Carbonyl Chemistry

Question 1

Types of carbonyl

Answer 1

• Aldehyde
• Ketone
• Carboxylic acid
• Ester
• Acyl chloride
• Anhydride
• Amide

Question 2

Glycine formula

Answer 2

NH2CH2COOH

Question 3

Alanine formula

Answer 3

CH3CH(NH2)COOH

Question 4

Phenylalanine formula

Answer 4

C6H5CH2CH(NH2)COOH

Question 5

Proline formula

Answer 5

C5H9NO2

Question 6

Paracetamol formula

Answer 6

OHC6H4NHCOOH

Question 7

Aspirin formula

Answer 7

COOHC6H4OCOOH

Question 8

Common name: propanone

Answer 8

Acetone

Question 9

Common name: Methanal

Answer 9

Formaldehyde

Question 10

Common name: diphenylmethanone

Answer 10

benzophenone

Question 11

Common name: 1-phenylethanone

Answer 11

acetophenone

Question 12

Common name: 1-phenylmethanal

Answer 12

Benzaldehyde

Question 13

Common name for when a benzaldehyde substituent bonds with R

Answer 13

Benzoyl-

Question 14

Common name for when a formaldehyde substituent bonds with R

Answer 14

Formyl-

Question 15

Common name for when an acetone substituent bonds with R

Answer 15

Acetyl-

Question 16

Characteristics of a C=O bond

Answer 16

• Comprised of a sigma and pi bond
• Constructed in a similar manner to a C=C bond, however is shorter and much more polar.

Question 17

Aldehyde and ketone properties

Answer 17

• Polar molecules due to the dipole moment on the C=O bond
• Hydrogen bond acceptors; making them soluble in water
• Ketones make good solvents as they dissolve both aqueous and organic compounds.
• Good electrophiles

Question 18

Oxidation levels: 0

Answer 18

Carbon atoms with no bonds to elements that are more electronegative than itself

Question 19

Oxidation levels: 1

Answer 19

Carbon atoms with one bond to an electronegative atom

Question 20

Oxidation levels: 2

Answer 20

Carbon atoms with 2 bonds to electronegative atoms

Question 21

Oxidation levels: 3

Answer 21

Carbon atoms with three bonds to electronegative atoms

Question 22

Special properties of carbonyls

Answer 22

C and O are electrophilic and basic respectively, therefore C can act as electrophilic centres for nucleophiles, and O can act as a weak lewis base.

Question 23

Alpha carbons on carbonyls

Answer 23

The hydrogens attached to the alpha carbon are more acidic than those of alkanes. This is due to the electron-withdrawing effect of the carbonyl group; when the alpha carbon is deprotonated, the resulting negative charge is stabilised by the nearby carbonyl group. A more stable conjugate base is more readily able to donate protons, making it more acidic.

Question 24

pKa: Aldehydes and Ketones

Answer 24

19-20
- More acidic alpha carbons
- However, due to a lack of other stabilising factors (electron-withdrawing groups or spread of negative charge over more atoms) the pKa is still relatively high

Question 25

pKa: Carboxylic acids

Answer 25

4-5 - Much more acidic than aldehydes and ketones because the carboxylate ion is highly stabilised by resonance - The negative charge formed can be delocalised between the oxygen atoms, further increasing stability and acidity

Question 26

pKa: Esters

Answer 26

Around 25 - Experience an electron-withdrawing effect from the carbonyl group so are more acidic than A+K - Less acidic than CAs, due to fewer resonance forms

Question 27

pKa: Amides

Answer 27

17-18 - Have the most resonance stabilisation of the conjugate base - Still less acidic than CAs as the nitrogen group is less electronegative than the oxygen and thus cannot stabilise the negative charge on the anion as effectively.

Question 28

pKa: Acid Chlorides

Answer 28

11-13 - Have chlorine as an electron-withdrawing group, making them fairly reactive and more acidic relative to other carbonyl compounds. Cl pulls electron density away from the carbonyl carbon, making it more electrophilic and acidic. - Though this makes the conjugate base less stable, it is still easier to form compared to A+Ks

Question 29

pKa: Anhydrides

Answer 29

7-8 - Same reasoning as A+Ks, but since they have two carbonyl groups, the electron withdrawing effect is greater.

Question 30

Addition reactions of A+K: stereochemical properties

Answer 30

If the 4 substituents on the product are all different, a stereogenic centre is formed. The ratio of enantiomers is equal, therefore a racemic mixture forms.

Question 31

Factors affecting equilibria in carbonyl addition reactions

Answer 31

Reactant and product stability

Question 32

Reactant stability

Answer 32

- Alkyl groups stabilise C=C and C=O groups - Ketones are more stable than aldehydes - Ketone addition is less favoured to aldehyde addition

Question 33

Product stability

Answer 33

- The 4 product substituents are closer than the 3 reactant substituents - Alkyl groups cause more steric destabilisation, therefore the ketone addition product is less favoured in comparison to the aldehyde product.

Question 34

Equilibrium in carbonyl addition reaction summary

Answer 34

Ketones: more stable reactants and less stable products Aldehydes: less stable reactants and more stable products Therefore aldehydes are much more likely to undergo addition reactions.