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1 General Organic Chemistry
Level - 1
H H
H Cl
1. (c) 2° H are seven.
H H
H H
ketone
O O amide
2. (d) NH
O O
ester
3. (d) Potential energy of (A) and (B) is same and transition state has the characteristics of sp 2 .
4. (a) More the numbers of carbons more will be the heat of combustion.
O
5. (d) is not the resonating structure of others.
s
6. (d) Acidic strength µ stability of resulting anion. (i . e. , conjugate base)
d–
O
| d+
7. (b) CH3 — C — O — CH3
due to resonance this bond has partial double bond characters
sp2
sp2 sp2
Total 4 s-bonds
8. (c)
has sp2 – sp2 overlapping
sp2 sp2
sp2
..
9. (b) :O: N—H Total ‘3’ lone pairs in molecule.
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1
10. (c) Ring strain µ
size of ring
11. (b) Alcohol, ketone, alkene and ether.
1
12. (b) Acidic strength µ -I; - H; - M µ
+I; + H; + R
13. (a) C r stability µ +H on carbocation
14. (b) Stability of resonance hybrid µ no. of equivalent R.S.
So stability order is
O O
|| s
|| s
Me—S—O > Me—C—O > Me—Os
|| 2- eq. R.S.
O
3- eq. R.S.
So Acidic strength order is x > y > z so pK a is z > y > x.
Involved in
H Delocalised (l.p.)
resonance
|
Not Involved in
..
N
Localised (l.p.) resonance
15. (b)
..
N— (so more basic)
and protonation takes place
H
16. (b) The ortho-effect : This is a special effect that is shown by o-substituents of benzene and
its derivatives, but is not necessarily just a steric effect, e. g. , the basicities of some
o-substituted anilines were explained in terms of steric effects and differences in crowding
round the nitrogen atom. This ortho-effect also operates with the benzoic acids.
Irrespective of the polar type, nearly all o-substituted benzoic acids are stronger than
benzoic acid. As we have seen, benzoic acid is a resonance hybrid, and so the carboxyl
groups is coplanar with the ring. An o-substituent tends to prevent this coplanarity. Thus
resonance is diminished (or prevented), and so the O-atom of the OH groups has a greater
positive charge, resulting increased acid strength. It follows from this that the greater the
steric inhibition to resonance, the stronger is the acid. Support for this is the following
order of strengths of substituted benzoic acids.
2,6-di-Me (pK a 3.21) > 2-t-Bu (pK a 3.46) > 2-Me (pK a 3.91).
Here again, if we consider the stability of the anion, steric inhibition of resonance prevents
the +R effect of the ring coming into operation (see above), and since this weakens acid
strength, its absence results in increased acid strength.
COOH COOH
CH3
K a order: > (due to ortho effect)
NH2 NH2
CH3
K b order: < (due to ortho effect)
For options B and D, no ortho effect is valid and order of acidity and basicity is calculated
by nearly examining the inductive effect.
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1 General Organic Chemistry
Level - 1
H H
H Cl
1. (c) 2° H are seven.
H H
H H
ketone
O O amide
2. (d) NH
O O
ester
3. (d) Potential energy of (A) and (B) is same and transition state has the characteristics of sp 2 .
4. (a) More the numbers of carbons more will be the heat of combustion.
O
5. (d) is not the resonating structure of others.
s
6. (d) Acidic strength µ stability of resulting anion. (i . e. , conjugate base)
d–
O
| d+
7. (b) CH3 — C — O — CH3
due to resonance this bond has partial double bond characters
sp2
sp2 sp2
Total 4 s-bonds
8. (c)
has sp2 – sp2 overlapping
sp2 sp2
sp2
..
9. (b) :O: N—H Total ‘3’ lone pairs in molecule.
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1
10. (c) Ring strain µ
size of ring
11. (b) Alcohol, ketone, alkene and ether.
1
12. (b) Acidic strength µ -I; - H; - M µ
+I; + H; + R
13. (a) C r stability µ +H on carbocation
14. (b) Stability of resonance hybrid µ no. of equivalent R.S.
So stability order is
O O
|| s
|| s
Me—S—O > Me—C—O > Me—Os
|| 2- eq. R.S.
O
3- eq. R.S.
So Acidic strength order is x > y > z so pK a is z > y > x.
Involved in
H Delocalised (l.p.)
resonance
|
Not Involved in
..
N
Localised (l.p.) resonance
15. (b)
..
N— (so more basic)
and protonation takes place
H
16. (b) The ortho-effect : This is a special effect that is shown by o-substituents of benzene and
its derivatives, but is not necessarily just a steric effect, e. g. , the basicities of some
o-substituted anilines were explained in terms of steric effects and differences in crowding
round the nitrogen atom. This ortho-effect also operates with the benzoic acids.
Irrespective of the polar type, nearly all o-substituted benzoic acids are stronger than
benzoic acid. As we have seen, benzoic acid is a resonance hybrid, and so the carboxyl
groups is coplanar with the ring. An o-substituent tends to prevent this coplanarity. Thus
resonance is diminished (or prevented), and so the O-atom of the OH groups has a greater
positive charge, resulting increased acid strength. It follows from this that the greater the
steric inhibition to resonance, the stronger is the acid. Support for this is the following
order of strengths of substituted benzoic acids.
2,6-di-Me (pK a 3.21) > 2-t-Bu (pK a 3.46) > 2-Me (pK a 3.91).
Here again, if we consider the stability of the anion, steric inhibition of resonance prevents
the +R effect of the ring coming into operation (see above), and since this weakens acid
strength, its absence results in increased acid strength.
COOH COOH
CH3
K a order: > (due to ortho effect)
NH2 NH2
CH3
K b order: < (due to ortho effect)
For options B and D, no ortho effect is valid and order of acidity and basicity is calculated
by nearly examining the inductive effect.
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