Reactions of phenol

1
Reactions of phenol

• Alcohol can react with sodium to give off
  hydrogen, but it is not acidic enough to
  neutralize NaOH. 2CH3O-H 2Na ?
  2CH3O-Na H2
• Alkyl groups in alcohols push electrons toward
  the OH group, so that the oxygen does not
  attract the electrons in the O-H bond
• CH3O-H CH3O- H Ka
  10-17 mol dm-3
• The negative charge on the CH3O- is localized by
  the electron-releasing effect from the CH3-
  group, so that stabilization by charge
  delocalisation is not possible.

2
Acidity of phenols

• Phenol is acidic enough to react with both sodium
  and sodium hydroxide. Phenol easily loses a
  proton to form the phenoxide ion, which is
  stabilized by resonance. (mesomeric effect)
• 
  Ka0.1 mol dm-3

3
Acidity of phenols

• Phenol is acidic due to two reasons
• Non bonded electrons on the oxygen atom become
  partially incorporated in the delocalized system
  of the benzene ring. This electron withdrawal
  from the O-atom makes it slightly electron
  deficient, thus facilitating the loss of a proton
  by weakening the O-H bond.
• The phenoxide ion is stabilized relative to
  phenol by delocalization of the negative charge
  throughout the benzene ring. The presence of
  electron-withdrawing -NO2 group further
  stabilizes the phenoxide ion, making nitrophenol
  a very acidic compound
• Phenol is, however, not acidic enough to
  neutralize NaHCO3 to give carbonic acid (CO2
  H2O).
  

4
Separate acid-phenol mixture

• Phenols dissolve in aqueous sodium hydroxide by
  neutralization whereas alcohols do not. This
  helps to distinguish separate between phenols
  alcohols
• Due to its weaker acidity, phenol does not react
  with NaHCO3 solution, whereas carboxylic acids
  react to liberate carbon dioxide. NaHCO3(aq)
  offers a method for distinguishing separating
  most phenols from carboxylic acids.
• R-COOH HCO3- R-COO- H2O CO2

5
Separate an organic mixture
6
Characteristic reactions of phenols

• The delocalization of electrons has strengthened
  the C-O bond, the partial double bond character
  between the carbon and oxygen is confirmed by its
  bond length being shorter than that of normal C-O
  bonds.
• As a result of this strengthening of C-O bond,
• Displacement of the OH group is difficult
• Oxidation does not give such breakdown products
  as acid, alkanal, but form complex polymers
• Formation of alkenes by dehydration is not
  possible
• Delocalization of the lone pair in the oxygen
  atom with the benzene ring makes the oxygen less
  readily available to attack the electropositive
  carbon of the COOH group of carboxylic acids
  esterification is slower than with alcohols
• Prior change to the more reactive phenoxide ion
  will help phenol esterify with the reactive acid
  derivatives

7
Phenol Reactions

• Aqueous solubility lt 1 g cm-3, pH of solution 4
• Dissolves readily in NaOH(aq) but not in
  NaHCO3(aq)
• Melts easily in hot water (m.p.42oC)
• Na shows vigorous effervescence with phenol to
  give H2
• Adding Na2CO3, drop by drop, to neutralize
  FeCl3(aq) until a trace of the brown precipitate
  just remains after shaking Violet coloration
  appears when a few drops of the neutralized FeCl3
  solution is added to a phenol solution.
• Through delocalization of the non-bonded
  electrons, the OH group activates the benzene
  ring toward electrophilic substitution. Phenol
  rapidly decolorizes bromine water as
  2,4,6-tribromophenol is formed from bromination
  at RT.

8
Esterification of phenol
Phenols contain an active hydrogen, which can be
replaced by an acetyl group in a reaction called
acetylation. The acetylating agent is CH3COCl or
CH3CO2-COCH3 , which can react with the compounds
containing active hydrogen such as phenol or
amine (primary, secondary)
9
Carbonyl Compounds

• Aldehydes ketones contain the carbonyl group.
  R-C-H and R-C-R are the general structure of an

O
O
aldehyde and a ketone respectively
R H or an alkyl or aryl group
R alkyl or aryl group
Both classes of compounds show
reactions characteristic of the carbonyl group
The carbonyl carbon is sp2 hybridized, with its 3
attached atoms lying in the same plane. The bond
angles between the three attached atoms are about
120o.(trigonal planar)
Within the carbonyl group, the electrons in the ?
and ? bonds are drawn toward the more
electronegative oxygen atom. The carbonyl oxygen
thus bears a substantial partial negative charge,
whereas the carbonyl carbon bears a substantial
positive charge.
?-
?
C
O
10
Naming alkanals and alkanones

