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Organic Chemistry

Blazing goIITian

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5 Jul 2008 16:45:07 IST

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Give the order of Acidity

None

Give the order of Acidity.

2,4-dinitrophenol

3,5-dinitrophenol

4-nitrophenol

2-nitrophenol

Also, give the reason for each.

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Comments (6)

Shikhar

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5 Jul 2008 19:26:14 IST

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as H+ is released, negative charge will be on oxygen...
NO2 grp will withdraw the -ve charge from the ring, thus stabalizing it.... from ortho n para positions....
NO2 at para is more acidic due to HB
thus the order is
3,4dinitro phenol, then 2 nitro phenol then 4nitro phenol

Shikhar

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5 Jul 2008 19:26:57 IST

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i think......

vnkt. swaroop

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5 Jul 2008 19:29:49 IST

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2-nitro phenol<4-nitro phenol<2,4dinitro phenol<3,5dinitro phenol.

because it depends their pKa values.Greater the pKa value weaker the acid.

if wrong corrct me.

Saurabh Sood

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5 Jul 2008 21:03:55 IST

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2 nitrophenol > 4 nitrophenol > 2,4 nitrophenol > 2-nitrophenol

more no. of -I gps, more the acidity.

3,5 dinitrophenol is more acidic than 2,4 dinitrophenol as it is a symmetric compound. 4 nitrophenol is more acidic than 2 nitrophenol as it is attached at para position, which increases it's acidity.

pk kc

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5 Jul 2008 21:28:52 IST

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2,4 nitrophenol >3,5dinitro phenol.>4-nitro phenol>2-nitro phenol

because two no2 grps i.e. ecectron donating grps r present which would increase the acidity.

4 nitrophenol >2 nitrophenol because

ortho grp is having intramolecular h-bonding.

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Neeraj Phadnis

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5 Jul 2008 23:19:21 IST

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More NO2 groups, more -I effect which will decrease electron density on ring and make it more acidic.

So 3,5-dinitrophenol and 2,4-dinitrophenol which have 2 NO2 groups will be more acidic. But H-bonding in 2,4-dinitrophenol decreases its acidic nature.

Similarly 2-nitrophenol will be less acidic than 4-nitrophenol due to H-bonding.

ORDER : 3,5-dinitrophenol

2,4-dinitrophenol

4-nitrophenol

2-nitrophenol

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