CHEMISTRY

RESONANCE
Q.1 Whichofthe following statements arecorrect :
Delocalization ofelectronsincreases molecular stabilitybecause.
(a) electrons–nucleiattractionincreases.
(b) electron–electronrepulsion decreases.
(c) potentialenergyofthe molecule increases.
(d) potentialenergyofthe molecule decreases.
Q.2 Whichofthe following statements is (are) true about resonance.
(a) Resonance isanintramolecular process.
(b) Resonance involves delocalization ofbothand  electrons.
(c) Resonance involves delocalizationof electrons only.
(d) Resonance decreases potentialenergyofa molecule.
(e) Resonance has no effect onthe potentialenergyofa molecule.
(f) Resonance is the onlywayto increase molecular stability.
(g) Resonance is not the onlywayto increase molecular stability.
(h) Anyresonating moleculeis always more stable thananynonresonating molecule.
(i) The canonicalstructure explains allfeaturesofa molecule.
(j) The resonancehybrid explains allfeatures ofa molecule.
(k) Resonating structures are realand resonance hybrid is imaginary.
(l) Resonance hybrid is realand resonating structures are imaginary.
(m) Resonance hybrid isalways more stable thanallcanonicalstructures.
Q.3 Which ofthefollowing statements are correct about canonicalstructures
Allcanonicalstructuresofa molecule :
(a) must have same number ofunpaired electrons.
(b) must have different numbers ofpaired electrons.
(c) need not be always equivalent but theyshould not differ muchin stability.
(d) should be always equivalent.
(e) must have  electronsinparallelorbital.
(f) must have  electronsindifferent orbitals.
Q.4 Whichofthe following statements are correct about Resonance energy
Resonance energyis
(a) equalto the energyofresonance hybrid.
(b) equalto the energyofmost stable canonicalstructure.
(c) equalto the energyofleast stable canonicalstructure.
(d) equalto thedifference in energies ofthe most stable canonicalstructure & resonance hybrid.
(e) equalto the potentialenergyofmolecule.
Q.5 Mark thecorrect statements
Resonance energyis
(a) stored bythe molecule
(b) released bythe molecule
(c) neither stored nor released bythe molecule
(d) sometimes stored and somtimes released bythe molecules.
Q.6 Resonance energywillbe more if
(a) canonicalstructures areequivalent thanifcanonicalstructures are non-equivalent.
(b) molecule isaromatic thanifmolecule is not aromatic.

Q.7 Acanonicalstructure willbe morestable if
(a) it has more number of  bonds than if it has less number of bonds.
(b) the octets ofallatoms are complete than ifoctets ofallatoms are not complete.
(c) it involves cyclic delocalization of (4n + 2) – electrons than if it involves acyclic delocalization of
(4n + 2)  – electrons.
(d) it involves cyclic delocalization (4n)  – electrons than if it involves acyclic delocalizationof
(4n)  – electrons.
(e) +ve charge is onmore electronegative atomthanif+ve charge is on lesselectronegative atoms.
(f) –ve charge isonmore electronegative atomthanif–ve
Q.8 Inwhichofthe following molecules resonancetakes place through out the entire system.
(a) (b) (c) (d)
(e)
3
3
COOCH
|
COOCH
(f)
Q.9 Which ofthefollowing groups cannot participateinresonance withothersuitable group :
(a) – COOH (b)
—
O
CO
 (c) – COCl (d)

 3
NH
(e) 2
H
C

 (f) 2
H
C

 (g)
3
2
CH
|
N
CH 


Q.10 Whichofthe following group canparticipateinresonance withothersuitable group :
(a) 


O
CH2 (b) 2
—
2 H
C
CH 
 (c)
2
2 H
C
CH


 (d)
(e) (f) – BH2 (g)
3
Ph
P


Q.11 Inwhichofthe following lone-pair indicated is involved inresonance :
(a) (b) (c) (d)
(e) CH2= CH – 
2
H
C (f) CH2 = CH – CH = H
N


Q.12 In which ofthe following lone-pair indicatedis not involvedinresonance :
(a) CH2 = CH – H
N


– CH3 (b) CH2 = CH – CH =




O
(c) CH2 = CH –




O – CH = CH2 (d) CH2 = CH – C  

N
(e) (f)

Q.13 Identifyelectron–donating groups inresonance amongthe following :
(a) – CONH2 (b) – NO2 (c) – OCOCH3 (d) – COOCH3
(e) – CHO (f) – NHCOCH3
Q.14 Identifyelectron–withdrawing groups inresonance amongthe following :
(a) – COOH (b) – CONHCH3 (c) – COCl (d) – CN
(e) – O – CH = CH2 (f)
Q.15 Whichofthe following groups caneither donate or withdrawa pair ofelectronsinresonance depending
uponsituation:
(a) – NO2 (b) – NO (c) – CH = CH (d) – CHO
(e) – NH2 (f) – N = NH
Q.16 Which of the following groups can only withdraw a pair of electrons in resonance depending upon
situation:
(a) – Ph (b) (c) (d)
(e) 3
Me
N