• The reactions of aldehydes and ketones include
• ?Nucleophilic addition reactions
• Addition-elimination (condensation) reactions
• Oxidation and reduction
• Triiodomethane reaction

11
Nucleophilic Addition Reactions

• The carbonyl group is strongly polarized, with
  the electrons in the ? and ? bonds shifted toward
  the more electronegative oxygen atom. The
  carbonyl carbon is thus electron-deficient or
  electrophilic, whereas the oxygen is
  electron-rich or nucleophilic.
• The carbonyl carbon is readily attacked by an
  electron-rich nucleophile, and addition reactions
  of nucleophiles at the carbonyl carbon dominate
  the reactivity of carbonyl compounds.
• Neutral/anionic nucleophiles offer the extra pair
  of electrons for co-ordinating with the carbonyl
  carbon Once a new bond is formed from the
  nucleophile to the carbonyl carbon, the carbonyl
  oxygen gains an unshared electron pair. This
  electron rich oxygen can transfer its electron
  pair to a proton, completing the overall addition
  of Nu-H to the carbonyl group.

12
The Carbonyl Group Structure and Mechanism

• Due to the higher electronegativity of the oxygen
  atom, there exists an electropositive carbon in
  the carbonyl group where an electron-rich
  nucleophile initiate an attack on it. Despite the
  high electron density of the carbonyl group, a
  nucleophile-induced addition occurs
• HNu adds across the CO double bond in such a way
  that the electron-rich nucleophile attacks the
  electropositive carbon to form a Nu-C bond, and a
  H then attacks the intermediate anion to form
  the O-H bond.

? ?-
13
Nucleophlic and Electrophilic Addition

• The carbonyl carbon in the highly polarized CO
  bond can act as an electron-deficient site to
  attract electron-rich species (nucleophiles).
  Addtion to the CO bond is a nucleophilic
  addition, with the initial attack from an
  nucleophiles, e.g.
• The CC ond is non-polar and acts as an electron-
  rich centre instigating an initial attack onto
  the electron-deficient species, e.g.

?H-CN?-
The Br- acts as the electrophile attacked by the
electron rich CC bond
14
Stereochemical aspect of nucleophilic addition

• In the nucleophilic addition across the CO bond,
  nucleophilic attack can come from above or below
  the planar carbonyl group, in order to minimize
  steric hindrance. Since addition can occur at
  both sides of the plane at equal rates, both
  enantiomers are formed in exactly the same
  amount, resulting in a racemic mixture of
  products.

Propanone does not form a racemic mixture in its
reaction with cyanide
Aldehydes are generally more reactive than
ketones toward nucleophilic addition
Aldehydes have fewer bulky groups than ketones
Aldehydes are less reactive than ketones toward
nucleophilic addition
15
Relative reactivities of carbonyl compounds

• The relative reactivities of aldehydes ketones
  toward nucleophilic addition reactions depend on
  2 factors
• Electronic influence of the groups attached to
  the carbonyl carbon - The higher the number of
  electron-releasing groups, the less
  electron-deficient is the carbonyl carbon, an the
  less reactive it is toward nucleophiles.
• Steric hindrance of the groups.
• Alkyl groups are electron-releasing relative to
  hydrogen and are also much more bulky. Hence, for
  both electronic and steric reasons, ketones with
  the carbonyl group flanked by two alkyl or aryl
  groups, are generally less reactive than
  aldehydes.

Least reactive
Delocalization of electrons from the ring reduces
the electron deficiency of the carbonyl carbon
and makes it much less reactive.
16
Addition of hydrogen cyanide (KCN)

• Hydrogen cyanide adds to the carbonyl groups of
  aldehydes and most ketones to form
  2-hydroxynitriles
• HCN is never used for addition across the CO
  bond
• HCN is a dangerously toxic gas at RT
• HCN itself is a poor nucleophile and a weak acid
• CN-, being a stronger nucleophile than HCN, is
  able to attack the carbonyl carbon very rapidly.
  As a weak acid, it adds slowly. The reaction is
  base catalysed as the base can increase the CN-

R H or alkyl group
17
Nucleophilic addition with KCN(aq)

• Its safer to replace HCN OH- by CN- and acid.
  This can be done by mixing the aldehyde or ketone
  with aqueous NaCN and then slowly adding
  sulphuric acid to the mixture. Even with this
  procedure, great care must be taken the reaction
  must be done in fume cupboard.
• Hydroxynitriles are useful intermediates in
  organic syntheses, especially for preparing
  ?-hydroxyacids or ?,?-unsaturated acids the
  CN- group being readily hydrolysed to -COOH by
  refluxing with 70 sulphuric acid or dilute
  alkaline solutions.
• Formation of cyanohydrins offers a useful way of
  making molecules with 2 functional groups and
  with a longer carbon chain than the original
  reactant.

