This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Organometallic Compounds – 1”.
1. What are oxidation states of metal ion in following complexes?
I. PdCl2 II. Pd(PPh3)4 III. Pd(OAc)2 IV. ArPdBr where Ar is aryl
a) 2, 4, 2, 2
b) 2, 0, 2, 1
c) 2, 0, 2, 2
d) 0, 0, 0, 2
View Answer
Explanation: n → oxidation states of metal ion
PdCl2: n – 2 = 0 ⇒ n = 2
Pd(PPh3)4 : Since PPh3 is neutral, Pd is in 0 Oxidation state.
Pd(OAc)2: n – 2 = 0 ⇒ n = 2
ArPdBr: n + [(–1) (–1)] ⇒ n = 2.
2. Which of the following complex has a highest oxidation state of metal?
a) (η6-C6H6)2Cr
b) Mn(CO)5Cl
c) Na2[Fe(CO)4]
d) K[Mn(CO)5]
View Answer
Explanation: Oxidation State of metal:
(a) (η6-C6H6)2Cr ⇒ 0, (b) Mn(CO)5Cl ⇒ +1
(c) Na2[Fe(CO)4] ⇒ +2 and (d) K[Mn(CO)5] ⇒ +1
3. Which of the following complex is in which organic ligand is having only bond with metal?
a) W(CH3)6
b) K[PtCl3(C2H4)]
c) (η5-C5H5)2Fe
d) (η5-C6H6)2Ru
View Answer
Explanation: CH3 is the only σ-donor ligand while C2H4, C5H5, C6H6 are π-acceptor ligands.
4. What is the oxidation state of molybdenum in [η7-tropylium) Mo(CO)3]+?
a) +2
b) +1
c) 0
d) -1
View Answer
Explanation: Let O.S. of Mo is η.
η + (0) + 1 = +1
η = 0.
5. Which of the following is the neutral complex which follows the 18- electron rule?
a) (η5-C5H5)Fe(CO)2
b) (η5-C5H5)2Mo(CO)3
c) (η5-C5H5)2Co
d) (η5-C5H5)2Re(η6-C6H6)
View Answer
Explanation:
(a) (η5-C5H5)Fe(CO)2
V.E.C. = 8 + 2(2) + 5 = 17
((b) η5-C5H5)2Mo(CO)3
V.E.C. = 8 + 2 + 2 + 5 = 17
(c) (η5-C5H5)2Co
V.E.C. = 9 + 5 + 5 = 19
(d) (η5-C5H5)2Re(η6-C6H6)
V.E.C. = 7 + 5 + 6 = 18
The correct answer is (η5-C5H5)2Re(η6-C6H6), obeys 18 e– rule.
6. If complex [W(Cp)2(CO)2] follows 18e- rule. What is Hapticity of Cp?
a) 5 and 5
b) 3 and 5
c) 3 and 3
d) 1 and 5
View Answer
Explanation: [W(Cp)2(Co)2].
Let hapticity of one Cp ligand = x and another y
VEC = 6 + 2(2) + x + y = 18
x + y = 18 – 10 = 8
Out of (1,3,5) the combination that is valid is (3 + 5).
7. Which of the following complexes show easy oxidation?
a) (η5-C5H5)2Fe
b) (η5-C5H5)2Ru
c) (η5-C5H5)2Co
d) (η5-C5H5)2Co+
View Answer
Explanation: (a) (η5-C5H5)2Fe: VEC = 8 + 5 + 5 = 18
(b) (η5-C5H5)2Ru: VEC = 8 + 5 + 5 = 18
(c) (η5-C5H5)2Co: Since it is one e– extra of stable no., oxidation i.e. loss of e– can take place easily, VEC = 9 + 5 + 5 = 19
(d) (η5-C5H5)2Co+: VEC = 9 + 5 + 5 – 1 = 18.
8. How many M — M bonds are present in [Cp Mo(CO3)]2?
a) 1
b) 2
c) 0
d) 4
View Answer
Explanation: No. of M-M bonds = (18×2-[(6+5+2×3)×2])/2=0.
9. Which of the following is the incorrect statement about Zeise’s salt?
a) Zeise’s salt is diamagnetic
b) Oxidation state of Pt in Zeis’s salt is +2
c) All the Pt-Cl bond length in Zeise’s salt are equal
d) C-C bond length of ethylene moiety in Zeise’s salt longer than that of free ethylene molecule
View Answer
Explanation: C2F4 is a better π acceptor than C2H4. So, metal-carbon bond order is more → Bond length is less in [PtCl3(C2F4)]– than in [PtCl3(C2H4)]–.
10. For metal olefin complexes (i) [PtCl3(C2F4)]– and (ii) [PtCl3(C2H4)]–, which of the following is the correct statement?
a) carbon-carbon bond length is same both in (i) and (ii)
b) carbon-carbon bond length in (i) is smaller
c) carbon-carbon bond length in (ii) is smaller
d) a metallacycle is formed in each complex
View Answer
Explanation: Since Metal-C bond order in (i) is smaller than (ii) C–C bond order in (i) is larger than in (ii) & carbon-carbon bond length in (i) is smaller.
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