic hydrocarbons increases as the character of the hybrid orbitals increases. An sp3 orbital has a 25% s character; an sp2 has 33% s character, and an sp orbital a 50% s character. A base but not the hydrogens of an alkene or an alkane can abstract the hydrogen of a terminal alkyne.

Background:

Alkanes and Alkynes and Alkenes

1- Alkanes:

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Alkanes are molecules with only carbon-carbon single bonds, therefore it are inactive chemical classification.

Hydrocarbons very weak acids and a very strong base can remove proton to produce carbanion (carbon with negative charge)

C

H

H

H

H + Base C

H

H

H

_+ Base-H

+

v. weak acid v. strong conjugate base

PKa’s of hydrocarbons ~62; very weak acids.

to define the acidity of alkanes comparison with another compound, if those compound contain hydrogen atom more acidity than Hydrocarbons’ hydrogen atom.

Example:

Rmg+ X¯ + H:O:H RH +RO¯ +Mg 2+ + X¯

Strong

acid

Strong base

Weak acid

Weak base

RH weak Conjugate acid is, also alkane.

3- Alkenes:2

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Alkenes are molecules with one or more carbon-carbon double bonds [R-CH= CH].

2- Alkyne

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Alkynes are molecules with one or more carbon-carbon triple bonds (RC

C- R).

The explanation for the correlation of bond length and acidity with is that both are related to the hybridization of the carbon orbital used for C-H bonding. Because (s) orbitals are lower in energy than (p) orbitals, a hybrid orbital with more s character will be lower in energy and closer to the nucleus than will a hybrid with less s character.

Acidity of Terminal Alkynes:

The lower energy orbital will be more electronegative and will hold a proton tighter and also be better able to stabilize a negative charge when a proton is removed in an acid-base reaction.

H–CC–H H+ +HCC K = 10

Examples:

R-CC-H + NH2⇨ R-CC:¯ + NH3

R-CC-H + NaNH2→ R-CC:¯ Na + + NH3

a26

Alkynes are stronger acid than alkenes and alkanes.

Questions 4

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Alcohol and Phenol 1

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1-Aliphatic Acidity of Alcohol:

Alcohols are organic compounds that possess one or more -OH groups attached to a hydrocarbon group (a group that contains only carbon and hydrogen).

We learned earlier that alcohols are acids, too, and again of roughly the same strength as water. Hydrogen bonded to the very electronegative element oxygen.

RO-H RRO-H RRRO-H

primary alcohols secondary alcohols tertiary alcohols

ROH+ H2O RO¯ +H3O+

Ka = [H3O]+ [RO]¯/ [ROH] [H2O]

Then, the Equilibrium constant value :

PKa = - log KaThe alcohols acidity depend on alcohols’ kind, so primary alcohols (RCH2OH) the stronger acid than secondary alcohols (RRCHOH), these are stronger acid than tertiary alcohols (RRRCOH), because of for return to the group alkyl related to carbon atom, that related to (OH) group, whenever electrons density to increase on the oxygen atom, then to find difficulty to ionization bond (O-H), thence the acidity of alcohol is become little.

 

The polarity of the O-H bond facilitates the separation of a relatively positive proton; viewed differently, electronegative oxygen readily accommodates the negative charge of electrons left behind.

The acidity of alcohols is appear by their reaction with active metals liberate hydrogen gas and from alkoxides.

ROH + Na RO¯Na+ +½ H2

A sodim alkoxide  

2- Phenol: 2OH

Phenols have an -OH group attached directly to a benzene ring. Phenol itself is the simplest of these with nothing else attached to the ring apart from the -OH group.

Acidity of phenols

Phenol (old name "carbolic acid") is a very weak acid, Ka 1.1 x 10-10. 

This is about a million times stronger than water and aliphatic alcohols, but about a million times weaker than aliphatic carboxylic acids.

:Ö:

..¯

:Ö :Ö ¯║

: ¯

:O: ║

:O:║

:¯

Phenols get this acidity from the ability of the conjugate base (phenoxide) to accomodate the negative charge by delocalization out over the aryl ring (producing four resonance structures in all).  Substitutents, like electron withdrawing groups in particular, enhance this ability, and produce even stronger phenolic acids.

Phenols are reactions as weakly acids, it is dissolve in water to give proton ion and phenoxide ion.

:Ö:H :Ö:¯

+ H2O + H+

Questions 3

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Aldehydes and Ketones 1

Aldehydes and Ketones are contain the carbonyl group.

Acidity α-hydrogen:

Carbonyl group to have two strong poles from electronic in π bond, and that to be formed move aside by direction the oxygen atom, that have more electronegative, therefore the carbonyl carbon atom to be formed deficient electron, this property to become

Carbonyl carbon is to work on strong the acidity of hydrogen atoms, those connections by hydrogen atom, that connection by α – carbon atom.

 

Carbonyl compound is containing upon proton, it is carbocatune by resonance to be stable.

>C=:O: C= O H

..

..

found the carbonyl compound is contain on α – hydrogen react to base OH¯ will given Enolates ion,it is consisting in resonance

Hybird:

Ketones are lower acidity than aldehydes, although it is include upon carbonyl group, because it is emptiness from hydrogen activity or movement.

The basic is more use to define the acidity of α- hydrogen by use hydroxyl ion.

CH3-Cyuyuuiuioopp[p[[]

Questions 3

Carboxylic acids 1

Carboxylic acids are a class of organic compounds which contain the carboxyl functional group. They are the most common class of acidic organic compound.

R C

O

OH R C

O

O + H

CarboxylicAcid

Carboxylate ion (named like Acyl part of an ester).

Carboxylic acids are, by definition, Bronsted acids that can donate a proton to there species with lone pairs.

carboxylic acids are much more acidic than alcohols (pKa = 16-

18).  One explanation for this is the resonance delocalization afforded by the carbonyl group:  

  

The carboxyl functionality is a compound functional group, containing both a carbonyl functionality and a hydroxyl functionality. However, this compound functionality is very different from either an alcohol or a ketone.

Because the carbonyl and hydroxyl groups are directly attached to one another, there is a strong resonance interaction between the two groups, which sharply modifies the properties of the compound functionality from that of either of the two component functionalities.

What is the reason for the much greater acidity of the OH protons of a carboxylic acid than those of an alcohol? Primarily the resonance stabilization of the conjugate base of a carboxylic acid, i.e., the carboxylate anion. Recall that there are two equivalent resonance structures for this anion, so that resonance stabilization is especially strong.

General Questions 1

CH2=CH2 is call:

1-Propane .

2- Ethanol .

3-Ethylene.

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Acidity Discovery

discovery to phenols Acidity.discovery to phenols Acidity.

discovery to formalic or oxalic Acidity.discovery to formalic or oxalic Acidity.

discovery to formalic or oxalic Acidity.

Presentation test chemistry

discovery to phenols Acidity.

Presentation test chemistry

1. ArOH + OH

1- ArO + H2O

2- ArO2 +H2O

3- ArO + H3O

2- ArO is

•Stronger acid

•Weaker acid

Hydrocarbons very weak acids and a very strong base can remove proton to produce carbanion (carbon with negative charge).

Alkynes are stronger than alkenes or alkanes, but still weak acids…weaker than carboxylic acids and alcohol.