6.1.2&3 - Carbonyl Compounds and -COOH

Question 1

Bond angle in carbonyl compounds

Answer 1

Trigonal Planar (120)

Question 2

How are sigma bonds formed

Answer 2

Direct overlap of orbitals

Question 3

Bonding and structure in carbonyl compounds

Answer 3

p-orbital overlapping sideways

Forms pi-orbital

Question 4

Nucleophilic addn in carbonyls

Answer 4

Nu-H -C=O
-C-O-H
I
Nu

Question 5

Boiling points of carbonyls

Answer 5

Ald < Alc < Acid
Low –> High
Ketones and aldehydes lack hydroxyl groups and so are incapable of H bond
Presence of only one oxygen in alc vs. two in acid

Question 6

Brady’s Reagent

Answer 6

2,4-DNP

2,4 dinitrophenyl hydrazine

Question 7

Reaction w/ Brady’s Reagent

Answer 7

Reacts w/ carbonyl group to form an orange ppt and water

Question 8

Why does Brady’s not work w/ carboxylic acids

Answer 8

Not electrophilic enough in comparison to ketone and aldehyde

Question 9

How to determine the identity of a specific carbonyl compounds

Answer 9

Add 2,4-DNPH and obtain orange ppt
Filter, recrystallise, filter and dry
Find mp of the 2,4-DNP derivative
Reference to a database of values

Question 10

Tollens Reagents

Answer 10

2 Ag(NH3)2 ^+
Silver nitrate dissolved in ammonia

Question 11

Reaction w/ Tollens if an aldehyde is present

Answer 11

Ag+ is reduced to Ag metal and creates a silver ‘mirror’ on the side of the test tube
Does not occur w/ ketones as it needs a hydrogen

Question 12

Why is the reaction w/ Tollens redox

Answer 12

Ag+ is reduced to Ag and the aldehyde is oxidised to COOH

RCHO + [O] —>RCOOH

Question 13

Carboxylic acid and metal —>

Answer 13

Salt and H2

Question 14

Carboxylic acid and Metal oxide —>

Answer 14

Salt and H2O

Question 15

Carboxylic acid and Base —>

Answer 15

Salt and H2O

Question 16

Carboxylic acid and Carbonate —>

Answer 16

Salt and CO2 and H2O

Question 17

Nucleophilic addn. of aldehydes (reduction)

Answer 17

Aldehyde + 2[H] —> primary alcohol

NaBH4/ H2O (warm)

Question 18

Nucleophilic addn. of ketones (reduction)

Answer 18

Ketone + 2[H] —> secondary alcohol

NaBH4/ H2O

Question 19

What allows nucleophilic addn in carbonyls

Answer 19

O is more elctro-ve therefore electron density in bond lies closer to O than C
C is electron-deficient and attacked by nucleophiles as they’re electron pair donors.

Question 20

Carbonyl compounds + HCN (addn. reactions)

Answer 20

(H2SO4/ NaCN)
C=O —-> - C- CN
I I
H OH

Question 21

Why is it useful to react carbonyl compounds w/ HCN

Answer 21

Can increase carbon chain lengths

Question 22

Hydroxynitriles

Answer 22

Cyanohydrins

Have 2 functional groups -OH (hydroxyl) and C triple bond N (nitriles)

Question 23

Nucleophilic vs Electrophilic addn

Answer 23

If the organic compound is an electrophile, its nucleophilic addn
If the organic compound is a nucleophile, it’s electrophilic addn

Question 24

Aldehyde and acidified dichromate —->

Answer 24

(Under reflux) - Carboxylic acid

Question 25

Esterification

Answer 25

Reacting an alcohol w/ a carboxylic acid w/ conc. H2SO4 (warm) - also makes H2O Acid anhydrides w/ alcohol (works w/ phenol - also makes -COOH

Question 26

Acid hydrolysis of esters

Answer 26

Reversible equation Ester is heated under reflux w/ dilute aq acid (HCl) Broken by water w/ acid as catalyst Reforms monomers

Question 27

Alkali hydrolysis of esters

Answer 27

Irreversible reaction Reacted with NaOH/KOH (aq) under reflux Ethyl propanoate + KOH ---> Potassium propanoate + ethanol

Question 28

Making esters from acyl chlorides

Answer 28

Acyl chloride + alcohol (nucleophile)---> Ester + HCl

Question 29

Making acyl chloride

Answer 29

Carboxylic acid + thionyl chloride (SOCL2) --> Acyl chloride + sulfur dioxide + HCl

Question 30

Naming amides

Answer 30

N (side chain attached to N) (side chain attached to carbonyl ) amide

Question 31

Test to distinguish -COOH and esters

Answer 31

Add NaHCO3/ Na2CO3 -COOH : effervescence (CO2 given off) Ester: no effervescence

Question 32

Reduction using NaBH4

Answer 32

Adds an H | oxidation removes an H/O

Question 33

How are acid anhydrides formed

Answer 33

Two molecules of a carboxylic acid

Question 34

What are carboxylic acid salts called

Answer 34

Carboxylate

Question 35

Formation of carboxylate salts

Answer 35

- COOH + NaOH ---> -COO-Na+ +H2O - COOH + Na ---> -COO-Na+ + 1/2 H2 - COOH + Na2CO3 ---> -COO-Na+ + CO2 + H2O

Question 36

Why are acyl halides very strong electrophiles

Answer 36

Halogens are more electronegative and the lone pair doesn't delocalise onto the carbonyl bond Leaves C very electron deficient so prone to attack by a nucleophile

Question 37

Strongest to weakest electrophiles

Answer 37

Acid anhydride/ acyl halide Ketones/ aldehyde Ester, -COOH, amides

Question 38

Why are acid anhydrides strong electrophiles

Answer 38

The lp gets split between both groups

Question 39

Why are ester, -COOH and amides weak electrophiles

Answer 39

The lp is delocalalised over the OCO bonds, reducing electron deficiency on C