Problems
4.1 IF3 O2 has three isomers, and the structures and point group assignment are as
following:
F
F
I
O
O
F
point group = C2v .
The electron-pairs of double bonds would occupy two of the equatorial sites to reduce
repulsive forces, similar to that of lone pairs. This is the lowest energy structure.
O
O
F
F
I
I
O
F
F
F
F
point group = Cs,
O
point group = D3h .
4.5
Energy
XH3 , (C 3v )
3a1
2e
XH3 , (D3h )
3a1
2e’
2a”
2a1
1e
1a1
109.5o
1e’
1a1’
Bond angle
120o
4.8
(a) the point group of BF 3 is D3h . number of vibrational modes = 3n-6= 3x4-6 = 6,
3 IR active peak: 2E’+ A2 ”, 3 Raman active peaks: A1 ’+ 2E’.
(b) the point group of NF3 is C3v , number of vibrational modes = 6,
4 IR active peaks: 2A1 + 2E, 4 Raman active peaks: 2A1 + 2E.
(c) the point group of ClF 3 is C2v . number of vibrational modes = 6,
6 IR active peaks: 3A1 + B1 + 2B2 , 6 Raman active peaks: 3A1 + B1 +2B2 .