Preparation of alcohols from alkenes involves the electrophilic attack on alkene carbon atom. Explain its mechanism.
The mechanism of acid catalysed addition of water (hydration) to alkenes involves the following three steps:
Step 1: Electrophilic attack by hydronium ion (H3O+) on alkene gives an intermediate, carbocation.
Assertion (A): Phenols give o-nitrophenol and p-nitrophenol on nitration with cone. HNO3 and H2SO4 mixture.
Reason (R): -OH group in phenol is o-,p-directing.
Give equations of the following reactions:
(i)Oxidation of propan-l-ol with alkaline KMnO4 solution.
(ii)Bromine in CS2 with phenol.
(iii)Dilute HNO3 acid with phehoL
(iv)Treating phenol with chloroform in presence of aqueous NaOH.
Predict the major product of acid catalysed dehydration of
(i) 1-nicthylcyclohcxanoland
(ii) butan-1-ol
Assertion (A): o-Nitrophenol is less soluble in water than the m- and p-isomers.
Reason (R): m-Nitrophenol and p-Nitrophenol exists as associated molecules.
In Kolbe's reaction, instead of phenol, phenoxide ion is treated with carbon dioxide. Why?
Assertion (A): Bond angle in ethers is slightly less than the tetrahedral angle. Reason (R): There is a repulsion between the two bulky (-R) groups.
Assertion (A): Like bromination of benzene, bromination of phenol is also carried out in the presence of Lewis acid.
Reason (R): Lewis acid polarizes the bromine molecule.
Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol.
Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
Give two reactions that show the acidic nature of phenol. Compare its acidity with that of ethanol.
Explain how does the – OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?
Explain the following with an example
(i) Kolbe's reaction (ii) Reimer – Tiemann reaction –
(iii) Williamson ether synthesis (iv) Unsymmetrical ether
How is 1-propoxypropane synthesised from propan-l-ol? Write the mechanism of this reaction.
Name the enzymes and write the reactions involved in the preparation of ethanol from sucrose by fermentation.
Explain why is OH group in phenols more strongly held as compared to OH group in alcohols.
Assertion (A): IUPAC name of the compound
Reason (R): In IUPAC nomenclature, ether is regarded as hydrocarbon derivative in which a hydrogen atom is replaced by -OR or -OAr group [where R = alkyl group and Ar = aryl group]
Which of the following is an appropriate set of reactants for the preparation of l-methoxy-4- nitrobenzene and why?
Write structures of the compounds whose IUPAC names are as follows:
(i)2-Methylbutan-2-ol
(ii)l-Phcnylpropan-2-ol
(iii)3,5-DimethyIhexane-l,3,5-triol
(iv)2,3-Dicthylphenol
(v)1-Ethoxypropane
(vi)2-Ethoxy-3-methylpentane
(vii) Cyclohexylmethanol
(viii) 3-Cyclohexylpcntan-3-ol
(ix)Cyclopcnt-3-en-l-ol
(x)4-ChIoro-3-ethylbutan-l-ol
While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.
Write the names of reagents and equations for the preparation of the following ethers by Williamson's synthesis:
(i)1-Propoxypropane
(ii)Ethoxybenzene
(iii)2-Methoxy-2-methylpropane
(iv)1-Methoxyethane
Write the structures of the isomers of alcohols with molecular formula C4H10O. Which one of these isomers exhibits optical activity?
Assertion (A): Phenol forms 2,4, 6-tribromophenol on treatment with Br2 in carbon disulphide at 273 K.
Reason (R): Bromine polarizes in carbon disulphide.
Explain a process in which a biocatalyst is used in industrial preparation of a compound known to you.
Phenol can be distinguished from ethanol by the reactions with ………….
(a) Br2/water (b) Na
(c) Neutral FeCl3 (d) All of these
Alcohols react with active metals, e.g., Na, K, etc., to give corresponding alkoxides. Write down the decreasing order or reactivity of sodium metal towards primary, secondary and tertiary alcohols.
Why is the reactivity of all three classes of alcohols with cone. HCl and ZnCl2 (Lucas reagent) different?
Nitration is an example of aromatic electrophilic substitution and its rate depends upon the group already present in the benzene ring. Out of benzene and phenol, which one is more easily nitrated and why?
Ethers can be prepared by Williamson's synthesis in which an alkyl halide is reacted with sodium alkoxide. Di-tert-butyl ether cannot be prepared by this method. Explain.