18
Hydroxyacids and unsaturated acids

• When reacted with HCN, ketone/aldehyde gives
  hydroxynitriles, which hydrolyzes to form
  ?-hydroxyacids. Then dehydration of the acid with
  conc. H2SO4 gives ?,?-unsaturated acids.
• Upon nucleophilic addition, all aldehydes and
  unsymmetrical ketones give a racemic mixture of
  enantiomers, which cannot be separated by careful
  distillation. HCN adds preferentially to the
  carbonyl group, leaving other unsaturated carbon
  centres intact.

19
Reactivity of carbonyl compounds

• Nucleophilic addition of carbonyl compounds is
  affected by electronic and steric factors.
• The presence of electron-withdrawing groups at
  the ?- carbon of aldehyde/ketone makes the
  carbonyl carbon more electron-deficient, thus
  increasing the reactivity of the carbonyl
  compound. CH3COCHCl2 is more reactive than
  propanone toward nucleophilic addition by HCN.
  The increased steric hindrance of Cl is less
  important in affecting reactivity in this case.
• Addition of HSO3- is more prone to steric
  factors. With more bulky groups attached to the
  carbonyl carbon, ketones are less reactive than
  aldehydes.

20
Addition of Sodium bisulphite NaHSO3

• 3,3-diethylpentan-2-one is unreactive toward
  hydroxynitrile formation because
• there are bulky substituents around the carbonyl
  group,
• the 3 ethyl groups produce positive inductive
  effect, reducing the electrophilic nature of the
  carbonyl carbon
• On shaking the aldehyde/ketone with excess 40
  aqueous sodium hydrogen sulphite at RT, colorless
  crystals called bisulphite adducts are formed

Its a nucleophilic addition with the attack
initiated by the -SO3H nucleophile This reaction
is very sensitive to steric hindrance and is
limited to aliphatic aldehydes and sterically
unhindered ketones (methyl ketones) only. The
reaction with NaHSO3 helps distinguish
aldehydes/ketones from others
21
Purification separation of aldehydes/methyl
ketones

• Bisulphite reaction is used for the separation
  and purification of aldehydes and methyl ketones
  from other compounds because these compounds can
  be regenerated by treating the bisulphite adducts
  with aqueous alkali or dilute acids, which
  reverse the bisulphite equilibria to the left
• A few derivatives of ammonia (amine/hydroxylamine/
  hydrazine/2,4-dinitrophenylhydrazine) serve as
  an active nucleophile, initiating nucleophilic
  addition on the carbonyl carbon of
  aldehydes/ketones. The adduct formed is easily
  dehydrated to form a product containing a -CN
  group.

22
Addition-Elimination (Condensation)

• The lone pair on the nitrogen atom of a
  derivative of ammonia attacks the carbonyl
  carbon, forming an unstable intermediate. This
  adduct then rapidly loses a water molecule to
  form a condensation product.

Aldehydes and ketones react with hydroxylamine to
form oximes, known as aldoximes and ketoximes
respectively. Due to the high solubility of
aliphatic oximes, careful crystallization is
required to get the crystalline oxime solid.
23
Condensation with ammonia derivatives

• Aldehydes ketones react with 2,4-dinitrophenylhy
  drazine to form 2,4-dinitrophenylhydrazones. The
  condensation products have sharp characteristic
  melting points and is useful for identification
  of the original compounds.

