Oxygen containing compounds (alcohols, ethers, esters, ketones, aldehydes and carboxylic acids)

Question 1

How are carboxylic acids named?

Answer 1

By replacing the -e of the corresponding alkane with -oic acid

The molecule is numbered suych that the carbonyl carbon is carbon number one

Question 2

Describe the physical properties of low molecular weight carboxylic acids

Answer 2

• Liquids
• Strong odour
• High boiling points (from polarity and hydrogen bonding)
• Water soluble (H bonding)
• Soluble in dilute bases because of acid properties

Question 3

Describe the reactivity of the hydrogen, hydroxyl and carboxyl carbon in carboxylic acid

Answer 3

Hydrogen: Weakly acidic due to attachment with oxygen and because carboxylate anion is resonance stabilized

Carboxyl carbon: Very susceptible to nucleophilic attack due to attached oxygen and the carbonyl oxygen, both atoms being electronegative

Hydroxyl group: A good leaving group in basic conditions. Protonated hydroxyl (water) is excellent leaving group in acid (promoting nucleophilic substitution)

Question 4

How is intermolecular and intramolecular bonding possible with carboxyl compounds?

Answer 4

The carbonyl and hydroxyl moieties (parts) are capable of hydrogen bonding with other molecules and within their own molecule (intramolecularly)

Question 5

What is the most acidic organic compound?

Answer 5

Carboxylic acid, though it is still a weak acid.

Question 6

List organic classes of molecules in order of decreasing acid strength (7)

Answer 6

1. Carboxylic acids (organic acids)
2. 5 Sometimes substituted phenols
3. Water
4. Alcohols
5. Alkynes
6. Ammonia
7. Alkanes

Question 7

What does the relative acid strength among carboxylic acids depends on?

Answer 7

The inductive effects of attached groups, and their proximity to the carboxyl.

Electronegative substituents (eg. Cl) withdraw electron density and stabilize carboxylate anions (resulting in stronger acidity).

Question 8

Which types of carboxylic acid decarboxylate easily (loss of CO2 after treatment with a base and heat)? (3)

Answer 8

• Those which have a keto group at the β position (β-keto acids)
• Malonic acids and its derivatives (ie β-diacids: those with two carboxyl groups separated by one carbon)
• Carbonic acid and its derivatives

Question 9

What is the advantage to forming acid halides, over carboxylic acid?

Answer 9

Acid halides can participate in nucleophilic reactions similar to carboxylic acids, but acid halides are more reactive

Question 10

Acid chlorides and acid anhydrides have boiling points comparable to what?

Answer 10

Esters of similar molecular weight

Question 11

What are the melting and boiling points like for amides? Why?

Answer 11

• Unsubstituted and monosubstituted amides form very strong intermolecular hydrogen bonds, and as a result, they have very high boiling and melting points
• The boiling points of disubstituted amides are similar to those of aldehydes and ketones

Question 12

Are amides basic or acidic?

Answer 12

They are basically neutral (no acidity compared to COOH and no basicity compared to NH2/amines)

Question 13

How does the boiling point of esters compare to acids or alcohols? Aldehydes and ketones?

Answer 13

• Lower than acids/alcohols
• Similar to aldehydes/ketones

This is because they are polar compounds, without hydrogens to form hydrogen bonds.

Esters with longer side chains (R-groups) are more nonpolar than esters with shorter side chains. Esters usually have pleasing, fruity odours.

Question 14

True or false? Carboxylic acids are generally more reactive than comparable non-carboxylic acid derivatives?

Why is this the case?

Answer 14

True

This is because the carbon in carboxylic acid is also attached to the electronegative oxygen atom of teh carbonyl group; threfore, carbon is more δ+, this being more attractive to a nucleophile .

Hence an acid chloride (R-COCl) is more reactive than a comparable alkyl chloride (R-Cl)

An ester (R-COOR’) is more reactive than a comparable ether (R-OR’)

And an amide (R-CONH2) is more reactive than a comparable amine (R-NH2)

Question 15

List the carboxylic acid derivatives, from most to least reactive

List three factors which may be responsible for this order

Answer 15

1. Acid chlorides
2. Anhydrides
3. Esters
4. Acid
5. Amides
6. Nitriles

• Resonance effect (stabilization of carbocation intermediates)
• Inductive effect (electronegative constituents pulling electrons away to increase partial positivity of carbonyl carbons
• Steric effects may play a role (eg. blocking nucleophile access to carbonyl carbon)

Question 16

A positive result of the iodoform test indicates what?

Answer 16

A methyl ketone.

