Carbonyl Compounds

1
Carbonyl Compounds
2
Carbonyl compounds
3
Polarity of carbonyl bond
Dipole moment propan-1-ol 1.69D propanone 2.88
ethanal 2.72
4
Chemical reaction
No electrophilic additions (why?)
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Chemical reaction
No electrophilic additions (why?)
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Chemical reaction
No electrophilic additions (why?)
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Chemical reaction
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Nucleophilic Addition

• Reactivity
• Electrophilicity of C atom
• of the CO group.
• Strength of Nu-
• Steric effect at the carbonyl
• group

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Addition of HCN
Reactivity HCHO gt CH3CHO gt ArCHO gt CH3COCH3
gt CH3COR gt RCOR gt ArCOAr
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Nucleophilic Addition
Addition of HCN (using KCNH)
H/R
H/R
slow
R
C
O-

• Note
• HCN is NOT
• used.
• Because
• Toxic
• Weak acid
• little CN-

CN-
R
CN
fast
H/R
HCN
R
C
OH
Cyanohydrin (2-hydroxynitrile)
CN
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Usefulness in organic synthesis

• 1 carbon (longer carbon
• chain)
• 2 functional group

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Addition of sodium hydrogensulphate(IV)
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Addition of sodium hydrogensulphate(IV)

• Limit to aliphatic aldehydes and sterically
• unhindered ketones (steric effect)

product from 1mol NaHSO3 in 1 hour
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Addition of sodium hydrogensulphate(IV)

• Reversible (can be reversed by aq. Alkali or
• acid by shifting eqm. position to LHS by
• HSO3- Hgt SO2 , HSO3- OH- gt SO32-)
• Use to purify liquid or gaseous carbonyl
• compounds which are difficult to purify
• by direct recrystallization.

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Addition-elimination (condensation)
16
Addition-elimination
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Phenylhydrazone

• Products have sharp and characteristic
• melting point.
• Used as the identification of the original
• aldehyde and ketone

• Note
• NH3 does not react
• Predict the product obtained by
• adding H2N-NH2 to propanal.

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Oxidation

• KMnO4/H , K2Cr2O7/H (Strong oxidizing agent)
• RCHO gt RCOOH
• RCH2COCH2R gt RCOOH R CH2COOH
• RCH2COOH
  RCOOH
• C6H5CHO gt C6H5COOH requiring reflux for
  hours

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Oxidation

• Tollens reagent (silver mirror test)
• Reagent 2Ag 2OH- gt Ag2O H2O
• Ag2O 4NH3 H2O gt
  2Ag(NH3)2OH
• 2Ag(NH3)2 RCHO 3OH-
• gt RCOO- 2H2O 4NH3 2Ag (mirror)

No reaction with ketone (Tollens reagent is a
mild O.A.)
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Oxidation

• Fehlings reagent
• Reagent alkaline solution of copper(II)
  tartrate
• RCHO 2Cu2 5OH- gt RCOO- 3H2O Cu2O
• (Fehling)
  (brick-red)
• Note No reaction with Ketones and Aromatic
  Aldehydes

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Reduction
Reducing agent LiAlH4 Lithium
Tetrahydridoaluminate NaBH4
Sodium Tetrahydridoborate Both equivalent to a
source of hydride ion, H-.
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Reduction
LiAlH4 must be kept dry i.e. in solution of dry
ether LiBH4 is less powerful, can be used in
aqueous solution.
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Tri-iodomethane reaction
(RCOCH3 I2/OH- gt RCOO- CHI3 ,yellow ppt.)