CHM 361/661, Fall 2008
Homework Assignment III
Symmetry/Vibrational Spectroscopy
A. For the molecules given below, determine (a) point groups, (b) IR-active and IR-
inactive FeCl normal stretching modes, and (c) assign Mulliken symbols to each
vibration.
The cis isomer belongs to the point group C2v and the trans isomer has D4h symmetry.
Cis has 2 IR active stretching modes (A1, B2), trans has 1 IR active (A2u) and 1 IR
inactive (A1g) stretch.
B. Determine the point groups for the following AO’s:
px C∞v; dxy D2h; dx2-y2 D2h; dz2 D∞h
C. Under ideal octahedral symmetry (Oh), identify the irreducible representations that
describe the symmetry of the dxy and dx2-y2 orbitals. Note: xy and x2-y2 denote off-axis and
on-axis orbitals, respectively. Answer: T2g and Eg, respectively.
D. Consider the molecules BF3 and SOCl2 and determine, for each of the molecules, the
IR-active stretching modes involving the halide atoms.
BF3: D3h symmetry, see p 104 in text, SOCl2: Cs symmetry; sym. stretch has A’
symmetry, asym. stretch has A’’ symmetry. Both are IR active.
Multi/Heteronuclear NMR of main group compounds
Chapter 13, p. 334: self-study exercises 1-3
Chapter 17, problems 17.9 and 17.10
Fe
OC Cl
OC Cl
CO
CO
Fe
OC CO
OC CO
Cl
Cl
cis-[Fe(CO)
4
Cl
2
]trans-[Fe(CO)
4
Cl
2
]
