Alcohols Phenols and Ethers
Multiple Choice Questions (MCQs)
1. Monochlorination of toluene in sunlight followed by hydrolysis with aq.
(a) o-cresol
(b)
(c) 2, 4- dihydroxytoluene
(d) benzyl alcohol
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Answer
(d) Monochlorination of toluene in sunlight gives benzyl chloride. On hydrolysis with aq.
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So, the correct option is (d).
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(a) o-cresol: Monochlorination of toluene in sunlight does not lead to the formation of o-cresol. o-Cresol is an ortho-substituted hydroxytoluene, which would require a hydroxyl group to be directly attached to the benzene ring in the ortho position relative to the methyl group. This is not achieved through monochlorination followed by hydrolysis.
-
(b) m-cresol: Similar to o-cresol, m-cresol is a meta-substituted hydroxytoluene. The monochlorination of toluene followed by hydrolysis does not introduce a hydroxyl group directly onto the benzene ring in the meta position relative to the methyl group.
-
(c) 2, 4-dihydroxytoluene: This compound has two hydroxyl groups attached to the benzene ring in the 2 and 4 positions relative to the methyl group. The monochlorination of toluene followed by hydrolysis does not introduce multiple hydroxyl groups onto the benzene ring.
2. How many alcohols with molecular formula
(a) 1
(b) 2
(c) 3
(d) 4
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Thinking Process
To solve this question, it should keep in mind that, if all four groups or atoms attached to the carbon atom are different, such a carbon is called asymmetric carbon or chiral carbon or stereocentre.
Answer
(a) The three isomers of butanol are possible. Structural formula of these isomers are given below
(i)
No carbon is chiral in this compound as none of the four carbon is bonded to four different substituents. (ii)
In this compound, asterisk marked carbon is chiral carbon as all four substituents, attached to it are different.
(iii)
Here, again carbon is not chiral in nature.
So, only one alcohol is chiral in nature and the correct option is (a).
-
Option (b) is incorrect because there is only one chiral alcohol with the molecular formula
, not two. The other isomers do not have a carbon atom bonded to four different substituents. -
Option (c) is incorrect because there are not three chiral alcohols with the molecular formula
. Only one of the isomers has a chiral center. -
Option (d) is incorrect because there are not four chiral alcohols with the molecular formula
. Only one isomer has a chiral center.
3. What is the correct order of reactivity of alcohols in the following reaction?
(a)
(b)
(c)
(d)
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Answer
(c) The given reaction is nucleophilic substitution reaction in which
This intermediate
So, the order of reactivity of alcohols in the given reaction is
-
Option (a)
: This option is incorrect because it suggests that primary alcohols are more reactive than secondary and tertiary alcohols. However, in the presence of , tertiary alcohols form more stable tertiary carbocations, which makes them more reactive than secondary and primary alcohols. -
Option (b)
: This option is incorrect because it implies that secondary alcohols are more reactive than tertiary alcohols. In reality, tertiary alcohols form more stable carbocations compared to secondary alcohols, making tertiary alcohols more reactive in this reaction. -
Option (d)
: This option is incorrect because it suggests that primary alcohols are more reactive than secondary alcohols. However, secondary alcohols form more stable carbocations than primary alcohols, making secondary alcohols more reactive than primary alcohols in this reaction.
Q.4
(a) catalytic hydrogenation
(b) treatment with
(c) treatment with pyridinium chlorochromate
(d) treatment with
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Answer
(c) Ethanal
The oxidation process can be stopped at the aldehyde stage if
-
(a) Catalytic hydrogenation: This process involves the addition of hydrogen to a molecule, typically reducing double or triple bonds. It does not oxidize ethanol to ethanal; instead, it would reduce any present double or triple bonds, which is not applicable in this context.
-
(b) Treatment with
: Lithium aluminium hydride is a strong reducing agent, which is used to reduce aldehydes, ketones, and carboxylic acids to alcohols. It does not oxidize ethanol to ethanal; rather, it would reduce any oxidized form back to ethanol or even further to ethane. -
(d) Treatment with
: Potassium permanganate is a strong oxidizing agent that typically oxidizes primary alcohols all the way to carboxylic acids. It would not stop at the aldehyde stage, thus converting ethanol to acetic acid rather than ethanal.
5. The process of converting alkyl halides into alcohols involves…… .
(a) addition reaction
(b) substitution reaction
(c) dehydrohalogenation reaction
(d) rearrangement reaction
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Answer
(b) An addition reaction is a reaction where two or more molecules combine to form a larger one. These reactions occur to change the unsaturated compound to saturated compound. In dehydrohalogenation reaction, alkyl halides give alkenes.
