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IIT JEE > Alcohols, Phenols and Ethers > Flashcards

Alcohols, Phenols and Ethers Flashcards

1
Q

how are Alcohols and phenols formed

A

Alcohols and phenols are formed
when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group.

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2
Q

what are ethers

A

The substitution of a hydrogen atom in a
hydrocarbon by an alkoxy or aryloxy group
(R–O/Ar–O) yields another class of compounds known
as ‘ethers

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3
Q

how are ethers formed

A

ethers as compounds formed by substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.

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4
Q

classification of Compounds containing C sp3 -OH bond

A

alkyl group
Allylic alcohols
Benzylic alcohols

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5
Q

what is alkyl group alcohol

A

the –OH group is attached to an sp-3 hybridized carbon atom of an
alkyl group… three types of
alcohols, the –OH group is attached to primary, secondary and
tertiary carbon atom

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6
Q

what is allylic alcohols

A

the —OH group is attached to
a sp-3 hybridized carbon adjacent to the carbon-carbon double
bond, that is to an allylic carbon

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7
Q

what is benzylic alcohols

A

, the —OH group is attached
to a sp3—hybridized carbon atom next to an aromatic ring

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8
Q

classification of Compounds containing C sp2 -OH bond

A

Vinylic alcohol

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9
Q

what is Vinylic alcohol

A

These alcohols contain —OH group bonded to a carbon-carbon double bond, i.e., to a
vinylic carbon or to an aryl carbon

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10
Q

what is phenol

A

The simplest hydroxy derivative of benzene is phenol.

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11
Q

Structures of Functional Groups in alcohol

A

the oxygen of the –OH group is attached to carbon by a sigma bond formed by the overlap of a sp3 hybridized orbital of carbon with a sp3 hybridized orbital of oxygen

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12
Q

what is the bond angle in alcohol

A

The bond angle in alcohols is slightly less than the tetrahedral angle (109°-28°).It is due to the repulsion between the unshared
electron pairs of oxygen

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13
Q

The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol. why?

A

This is due to (i) partial double bond character on account of the conjugation
of unshared electron pair of oxygen with the aromatic ring
(ii) sp2 hybridized state of carbon to which oxygen is attached.

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14
Q

Structures of Functional Groups in ethers

A

the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement
…The bond angle is slightly greater than the
tetrahedral angle due to the repulsive interaction between the two bulky (–R) groups….The C–O bond length (141 pm) is almost the same as in alcohols

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15
Q

Preparation of Alcohols list types

A

From alkenes
(i) By acid catalyzed hydration
(ii) By hydroboration–oxidation:
From carbonyl compounds
(i) By reduction of aldehydes and ketones
(ii) By reduction of carboxylic acids and esters
From Grignard reagents

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16
Q

Preparation of Alcohols From alkenes By acid catalyzed hydration

A

Alkenes react with water in the presence of acid as catalyst to form alcohols
Mechanism;- Step 1: Protonation of alkene to form carbocation by electrophilic
attack of H3O
Step 2: Nucleophilic attack of water on carbocation.
Step 3: Deprotonation to form an alcohol.

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17
Q

Preparation of Alcohols From alkenes By hydroboration–oxidation

A

Diborane (BH3)2 reacts with alkenes
to give trialkyl boranes as addition product. This is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide

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18
Q

Preparation of Alcohols From carbonyl compounds By reduction of aldehydes and ketones:

A

Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts The usual catalyst is a finely divided metal such as platinum, palladium or nickel. It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4)

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19
Q

Aldehydes yield ________alcohols
whereas ketones give ______ alcohols

A

primary and secondary

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20
Q

Preparation of Alcohols From carbonyl compounds By reduction of carboxylic acids and esters

A

Carboxylic acids are reduced to primary alcohols in excellent yields by lithium
aluminum hydride, a strong reducing agent LiAlH4 is an expensive reagent, and therefore Commercially, acids are reduced to alcohols by converting them to the esters followed by their reduction using hydrogen in the presence of catalyst

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21
Q

Preparation of Alcohols From carbonyl compounds From Grignard reagents

A

The first step of the reaction is the nucleophilic addition of Grignard
reagent to the carbonyl group to form an adduct. Hydrolysis of the adduct yields an alcohol

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22
Q

Phenol, also known as

A

carbolic acid

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23
Q

Preparation of Phenols

A

From haloarenes
From benzene sulphonic acid
From diazonium salts
From cumene

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24
Q

Preparation of Phenols From haloarenes

A

Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced

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25
Q

Preparation of Phenols From benzene sulphonic acid

A

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.

