IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

LAMPARD

Intramolecular hydrogen bonding occurs in which of the following??
1)2-chlorophenol 2)Salicylic acid
3)The enol form of acetone 4)4-nitrophenol.
Ans. is given as 2,3,4.But how is it possible in Acetone???It should be just 2 and 3 right?

sandeepramesh

do you mean intramolecular H bonding or only H bonding???

Well if its only H bonding, then what ans is given is right otw if its intramolecular, the answer will be only 2

sandy1990

why not

ch3--c----odelta +
| !
ch2--h

sandy1990

may be

sandeepramesh

he said enol form

LAMPARD

@sandeep,its given intramolecular
@sandy,but why will h be attracted towards carbon???And how come,there is a delta+ on oxygen??

sandeepramesh

surely 4 cant be an answer

LAMPARD

Yes,4-nitrophenol is same as p-nitrophenol....how can that show h-bonding????
But,i want to confirm about 3rd option...

sandeepramesh

most probably 3 might not be true bcos if enol form is H bonded, then it should be more stable but its known that acetone has a major keto form of 99% and odd

LAMPARD

Bt,how can h-bonding be possible???Is it possible with carbon???

sandeepramesh

no it isnt possible :)

As to sandy's answer, i think i might know why its wrong. It may be bcos the H attached to the C may not be sufficiently acidic for H bonding and also, the transition state isnt that stable

sahilgupta_iit

1 and 2 must be right. there is intamolecular H-bonding in 2-chlorophenol between chlorine and hydrogen attached to the oxygen

LAMPARD

@sahilgupta
H-bonding is not possible with chlorine as its size is large...H-bonding is possible only with atoms of small size...eg.flourine...but,someone confirm abt option 3...

towards.destination

hey its explained in p bahadur

LAMPARD

What??

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