Homework Problems Chapter 10
- Page ID
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Homework Problems
Section 1
Exercise 1
Predict the charge n of cobaltocene (Co(Cp)2)n. Cp=cyclopentadienyl. Explain briefly.
- Answer
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+1, because the 18 electron rule is fulfilled.
Exercise 2
Bis-benzene chromium (Ƞ4-C6H6)Cr is a sandwich compound having two parallel benzene rings in an eclipsed conformation. Sketch the ligand group orbitals for this molecule.
- Answer
-
Section 2
Exercise 1
The MO diagram of the CO molecule is given below. Identify the molecular orbitals that can act
a) As sigma-donors
b) Pi-acceptors in carbonyls.
- Answer
-
a) 5 σ, 4 σ, bonding π orbitals
b) anti-bonding π orbitals
Exercise 2
Which carbonyl will most likely exhibit the highest frequency for the C-O stretch vibration? Give a brief explanation for your decision.
a) V(CO)6-
b) Cr(CO)6
c) Mn(CO)6+
- Answer
-
c) Mn(CO)6+
Carbonyl cations have the weakest pi-backbonding, therefore the bond order for the C-O bond is the highest and thus the frequency of the C-O stretch vibration is the highest.
Exercise 3
Predict the right charge of the most stable pentacarbonyl of
a) Iron
b) Mn
c) Cr
- Answer
-
a) 0
b) 1-
c) 2-
Section 3
Exercise 1
What structure would you expect for a carbonyl made of the following fragments according to the concept of isolobality? Predict if the structure would likely be stable.
a) Cr(CO)5+
b) Cr(CO)4-
c) Mn(CO)4-
- Answer
-
a) 15VE -> tetrahedral cluster (not stable b/c CN too high)
b) 15 VE -> tetrahedral cluster (not stable b/c CN too high)
c) 16 VE -> trimer (stable b/c CN = 6, charge not too high).
Exercise 2
Which of the following fragments are isolobal to the CH2 fragment?
a) NH2
b) NH
c) OH
d) Fe(CO)3
e) Co(CO)4+
- Answer
-
b) NH
Exercise 3
Which of the following fragments are isolobal to the Mn(CO)5 fragment?
a) CH3
b) CH2CH3
c) OH
d) F
e) NH
- Answer
-
a) CH3
b) CH2CH3
c) OH
d) F