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26
Q

Preparation of Phenols From cumene

A

Phenol is manufactured from the hydrocarbon, cumene. Cumene
(isopropyl benzene) is oxidized in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid

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26
Q

Preparation of Phenols From diazonium salts

A

A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2 + HCl) at 273-278K. Diazonium salts are hydrolyzed to phenols by warming with water or by treating with dilute acids

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27
Q

The properties of alcohols and phenols are chiefly due to the _______ group

A

hydroxyl

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28
Q

The high boiling points of alcohols are mainly due to the presence of?

A

The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers and hydrocarbons.

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28
Q

Boiling Points in alcohols and phenols

A

The boiling points of alcohols and phenols increase with increase in the number of carbon atoms (increase in van der Waals forces)
In alcohols, the boiling points decrease with increase of branching in carbon chain
(because of decrease in van der Waals forces with decrease in surface
area)

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29
Q

explain Solubility of alcohols and phenols in water?

A

Solubility of alcohols and phenols in
water is due to their ability to form
hydrogen bonds with water molecules The solubility decreases with increase in size of alkyl/aryl

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30
Q

in alcohols The bond between O–H is broken when alcohols react with

A

nucleophiles

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31
Q

in alcohol The bond between C–O is broken when they react as

A

electrophiles

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32
Q

alcohol and phenol Reaction with metals

A

Alcohols and phenols react with active
metals such as sodium, potassium and aluminum to yield corresponding alkoxides/phenoxides and hydrogen

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33
Q

what is Brönsted acids

A

compounds can donate a proton to a stronger base

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34
Q

alcohols and phenols are _____ in nature

A

acidic

34
Q

explain Acidity of alcohols

A

The acidic character of alcohols is due to
the polar nature of O–H bond An electron-releasing group(–CH3, –C2H5) increases electron density on oxygen tending to
decrease the polarity of O-H bond. This decreases the acid strength

35
Q

Alcohols are weaker acids than water(true or false)

A

True

36
Q

explain Acidity of phenols

A

The hydroxyl group, in phenol is directly attached to the sp 2 hybridized carbon of benzene ring which acts as an electron withdrawing group. Due to this, the charge distribution in phenol molecule, as depicted in its resonance structures, causes the oxygen of –OH group to be positive

37
Q

phenols are stronger acids than alcohols and water. true or false

A

true

38
Q

the presence of electron withdrawing
groups such as nitro group, enhances the acidic strength of phenol

A

This effect is more pronounced when such a group is present at ortho and para positions. It is due to the effective
delocalization of negative charge in phenoxide ion when substituent is at ortho or para position

39
Q

Esterification

A

Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to form esters.

40
Q

explain the reaction to form esters

A

The reaction with carboxylic acid and acid anhydride is carried out in the presence of a small amount of concentrated sulphonic
acid The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to neutralize HCl which is
formed during the reaction. It shifts the equilibrium to the right
hand side

41
Q

what is acetylation

A

The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.

42
Q

how is aspirin produced

A

Acetylation of salicylic acid produces aspirin

43
Q

Alcohols Reaction with hydrogen halides

A

Alcohols react with hydrogen halides to form alkyl halides The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another (Lucas test). Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl2) while their halides are immiscible and produce turbidity in solution. In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily. Primary
alcohols do not produce turbidity at room temperature

44
Q

Alcohols Reaction with phosphorus trihalides

A

Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide

45
Q

Alcohols when Dehydrated

A

Alcohols undergo dehydration (removal of a molecule of water) to form alkenes on treating with a protic acid e.g., concentrated H2SO4 or H3PO4

46
Q

Alcohols when Oxidation

A

Oxidation of alcohols involves the formation of a carbon oxygen double bond with cleavage of an O-H and C-H bonds .Such a cleavage and formation of bonds occur in oxidation reactions. These are also known as dehydrogenation reactions as these involve loss of dihydrogen from an alcohol molecule

47
Q

the relative ease of dehydration of alcohols follows the following order:

A

Tertiary > Secondary > Primary

48
Q

The mechanism of dehydration of ethanol involves the following steps:

A

Mechanism Step 1: Formation of protonated alcohol
Step 2: Formation of carbocation: It is the slowest step and hence, the rate determining step of the reaction
Step 3: Formation of ethene by elimination of a proton

49
Q

a primary alcohol is oxidised to an
_________ which in turn is oxidised to _______

A

aldehyde carboxylic acid

50
Q

Strong oxidising agents such as acidified ____________ are used for getting carboxylic acids from alcohols directly

A

potassium permanganate

51
Q

______ in anhydrous medium is used as the oxidizing agent for the isolation of aldehydes.

A

CrO3

52
Q

A better reagent for oxidation of primary alcohols to aldehydes in good yield is

A

pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl.

