12 Carboxylic Acids

Question 1

What is the carboxylic acid group?

Answer 1

consists of C=O and -OH bonded to the same carbon

Question 2

Where does the name ‘carboxyl’ group come from?

Answer 2

CARBonyl (C=O)

hydrOXYL (-OH)

Question 3

Draw an aliphatic and an aromatic carboxylic acid.

Answer 3

see document

Question 4

Define:

a) aliphatic acid

b) aromatic acid

Answer 4

a) -COOH bonded to an alkyl group

b) -COOH bonded to an aryl group

Question 5

What are long chain monocarboxylic acids called?

Answer 5

fatty acids

Question 6

Describe the bond angle due to the bonding due to the C=O bond eclipsed with O-H?

Answer 6

Carbon and both oxygens are sp2 hybridized.
Bond angles are close to 120°
O-H eclipsed with C=O

Question 7

State the 2 bond lengths (C=O and C-O) and the bond angle that is shown on the document.

Answer 7

C=O = 1.21A
C-O = 1.36A
see document

Question 8

Draw the orbital-diagrams for a general carboxylic acid.

Answer 8

see document

Question 9

State the IUPAC process of naming carboxylic acids.

Answer 9

Select the longest carbon chain containing the carboxyl group. The -e ending of the parent alkane name is replaced by the suffix -oic acid.
e.g. HCOOH Methanoic acid, CH₃COOH Ethanoic acid

Question 10

How are aromatic carboxylic acids named (in the IUPAC method)?

Answer 10

Aromatic carboxylic acids are also named after the parent compound
e.g. Benzoic acid (benzene)

Question 11

State the process for the naming of common carboxylic acids.

Answer 11

End in –ic acid. e.g. HCOOH Formic acid, CH₃COOH Acetic acid etc.
Often derived from Latin or Greek word indicating the original source or properties of the acid

Question 12

Define ‘ester.’

Answer 12

Derivatives of carboxylic acids where alcohol replaces the OH group

Question 13

State the IUPAC process of naming esters.

Answer 13

First name the alkyl from the alcohol -yl

Then name the acid (with the C=O) -oate

Question 14

Give the IUPAC and common name of the ester shown on the document and state the alcohol and carboxylic acid that forms it.

Answer 14

IUPAC = ethyl ethanoate
Common = ethyl acetate
alcohol - ethanol
acid - acetic/ethanoic acid

Question 15

For the 2 stage reaction of chemically obtaining carboxylic acids via oxidation of an alcohol and state:

a) the 2 possible reagents
b) the intermediate product (or first product)
c) the reaction equation

Answer 15

a) K₂Cr₂O₇ OR KMnO₄
b) RC=O
c) see document

Question 16

For the 2 stage reaction of biologically obtaining carboxylic acids via oxidation and state:

a) the 2 possible reagents
b) the intermediate product (or first product)
c) the reaction equation

Answer 16

a) ADH, ALDH OR NAD(P)⁺
b) RC=O
c) see document

Question 17

For the reaction of chemically obtaining a carboxylic acid via oxidation of a substituted aromatic state:

a) the 2 possible reagents
b) the reaction equation

Answer 17

a) K₂Cr₂O₇ OR KMnO₄

b) see document

Question 18

For the reaction of chemically obtaining a carboxylic acid via hydrolysis, state the reagent needed.

Answer 18

use acid or base

Question 19

For the reaction of biologically obtaining a carboxylic acid via hydrolysis, state the reagent and enzyme needed.

Answer 19

esterases and water

Question 20

Give 2 biological examples of obtaining carboxylic acids via hydrolysis.