Rearrangement gives the structural isomers of the reactant while in substitution reaction one of the group or an atom is replaced by other group. Therefore, the process of converting alkyl halides into alcohols involves substitution reaction.
Reaction of alkyl halides
Reaction of alkyl halides
Primary alkyl halides
Secondary alkyl halides-
Tertiary alkyl halides
-
(a) Addition reaction: An addition reaction involves the combination of two or more molecules to form a larger molecule, typically converting unsaturated compounds to saturated compounds. This is not applicable to the conversion of alkyl halides to alcohols, which involves replacing a halogen atom with a hydroxyl group.
-
(c) Dehydrohalogenation reaction: Dehydrohalogenation is a reaction where an alkyl halide loses a hydrogen atom and a halogen atom, resulting in the formation of an alkene. This process does not produce alcohols but rather alkenes.
-
(d) Rearrangement reaction: A rearrangement reaction involves the reorganization of the molecular structure to form isomers of the original compound. This does not apply to the conversion of alkyl halides to alcohols, which involves the substitution of a halogen atom with a hydroxyl group rather than a structural rearrangement.
6. Which of the following compounds is aromatic alcohol?
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(a)
(b)
(c)
(d)
Show Answer
Answer
(c) Phenol is also known as, carbolic acid’ cannot be considered as aromatic alcohol. It is quite separate branch of compound called phenols. So, compound (A) i.e., phenol and compound
On the other hand, compound
-
Option (a) is incorrect because it includes compounds (A) and (D), which are phenols and not aromatic alcohols. Phenols have the -OH group directly attached to the benzene ring, making them a separate class of compounds.
-
Option (b) is incorrect because it includes compound (A), which is phenol and not an aromatic alcohol. Phenol has the -OH group directly attached to the benzene ring, making it a phenol rather than an aromatic alcohol.
-
Option (d) is incorrect because it includes only compound (A), which is phenol and not an aromatic alcohol. Phenol has the -OH group directly attached to the benzene ring, making it a phenol rather than an aromatic alcohol.
7. Give IUPAC name of the compound given below.
(a) 2-chloro-5-hydroxyhexane
(b) 2-hydroxy-5-chlorohexane
(c) 5-chlorohexan-2-ol
(d) 2-chlorohexan-5-ol
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Answer
(c)
The correct IUPAC name of the compound is 5-chlorohexan-2-ol. Hence, option (c) is the correct answer.
-
Option (a) 2-chloro-5-hydroxyhexane: This name is incorrect because the hydroxyl group (-OH) should be given priority over the chloro group (Cl) in the numbering of the carbon chain. The hydroxyl group should be assigned the lowest possible number, which is not the case here.
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Option (b) 2-hydroxy-5-chlorohexane: This name is incorrect for the same reason as option (a). The hydroxyl group should be given priority and assigned the lowest possible number, which is not reflected in this name.
-
Option (d) 2-chlorohexan-5-ol: This name is incorrect because the numbering of the carbon chain should prioritize the hydroxyl group, resulting in the hydroxyl group being at position 2 and the chloro group at position 5, not the other way around.
8. IUPAC name of
(a) 3-methylphenol
(b) 3-chlorophenol
(c) 3-methoxyphenol
(d) benzene-1, 3-diol
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Answer
(a) The structure of
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IUPAC name is 3-methylphenol because -
-
(b) 3-chlorophenol: This option is incorrect because it suggests the presence of a chlorine substituent at the 3-position on the benzene ring, whereas
-cresol has a methyl group at the 3-position, not a chlorine atom. -
(c) 3-methoxyphenol: This option is incorrect because it suggests the presence of a methoxy group (-OCH₃) at the 3-position on the benzene ring, whereas
-cresol has a methyl group at the 3-position, not a methoxy group. -
(d) benzene-1, 3-diol: This option is incorrect because it suggests the presence of two hydroxyl groups (-OH) at the 1 and 3 positions on the benzene ring, whereas
-cresol has only one hydroxyl group at the 1-position and a methyl group at the 3-position.
9. IUPAC name of the compound
(a) 1-methoxy-1-methylethane
(b) 2-methoxy-2-methylethane
(c) 2-methoxypropane
(d) isopropylmethyl ether
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Answer
(c)
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IUPAC name of the above compound is 2-methoxypropane and correct option is (c).
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Option (a) 1-methoxy-1-methylethane: This name suggests that the methoxy group (-OCH3) is attached to the first carbon of a two-carbon chain (ethane) with a methyl group also attached to the same carbon. However, the compound in question has a three-carbon chain (propane) with the methoxy group attached to the second carbon, not the first.
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Option (b) 2-methoxy-2-methylethane: This name implies that the methoxy group and a methyl group are both attached to the second carbon of a two-carbon chain (ethane). This is incorrect because the compound has a three-carbon chain (propane) with the methoxy group attached to the second carbon, and there is no additional methyl group attached to the second carbon.