 (f) – CONH2
Q.17 Write the canonicalstructures ofeachofthe following :
(a) CH3NO2 (b) CH3COOH (c) CH3COONa
(d) (e) H2N – CHO
Q.18 Write the resonance hybrid ofeach ofthe following :
(a) 2
—
2 H
C
CH
CH 
 (b) (c) (d) 2
2 H
C
CH
CH



(e) CH2 = CH – CH2
Q.19 Write the canonicalstructures ofeachofthe following :
(a) R – CO – CH = CH2 (b) CH3O – CH = CH – 3
Me
N

(c) RCOCl (d) HCONH2 (e)
Q.20 Write the resonance hybrid ofeach ofthe following :
(a) (b) CH2 = CH – CH = O (c) H
C
C
CH
—
2 
 (d)
(e) CH2 = CH – CH = CH2
Q.21 Write the canonicalstructures ofeachofthe following :
(a) (b)
—
2 N
N
CH 


(c) CH2 = C = O (d) (e)

Q.22 Inwhichofthe following molecules –electrondensityinringis minimum:
(A) (B) (C) (D)
Q.23 Inwhichofthe following molecules –electrondensityinringis maximum:
(A) (B) (C) (D)
Q.24 CH2 = CH – CH = CH – CH3 is more stable than CH3 – CH = C = CH – CH3 because
(I) (II)
(A) there is resonance in I but not in II (B) there istautomerismin I but not in II
(C) there ishyperconjugation in I but not in II (D) II has more cononicalstructuresthan I.
Q.25 Whichofthefollowing pairs has higherresonance energy:
(a) CH3COOH and CH3COONa (b) CH2 = CH –

O and CH2 = CH – OH
(c) and (d) and
(e) and CH2 = CH – CH = CH – CH = CH2
Q.26 Which ofthe following pairs has less resonance energy:
(a) 
2
3
CO and HCOO– (b) and CH2 = CH – 
2
CH
(c) and CH2 = CH – CH = CH2 (d) and CH2 = CH – 2
H
C

(e) and
Q.27 Whichofthefollowing pairs has higherresonance energy:
(a) and (b) and
(c) and
(d) CH2 = CH – OH and CH2 = CH – CH = CH – OH
(e) and

Q.28 Which ofthe following pairs has less resonance energy:
(a) and (b) and (c) and
(d) and (e) and
Q.29 Whichofthefollowing pairs has higherresonance energy:
(a) and
(b) CH2 = CH – O – CH = CH2 and CH2 = CH – NH – CH = CH2
(c) H
N
CH
CH2


 and H
N
CH
HN


 (d) CH2 = CH – F and CH2 = CH – Br
(e) and CH2 = CH – 2
H
C

Q.30 
 

These are threecanonicalstructuresofnaphthalene. Examinethemandfindcorrect statement amongthe
following:
(A)All C – C bonds are ofsame length
(B) CI – C2 bond is shorter than C2 – C3 bond.
(C) C1 – C2 bond is longer than C2 – C3 bond
(D) none.
Q.31 Which ofthe following is (are) the correct order ofbond lengths :
(A) C – C > C = C > C  C > C  N (B) C = N > C = O > C = C
(C) C = C > C = N > C = O (D) C – C > C = C > C  C > C – H
Q.32 Identifymorestable canonicalstructure ineachofthe followingpairs :
(a) (b) H
C
C
CH
CH
C
H
C 2
2








(c) (d)
(e) O
CH
CH
CH
O
CH
CH
H
C 2
2 









(f)

Q.33 Identifyless stable canonicalstructure ineach ofthe followingpairs :
(a) 3
2
3
2 CH
O
CH
CH
O
H
C 







(b)
(c) (d)
(e)
Q.34 In whichofthe following pairs, indicated bond is ofgreater strength:
(a)


 Br
CH
CH 2
3 and


 Cl
CH
CH 2
3
(b)



 Br
CH
CH
CH3 and
Br
|
CH
CH
CH 3
3



(c) and


 Cl
CH
CH 2
3
(d)



 2
2 CH
CH
CH
CH and



 3
2
2
2 CH
CH
CH
CH
(e)



 2
2 CH
CH
CH
CH and


 2
2 NO
CH
CH
(f) and
Q.35 In which ofthe following pairs, indicatedbond having less bond dissociation energy:
(a) and

 2
2 CH
CH
(b)


 CH
C
CH3 and

 CH
HC
(c) and
(d) and (e) and
(f) and

Q.36 Among the followingpairs identifythe onewhich gives less heat ofhydrogenation:
(a) and (b) and
(c) and
(d) CH2 = CH – CH and CH2 = C
Q.37 Which ofthe following has longest C – O bond :
(A) (B) (C) (D)
Q.38 CH2 = NH
I II III IV
Among these compounds, the correct order ofC – N bond lengths is :
(A) IV > I > II > III (B) III > I > II > IV (C) III > II > I > IV (D) III > I > IV > II
Q.39 C1 – C2 bond is shortest in
(A) (B) (C) (D)
Q.40 Among the followingmolecules, the correct order ofC – Cbond lenght is
(A) C2H6 > C2H4 > C6H6 > C2H2 (B) C2H6 > C6H6 > C2H4 > C2H2(C6H6 is benzene)
(C) C2H4 > C2H6 > C2H2 > C6H6 (D) C2H6 > C2H4 > C2H2 > C6H6
Q.41 CH3O – CH = CH – NO2 I
CH2 = CH – NO2 II
CH2 = CH – Cl III
CH2 = CH2 IV
Which ofthe following is the correct order ofC – C bond lengths among these compounds :
(A) I > II > III > IV (B) IV > III > II > I (C) I > III > II > IV (D) II > III > I > IV
Q.42 Inwhichofthe following molecules resonance is equivalent :
(A) HCOO (B) CH2 = CH – CH = CH2
(C) (D)

