9359alcohols and phenols

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Guess Paper 2012

Class XII

Subject ChemistryALCOHOLS AND PHENOLS

Question 11.1:

Classify the following as primary, secondary and tertiary alcohols:

(i)

(ii)

(iii)

(iv)

(v)

(vi)

Answer

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Primary alcohol (i), (ii), (iii)

Secondary alcohol (iv), (v)

Tertiary alcohol (vi)

Question 11.2:

Identify allylic alcohols in the above examples

Answer

The alcohols given in (ii) and (vi) are allylic alcohols

Question 11.3:

!ame the following compo"nds according to I#P$C system

(i)

(ii)

(iii)

(iv)




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(v)

Answer

(i)%&Chloromethyl&'&isopropylpentan&&ol

(ii)', &*imethylhexane&, %&diol

(iii)%&+romocyclohexanol

(iv)ex&&en&%&ol

(v)'&+romo&%&methylb"t&'&en&&ol

Question 11.4:

Show how are the following alcohols prepared by the reaction of a s"itable

-rignard reagent on methanal.

(i)

(ii)

Answer

(i)




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(ii)

Question 11.5:

/rite str"ct"res of the prod"cts of the following reactions:

(i)

(ii)

(iii)

Answer

(i)




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(ii)

(iii)

Question 11.6:

-ive str"ct"res of the prod"cts yo" wo"ld expect when each of the following alcohol reacts

with (a) Cl&0nCl'(b) +r and (c) S1Cl'

(i)+"tan&&ol

(ii)'&2ethylb"tan&'&ol

Answer

(a)

(i)

Primary alcohols do not react appreciably with 3"cas4 reagent (Cl&0nCl') at roomtemperat"re

(ii)




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Tertiary alcohols react immediately with 3"cas4 reagent

(b)

(i)

(ii)

(c)

(i)

(ii)

Question 11.7:

Predict the ma5or prod"ct of acid catalysed dehydration of




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(i)&methylcyclohexanol and

(ii)b"tan&&ol

Answer

i

(ii)

Question 11.8:

Orthoandparanitrophenols are more acidic than phenol *raw the resonance str"ct"res of

the corresponding phenoxide ions

Answer

6esonance str"ct"re of the phenoxide ion




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6esonance str"ct"res ofp&nitrophenoxide ion

6esonance str"ct"res of m&nitrophenoxide ion

It can be observed that the presence of nitro gro"ps increases the stability of phenoxide ion

Question 11.9:

/rite the e7"ations involved in the following reactions:

(i)6eimer&Tiemann reaction

(ii)8olbe4s reaction




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Answer

i. Reimer&iema!! reacti"!

ii. #"lbe$s reacti"!

Question 11.10:

/rite the reactions of /illiamson synthesis of '&ethoxy&%&methylpentane starting from ethanol

and %&methylpentan&'&ol

Answer

In /illiamson synthesis, an al9yl halide reacts with an al9oxide ion $lso, it is an S!' reactionIn the reaction, al9yl halides sho"ld be primary having the least steric hindrance ence, anal9yl halide is obtained from ethanol and al9oxide ion from %&methylpentan&'&ol




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Question 11.11:

/hich of the following is an appropriate set of reactants for the preparation of &methoxy&&

nitroben;ene and why.

(i)

(ii)

Answer

Set (ii) is an appropriate set of reactants for the preparation of &methoxy&&nitroben;ene




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In set (i), sodi"m methoxide (C%1!a) is a strong n"cleophile as well as a strong base ence,an elimination reaction predominates over a s"bstit"tion reaction

Question 11.12:

Predict the prod"cts of the following reactions:

(i)

(ii)

(iii)

(iv)

Answer

(i)

(ii)

(iii)




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(iv)

Question 11.1:

/rite I#P$C names of the following compo"nds:

(i)

(ii)

(iii)

(iv)

(v)




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(vi)

(vii)

(viii)

(i%)

(%)

(%i)

(%ii)




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Answer

(i) ', ', &Trimethylpentan&%&ol

(ii) & *iethylphenol

(v) >


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(vi)'&


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(vi)

(vii)

(viii)

(i%)

(%)

Question 11.3:

(i)*raw the str"ct"res of all isomeric alcohols of molec"lar form"la C'1 and give their

I#P$C names




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(ii)Classify the isomers of alcohols in 7"estion % (i) as primary, secondary and tertiary

alcohols

Answer

(i) The str"ct"res of all isomeric alcohols of molec"lar form"la, C'1 are shown below:

(a)

Pentan&&ol (?)

(b)

'&2ethylb"tan&&ol (?)

(c)

%&2ethylb"tan&&ol (?)

(&)

', '&*imethylpropan&&ol (?)

(e)

Pentan&'&ol ('?)




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(')

%&2ethylb"tan&'&ol ('?)

()

Pentan&%&ol ('?)

(h)

'&2ethylb"tan&'&ol (%?)

