Org 8 - Carboxylic Acids Flashcards
What is general formula for a Carboxylic acid ?
What are Carboxylates ?
Salts and Anions of Carboxylic acids
How are Carboxylic acids named ?
Replace the -e of the corresponding alkane with -oic acid. The Carbonyl Carbon is the Carbon 1.
What is the nature of Low MR Carboxylic acids ?
Liquids with strong odours and high boiling points due to polarity and hydrogen bonding. They boil at much higher temperatures than corresponding alcohols.
Describe the solubility of Carboxylic Acids
Water soluble due to a good ability to hydrogen bond. > 6 Carbon chains are less water soluble but their alkali salts are quite soluble due to ionic properties.
Name the four important considerations for Carboxylic acids ?
- The hydrogen is weakly acidic
- The Carbonyl Carbon is very suscepitble to nucleophilic attack
- In basic conditions, the hydroxyl group is a good leaving group
In acidic conditions, the H2O+is an excellent leaving group - They can inter and intra molecularly hydrogen bond
Why is the hydrogen in Carboxylic acids weakly acidic ?
Due to its attachment to Oxygen, as the Carboxylate anion is resonance stabilised.
Why is the Carbonyl Carbon very susceptible to nucleophillic attack ?
What are Organic acids ?
This is just another name for Carboxylic acids
What is the increasing order of acid strength displayed by organic compounds ?
Alkanes < Ammonia < Alkynes < Alcohols < water < Carboxylic acids
What is the impact of adding electron withdrawing groups such as -Cl or NO2 to Carboxylic acids ?
Withdrawing groups withdraw electrons and delocalise the negative charge, which stabilises the Carboxylate anion and increases acidity.
What electron donating groups destabilise the Carboxylate anion and therefore decrease acidity ?
E.g. NH2 or OCH3
What determines relative acidic strength among the carboxylic acids ?
The inductive effects of the attached groups.
Name four mechanisms by which Carboxylic acids are synthesised ?
- Oxidative cleavage of alkenes/alkynes
- Oxidation of 1º Alcohols and aldehydes
- Hydrolysis of Nitriles
- Hydroxylation of Grignards or other organometallic reagents
How are tertiary alkyl halides converted into carboxylic acids ?
Using Grignard reagents
What is the product if an -OR nucleophile reacts with a carboxylic acid ?
An ester
What is the product if a Carboxylic acid reacts with -Cl ?
Acid Chloride
What is the product if a Carboxylic acid reacts with NH2 ?
An amide
What is the general structure of an acid halide ?
R-C=O-X
Compare the reactivity of Acid halides and Carboxylic acids ?
Acid halides are more reactive
How can Acyl halides be converted back to carboxylic acids ?
Simple hydrolysis with H2O
What is the general structure of an acid anhydride ?
How are acid anhydrides synthesised ?
Reaction of an Acyl halide with a Carboxylate salt
Describe the relative reactivity of Carboxylic acid derivitives toward nucleophilic acyl substitution ?
Amide < Ester < Acid anhydride < Acid chloride
Name 6 important reactions of Acid halides ?
- Friedel-Crafts reaction
- Conversion into acids
- Conversion into Esters
- Conversion into amides
- Conversion into alcohols
- Synthesis of acid anhydrides
Name 4 important reactions of acid anhydrides ?
- Conversion into acids
- Conversion into amides
- Conversion into esters
- Conversion into alcohols
What is the general structure of an amide ?
Describe the boiling and melting point characteristics of amides ?
Unsubstituted and mono-substituted amides form very strong intermolecular hydrogen bonds, and as a result have very high boiling and melting points
What is the approximate pH of amides ?
Essentially neutral, no acidity compared to Carboxylic acids, and no basicity as compared to amines.
Describe Hoffman rearrangement ?
Amides can be converted to primary amines with the loss of the Carbonyl carbon
Name two important reactions of amides ?
- Conversion into acids
- Conversion into alcohols
What is the general structure of an ester ?
Explain the boiling point trends displayed by Esters ?
Lower than those of comparable acids or alcohols because they are polar molecules but without hydrogens to form hydrogen bonds.
Esters with longer R groups are more non-polar than esters with short side chains
What is transesterification ?
The process of transforming one ester into another using a nucleophile
What is Claisen condensation ?
The combination of two ester molecules to form an acetoacetic ester
What are fatty acids ?
Long chain carboxylic acids
What is Saponification ?
Fats may be hydrolysed by a base to the components glycerol and the salt of the fatty acid.
The salts of long chain Carboxylic acids are called soaps
What are ß-Keto acids ?
Carboxylic acids with a keto group at the ß position
What is decarboxylation ?
When a beta keto acid is heated, the carboxyl group can be readily removed as CO2.
Explain Carbonyl reactivity amongst carboxylic acid derivatives ?
Acid chlorides > Anhydrides >> Esters > Acids > Amides > Nitriles
What is the inductive effect ?
The ability of the substituent group, by virtue of its electronegativity, to pull electrons away. This increases the sigma (partially positive) charge of the carbonyl carbon
What is the resonance effect ?
The ability of the substituent group stabilise the carbocation intermediate by the delocalization of electrons.
What is a cyclic ester ? And what is it also known as ?
AKA a lactone.