Answer 20

Lipases: produced in the pancreas – digestion of fats
acetylcholine → acetic acid + choline
(H₂O and acetylcholinesterase)
see document

Question 21

For the 2 stage reaction for chemically obtaining carboxylic acids via a bromoalkane, state:

a) the reagent for each stage
b) the intermediate product (or first product)
c) the reaction equation

Answer 21

a) step 1: NaCN, step 2: H₃O⁺
b) R-C-C≡N
c) see document

Question 22

For the 2 stage reaction for chemically obtaining carboxylic acids via Grignard reagents, state:

a) the reagents
b) draw the mechanism for the first stage (curly arrows)
c) the intermediate product (or first product)
d) the reaction equation

Answer 22

a) step 1: R-⁺MgBr, step 2: H₃O⁺
b) see document
c) RC=O-MgBr⁺
d) see document

Question 23

Give a biological example of a reaction for chemically obtaining carboxylic acids via Grignard reagents and the enzyme used. (draw the structures)

Answer 23

ribulose-1,5-biphosphate → enol → carboxylic acid
(see document)
Rubisco = biotin-dependent carboxylases

Question 24

In terms of the physical properties and bonds, state and explain the solubility of carboxylic acids.

Answer 24

Carboxylic acid group - hydrogen bonds to water molecules
Carboxylate salt – ion-dipole interactions
Larger saturated alkyl groups are not water-soluble as they are waxy, odourless solids with Van der Waal’s forces

Question 25

In terms of the physical properties and bonds, state and explain the boiling points of carboxylic acids.

Answer 25

Low molecular weight carboxylic acids have high boiling points Strong intermolecular bonds Form dimers by hydrogen bonding

Question 26

Draw a carboxylate salt with a sodium ion in it.

Answer 26

see document

Question 27

What do carboxylic acids form?

Answer 27

Form dimers by hydrogen bonding A dimer is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular (see document)

Question 28

In terms of the physical properties and bonds, what type of acids are carboxylic acids?

