References
161
asymmetric and symmetric stretches of the nitro (NO 2 ) linkage. These frequencies
may be compared with 1748 cm
–1 and 1261 cm
–1 for the sym N 2 O 4 (O 2 NNO 2 )
isomer
28 in a nitrogen matrix. (The gas-phase frequencies
29 for the latter isomer
are 1758 cm
–1 and 1264 cm
–1
.) An 1829 cm
–1 frequency for asym N 2 O 4 is similar
to the 1876 cm
–1 frequency for the N-O stretch of free NO, and both are rather
larger than the 1562 cm
–1 and 1564 cm
–1 stretching frequencies for the N-O double
bonds
30 of HNO and CH 3 NO. “Increased-valence” structures of type (71), which
may be generated by spin-pairing the odd electrons of NO and NO 3 with the
valence-bond structures (62) and (70), are in accord with these observations.
Spin-pairing of the odd electrons of “increased-valence” structures of type (64)
for two NO 2 molecules, cis and trans “increased-valence” structures can be constructed for asym N 2 O 4 , as well as those of type (66) for sym N 2 O 4 .
The peroxy O 2 NO isomer of NO 3 has been identified
31 as one of the products of
the gas phase reactions NO + O 2 and NO + O 3 . “Increased-valence” structures for
the cis and trans isomers may be obtained by spin-pairing the unpaired electron of
structure (62) for NO with one of the unpaired electrons of structure (23) for O 2 ,
as described in Ref. 32.
11-12 Conclusions
By starting with Pauling “3-electron bond” structures for one or more diatomic
systems, we have found that it is possible to construct “increased-valence” structures for polyatomic molecules. Often, use of the ground-states of the diatomic
systems leads quickly to suitable polyatomic valence-bond structures. To obtain a
suitable “increased-valence” structure for NO 2 , we needed to proceed through an
excited state of NO. This is also the case for various other molecules. However,
valence-bond structures for excited states for diatomic systems might not always
be easy to construct. Fortunately, it is possible to circumvent this problem by
generating “increased-valence” structures from familiar standard Lewis structures
for polyatomic molecules. In the following chapters, we shall describe how this
may be done.
References
1. R.D. Harcourt, J. Amer. Chem. Soc., 100, 8060 (1978), 101, 5456 (1979).
2. R.D. Harcourt and W. Roso, Canad. J. Chem., 56, 1093 (1978) – References 4-19
therein.
3. P.C. Hiberty and C. Leforestier, J. Amer. Chem. Soc., 100, 2012 (1978); P.C. Hiberty
and G. Ohanessian, J. Amer. Chem. Soc., 104, 66 (1982).
4. L. Pauling, “The Nature of the Chemical Bond”, (Cornell, 1960), p. 346.
5. R.D. Harcourt and W. Roso, Int. J. Quantum Chem., 16, 1033 (1979).
6. J.J. Turner, Endeavour, 27, 42 (1968).
161
asymmetric and symmetric stretches of the nitro (NO 2 ) linkage. These frequencies
may be compared with 1748 cm
–1 and 1261 cm
–1 for the sym N 2 O 4 (O 2 NNO 2 )
isomer
28 in a nitrogen matrix. (The gas-phase frequencies
29 for the latter isomer
are 1758 cm
–1 and 1264 cm
–1
.) An 1829 cm
–1 frequency for asym N 2 O 4 is similar
to the 1876 cm
–1 frequency for the N-O stretch of free NO, and both are rather
larger than the 1562 cm
–1 and 1564 cm
–1 stretching frequencies for the N-O double
bonds
30 of HNO and CH 3 NO. “Increased-valence” structures of type (71), which
may be generated by spin-pairing the odd electrons of NO and NO 3 with the
valence-bond structures (62) and (70), are in accord with these observations.
Spin-pairing of the odd electrons of “increased-valence” structures of type (64)
for two NO 2 molecules, cis and trans “increased-valence” structures can be constructed for asym N 2 O 4 , as well as those of type (66) for sym N 2 O 4 .
The peroxy O 2 NO isomer of NO 3 has been identified
31 as one of the products of
the gas phase reactions NO + O 2 and NO + O 3 . “Increased-valence” structures for
the cis and trans isomers may be obtained by spin-pairing the unpaired electron of
structure (62) for NO with one of the unpaired electrons of structure (23) for O 2 ,
as described in Ref. 32.
11-12 Conclusions
By starting with Pauling “3-electron bond” structures for one or more diatomic
systems, we have found that it is possible to construct “increased-valence” structures for polyatomic molecules. Often, use of the ground-states of the diatomic
systems leads quickly to suitable polyatomic valence-bond structures. To obtain a
suitable “increased-valence” structure for NO 2 , we needed to proceed through an
excited state of NO. This is also the case for various other molecules. However,
valence-bond structures for excited states for diatomic systems might not always
be easy to construct. Fortunately, it is possible to circumvent this problem by
generating “increased-valence” structures from familiar standard Lewis structures
for polyatomic molecules. In the following chapters, we shall describe how this
may be done.
References
1. R.D. Harcourt, J. Amer. Chem. Soc., 100, 8060 (1978), 101, 5456 (1979).
2. R.D. Harcourt and W. Roso, Canad. J. Chem., 56, 1093 (1978) – References 4-19
therein.
3. P.C. Hiberty and C. Leforestier, J. Amer. Chem. Soc., 100, 2012 (1978); P.C. Hiberty
and G. Ohanessian, J. Amer. Chem. Soc., 104, 66 (1982).
4. L. Pauling, “The Nature of the Chemical Bond”, (Cornell, 1960), p. 346.
5. R.D. Harcourt and W. Roso, Int. J. Quantum Chem., 16, 1033 (1979).
6. J.J. Turner, Endeavour, 27, 42 (1968).