(ii) Primary alcohol: Pentan&&ol@ '&2ethylb"tan&&ol@

%&2ethylb"tan&&ol@ ', '>*imethylpropan&&ol

Secondary alcohol: Pentan&'&ol@ %&2ethylb"tan&'&ol@

Pentan&%&ol

Tertiary alcohol: '&methylb"tan&'&ol

Question 11.4:

1 gro"p 1n the

other hand, b"tane does not




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Therefore, extra energy is re7"ired to brea9 hydrogen bonds Aor this reason, propanol has ahigher boiling point than hydrocarbon b"tane

Question 11.5:

$lcohols are comparatively more sol"ble in water than hydrocarbons of comparable molec"lar

masses


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Question 11.7:

-ive the str"ct"res and I#P$C names of monohydric phenols of molec"lar form"la, CB1

Answer

Question 11.8:

/hile separating a mixt"re of ortho andpara nitrophenols by steam distillation, name the

isomer which will be steam volatile -ive reason

Answer

Intramolec"lar &bonding is present in o&nitrophenol Inp&nitrophenol, the molec"les arestrongly associated d"e to the presence of intermolec"lar bonding ence, o&nitrophenol issteam volatile




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Question 11.9:

-ive the e7"ations of reactions for the preparation of phenol from c"mene

Answer

To prepare phenol, c"mene is first oxidi;ed in the presence of air of c"mene hydro&peroxide

Then, c"mene hydroxide is treated with dil"te acid to prepare phenol and acetone as by&

prod"cts

Question 11.10:

/rite chemical reaction for the preparation of phenol from chloroben;ene

Answer

Chloroben;ene is f"sed with !a1 (at ='% 8 and %'D atm press"re) to prod"ce sodi"mphenoxide, which gives phenol on acidification




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Question 11.11:

/rite the mechanism of hydration of ethene to yield ethanol

Answer

The mechanism of hydration of ethene to form ethanol involves three steps

Step 1

Protonation of ethene to form carbocation by electrophilic attac9 of %1E:

Step 2

!"cleophilic attac9 of water on carbocation:

Step *

*eprotonation to form ethanol:

Question 11.12:




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Fo" are given ben;ene, conc 'S1and !a1 /rite the e7"ations for the preparation of

phenol "sing these reagents

Answer

Question 11.13:

Show how will yo" synthesi;e:

(i)&phenylethanol from a s"itable al9ene

(ii)cyclohexylmethanol "sing an al9yl halide by an S!' reaction

(iii)pentan&&ol "sing a s"itable al9yl halide.

Answer

(i)+y acid&cataly;ed hydration of ethylben;ene (styrene), &phenylethanol can besynthesi;ed

(ii)/hen chloromethylcyclohexane is treated with sodi"m hydroxide, cyclohexylmethanol isobtained




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(iii)/hen &chloropentane is treated with !a1, pentan&&ol is prod"ced

Question 11.14:

-ive two reactions that show the acidic nat"re of phenol Compare acidity of phenol with that

of ethanol

Answer

The acidic nat"re of phenol can be represented by the following two reactions:

(i)Phenol reacts with sodi"m to give sodi"m phenoxide, liberating '

(ii)Phenol reacts with sodi"m hydroxide to give sodi"m phenoxide and water as by&prod"cts

The acidity of phenol is more than that of ethanol This is beca"se after losing a proton, thephenoxide ion "ndergoes resonance and gets stabili;ed whereas ethoxide ion does not




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Question 11.15:


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Question 11.17:

-ive e7"ations of the following reactions:

(i)1xidation of propan&&ol with al9aline 82n1sol"tion

(ii)+romine in CS'with phenol

(iii)*il"te !1%with phenol

(iv)Treating phenol with chloroform in presence of a7"eo"s !a1

Answer

(i)

(ii)

(iii)

(iv)




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Question 11.18:


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(ii)Reimer+iema!! reacti"!

/hen phenol is treated with chloroform (CCl%) in the presence of sodi"m hydroxide, a >C1

gro"p is introd"ced at the ortho position of the ben;ene ring

This reaction is 9nown as the 6eimer&Tiemann reaction

The intermediate is hydroly;ed in the presence of al9alis to prod"ce salicyclaldehyde

(iii),illiams"! ether sy!thesis

/illiamson ether synthesis is a laboratory method to prepare symmetrical and "nsymmetricalethers by allowing al9yl halides to react with sodi"m al9oxides

This reaction involves S!' attac9 of the al9oxide ion on the al9yl halide +etter res"lts areobtained in case of primary al9yl halides

If the al9yl halide is secondary or tertiary, then elimination competes over s"bstit"tion

(iv)-!symmetrical ether




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$n "nsymmetrical ether is an ether where two gro"ps on the two sides of an oxygen atomdiffer (ie, have an "ne7"al n"mber of carbon atoms) Aor example: ethyl methyl ether(C%>1>C'C%)

Question 11.20:

ow are the following conversions carried o"t.