Q.43 CH2 = CH – CH = CH – CH = CH2 I
CH2 = CH – H
C

– CH = CH – 2
H
C

II
2
H
C

– CH = CH – CH = CH – 2
H
C

III
Among these three canonical structures (through more are possible) what would be their relative
contributioninthe hybrid :
(A) I > II > III (B) III > II > I (C) I > III > II (D) III > I > II
Q.44 For 1-methoxy-1, 3-butadiene, which of thefollowing resonating structureistheleast stable?
(A)

C
H2 — H
C

–CH = CH – O – CH3 (B)

C
H2 — CH = CH – CH =

O– CH3
(C) H2C = CH – H
C

– H
C

– O – CH3 (D) H2C = CH – H
C

– CH =

O– CH3
Q.45 In whichofthe following molecules allbond angles are allmost same :
(a) CH3 – CH3 (b) CH2 = CH – CH = CH2
(c) CH3 COCl (d) HCOO (e)
(f) (g) (h) (i)
(j) (k) 2
2 CH
CH
H
C 


Q.46 Inwhichofthe following molecules allatomsare coplanar :
(a) (b) (c) (d) HCOCl (e) C3H8
(f) C (CN)4 (g) CH3–CH=CH2 (h) (i) (j) CH2 = C = CH2
Q.47 Inwhichofthe following molecules allatoms are not coplanar :
(a) CH2 = C = C = CH2 (b)
3
COOCH
|
CHO
(c)
(d) (e) HCOOCH3 (f)

(g) CH2 = CH – CH = CH2 (h) CH2 = CH – C  CH (i)
(j)
Q.48 Among the followingpairs identifythe onewhichgives higher heat ofhydrogenation:
(a) and (b) and
(c) CH3 – CH = CH – CH3 and CH3 – CH2 – CH = CH2
(d) and
Q.49 Whichofthe following statements wouldbe true about thiscompound :
(A)Allthree C – N bonds are ofsame length.
(B) Cl – N and C3 – N bonds are of same length but shorter than C5 – N bond.
(C) Cl – N and C3 – N bonds are of same length but longer than C5 – N bond.
(D) Cl– N and C3 – N bonds are of different length but both are longer than C5 – N bond.
Q.50 ;Cl– H, C2 –H, C3 – H and C4 – Hhomolytic bond dissociation
energyis inthe order:
(A) C2 – H > C3 – H > C4 – H > C1 – H (B) C1 – H > C4 – H > C2 – H > C3 – H
(C) C2 – H > C3 – H > C1 – H > C4 – H (D) C1 – H > C4 – H > C3 – H > C2 – H

ANSWER KEY
Q.1 (a), (b), (d) Q.2 (a), (c), (d), (g), (j), (l), (m) Q.3 (a), (c), (e)
Q.4 (d) Q.5 (c) Q.6 (a), (b) Q.7 (a), (b), (c), (f)
Q.8 (b), (c) Q.9 (d) Q.10 (a), (e), (f), (g) Q.11 (b), (d), (e)
Q.12 (b), (d), (e) Q.13 (c), (f) Q.14 (a), (b), (c), (d), (f)
Q.15 (b), (c), (f) Q.16 (f) Q.22 D Q.23 B
Q.24 A Q.25 (a) II, (b) I, (c) I, (d) II, (e) I
Q.26 (a) II, (b) I, (c) I, (d) II , (e) II Q.27 (a) II, (b) II, (c) II, (d) II, (e) II
Q.28 (a) II, (b) II, (c) II, (d) II, (e) II Q.29 (a) I, (b) II, (c) II, (d) I, (e) I
Q.30 B Q.31 A, C, D Q.32 (a) I, (b) I, (c) I, (d) I, (e) II, (f) II
Q.33 (a) I, (b) II, (c) II, (d) II, (e) I Q.34 (a) II, (b) I, (c) I, (d) I, (e) II, (f) II
Q.35 (a) I, (b) I, (c) II, (d) I, (e) I, (f) I Q.36 (a) I, (b) II, (c) I, (d) II
Q.37 B Q.38 C Q.39 D Q.40 B
Q.41 A Q.42 A Q.43 C Q.44 C
Q.45 (a), (b), (d) ,(f), (g), (h), (i), (j), (k) Q.46 (a), (b), (d) Q.47 (b), (d), (e)
Q.48 (a) I, (b) I, (c) II, (d) I Q.49 C Q.50 D