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Question
The increasing order of boiling points of the below mentioned alcohols is
(I) 1,2−dihydroxybenzene
(II) 1,3−dihydroxybenzene
(III) 1,4−dihydroxybenzene
(IV) Hydroxybenzene
The increasing order of boiling points of the below mentioned alcohols is
(I) 1,2−dihydroxybenzene
(II) 1,3−dihydroxybenzene
(III) 1,4−dihydroxybenzene
(IV) Hydroxybenzene
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Solution
The correct option is D IV<I<II<III
Among the given compounds, hydroxybenzene has least molar mass and hydrogen bonding, therefore possess least boiling point. Among the three isomeric dihydroxybenzenes,
1,2− dihydroxybenzene forms intramolecular H-bonding and so it has lower boiling point than its isomers. On the other hand 1,3−dihydroxybenzene and 1,4−dihydroxybenzene do not undergo chelation, hence they have extensive intermolecular H-bonding leading to higher boling point. Further intermolecular hydrogen bonding is stronger in the p−isomer than the m−isomer, hence former has highest boiling point. Thus the decreasing order of boiling point is III>II>I>IV
Hence, (d) is the correct option.
Among the given compounds, hydroxybenzene has least molar mass and hydrogen bonding, therefore possess least boiling point. Among the three isomeric dihydroxybenzenes,
1,2− dihydroxybenzene forms intramolecular H-bonding and so it has lower boiling point than its isomers. On the other hand 1,3−dihydroxybenzene and 1,4−dihydroxybenzene do not undergo chelation, hence they have extensive intermolecular H-bonding leading to higher boling point. Further intermolecular hydrogen bonding is stronger in the p−isomer than the m−isomer, hence former has highest boiling point. Thus the decreasing order of boiling point is III>II>I>IV
Hence, (d) is the correct option.
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