(i)Propene Propan&'&ol

(ii)+en;yl chloride +en;yl alcohol

(iii)


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(iv)/hen methyl magnesi"m bromide is treated with propane, an add"ct is the prod"ctwhich gives '&methylpropane&'&ol on hydrolysis

Question 11.21:

!ame the reagents "sed in the following reactions:

(i)1xidation of a primary alcohol to carboxylic acid

(ii)1xidation of a primary alcohol to aldehyde

(iii)+romination of phenol to ',,=&tribromophenol

(iv)+en;yl alcohol to ben;oic acid

(v)*ehydration of propan&'&ol to propene

(vi)+"tan&'&one to b"tan&'&ol

Answer




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(i) $cidified potassi"m permanganate

(ii) Pyridini"m chlorochromate (PCC)

(iii) +romine water

(iv) $cidified potassi"m permanganate

(v) G phosphoric acid

(vi) !a+or 3i$l

Question 11.22:

-ive reason for the higher boiling point of ethanol in comparison to methoxymethane

Answer


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(iv)

(v)

(vi)

Answer

(i) &


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(ii)


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Answer

The reaction of /illiamson synthesis involves S!' attac9 of an al9oxide ion on a primary al9yl

halide

+"t if secondary or tertiary al9yl halides are ta9en in place of primary al9yl halides, thenelimination wo"ld compete over s"bstit"tion $s a res"lt, al9enes wo"ld be prod"ced This isbeca"se al9oxides are n"cleophiles as well as strong bases ence, they react with al9ylhalides, which res"lts in an elimination reaction

Question 11.26:

ow is &propoxypropane synthesised from propan&&ol. /rite mechanism of this reaction

Answer

&propoxypropane can be synthesi;ed from propan&&ol by dehydration

Propan&&ol "ndergoes dehydration in the presence of protic acids (s"ch as 'S1, %P1) togive &propoxypropane

The mechanism of this reaction involves the following three steps:

Step 1 Protonation

Step 2 !"cleophilic attac9




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Step * *eprotonation

Question 11.27:

Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a s"itablemethod -ive reason

Answer

The formation of ethers by dehydration of alcohol is a bimolec"lar reaction (S!') involving theattac9 of an alcohol molec"le on a protonated alcohol molec"le In the method, the al9yl gro"psho"ld be "nhindered In case of secondary or tertiary alcohols, the al9yl gro"p is hindered $sa res"lt, elimination dominates s"bstit"tion ence, in place of ethers, al9enes are formed

Question 11.28:

/rite the e7"ation of the reaction of hydrogen iodide with:

(i)&propoxypropane

(ii)2ethoxyben;ene and

(iii)+en;yl ethyl ether

Answer

(i)

(ii)




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(iii)

Question 11.29:


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(ii)It can also be observed from the resonance str"ct"res that the electron density increasesmore at the ortho and para positions than at the meta position $s a res"lt, the incomings"bstit"ents are directed to the ortho and para positions in the ben;ene ring

Question 11.30:

/rite the mechanism of the reaction of I with methoxymethane

Answer

The mechanism of the reaction of I with methoxymethane involves the following steps:

Step1Protonation of methoxymethane:

Step2 !"cleophilic attac9 of I>:

Step*

/hen I is in excess and the reaction is carried o"t at a high temperat"re, the methanolformed in the second step reacts with another I molec"le and gets converted to methyliodide

Question 11.31:

/rite e7"ations of the following reactions:

(i)Ariedel&Crafts reaction>al9ylation of anisole




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(ii)!itration of anisole

(iii)+romination of anisole in ethanoic acid medi"m

(iv)Ariedel&Craft4s acetylation of anisole

Answer

(i)

(ii)

(iii)




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(iv)

Question 11.32:

Show how wo"ld yo" synthesise the following alcohols from appropriate al9enes.

(i)

(ii)

(iii)

(iv)

Answer

The given alcohols can be synthesi;ed by applying 2ar9ovni9ov4s r"le of acid&cataly;edhydration of appropriate al9enes




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(i)

(ii)

(iii)

$cid&cataly;ed hydration of pent&'&ene also prod"ces pentan&'&ol b"t along with pentan&%&ol

Th"s, the first reaction is preferred over the second one to get pentan&'&ol

(iv)




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Question 11.33:

/hen %&methylb"tan&'&ol is treated with +r, the following reaction ta9es

place:

-ive a mechanism for this reaction

(int : The secondary carbocation formed in step II rearranges to a more

stable tertiary carbocation by a hydride ion shift from %rd carbon atom

Answer

The mechanism of the given reaction involves the following steps:

Step 1 Protonation

Step 2Aormation of '? carbocation by the elimination of a water molec"le

Step * 6e&arrangement by the hydride&ion shift




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Step !"cleophilic attac9

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9359alcohols and phenols

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