Chemical Bonding and Molecular Structure - Result Question 21

####21. The boiling point of p-nitrophenol is higher than that of o-nitrophenol because

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(a) NO2 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:

  1. (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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