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Option (d) isopropylmethyl ether: This name describes an ether with an isopropyl group (CH3-CH-CH3) and a methyl group (CH3) attached to the oxygen atom. However, the compound in question is an ether with a methoxy group (-OCH3) attached to the second carbon of a propane chain, not an isopropyl group.
10. Which of the following species can act as the strongest base?
(a)
(b)
(c)
Show Answer
Thinking Process
To compare the species, the point to be noted that weak acid has strong conjugate base and vice-versa. Write the corresponding acid of the given base and choose the weakest acid among these.
Answer
(b) Weakest acid has the strongest conjugate base. is the acid of
. Among all these acids, ROH is the weakest acid.
Therefore, the strongest base is
-
Option (a)
: The conjugate acid of is water (HOH), which is a stronger acid compared to ROH. Therefore, is a weaker base compared to . -
Option (c)
: The conjugate acid of is phenol ( ), which is a stronger acid compared to ROH. Therefore, is a weaker base compared to .
11. Which of the following compounds will react with sodium hydroxide solution in water?
(a)
(b)
(c)
(d)
Show Answer
Answer
(a) Phenol is more acidic in nature because by the loss of one proton, it gives phenoxide ion. This phenoxide ion is resonance stabilised. As phenoxide ion is a stable intermediate so, the tendency to give proton is more in phenol than the others. Phenols being more acidic than alcohols, dissolves in
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Therefore, option (a) is the correct.
-
(b)
: Benzyl alcohol ( ) is not acidic enough to react with sodium hydroxide. It does not form a stable ion like phenoxide ion, and thus does not dissolve in . -
(c)
: Tertiary butyl alcohol ( ) is also not acidic enough to react with sodium hydroxide. It does not have the ability to form a stable ion upon losing a proton, and therefore does not dissolve in . -
(d)
: Ethanol ( ) is a typical alcohol and is not acidic enough to react with sodium hydroxide. It does not form a stable ion upon losing a proton, and thus does not dissolve in .
12. Phenol is less acidic than…… .
(a) ethanol
(b) 0 -nitrophenol
(c)
(d)
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Thinking Process
This question is based on the acidic character of phenol. Electron withdrawing group at o - and p-position w.r. t. - OH group of phenol, increases the acidic strength.
Answer
(b) In o-nitrophenol, nitro group is present at ortho position. Presence of electron withdrawing group at ortho position increases the acidic strength. On the other hand, in o-methylphenol and in o-methoxyphenol, electron releasing group
Presence of these groups at ortho or para positions of phenol decreases the acidic strength of phenols. So, phenol is less acidic than o - nitrophenol.
-
Ethanol: Ethanol is less acidic than phenol because the hydroxyl group in ethanol is attached to an alkyl group, which is electron-donating. This decreases the ability of the oxygen to stabilize the negative charge on the conjugate base, making ethanol less acidic than phenol.
-
o-Methylphenol: In o-methylphenol, the methyl group is an electron-donating group. The presence of this group at the ortho position increases the electron density on the phenol ring, making it less able to stabilize the negative charge on the conjugate base, thus decreasing its acidity compared to phenol.
-
o-Methoxyphenol: In o-methoxyphenol, the methoxy group is also an electron-donating group. The presence of this group at the ortho position increases the electron density on the phenol ring, making it less able to stabilize the negative charge on the conjugate base, thus decreasing its acidity compared to phenol.
13. Which of the following is most acidic?
(a) Benzyl alcohol
(b) Cyclohexanol
(c) Phenol
(d)
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Answer
(d) Alpha carbon of benzyl alcohol and cyclohexanol is
Presence of electron withdrawing group increases the acidic strength. So,
-
Benzyl alcohol: The alpha carbon of benzyl alcohol is
hybridized, which makes it less capable of stabilizing the negative charge on the conjugate base after deprotonation. Additionally, benzyl alcohol lacks any electron-withdrawing groups that could enhance its acidity. -
Cyclohexanol: Similar to benzyl alcohol, the alpha carbon of cyclohexanol is
hybridized, which does not favor the stabilization of the conjugate base. Cyclohexanol also lacks any electron-withdrawing groups that could increase its acidic strength. -
Phenol: Although phenol has an
hybridized carbon, which is better at stabilizing the negative charge on the conjugate base compared to hybridized carbons, it does not have an additional electron-withdrawing group like -chlorophenol. This makes phenol less acidic than -chlorophenol.