Purification of the condensation products is done
by recrystallization from ethanol. Its melting
point is then determined after washing and drying
the crystals. The m.p. values can be compared
with that from data book for the purpose of
identification of the original aldehyde or ketone.
24
Identification of a carbonyl compound

• 2,4-dinitrophenylhydrazine, dissolved in ethanol,
  is mixed with a little concentrated sulphuric
  acid to give an orange reagent commonly used in
  the identification of aldehydes and ketones.
• When it reacts with an aldehyde or ketone, the
  reagent gives an orange-yellow solid of
  2,4-dinitrophenylhydrazone. These hydrazones can
  be isolated in relatively pure forms, which have
  characteristic melting points.
• 2,4-dinitrophenylhydrazine is preferred to
  hydroxylamine for the formation of derivatives
  because 2,4-dinitrophenylhydrazones have higher
  melting points and are less soluble.
• The hydrazone solid is often much more soluble in
  ethanol near its boiling point than at room
  temperature. Boiling ethanol is thus added to an
  impure hydrazone until just enough has been added
  to dissolve it all. Any insoluble impurities can
  be removed by filtering with suction
• The hot filtrate (hydrazone) collected is cooled
  slowly in an ice-water mixture until crystals
  reappear. Since the solid derivative is much less
  soluble at RT, it will precipitate out from the
  filtrate and can be removed by further
  filtration. Any soluble impurities (such as
  unreacted aldehydes or ketones, minerals), will
  remain dissolved in the solvent.

25
Identification of a carbonyl compound (2)

• The hydrazone is said to be purified by
  recrystallization. The effectiveness of this
  method depends very much on the selection of a
  suitable solvent in which the hydrazone is much
  more soluble at high temperature than low
  temperature, thus regenerating purer product
  crystals in good yield.
• After recrystallization the derivative is further
  washed under suction with a few drops of ethanol
  and then dried by drawing air through them. The
  crystals are spread on a dry watch glass left
  overnight for drying.
• Proper recrystallization is vital because any
  impurities left will depress the m.p. of the
  hydrazone, thus leading to a false
  identification.
• A dilute solution of 2,4-dinitrophenylhydrazine
  is used because solid 2,4-dinitrophenylhydrazine
  easily precipitates out and the solid might be
  mistaken as the hydrazone.
• Ethanol in this case is chosen largely out of
  trial and error, careful tests being made on
  small product samples with different solvents.
• By comparing the measured m.p. with those in a
  data book, the particular aldehyde or ketone can
  be identified. Further chemical tests (Tollens
  test), may be necessary to distinguish the
  aldehyde from the ketone if there are two
  2,4-dinitrophenylhydrazones with the same m.ps.

26
Triiodomethane Reaction

• Ethanal and methyl ketones contain the CH3CO-
  group, which would react with iodine in aqueous
  NaOH to give yellow crystals of triiodomethane.
• A small sample of ethanal or methyl ketone can be
  warmed with NaOH(aq) and a large amount of iodine
  (2 drops of propanone require 1 g of iodine).
  Pale yellow crystalline precipitates of
  triiodomethane appear on cooling.
• CH3CH2OH reacts with I2/NaOH to give ethanal and
  thus ethanol also shows positive triiodomethane
  test.

A secondary alcohol with the -OH group at C-2
also shows postive iodoform test
27
Structural Determination
The equations involved in the deduction
Yellow precipitate
The possible structures for C5H8O are
28
Oxidation and Reduction

• Aldehydes are oxidized to carboxylic acids redily
  by a number of oxidants such as acidified KMnO4,
  K2Cr2O7 or even mild oxidant such as ammoniacal
  silver nitrate and Fehlings solution.
• Unlike aliphatic aldehydes, aromatic counterparts
  do not undergo oxidation readily. (Benaldehyde
  does not change easily to benzoic acid)
• Ketones do not undergo oxidation readily. It
  requires more drastic conditions to bring about
  the cleavage of the carbon-carbon single bond,
  forming 2 acids.

29
The Silver Mirror Test (Tollens reagent)

• Mixing aqueous silver nitrate with aqueous
  ammonia forms a solution known as Tollens
  reagent, a weak oxidant but when heated gently in
  water it can oxidize aldehydes to carboxylate
  ions, itself being reduced to metallic silver
  which deposits on the wall of the test tube as
  silver mirror.
• The Tollens reagent is prepared by adding excess
  aqueous ammonia solution to a clean test tube of
  silver nitrate solution, drop by drop, until the
  precipitate is just dissolved. 2Ag 2OH-
  Ag2O(s) H2O
  Ag2O 4NH3 H2O 2Ag(NH3)2OH
• A few drops of aldehyde are then added to the
  reagent and the tube placed in a beaker of warm
  water

30
Fehlings Test
If the mixture left after the silver mirror test
is heated to dryness

• Tollens reagent gives a negative result with all
  ketones and thus can serve as a specific test for
  distinguishing aldehydes from ketones.
• A Fehlings reagent is an alkaline solution of
  copper(II) tartrate (clear royal blue in color).
• Aliphatic aldehydes reduce the copper(II) ion in
  Fehlings reagent to the reddish-brown copper(I)
  oxide precipitate.
• Ketones and aromatic aldehydes give negative
  result to the Fehlings test, so the reagent acts
  to distinguish alehydes ketones.

