module 6.1.2 - 6.1.3 - carbonyls, carboxylic acids and esters

Question 1

what is a carbonyl?

Answer 1

contain a C-O double bond and are either aldehydes or ketones

Question 2

describe the orbital overlaps in a carbonyl C-O bond

Answer 2

sideways overlap of the p-orbitals on C and O form a pi-bond above and below the place of the C-O sigma bond.

Question 3

describe the polarity of a C-O double bond in a carbonyl

Answer 3

O is more electronegative than carbon, there is a permanent dipole across the bond resulting in a polar bond.

Question 4

describe the partial oxidation of a primary alcohol.

Answer 4

distil with H2SO4 and K2Cr2O7 (represented as [O] in equations). one molar equivalent of [O] is required. forms aldehyde and 1 mol of water. colour change from orange to green.

Question 5

describe the complete oxidation of a primary alcohol.

Answer 5

reflux with H2SO4 and K2Cr2O7 (represented as [O] in equations). two molar equivalents of [O] is required. forms carboxylic acid and 1 mol of water. colour change from orange to green.

Question 6

describe the complete oxidation of a secondary alcohol.

Answer 6

distil or reflux with H2SO4 and K2Cr2O7 (represented as [O] in equations). one molar equivalent of [O] is required. forms ketone and 1 mol of water. colour change from orange to green.

Question 7

describe the oxidation of a tertiary alcohol

Answer 7

tertiary alcohols cannot be oxidised. when refluxed with K2Cr2O7, colour remains orange.

Question 8

what is the name of the mechanism that converts carbonyls to alcohols

Answer 8

nucleophilic addition (of H-)

Question 9

what reagents are needed in the reduction of a carbonyl to form an alcohol

Answer 9

NaBH4 and H2O (warmed). NaBH4 is represented and [H] in the equation and 2[H] is needed for every C-O double bond reduced.

Question 10

in the reduction of a carbonyl by nucleophilic addition, what is the nucleophile and what is the electrophile?

Answer 10

H- acts as the nucleophile and the carbonyl is the elctrophile.

Question 11

what kind of bond breaking occurs in nucleophilic addition (of H-) (with a carbonyl)

Answer 11

heterolytic fission. both e- in the covalent bond go to the more electronegative of the 2 atoms.

Question 12

in the nucleophilic addition of CN-, how is the nucleophile formed?

Answer 12

CN- is the nucleophile. HCN is generated “in situ” by reacting H2SO4 with aqueous NaCN.

Question 13

describe the test for aldehydes and ketones and what a positive result looks like.

Answer 13

add 2,4-DNPH (2,4 - dinitrophenylhydrazine) aka Brady’s reagent. and orange hydrazone precipitate indicates the presence of an either aldehyde or ketone