14. Mark the correct order of decreasing acid strength of the following compounds.
(a) V
(b) II
(c) IV
(d) V
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Answer
(b) Presence of electron withdrawing group on phenols, increases its acidic strength. So, both compounds i.e.,
On the other hand, presence of electron releasing group on phenol, decreases its acidic strength. If
But, if it is present at para position, then it will exert
Hence, the correct option is (b).
-
Option (a) V
IV II I III:- This option incorrectly places
-methoxy phenol (V) as the strongest acid. The group is an electron-donating group, which decreases the acidity of phenol. Therefore, -methoxy phenol cannot be stronger than -nitrophenol (II) and -nitrophenol (IV), which have electron-withdrawing groups.
- This option incorrectly places
-
Option (c) IV
V III II I:- This option incorrectly places
-methoxy phenol (V) as stronger than -nitrophenol (II). The group in -nitrophenol exerts both and effects, making it a stronger acid than -methoxy phenol, which only has a effect and no effect.
- This option incorrectly places
-
Option (d) V
IV III II I:- This option incorrectly places
-methoxy phenol (V) as the strongest acid. As mentioned, the group is an electron-donating group, which decreases the acidity of phenol. Therefore, -methoxy phenol cannot be stronger than -nitrophenol (II) and -nitrophenol (IV), which have electron-withdrawing groups.
- This option incorrectly places
15. Mark the correct increasing order of reactivity of the following compounds with
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(a) I
(b) II
(c) II
(d) III
Show Answer
Thinking Process
This question is based on conceptual mixing of substitution reaction carbocation and reactivity. Nucleophilic substitution reactions depend upon the stability of carbocation. Higher the stability of carbocation (intermediate), higher will be the reactivity of reactant molecule.
Answer
(c) Reaction of the given compounds with
Since,
Thus, the order of stability of carbocation is
Therefore, compound (II) is least reactive and correct option is(III).
-
Option (a) I < II < III:
- This option suggests that compound I is the least reactive and compound III is the most reactive. However, compound I has no electron-withdrawing group, making its carbocation the most stable and thus the most reactive. Therefore, this order is incorrect.
-
Option (b) II < I < III:
- This option suggests that compound II is the least reactive and compound III is the most reactive, with compound I in between. However, compound I should be the most reactive due to the absence of electron-withdrawing groups, making its carbocation the most stable. Therefore, this order is incorrect.
-
Option (d) III < II < I:
- This option suggests that compound III is the least reactive and compound I is the most reactive, with compound II in between. While it correctly places compound I as the most reactive, it incorrectly places compound III as the least reactive. Compound II should be the least reactive due to the stronger electron-withdrawing effect of the
group compared to the group in compound III. Therefore, this order is incorrect.
- This option suggests that compound III is the least reactive and compound I is the most reactive, with compound II in between. While it correctly places compound I as the most reactive, it incorrectly places compound III as the least reactive. Compound II should be the least reactive due to the stronger electron-withdrawing effect of the
16. Arrange the following compounds in increasing order of boiling point. Propan-1-ol, butan-1-ol, butan-2-ol, pentan-1-ol
(a) Propan-1-ol, butan-2-ol, butan-1-ol, pentan-1-ol
(b) Propan-1-ol, butan-1-ol, butan-2-ol, pentan-1-ol
(c) Propan-1-ol, butan-2-ol, butan-1-ol, pentan-1-ol
(d) Propan-1-ol, butan-1-ol, butan-2-ol, pentan-1-ol
Show Answer
Thinking Process
This question is based on the boiling point of the compound. Boiling point increases with increase in the number of carbon atoms and decreases with increase of brancing in carbon chain.
Answer
(a) Boiling point increases with increase in the number of carbon atoms because of increase in molecular mass. So, the boiling point of pentan-1-ol is more than that of all other given compounds. Further, among isomeric alcohols,
-
Option (b) is incorrect because it places butan-1-ol before butan-2-ol. However, butan-1-ol has a higher boiling point than butan-2-ol due to its primary alcohol structure, which has a higher surface area and stronger intermolecular hydrogen bonding compared to the secondary alcohol structure of butan-2-ol.
-
Option (c) is incorrect because it repeats the same order as option (a), which is actually the correct order. Therefore, it does not provide a different incorrect order to analyze.
-
Option (d) is incorrect because it places butan-2-ol after butan-1-ol. However, butan-2-ol should come before butan-1-ol in the order of increasing boiling points due to the reasons mentioned above regarding primary and secondary alcohols.
Multiple Choice Questions (More Than One Options)
17. Which of the following are used to convert
(a)
(b)
(c)
(d) Reaction with
Show Answer
Answer
Conversion of aldehyde into alcohol is a reduction reaction. This reduction can be carried out by adding hydrogen in presence of finely divided metal catalyst such as platinum, palladium or nickel.
