6.1.2&3 - Carbonyl Compounds and -COOH Flashcards
Bond angle in carbonyl compounds
Trigonal Planar (120)
How are sigma bonds formed
Direct overlap of orbitals
Bonding and structure in carbonyl compounds
p-orbital overlapping sideways
Forms pi-orbital
Nucleophilic addn in carbonyls
Nu-H -C=O
-C-O-H
I
Nu
Boiling points of carbonyls
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
Brady’s Reagent
2,4-DNP
2,4 dinitrophenyl hydrazine
Reaction w/ Brady’s Reagent
Reacts w/ carbonyl group to form an orange ppt and water
Why does Brady’s not work w/ carboxylic acids
Not electrophilic enough in comparison to ketone and aldehyde
How to determine the identity of a specific carbonyl compounds
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
Tollens Reagents
2 Ag(NH3)2 ^+ Silver nitrate dissolved in ammonia
Reaction w/ Tollens if an aldehyde is present
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
Why is the reaction w/ Tollens redox
Ag+ is reduced to Ag and the aldehyde is oxidised to COOH
RCHO + [O] —>RCOOH
Carboxylic acid and metal —>
Salt and H2
Carboxylic acid and Metal oxide —>
Salt and H2O
Carboxylic acid and Base —>
Salt and H2O
Carboxylic acid and Carbonate —>
Salt and CO2 and H2O
Nucleophilic addn. of aldehydes (reduction)
Aldehyde + 2[H] —> primary alcohol
NaBH4/ H2O (warm)
Nucleophilic addn. of ketones (reduction)
Ketone + 2[H] —> secondary alcohol
NaBH4/ H2O
What allows nucleophilic addn in carbonyls
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.
Carbonyl compounds + HCN (addn. reactions)
(H2SO4/ NaCN)
C=O —-> - C- CN
I I
H OH
Why is it useful to react carbonyl compounds w/ HCN
Can increase carbon chain lengths
Hydroxynitriles
Cyanohydrins
Have 2 functional groups -OH (hydroxyl) and C triple bond N (nitriles)
Nucleophilic vs Electrophilic addn
If the organic compound is an electrophile, its nucleophilic addn
If the organic compound is a nucleophile, it’s electrophilic addn
Aldehyde and acidified dichromate —->
(Under reflux) - Carboxylic acid
Esterification
Reacting an alcohol w/ a carboxylic acid w/ conc. H2SO4 (warm) - also makes H2O
Acid anhydrides w/ alcohol (works w/ phenol - also makes -COOH
Acid hydrolysis of esters
Reversible equation
Ester is heated under reflux w/ dilute aq acid (HCl)
Broken by water w/ acid as catalyst
Reforms monomers
Alkali hydrolysis of esters
Irreversible reaction
Reacted with NaOH/KOH (aq) under reflux
Ethyl propanoate + KOH —> Potassium propanoate + ethanol
Making esters from acyl chlorides
Acyl chloride + alcohol (nucleophile)—> Ester + HCl
Making acyl chloride
Carboxylic acid + thionyl chloride (SOCL2) –> Acyl chloride + sulfur dioxide + HCl
Naming amides
N (side chain attached to N) (side chain attached to carbonyl ) amide
Test to distinguish -COOH and esters
Add NaHCO3/ Na2CO3
-COOH : effervescence (CO2 given off)
Ester: no effervescence
Reduction using NaBH4
Adds an H
oxidation removes an H/O
How are acid anhydrides formed
Two molecules of a carboxylic acid
What are carboxylic acid salts called
Carboxylate
Formation of carboxylate salts
- COOH + NaOH —> -COO-Na+ +H2O
- COOH + Na —> -COO-Na+ + 1/2 H2
- COOH + Na2CO3 —> -COO-Na+ + CO2 + H2O
Why are acyl halides very strong electrophiles
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
Strongest to weakest electrophiles
Acid anhydride/ acyl halide
Ketones/ aldehyde
Ester, -COOH, amides
Why are acid anhydrides strong electrophiles
The lp gets split between both groups
Why are ester, -COOH and amides weak electrophiles
The lp is delocalalised over the OCO bonds, reducing electron deficiency on C