53
Q

Tertiary alcohols on oxidation reaction

A

Tertiary alcohols do not undergo oxidation reaction. Under strong reaction conditions gives a mixture of carboxylic
acids containing lesser number
of carbon atoms is formed

54
Q

Common electrophilic aromatic substitution reactions taking place
in phenol are

A

Nitration
Halogenation

55
Q

what if i drank ethanol, mixed with methanol

A

In the body, methanol is oxidised
first to methanal and then to methanoic acid, which may cause blindness and
death. A methanol poisoned patient is treated by giving intravenous infusions of
diluted ethanol. The enzyme responsible for oxidation of aldehyde (HCHO) to acid
is swamped allowing time for kidneys to excrete methanol.

56
Q

Reactions of phenols Electrophilic aromatic substitution

A

In phenols, the reactions that take place on the aromatic ring are electrophilic substitution reactions The –OH group
attached to the benzene ring activates it towards electrophilic substitution it directs the incoming group to ortho and para
positions in the ring as these positions become electron rich due to
the resonance effect caused by –OH group

57
Q

electrophilic aromatic substitution reactions Nitration

A

Nitration: With dilute nitric acid at low temperature (298 K), phenol yields a mixture of ortho and para nitrophenols The ortho and para isomers can be separated by steam distillation. o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association
of molecules

58
Q

what is picric acid

A

With concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol. The product is commonly known as picric
acid

58
Q

electrophilic aromatic substitution reactions Halogenation

A

On treating phenol with bromine When the reaction is carried out in solvents of low polarity such as CHCl3or CS2and at low temperature, monobromophenols are formed

59
Q

The usual halogenation of benzene takes place in the presence of a

A

Lewis acid which polarises the halogen molecule.

60
Q

In case of phenol, the polarization of bromine molecule takes place even in the
absence of Lewis acid.why

A

It is due to the highly activating
effect of –OH group attached to the benzene ring.

61
Q

When phenol is treated with bromine water, ________ is formed as white precipitate

A

2,4,6-tribromophenol

62
Q

explain Kolbe’s reaction

A

Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitutionHence, it undergoes electrophilic substitution with
carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product

63
Q

Reimer-Tiemann reaction

A

On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction… The intermediate substituted benzal chloride is hydrolyzed in the presence of alkali to produce salicylaldehyde

63
Q

Oxidation of phenol

A

Oxidation of phenol with chromic
acid produces a conjugated diketone
known as benzoquinone. In the
presence of air, phenols are slowly
oxidised to dark coloured mixtures
containing quinones

63
Q

Reaction of phenol with zinc dust

A

Phenol is converted to benzene on heating with zinc dust

64
Q

explain Methanol

A

Methanol, CH3OH, also known as ‘wood spirit’, was produced by destructive distillation of wood the methanol is
produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of ZnO – Cr2O3 catalyst.Methanol is a colourless liquid and boils at 337 K. It is highly
poisonous in nature. Ingestion of even small quantities of methanol can cause blindness and large quantities causes even death. Methanol is used as a solvent in paints, varnishes and chiefly for making
formaldehyde

65
Q

explain Ethanol

A

Ethanol, C2H5OH, is obtained commercially by fermentation The sugar in molasses, sugarcane or fruits such as grapes is converted to glucose and fructosein the presence of an enzyme, invertase. Glucose and fructose undergo fermentation in the
presence of another enzyme, zymase, which is found in yeast Ethanol is a colourless liquid with boiling point 351 K. It is used
as a solvent in paint industry and in the preparation of a number of
carbon compounds. The commercial alcohol is made unfit for drinking
by mixing in it some copper sulphate (to give it a colour) and pyridine
(a foul smelling liquid). It is known as denaturation of alcohol.