It can also be prepared by using
Reaction of
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(Where,
- Option (d) Reaction with
followed by hydrolysis:- This option is incorrect because the reaction of
(Grignard reagent) with an aldehyde other than methanal (formaldehyde) results in the formation of secondary alcohols, not primary alcohols. The question specifically asks for the conversion of (an aldehyde) into (a primary alcohol).
- This option is incorrect because the reaction of
18. Which of the following reactions will yield phenol?
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Answer
(a)
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Haloarenes are less reactive towards nucleophilic substitution reaction. Therefore, it requires very high temperature and pressure. Chlorobenzene does not undergo hydrolysis on treatment with aq.
Therefore, correct options are (a), (b) and (c).
-
Option (d): The reaction conditions are not specified, and without high temperature and pressure, chlorobenzene will not undergo hydrolysis to yield phenol. Haloarenes are less reactive towards nucleophilic substitution reactions under standard conditions.
-
Option (e): The reaction involves a different mechanism or reagent that does not lead to the formation of phenol. The specific conditions or reagents required to convert the starting material to phenol are not met in this option.
-
Option (f): Similar to option (d), the reaction conditions are not conducive for the nucleophilic substitution required to form phenol. Haloarenes need specific conditions (high temperature and pressure) to undergo hydrolysis, which are not provided here.
19. Which of the following reagents can be used to oxidise primary alcohols to aldehydes?
(a)
(b)
(c) Pyridinium chlorochromate
(d) Heat in the presence of
Show Answer
Answer
Acidic
Pyridinium chlorochromate
When the vapours of primary alcohols are passed over heated copper at
- Acidic
is a very strong oxidising agent. It oxidises primary alcohols into carboxylic acid, not aldehydes.
20. Phenol can be distinguished from ethanol by the reactions with…… .
(a)
(b)
(c) neutral
(d) All of these
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Answer
(a, c)
Ethanol does not react with
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Ethanol and phenol both react with sodium, so phenol cannot be distinguished from ethanol by the reaction with sodium.
Ethanol does not give any reaction with neutral
Therefore, correct options are (a) and (c).
-
Option (b)
: Ethanol and phenol both react with sodium, producing hydrogen gas and forming their respective sodium alkoxides. Therefore, phenol cannot be distinguished from ethanol by the reaction with sodium. -
Option (d) All of these: This option is incorrect because ethanol reacts with sodium, so it cannot be used to distinguish phenol from ethanol. Only reactions with
/water and neutral can be used to distinguish phenol from ethanol.
21. Which of the following are benzylic alcohols?
Show Answer
Answer
In benzylic alcohols, the
On the other hand, in compound (a) and (c), the
- In compound (a), the
group is attached to a hybridised carbon atom, but this carbon is not attached to the benzene ring. - In compound (d), the
group is attached to a hybridised carbon atom, but this carbon is not attached to the benzene ring.
Short Answer Type Questions
22. What is the structure and IUPAC name of glycerol?
Show Answer
Answer
Glycerol is the trihydric alcohol. Structure of glycerol is
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So, IUPAC name is - propan- 1, 2, 3-triol.
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Answer
The correct IUPAC name of the following compounds are given below
(a)
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IUPAC name
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IUPAC name
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Answer
The IUPAC name of the compound given below is
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3-methylpent-2-ene-1, 2-diol.
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Answer
Solubility of alcohols in water depends upon the two factors.
(i) Hydrogen bonding Higher the extent of hydrogen bonding, higher is the solubility. The hydrogen group of alcohol form hydrogen bonding. Solubility increases with increase in the number of
(I) Compound (II) will form stronger
(ii) Size of alkyl/aryl group Higher the size of alkyl/aryl group (hydrocarbon part), lower is the extent of hydrogen bonding and lower is the solubility. Hence,
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Answer
Alcohol is used in large quantities in the manufacture of alcoholic liquors. Its continuous use damages the various vital organs. Therefore, to refrain the people from drinking alcohol, heavy excise duty is levied on the sale of alcoholic beverages. But, it is used in various industries as it is a very good solvent.
Therefore, industrial alcohol must be cheap. Thus, to provide cheaper alcohol to industries and to refrain people from drinking alcohol, it is mixed with some copper sulphate, pyridine, methyl alcohol or acetone.
Alcohol is made unfit for drinking by mixing some quantity of any of these substances in it. This is called denatured alcohol.
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Answer
The given reactant is
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Answer
2-chloroethanol is more acidic than ethanol. Due to
Stronger acid due to
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Answer
Ethanol can be oxidises into ethanal by using pyridinium chlorochromate.
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Answer
Ethanol can be converted into ethanoic acid by using acidified
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Answer
o-nitrophenol is more volatile than
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Answer
The acidic character of alcohols is due to the polar nature of
Whereas due to
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Answer
When phenol is treated with bromine water, white ppt. of 2, 4,6-tribromophenol is obtained.
