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  1. >>Class 12
  2. >>Chemistry
  3. >>Alcohols, Phenols and Ethers
Patterns of problems
4 min read

Alcohols, Phenols And Ethers

- Get the best out of this chapter by practicing the kind of problems asked in various Exams
1

Problems related to nomenclature of alcohol and phenols.

Description:
Most important questions in this chapter can be asked from the IUPAC nomenclature of alcohols, phenols and ethers. The structures of compounds can be given and you will have to write their IUPAC name, or the name can be given and you will have to write their structure. Sometimes, you will also be asked to write the common name.
How to Approach:
Remember these tips to write the IUPAC names of alcohols, phenols and ethers.
1. When structure is given and you have to write the IUPAC name:
Naming of Alcohols
  • The longest continuous chain of carbon atoms containing the -OH group is taken as the parent
  • The chain is numbered from the end nearest to the -OH group.
  • The number that indicates the position of the OH group is prefixed to the name of the parent hydrocarbon, and the -e ending of the parent alkane is replaced by the suffix -ol
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6,8-dimethyl-3-decanol
Naming of Phenols
  1. The term phenol is the IUPAC name of a compound when a -OH group is bonded to a benzene ring
  2. When there is a second substituent , the benzene ring is numbered such that the carbon bonded to the hydroxyl group gets the lowest position.
  3. For benzene rings attached to more than one hydroxyl groups - The number of similar hydroxyl groups attached to the benzene ring are denoted by Greek numerical prefixes such as di, tri, tetra.
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2

Problems related to the trends in physical properties

Description:
You will be given specific properties of alcohol, phenols and ethers and asked to arrange them in increasing or decreasing order. Questions may be related to boiling points and solubility.
How to Approach:
Pay attention to the type of compounds mentioned in the question and arrange them according to the following trend.
Boiling point:-
  • Alcohols and phenols have higher boiling points than ethers and other hydrocarbons of comparable molecular mass because of presence of intermolecular hydrogen bonding.
  • The boiling point of isomeric alcohols decreases with branching due to decrease in surface area.
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  • The boiling point of alcohols increases with molecular mass.
  • Ethers have weak polarity and no inter molecular hydrogen bonding, hence their melting and boiling point is comparable to that of hydrocarbons.
Solubility:-
  • Solubility of alcohols in water is due to their ability to form hydrogen bonding with water.
  • Only lower members of alcohols are completely soluble in water.
  • Ethers can also form hydrogen bond with water and hence their solubility is similar to that of alcohols of similar molecular mass.
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3

Problems related to preparation and chemical properties of alcohols and phenols

Description:
Most questions from this chapter are concerned with the preparation reactions or conversions. You would be given a chemical to convert into a second chemical and be asked to write the whole set of chemical reactions you will undertake for the conversion.
Or you may be given the reactants of a reaction and asked to predict the product, or draw the structure of the product. Some questions show reactions with missing starting material, intermediate or reagent, and you have to identify it.
How to Approach:
Be thorough with all the preparation reactions in the chapter, the reactants, reagents, intermediates if any, and also other chemical reactions. Here's a list of the all the reactions from the chapter
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4

Problems related to arranging the given alcohols or phenols on the order of their acidic strength.


Description:
You can expect questions that give the structures of different alcohols and ask you to arrange them in ascending or descending order of acidic strength. Questions related to the effect of substituents on acidity are also asked. Some assertion and reasoning questions will also be asked for the same topic.
How to Approach:
For the acidity of alcohols and phenols remember these points:
  • Phenols are more acidic than aliphatic alcohols.
  • Alcohols are weaker acids than water
  • Alcohols are weaker acids than carboxylic acids
  • Substituents that stabilise the alkoxide/phenoxide anion increase acidity.
  • Electron-withdrawing groups like, halogens (F, Cl),nitriles (CN), nitro groups ), increase acidity.
  • Electron-donating groups like methyl groups decrease acidity
  • For aliphatic alcohols, the substituents that are closest to the functional group have the strongest effect.
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