Carbonyl Compounds Flashcards
[Carbonyl] hybridisation of carbonyl compounds
sp2 hybridised
trigonal planar
same plane as the 3 atoms
120 bond angle
[Carbonyl] R-COH vs R-CHO
R-COH is alcohol
R-CHO is aldehyde
[Carbonyl]
- boiling/melting points
- Solubility in polar/non-polar solvents
- miscibility in H2O
- Type of molecular attraction
bp
Alcohol/carbo acid> carbonyl > alkane/alkene
miscible in H20 when C is less because H-bonds formed
decrease solubility when C increases
larger proportion of alkyl/aryl groups
less soluble
pd-id insufficient energy for H-bonds
large
size also hinders formation of H bond
[Carbonyl] bp/mp
bp
carbonyl > alkane/alkene
pdpd vs weaker idid
alcohol/carbo acid> carbonyl
H-bond vs pdpd
[Carbonyl] alcohol to carbonyl
oxidation
Primary to aldehyde
(KMnO4/K2Cr2O7, IMMEDIATE DISTIL)
Secondary to ketone
(K2Cr2O7, heat only because KMnO4 too strong, [O] to carbo acid instea)
tertiary is resistant
[Carbonyl] oxidation of carbonyls
aldehyde to carbo acid
ketones are inert
Reagents acidified KMnO4/K2Cr2O7 and heat
[Carbonyl] reduction of carbonyls
aldehyde to pri OH
ketones to sec OH
Reagents
LiAlH4, dry ether, rt (+2[H])
NaBH4, ethanol, rt (+2[H])
H2 (g), Ni,Pd,Pt, rt (+H2)
[Carbonyl] Why cant LiAlH4 in dry ether/ NaBH4 reduce alkenes and alkynes?
these provide nucleophiles
attack e deficient C atoms
the C=C bonds are e rich
but non polar
will no react
[Carbonyl] NABH4 vs LiAlH4 strength
LiAlH4 > NaBH4
Al is less electroneg than B and H
H- more readily produced
[Carbonyl] nucleophilic addition
O highly electroneg
C=O highly polar
partial pos C
is electron deficient
electrophile
will be attacked by nucleophile
unsaturated C
hence addition reaction
[Carbonyl] Nucleophili reagents
alkenes vs carbonyl
Carbonyl susceptible to nucleophilic attack
alkenes not suscpetible to nucleophilic attack
Carbonyl C e deficient
bond to electroneg O atom
alkene C=C bond
e rich C
[Carbonyl] Nucleophilic addition (aldehyde/ketone to cyanohydrin)
add hydrogen cyanide, trace amounts of NaCN/NaOH, cold
[Carbonyl] Nucleophilic addition MECHANISM
HCN addded dissociates partially to give CN-
to increase CN- conc in reversible reaction, either
-add amall amt strong base NaOH/KOH
-add strong electrolyte NaCN/KCN
rate=k[carbonyl][CN-]
- :CN- nucleophile attacks e def C on carbonyl
pi e pair of C=O shift to O to form tetrahedral intermediate with - charge - intermediate undergoes protonation with HCN, yield cyanohydrin and regen the :CN- catalyst
[Carbonyl] Nucleophilic addition HCN
role of HCN
B-L acid/ lewis acid in step 2
protonating immediate
[Carbonyl] Nucleophilic addition HCN
why is racemic mixture produced?
equal probability of CN- nucleophile
attack either side of C
racemix mixture
50:50 chance of attack from bottom/top
[Carbonyl] Nucleophilic addition HCN
why cold
prevent poisonous HCN gas from escaping
low bp, is a gas
[Carbonyl] Nucleophilic addition HCN
why aldehyde more rapid than ketone
- Electronic
ketone has one more e donating R group
C is less e deficient - Steric
one more bulky alkyl group
hinders approach of nucleophiles
[Carbonyl] Nucleophilic addition of HCN is useful because
STEP UP REACTION WOO
hydrolysed to give OH + COOH
reduced to give amines
[Carbonyl] Distinguishing test for carbonyl summary
add 2,4-DNPH (do not play her) rt
orange ppt
condensation
Tollens reagent, heat
(YES ALDEHYDE NO KETONE)
silver mirror
Oxidation
Fehling’s solution, heat
(aldehyde vs aromatic aldehyde)
brick red ppt vs no ppt
Oxidation
Iodoform for COCH3 group
I2 decolourisd
yellow CHI3 ppt
[Carbonyl] Distinguishing test for carbonyl
FOR ALL CARBONYLS
add 2,4-DNPH (do not play her)
rt
orange ppt
condensation reaction
only works for carbonyl, any other C=O doesnt work (COOH/ester/amide/acyl chloride)
[Carbonyl] Distinguishing test for carbonyl
FOR aromatic and normal aldehydes but not ketone
Tollens reagent, heat
(YES ALDEHYDE NO KETONE)
silver mirror
Oxidation
[Carbonyl] Distinguishing test for carbonyl
FOR aldehyde vs aromatic aldehyde
Fehling’s solution, heat
(aldehyde vs aromatic aldehyde)
brick red ppt Cu2O vs no ppt
Oxidation
[Carbonyl] Distinguishing test for carbonyl
FOR COCH3 group
Iodoform test
I2 in NaOH, heat
Brown I2 decolourised
Pale yellow ppt CHI3
carboxylate salt O-
Oxidation
[Carbonyl] Iodoform test is useful for
step down reaction