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Phenol, o-nitrophenol, o-cresol
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Answer
Nitro group shows
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Due to this
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Thinking Process
This question is based on the concept of the acidity and reactivity. The acidic character of alcohols is due to the polar nature of the
Answer
An electron releasing group produces
It will finally decrease the polarity and increase the strength of
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As we know that, sodium metal is basic in nature and alcohols are acidic in nature. Thus, reactivity of alcohol with sodium metal decreases with decrease in acidic strength. Therefore, the correct order is
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Answer
When benzene diazonium chloride is heated with water then phenol is formed.
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Answer
A stronger acid displaces a weaker acid from its salt. When
Similarly, when sodium ethynide is treated with water and alcohol, then acetylene is obtained.
Thus, water and alcohol are stronger acid than ethyne and the decreasing order of acidity of given compounds are
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Answer
Sucrose is converted to glucose and fructose in the presence of an enzyme, invertase or sucrase. Glucose and fructose undergo fermentation in the presence of another enzyme, zymase. Both these enzymes are present in yeast.
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Propan-2-one is a ketone. Its structural formula is
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Some compounds can rotate the plane polarised light, when it is passed through their solution. Such compounds are called optically active compounds. The structures of the isomers of alcohols with molecular formula
The asymmetry of the molecule is responsible for the optical activity in a molecule. If all the four substituents attached to the carbon are different then the carbon is called asymmetric or chiral carbon and such a molecule is called asymmetric molecule.
In the above explained structure, it is only butan-2-ol which contains a chiral carbon and hence it is optically active.
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In phenols, the electron pairs on oxygen atom of
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Out of these five resonating structures, II, III and IV structures contain a carbon-oxygen double bond character. In other words, carbon-oxygen bond in phenol acquires a partial double bond character due to resonance.
But in alcohols carbon-oxygen bond in alcohols is purely single bond. Therefore,
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Resonance is an important factor in phenols. During resonance
Therefore, nucleophiles cannot attack the benzene ring and phenols usually do not give nucleophilic substitution reaction.
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Preparation of alcohols from alkene by the hydration of alkenes in presence of sulphuric acid.
This addition reaction takes place in accordance with Markownikoff’s rule.
Mechanism The mechanism of the reaction involves the following three steps
Step 1 Protonation of alkene to form carbocation by electrophilic attack of
Step 2 Attack of water molecule to the secondary carbocation.
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Step 3 Loss of the hydrogen from the protonated alcohol.
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While for ethers, two dipoles are pointing in the same direction. These two dipoles do not cancel the effect of each other. Therefore, there is a finite resultant dipoles and hence
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The reaction of alcohols with Lucas reagent (conc.
Tertiary carbocations are most stable among the three classes of carbocations and the order of the stability of carbocation is
Thus, as the stability of carbocations are different so the reactivity of all the three classes of alcohols with Lucas reagent is different.
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Aspirin can be prepared by the reaction of salicylic acid with acetic anhydride. Salicylic acid is prepared by the reaction of phenol with
This process is known as Kolbe’s reaction. The product salicylic acid is used in the preparation of aspirin. After wards, when salicylic acid is treated with acetic anhydride then acetyl group replaces the hydrogen of
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Nitration of benzene and phenol is an electrophilic substitution reaction. During nitration
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This nitronium ion (electrophile) attacks on benzene or on phenol. Phenol is more easily nitrated than benzene as the presence of
Since, the electron density is more in phenol than in benzene, therefore, phenol is more easily nitrated than benzene.
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In phenoxide ion, the ability to give lone pair of electrons to the benzene ring is more in comparison to phenols. Therefore, the reactivity of phenoxide ion towards electrophilic substitution reaction is more in comparison to phenols.
Thus, phenoxide ion being a stronger nucleophile reacts easily with
Note Kolbe’s process is also known as Kolbe - Schmitt reaction. This reaction is precursor to aspirin.
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Dipole moment depends upon the polarity of bonds. Higher the polarity of bonds in molecule, higher will be its dipole moment. In phenol carbon is
On the other hand, carbon of methanol is
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In order to prepare di-tert-butyl ether, sodium tert-butoxide must be reacted with tert-butyl bromide. Alkoxides are not only nucleophiles but they are strong base as well. They react with
When tert-butyl-bromide reacts with sodium tert-butoxide instead of substitution, elimination takes place. As a result of this elimination reaction, Iso butylene is formed instead of di-tert butyl ether.
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Thinking Process
To solve this question, it should keep in mind that the order of repulsion between electron pairs is
Answer
The bond angle in
The
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Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecule. The hydrocarbon part methoxy methane (i.e.,
Alcohols with lower molar mass will have smaller hydrocarbon part and therefore tendency to form hydrogen bonding is more and they are more soluble in water.