there may be an explosive hazard
Fehlings reagent is a solution mixture of CuSO4
sodium potassium tartrate in excess NaOH
31
Reduction

• Aldehydes ketones are reduced to primary
  secondary alkanols respectively by the two
  reductants
• Lithium tetrahydridoaluminate (LiAlH4) in
  ethoxyethane solution followed by addition of
  water, or
• Sodium tetrahydridoborate (NaBH4) in aqueous
  solution/ethanol
• These reductants generate the nucleophile H-, the
  hydride ion, which is attracted to the
  electropositive carbonyl carbon The nucleophilic
  attack by the hydride ions gives alcohols as the
  reduction product. The alcohol is released upon
  hydrolysis of the addition intermediate.
• A ketone gives a secondary alcohol
• An aldehyde gives a primary alcohol
• NaBH4 is used to reduce aldehydes (to minimize
  hazard). However, LiALH4 is a more versatile ????
  reductant.

32
Reduction (2)

• LiAlH4 can reduce carboxylic acid, acid
  anhydride, ester and acid chloride to alcohols
  whereas NaBH4 cannot.
• LiAlH4 and NaBH4 produce H- ion for their
  reducing action, both of them cannot reduce
  carbon-carbon double, triple bonds and aromatic
  rings to full saturation. The H- ions are simply
  repelled by the non-polar and electron-rich ?
  bonds in the carbon-carbon double bond.

33
Reduction (3)

• LiAlH4 must be used in dry ether because it
  reacts violently with water to give hydrogen and
  an alkaline solution.

34
IR Spectra of the carbonyl compounds

• The gtCO group shows a prominent dip at around
  1700 cm-1 as a result of CO bond vibration. The
  dip is often strong sharp. In aldehydes it is
  at between 1720 and 1740 cm-1. In ketones it is
  between 1705 and 1725 cm-1.

Infra-red spectrum of propanone
90
50
30
CO bond stretch
C-H bond stretch
Wavenumber cm-1
3400
3000
1330
1700
35
Carboxylic acids

• The carboxyl group CO2H is a combination of the
  carbonyl group and the hydroxyl group. These two
  groups modify the behavior of each other, so that
  the chemistry of the acids differs from that of
  aldehydes, ketones and alcohols.

2-chlorobutanoic acid
3-hydroxy-5-methylhexanoic acid
Benzoic acid
Propanedioic acid
Benzene-1,2-dicarboxylic acid
Hex-4-enoic acid (cis, trans)
Aldehydes ketones can be changed to
?-hydroxynitriles, which hydrolyze to
?-hydroxycarboxylic acids.
36
Carboxylic acids (2)

• Nitriles, precursors of carboxylic acids, can
  also be made from haloalkanes by nucleophilic
  substitution with NaCN. Only primary haloalkanes
  are useful in making the nitriles useful for
  conversion into carboxylic acids. As CN- ion is a
  relatively strong base, the use of secondary or
  tertiary haloalkanes leads to elimination rather
  than substitution

Alkaline hydrolysis of nitriles produces the
acid salt and ammonia. Prolonged reflux in acid
solution produces the carboxylic acid and
ammonium salt.


37
Oxidation of primary alcohols, aldehydes
alkylbenzenes

• Strong oxidants such as K2Cr2O7 or KMnO4 oxidizes
  primary alcohols to give carboxylic acids in
  fairly good yield. Since aldehydes are formed as
  an intermediate in the course of such oxidation,
  most aldehydes undergo oxidation to acids under
  even milder conditions. RCHO O ? RCOOH
  RCH2OH 2O ? RCOOH H2O
• The side chains of alkylbenzenes are always
  susceptible to oxidation by strong oxidants such
  as hot alkaline KMnO4

Dil KMnO4
Alkaline KMnO4, H3O
Alkylbenzenes with alkyl groups larger than
methyl are also degraded to benzoic acids. Since
oxidation of side chain occurs at the
phenylmethyl Carbon, 2-methyl-2-phenylpropane is
resistant to side chain oxidation.
38
Oxidation of methyl ketones and some alcohols

• Methyl ketones, with the group COCH3 or alcohols
  with the group CH(OH)-CH3 are liable to undergo
  iodoform reaction to form CHI3 as well as a
  carbon skeleton with a carboxylate group