66
Q

explain mechanism of Preparation of Ethers By dehydration of alcohols

A

The formation of ether is a nucleophilic bimolecular reaction (SN2) involving the attack of alcohol molecule on a protonated alcohol Acidic dehydration of alcohols, to give an alkene is also associated
with substitution reaction to give an ether
The method is suitable for the preparation of ethers having primary alkyl groups only. The alkyl group should be unhindered
and the temperature be kept low. Otherwise the reaction favours the
formation of alkene The reaction follows SN1 pathway when the alcohol
is secondary or tertiary

66
Q

Preparation of Ethers

A

By dehydration of alcohols
Williamson synthesis

67
Q

Preparation of Ethers By dehydration of alcohols

A

Alcohols undergo dehydration in the presence of protic acids (H2SO4, H3PO4). The formation of the reaction product, alkene or ether depends on the reaction conditions

68
Q

Williamson synthesis

A

method for the preparation of symmetrical and unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium alkoxide Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by this method. The reaction involves SN2 attack
of an alkoxide ion on primary alkyl halideEthers containing substituted alkyl groups (secondary or tertiary)
may also be prepared by this method. The reaction involves SN2 attack
of an alkoxide ion on primary alkyl halide

69
Q

what effect Williamson synthesis has on phenols

A

Phenols are also converted to ethers by this method. In this, phenol is used as the phenoxide moiety.

69
Q

Physical Properties of ethers

A

The C-O bonds in ethers are polar and thus, ethers have a net dipole moment. The weak polarity of ethers do not appreciably affect their boiling points which are comparable to those of the alkanes but are much lower than the boiling points of alcohols The large difference in boiling points of alcohols and ethers is due to the presence of hydrogen bonding in alcohols.The miscibility of ethers with water resembles those of alcohols of
the same molecular mass

70
Q

Chemical Reactions of ether

A

Cleavage of C–O bond in ethers
Electrophilic substitution

71
Q

Cleavage of C–O bond in ethers

A

Ethers are the least reactive of the functional groups. The cleavage of
C-O bond in ethers takes place under drastic conditions with excess
of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl-oxygen bond. The reaction yields phenol and alkyl
halide

72
Q

The order of reactivity of hydrogen halides

A

HI > HBr > HCl
The cleavage of ethers takes place with concentrated
HI or HBr at high temperature

73
Q

Mechanism for Cleavage of C–O bond in ethers

A

Step 1:The reaction of an ether with concentrated HI starts with protonation of ether molecule. The reaction takes place with HBr or HI because these reagents are sufficiently acidic.
Step 2:Iodide is a good nucleophile. It attacks the least substituted carbon of the oxonium ion formed in step 1 and displaces an alcohol molecule by SN2 mechanism.
Thus, in the cleavage of mixed ethers with two different alkyl groups, the alcohol
and alkyl iodide formed, depend on the nature of alkyl groups. When primary or
secondary alkyl groups are present, it is the lower alkyl group that forms alkyl
iodide (SN2 reaction).
Step 3:When HI is in excess and the reaction is carried out at high temperature,
ethanol reacts with another molecule of HI and is converted to ethyl iodide

74
Q

when one of the alkyl group is a tertiary group, the halide formed is a tertiary halide how?

A

It is because in step 2 of the reaction, the departure of leaving group (HO–CH3) creates a more stable carbocation [(CH3)3C+], and the reaction
follows SN1 mechanism

75
Q

how is anisole formed

A

anisole (methylphenyl oxonium ion) is
formed by protonation of ether

76
Q

Electrophilic substitution in ethers

A

The alkoxy group (-OR) is ortho, para directing and activates the
aromatic ring towards electrophilic substitution in the same way as
in phenol

77
Q

Electrophilic substitution in ethers by Halogenation

A

Phenyl alkyl ethers undergo usual halogenation in the benzene ringe.g., anisole undergoes bromination with
bromine in ethanoic acid even in the absence of iron (III) bromide
catalyst. It is due to the activation of benzene ring by the methoxy
group. Para isomer is obtained in 90% yield.

78
Q

Electrophilic substitution in ethers by Friedel-Crafts reaction

A

Anisole undergoes Friedel-Crafts reaction,
i.e., the alkyl and acyl groups are introduced at ortho and para positions by reaction with alkyl halide and acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) as catalyst

79
Q

Electrophilic substitution in ethers by Nitration

A

Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitroanisole.

80
Q
A

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