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Chemistry 417-01 Inorganic Chemistry Exam 2 October 29, 2001
GROUND RULES:
a. Closed book; closed notes; no consulting b. allowed: calculator; model set; point group flowchart; ruler c. 180 minute (3 h) time limit d. Due Saturday Nov. 3, 5:00 p.m. e. please fill in and sign: time started
time finished
I have abided by the ground rules in taking this exam:
Notes on exam format:
This exam consists of 7 “short” questions and 3 “long” questions
Short Answer Section
a. The enthalpies of reaction of trimethylboron with NH 3 , CH 3 NH 2 , (CH 3 ) 2 NH and (CH 3 ) 3 N are -58, -74, -81, and -74 kJ/mol respectively. Briefly explain the likely reason why trimethylamine is out of line.
b. (i) HBr and HI are equivalently strong acids in water due to solvent leveling. Explain.
(ii) What is a solvent in which the relative strengths of HBr and HI could be determined? (Show, using a chemical equation.)
c. In terms of hard-soft acid-base theory, which end of the SCN-^ anion would coordinate to:
(a) Cr3+^ (b) Pt2+
Briefly explain your choices.
g. Using Drago-Wayland E, C parameters, determine which of Et 3 N, Et 2 O and PMe 3 is the stronger base toward GaMe 3.
Longer questions
- Consider the following series of six platinum compounds.
number molecular formula # of ions 1 PtCl 2 ·4NH 3 3 2 PtCl 2 ·3NH 3 2 3 PtCl 2 ·2NH 3 0 4 PtCl 2 ·2NH 3 0 5 KPtCl 3 ·NH 3 2 6 K 2 PtCl 4 3
From the molecular formulas and numbers of ions produced when each compound is dissolved in water, deduce the structural formula of each compound, being explicit as to which ligands are in the coordination sphere. Draw structures for each platinum containing molecule or ion. Note that compounds 3 and 4 are isomers (one is polar, one is non-polar). All of the compounds have the same geometry at platinum—what is that geometry?
- Give a clear well-labeled molecular orbital diagram for the HCl molecule. Pay attention to the relative energies of the orbitals used to make the diagram. Valence orbital energy levels are given at the end of the exam. Include pictures of all orbitals (atomic and molecular).
Useful information:
Selected E and C parameters for the Drago E,C equation:
- ∆H° (kJ/mol) = EAEB + CACB
acid EA (kJ/mol)1/
CA
(kJ/mol)1/
base EB (kJ/mol)1/
CB
(kJ/mol)1/ BMe 3 11.84 3.21 py 2.66 13. AlMe 3 35.43 1.92 NH 3 3.03 6. AlEt 3 28.39 2.88 Me 3 N (^) 2.43 22. GaMe 3 28.29 0.82 Et 3 N (^) 2.64 22. GaEt 3 25.63 0.39 Me 2 O (^) 2.21 5. InMe 3 26.98 0.76 Et 2 O (^) 2.21 6. SbCl 5 16.12 10.41 THF 2.17 8. BF 3 24.93 1.66 Me 2 S (^) 1.17 14. Et 2 S (^) 1.13 15. Me 3 P (^) 2.27 13. Me 2 Se (^) 1.00 16.
linear?
Group of low symmetry? (lacking any Cn ?)
Group of high symmetry? (≥2 C n w/ n>2 for each)
Highest order rotation axis (n)?
σh?
Are there n ⊥ C 2 ’s?
C 1 , Ci, Cs
D∞h C∞v
Td, Oh, Ih
Dn groups Cn or S2n groups
No
No
No
Cn
Yes
Yes No
σh?
Yes
Yes
Yes
σd?
No
σh?
Dnh
Yes No
Yes No
Dnd Dn
Cnh
Yes No
σv?
Cnv^ S2n?
Yes No
Yes^ No
S2n Cn