Answer 28

``` weak acid partial dissociation (reversible arrow) ⇌ ```

Question 29

Write out the equation for the dissociation of methanoic acid including the pKa of the acid and state how the charge is distributed in a carboxylic acid.

Answer 29

see document the charge is delocalised over 3 atoms pi-system stable anion if formed

Question 30

What happens to the pKa of a carboxylic acid as carbon chain length increases?

Answer 30

the pKa increases (less dissociation) | see document for graph

Question 31

Explain the role and properties of the following groups within the carboxylic acid: a) alcohol (-OH) b) carbonyl (C=O)

Answer 31

a) leaving group for substitution reactions | b) (positive carbon-centre) attacked by nucleophiles

Question 32

What is a condensation reaction with a carbonyl also known as?

Answer 32

nucleophilic acyl substitution

Question 33

Draw out the 3-step general addition-elimination mechanism using X as the -OH group and Nu as the nucleophile (include curly arrows, charges and electrons).

Answer 33

see document

Question 34

For the reaction to chemically obtain an acid chloride from a carboxylic acid, state: a) the 3 possible reagents b) the reaction equation

Answer 34

a) SOCl₂ OR PCl₃ OR PCl₅ | b) see document

Question 35

Why is it useful to synthesise acid chlorides.

Answer 35

more reactive than the acid | useful for synthesis of amides, esters etc...

Question 36

For the reaction to chemically obtain an ester from a carboxylic acid, state: a) the 2 reagents b) the reaction equation c) the single by-product d) what the reaction is known as

Answer 36

a) ROH (alcohol) and H⁺ b) see document c) H₂O d) esterification

Question 37

For the reaction to biologically obtain an ester from a carboxylic acid, state: a) the 2 reagents b) the reaction equation c) the single by-product d) what the reaction is known as

Answer 37

a) glutamate b) glutamate synthetase and ATP c) see document d) esterification

Question 38

For the reduction of a carboxylic acid, state: a) what needs to be added b) the reagent c) the reaction equation

Answer 38

a) add H- ions b) LiALH₄ c) see document

Question 39

For the C-C bond formation from a thioester to form a ketone, state: a) what the reaction is also known as b) the reagents c) the enzyme d) the reaction equation e) the type of reaction

Answer 39

a) Claisen reaction b) RC=O-SCoA and OC=O-C-C=OSCoA c) synthase d) see document e) Reversible reaction

Question 40

What is the RC=O-SCoA converted into?

Answer 40

(−)C=O-SCoA

Question 41

Why is a thioester used instead of a carboxylic acid in C-C bond formation?

Answer 41

thioester is more reactive than a carboxylic acid

Question 42

What is the Claisen reaction used for biologically and what does it allow?

Answer 42

Fatty acid and polyketide biosynthesis | allows loss of 2-carbon unit from FAs

Question 43

Describe the acid hydrolysis of an ester, state: a) the reagents b) the reaction equation for ethyl methanoate

Answer 43

Esters react with water and an acid catalyst yielding a carboxylic acid and alcohol a) H⁺ (from an acid) and H₂O b) see document

Question 44

Describe the basic hydrolysis of an ester, state: a) the reagents b) the reaction equation for ethyl methanoate c) the 2 possible products d) the other name for base hydrolysis

Answer 44

Esters react with bases to produce the salt of the carboxylic acid and alcohol a) NaOH (or another alkali) b) see document c) salt (HC=O-O-⁺Na) or carboxylic acid (HC=O-OH) d) saponification

Question 45

What are fatty acids?

Answer 45

Long hydrocarbon chain monocarboxylic acids

Question 46

# Define: a) Saturated fatty acids | b) Unsaturated fatty acids

Answer 46

a) no double bonds | b) contain one (mono-) or more (poly-unsaturated) alkenes

Question 47

Which alkenes are naturally-occurring?

Answer 47

Cis-alkenes

Question 48

What do trans alkenes often result from chemically?

Answer 48

from isomerising the double bond during hydrogenation

Question 49

Identify the different names and draw out the fatty acids for each of the following melting points: a) -50°C b) -9 °C c) 13°C d) 46.5 e) 43°C f) 76°C (ALEOLA)

Answer 49

a) Archadonic acid OR 20:4 cis,cis,cis,cis-Δ5Δ8,Δ11,Δ14 OR n-6 b) Linoleic acid c) Oleic acid OR 18:1 cis-Δ9 OR n-9 d) Elaidic acid OR 18:1 trans-Δ9 OR n-9 e) Lauric acid f) Arachidic acid

Question 50

What is arachidonic acid the precursor to?

Answer 50

many prostaglandins – biological signalling molecules

Question 51

What are fatty acids the components of?

Answer 51

Triacylglycerols and Glycerophospholipids

Question 52

What are Triacylglycerols?

Answer 52

fats and oils

Question 53

What are Glycerophospholipids?

Answer 53

cell membranes

Question 54

Draw out the equation for triglyceride formation.

Answer 54

see document

Question 55

Why are glycerophospholipids useful?

Answer 55

to maintain the fluid environment of cell membranes | hydrophilic heads on the outside and hydrophobic tails inwards to create a hydrophobic core

Question 56

Draw out and label the structure of a single phospholipid with glycerol within its stricture.

Answer 56

see document

Question 57

Draw out the structure of glycerol choline.

Answer 57

see document

Question 58

What are soaps in terms of carboxylic acids?

Answer 58

sodium or potassium salts of fatty acids.

Question 59

What are detergents in terms of carboxylic acids and how does their structure remove stains?

Answer 59

Sulfate salts Hydrophobic tails dissolve in grease/dirt. Polar heads point out making particles water soluble

Question 60

What is shown in the picture on the document?

Answer 60

a soap

Question 61

Label the fat-soluble and water-soluble on the following molecule.

Answer 61

see document

Question 62

Where are bile acids/salts biosynthesised?

Answer 62

Biosynthesised from cholesterol in the liver.

Question 63

What do bile acids/salts allow in the body and how?

Answer 63

Allow absorption of fats and fat-soluble vitamins from the small intestine by acting as detergents.

Question 64

Draw out the 3-stage conversion of cholesterol into (carboxylic acid) glycocholic acid naming the intermediate product too.

Answer 64

cholesterol → cholic acid → glycocholic acid | see document

Question 65

For both 'aryl' and 'phenyl' groups, state the: a) definition b) formation c) number of carbon atoms

Answer 65

aryl: a) always contains an aromatic ring b) when H is lost from an aromatic group c) Different number depending on the group phenyl: a) derived from benzene by removal of 1 H atom b) when H is lost from a benzene group c) can only have 6 groups

Question 66

From the structures a) and b) shown on the document, distinguish between phenyl and aryl.

Answer 66

a) aryl (double bond is on the right of the R-group) | b) phenyl (double bond is on the left of the R-group)