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Nitro group of phenol produces
The decrease in electron density of the
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Boiling point depends upon the strength of intermolecular forces of attraction. Higher these forces of attraction, more will be the boiling point. Alcohols undergo intermolecular hydrogen bonding. So, the molecules of alcohols are held together by strong intermolecular forces of attraction.
But in ethers no hydrogen atom is bonded to oxygen. Therefore, ethers are held together by weak dipole-dipole forces, not by strong hydrogen bond.
Since, lesser amount of energy is required than to break weak dipole-dipole forces in ethers than to break strong hydrogen bonds in alcohol.
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Positive resonance effect is observed in phenols. Due to this
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From the above resonating structure, it is very clear that
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The phenoxide ion obtained after the removal of a proton is resonance stabilised as follows
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Whereas, the ethoxide ion obtained after the removal of a proton is not stabilised but destabilised due to
ethanol
Matching The Columns
57. Match the structures of the compounds given in Column I with the name of the compounds given in Column II.
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A.
B.
C.
D.
E.
F.
A. Cresols are organic compounds which are methyl phenols. There are three forms of cresol-o-cresol,
B. Catechol is also known as pyrocatechol. Its IUPAC name is 1,2-dihydrobenzene. It is used in the production of pesticides, perfumes and pharmaceuticals.
C. Its IUPAC name is 1, 3-dihydroxybenzene. Resorcinol is used to treat acne, seborrheic dermatitis and other skin disorder.
D. Hydroquinone is also known as quinol. Its IUPAC name is 1, 4- dihydroxybenzene. It is a white granular solid. It is a good reducing agent.
E. Anisole or methoxy benzene, is a colourless liquid with a smell reminiscent of anise seed.
F. Phenetole is an organic compound. It is also known as ethylphenyl ether. It is volatile in nature and its vapours are explosive in nature.
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Answer
A.
B.
C.
D.
A.
B. In
C. In this case, one of the alkyl group is tertiary and the other is primary. It follows
D. Here, the unsymmetrical ether is alkyl aryl ether. In this ether
Column I | Column II | ||
---|---|---|---|
A. | Antifreeze used in car engine | 1. | Neutral ferric chloride |
B. | Solvent used in perfumes | 2. | Glycerol |
C. | Starting material for picric acid | 3. | Methanol |
D. | Wood spirit | 4. | Phenol |
E. | Reagent used for detection of phenolic group | 5. | Ethylene glycol |
F. | By product of soap industry used in cosmetics | 6. | Ethanol |
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A.
B.
C.
D.
E.
F.
A. IUPAC name of ethylene glycol is ethane
B. Ethanol is a good solvent for fatty and waxy substances. Fats and waxes provide odour to the perfumes. Apart from being a good solvent, it is less irritating to the skin. So, it is used in perfumes.
C. Phenol is converted into picric acid (2, 4, 6-trinitro-phenol) by the reaction of phenol with conc.
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D. Methanol,
E. Neutral ferric chloride give purple/red colour when treated with phenols. It is the reagent used for detection of phenolic group.
F. Soaps are prepared by the reactions of fatty acid with
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This glycerol (propan -1, 2, 3 - triol) is the by product of soap industry and used in cosmetics.
Column I | Column II | ||
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A. | Methanol | 1. | Conversion of phenol to o-hydroxysalicylic acid |
B. | Kolbe’s reaction | 2. | Ethyl alcohol |
C. | Williamson’s synthesis | 3. | Conversion of phenol to salicylaldehyde |
D. | Conversion of ketone |
4. | Wood spirit |
E. | Reimer-Tiemann reaction | 5. | Heated copper at |
F. | Fermentation | 6. | Reaction of alkyl halide with sodium alkoxide |
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A.
B.
C.
D.
E.
F.
A. Methanol is also known as ‘wood spirit’ as it was produced by the destructive distillation of wood.
B. In Kolbe’s reaction, 2 - hydroxy benzoic acid (salicylic acid) is prepared by the reaction of phenol with
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C. Williamson synthesis is an important method for the preparation of ethers. In this method, an alkyl halide is allowed to react with sodium alkoxide.
D. When a
E. On treating phenol with chloroform in the presence of
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F. Ethanol is prepared by the fermentation of sugars.
Assertion and Reason
In the following questions a statement of Assertion (A) followed by a statement of Reason
(a) Assertion and reason both are correct and reason is correct explanation of assertion.
(b) Assertion and reason both are wrong statements.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.
(e) Both assertion and reason are correct statements but reason is not correct explanation of assertion.