R-CO-CH3

Question 17

What is a Grignard reaction? What are the two constituents that are needed? What is the intermediate?

Answer 17

A Grignard reaction involved attaching an alkyl group (the Grignard reagent, R-MgBr) to a double bonded carbonyl carbon (eg. a ketone).

The first step requires the Grignard reagent and diethyl ether solvent. This will produce a compound with the alkyl group attached to the carbonyl carbon and the carbonyl oxygen associated with MgBr.

You must add acid in the second step to protonate the carbonyl oxygen (it becomes a hydroxyl).

Question 18

Carboxylic acids can form intramolecular hydrogen bonds. How must the molecule be arranged to allow this to happen?

Answer 18

The carboxylic acid group must be adjacent or very near to a hydroxyl or other hydrogen bonding substituent.

Eg. Carboxylic acid cannot form intramolecular hydrogen bonds with para or meta hydroxyls on a cyclohexane, but they can with an ortho OH.

Question 19

What are two characteristics of antioxidants? List the first three steps in the mechanism of ‘autoxidation’ and how an antioxidant can end the chain reaction.

Answer 19

1. Have a hydrogen atom that can be removed to form a radical
2. Have an aromatic ring that will permit subsequent coupling with a peroxy radical.

Initiation: (STEP 1) Radical is formed from molecule by sigma bond cleavage yielding H* and R*

Propagation: (STEP 2) Molecule radical (R) binds with atmospheric oxygen gas to form RO2 (peroxy radical)

(STEP 3) RO2* abstracts H from another R-H to form ROOH (hydroperoxide) and new radical R*

This acts as a chain reaction. It can quickly cause the spoilage of food and deterioration of rubber objects.

Antioxidants inhibit the chain reaction by forming an antioxidant radical with removal of their hydrogen atom, the radical can bind with a peroxy radical to yield an inert compound (eg. quinone from BHT and peroxy radical)

Question 20

Why should an ester not be extracted with NaOH?

Answer 20

NaOH can hydrolyse an ester to produce a water soluble sodium alt of a carboxylic acid and this product will partition into the aqueous layer during extraction.

Question 21

A compound that produces proton signals after workup with D2O can not be:

A. Hydrophobic
B. Hydrophilic
C. Containing sulfur
D. Containing nitrogen

Answer 21

A. Hydrophobic

If a NMR spectrum is obtainable in D2O solution, the compound cannot be hydrophobic, it is hydrophilic.

Question 22

True or false, SN2 reactions are concerted.

Answer 22

True

SN2 reactions happen in one step.

Question 23

A reaction involves the treatment of isopropyl iodide with potassium ethoxide in ethanol. Propylene is the major product.

The reaction revealed first order kinetics in alkyl halides and first order kinetics in base.

What is the reaction mechanism?

Answer 23

E2

By telling you that the reaction is first order with respect to each of the two reagents, this shows that the reaction is second order overall (E2).

In this case, the ethoxide acts as a strong base, removing a hydrogen from the isopropyl iodide, causing those electrons to get transferred to a double bond, subsequently causing iodine to leave. This all happens at once due to the overall second order nature of this bimolecular reaction.

Question 24

SN1 and E1 are almost always in competition with each other in a reaction, yielding a major product and a minor product. The same is true for SN2 and E2.

What conditions favour SN2 over E2?

Answer 24

SN2 is most common because it is favoured by:

• Low temperature
• Modest bases
• Good nucleophiles
• Sterically small bases
• Primary is best, tertiary is worst

Question 25

What happens to the stereochemistry in SN2 reaction? Why?

How does this differ from SN1 reactions?

Answer 25

Because of the backside nucleophilic attack, the stereochemistry of a SN2 product is reversed.

SN1 reactions produce a racemic mixture of stereoisomers.

Question 26

What happens when you react a primary alcohol with an oxidizing agent?

Answer 26

You get an aldehyde

This is detectable in IR spectra by a band around 1680-1750

Question 27

What is a:

• Thiol
• Diol

Answer 27

Thiol:
R-SH

Diol:
HO-R’R-OH

Question 28

Acetyl chloride can be used as an acetylating agent. Which of the following can replace it?

A. Aldehyde
B. Amino
C. Ether
D. Anhydride

Answer 28

D. Anhydride (specifically acetic anhydride, which includes 1 methyl group (acetyl) on either side of the carbonyl carbons).

Question 29

How does leaving group ability change as you go down the halides (F to I)?

Answer 29

Worst to best

Fluoride is the worst leaving group, iodide is the best leaving group.

WORST - F- Br - Cl - I - BEST