The group to which the -COCH3 or -CH(OH)CH3
function is attached can be aromatic, alkyl or
hydrogen. The resulting carboxylate has one
carbon less than the original carbon skeleton.
By utilizing different oxidants, CH3-C6H4-COCH3
can form different products
39
Acidity of Carboxylic acids

• Ethanoic acid, CH3COOH, is the key ingredient in
  vinegar. It is the COOH group in the molecule
  that is responsible for its acidity. In water the
  molecule dissociates into ions
• The ethanoate ion is stabilized by the spreading
  of the negative charges over a carbon and two
  oxygen atoms. Being a weak acid, the acid
  dissociation constant is small.
• The smaller the pKa value, the greater is the
  acid strength

Electron releasing groups such as -CH3 reduce the
acid strength. HCOOH is slightly more acidic than
CH3CO2H as it has no -CH3.
40
Acidity of carboxylic acids (2)

• There are 3 factors affecting the acidity of
  organic acids
• the strength of the H-A bond
• the electronegativity of A (electronic factor)
• factors stabilizing its conjugate anion A- with
  respect to HA
• Since the O-atom is considerably more
  electronegative than carbon, the O-H bond in
  methanol breaks more readily than the C-H bond in
  methane. Also the resulting conjugate anion,
  CH3O- is more stable than CH3-.

pKa(methanol) 16
pKa(methane) 50
The pKa of methanoic acid is 4. The
electron-withdrawing gtCO group, which enhances
the electron affinity of the oxygen atom to which
the incipient proton is attached and weakens the
O-H bond. Factor 3 is the most important factor
the stabilization of the resulting conjugate
anion HCO2- when compared with the methanoic acid
molecule itself. In the anion, negative charge
is spread over 3 atoms and is thus stabilized.
41
Influence of substituents on acidity

• Electron-withdrawing groups weakens the O-H bond
  and helps spread out the negative charge on the
  resulting carboxylate ion, thus raising the
  acidity of carboxylic acid.
• The acidity of a carboxylic acid is greatly
  increased when the number of electron-withdrawing
  chlorine attached to the ?-carbon increases. The
  electron-withdrawing groups can increase acid
  strength as the O-H bond is weakened and the acid
  anion is stabilized. Inductive effects are
  additive the more numerous the
  electron-withdrawing groups on the ?-carbon, the
  stronger will then be the acid. The more
  electronegative the ?-substituent, the stronger
  is the acid.
• The Inductive effect on acidity decreases rapidly
  when the substitutents are placed farther away
  from the -CO2H group

42
Influence of substituents on acidity

• The presence of electron-releasing group in the
  acid will result in reduction of the acid
  strength for 2 reasons
• The electron-donating group pushes electrons
  toward the electron deficient carbonyl carbon
  atom, thus reducing its charge. The hydroyl
  oxygen will then have a better chance of
  attracting more than its fair share of electrons
  in the C-O bond, thus strengthening the O-H bond
  and consequently it will not break easily.
• When dissociation has occurred, the
  electron-donating substituent will push electrons
  toward the electron-rich -CO2- group, thus
  intensifying the negative charge and consequently
  destabilizes the resulting anion.

Carboxylic acids are more acidic than phenols and
they displace CO2 from. HCO3-. Carboxylic acids
react with ammonia to give ammonium salts,
which can be dehydrated by strong heating to give
amides
43
Acidity of organic compounds

• In the case of alcohols there is no
  delocalization of charge stabilizing the alkoxide
  anion, RO-, with respect to alcohol molecule
  itself. Alcohols are neutral.
• In the case of phenol, there is also the
  stabilization of the conjugate ion by the
  delocalization of its negative charge through
  interaction with the p orbitals of the benzene
  ring The negative charge spreads over the
  electropositive C- atoms and the stability of the
  phenoxide ion is less stable than the carboxylate
  as the negative charge in it is spread over two
  highly electronegative oxygen atoms.
• The order of stability follows the order of
  stability of their conjugate anions

gt
gt
44
IR Spectra of the carbonyl compounds

• The gtCO group shows a prominent dip at around
  1700 cm-1 as a result of CO bond vibration. The
  dip is often strong sharp. In aldehydes it is
  at between 1720 and 1740 cm-1. In ketones it is
  between 1705 and 1725 cm-1.

Infra-red spectrum of propanone
90
50
30
CO bond stretch
C-H bond stretch
Wavenumber cm-1
3400
3000
1330
1700
45

• L

46

• L

47

• L

48

• L