Chemical Bonding And Molecular Structure Ques 42
42. The boiling point of $p$-nitrophenol is higher than that of $o$-nitrophenol because
[1994]
(a) $NO_2$ group at $p$-position behave in a different way from that at $o$-position.
(b) intramolecular hydrogen bonding exists in p-nitrophenol
(c) there is intermolecular hydrogen bonding in $p$-nitrophenol
(d) p-nitrophenol has a higher molecular weight than $o$-nitrophenol.
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Solution:
- (c) The b.p. of $p$-nitrophenol is higher than that of $o$-nitrophenol because in $p$-nitrophenol there is intermolecular $H$-bonding but in $o$-nitrophenol it is intramolecular H-bonding. Intramolecular Hydrogen bonding in $o$-nitrophenol is a interaction with in the molecule whereas the intermolecular $H$-bonding in $p$-nitrophenol is a interaction between the molecules which results into higher boiling point. Intermolecular hydrogen bonding also results in a stronger driving force for cystal formation in other molecules generating higher melting temperature e.g. p-hydroxy benzoic acid.
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