61. Assertion (A) Addition reaction of water to but-1-ene in acidic medium yields butan-1-ol.
Reason (
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Answer
(b) Assertion and reason both are wrong statements.
Correct Assertion Addition reaction of water to but-1-ene in acidic medium yields butan-2-ol.
Correct Reason Addition of water in acidic medium proceeds through the formation of secondary carbocation.
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Reason (R) Nitro group helps in the stabilisation of the phenoxide ion by dispersal of negative charge due to resonance.
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(a) Assertion and reason both are correct and reason is correct explanation of assertion.
Reason (R) In IUPAC nomenclature, ether is regarded as hydrocarbon derivative in which a hydrogen atom is replaced by
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(d) Assertion is wrong statement but reason is correct statement.
Correct Assertion The IUPAC name of the given compound is 1-(2-propoxy) propane.
Reason (R) There is a repulsion between the two bulky
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(d) Assertion is wrong statement but reason is correct statement.
Correct Assertion Bond angle in ether is slightly more than the tetrahedral angle.
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Reason (R) They can form intermolecular hydrogen-bonding.
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(b) Assertion and reason both are wrong statements.
Correct Assertion Boiling points of alcohols are higher than that of ethers of comparable molecular mass.
Correct Reason Alcohols can form intermolecular hydrogen bonding while ethers cannot.
Reason (R) Lewis acid polarises the bromine molecule.
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(d) Assertion is wrong statement but reason is correct statement.
Correct Assertion Bromination of benzene but not of phenol is carried out in presence of a Lewis acid.
Reason (
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(d) Both assertion and reason are correct statements but reason is not correct explanation of assertion.
Correct Explanation Due to the presence of intramolecular hydrogen bonding, o-nitrophenol does not form hydrogen bonds with
Reason (R) Sodium ethoxide may be prepared by the reaction of ethanol with aqueous
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(c) Assertion is correct statement but reason is wrong statement.
Correct Reason Phenoxide ion is stabilised by resonance but ethoxide ion is not stabilised by resonance.
Resonance in phenoxide ion
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Reason (R) Bromine polarises in carbon disulphide.
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(b) Assertion and reason both are wrong statements.
Correct Assertion Phenol form 2, 4, 6-tribromophenol on treatment with bromine in water.
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Correct Reason In water, phenol gives phenoxide ion. This phenoxide ion activates the ring towards electrophilic substitution reaction.
Reason
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Answer
(d) Assertion is wrong statement but reason is correct statement.
Correct Assertion Phenols give
Long Answer Type Questions
71. Write the mechanism of the reaction of HI with methoxybenzene.
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In case of alkyl aryl ethers, the products are always phenol and an alkyl halide because due to resonance
Mechanism Protonation of anisole gives methylphenyl oxonium ion.
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In this ion, the bond between
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(b) Write complete reaction for the bromination of phenol in aqueous and non-aqueous medium.
(c) Explain why Lewis acid is not required in bromination of phenol?
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(a) The starting material used in the industrial preparation of phenol is cumene.
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(b) Phenols when treated with bromine water gives polyhalogen derivatives in which all the hydrogen atoms present at ortho and para positions with respect to
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However, in non-aqueous medium such as
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In aqueous solution, phenol ionises to form phenoxide ion. This ion activates the benzene ring to a very large extent and hence the substitution of halogen takes place at all three positions.
On the other hand, in non-aqueous solution ionisation of phenol is greatly suppressed. Therefore, ring is activated slightly and hence monosubstitution occur.
(c) Lewis acid is an electron deficient molecule. In bromination of benzene, Lewis acid is used to polarise
In case of phenol, oxygen atom of phenol itself polarises the bromine molecule to form
Mechanism of bromination of phenol
Mechanism of bromination of benzene
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Phenol is converted into salicylic acid. This salicylic acid is treated with acetic anhydride. On acetylation of salicylic acid, aspirin (acetyl salicylic acid) is formed.
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Enzymes are biocatalyst. These biocatalysts (enzymes) are used in the industrial preparation of ethanol. Ethanol is prepared by the fermentation of molasses - a dark brown coloured syrup left after crystallisation of sugar which still contains about
The process of fermentation actually involves breaking down of large molecules into simple ones in the presence of enzymes. The source of these enzymes is yeast. The various reactions taking place during fermentation of carbohydrates are
In wine making, grapes are the source of sugars and yeast. As grapes ripen, the quantity of sugar increases and yeast grows on the outer skin. When grapes are crushed, sugar and the enzyme come in contact and fermentation starts. Fermentation takes place in anaerobic conditions i.e., in absence of air.
The action of zymase is inhibited once the percentage of alcohol formed exceeds 14 per cent. If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid which in turn destroys the taste of alcoholic drinks.