CArefully see the interplay of ortho effect,h-bond and mesomeric effect
Arrange the following in increasing acidity
1) a. o-nitroaniline
b. 
29see in the first part in case of o-nitroaniline we will have hydrogen bonding in the first one.so the plane of NH2 wont change much..but in the second case due to steric repulsion the NH2 grp will change it's plane and now the lone pair are no more under delocalisation so second one is more basic than first..
so A is more acidic than B
1but hydrogen bonding in first will affect it's acidity na ??
24Lets remember two things...
Ortho effect increases acidity
H bonding formes rings which prevents release of H ion..as a result decresing acidity
in case 1 , we have ortho effect as well as H bonding
in case 2 we have only ortho effect
H bonding in case 1 decreases extent of ortho effect to some extent...therby making 2 more acidic
2>1
1so far so good.....lets add a new member in the race...
...lets name this c.....now predict the acidity of the compounds a,b and c!!!!
24@grandmaster..u didnt confirm answer for first one...
NO2 is bulkier...so more ortho effect in 1)..hence 1>3
H bonding exist in 3 too....so its acdity is less than 2 ofcourse..
so 2>1>3
1me too b>a>c as eure mentioned H- bond is much more pronounced in c than in a since electronegativity of OXYGEN is more than that of NITROGEN[9]
