168
Chapter 13 “Increased-Valence” Structures for N-Centre Bonding Units
Figure 13-1: Standard Lewis and “increased-valence” structures for N2O, 3
N
 , CO2,
2
NO
 and
HNCO. For 3
N
 , CO2, and
2
NO
 , the symmetrically-equivalent structures are not displayed.
Table 13-1: Bond-lengths
1-7 (Å) for some isoelectronic systems with 16 valence-shell electrons.
See also Ref. 8. Estimates of standard triple and double bond lengths are
9
: C N
 , 1.15 Å;
N N
 , 1.10 Å; C N
 , 1.27 Å; N N
 , 1.24 Å; C O
 , 1.21 Å; N O
 , 1.20 Å.
N-N or C-N
N-O, C-O or N-NH
N2O
1.129
1.188
HN3
1.133
1.237
3
N

1.176
HCNO
1.161
1.207
2
NO

1.153
CO2
1.162
HNCO
1.207
1.171
For HN 3 and HCNO, which are isoelectronic with N 2 O, the standard Lewis and
“increased-valence” structures are similar to those for N 2 O, except for the
replacement of the O and terminal Ν of N 2 O with N-H and H-C, respectively.
From the “increased-valence” structures of type (I), namely