US EPA

1690952 

Journal Article 

The N-O bond in covalent nitrates and nitrites 

Oberhammer, H 

2002 

1 

Journal of Molecular Structure: Theochem
ISSN: 0166-1280
EISSN: 1872-7999 

605 

2-3 

177-185 

WOS:000174309100005 

The N-O single bond length in gaseous nitrates MO-NO2 depends strongly on the substituent M. In 'simple' nitrates (M = SiMe3, CH3, H, halogens, or CF3) this bond lengthens with increasing electronegativity of M from 1.383(5) Angstrom in Me3SiONO2 to 1.507(4) Angstrom in FONO2, In peroxynitrates ROONO2 with R = H, CF3, FC(O), CH3C(O) and CF3C(O) the N-O bond length varies between 1.492(7) Angstrom in CH3C(O)OONO2 and 1.526(10) Angstrom in CF3C(O)OONO2 The longest bond Angstrom occurs in (CF3)(2)NO-NO2 with 1.588(14) Angstrom. This large variation of N-O bond lengths can be rationalized qualitatively by different ionic contributions M+NO3- and by partial decomposition into MO and NO2 radicals. Quantum chemical calculations with standard methods (HF, MP2 and B3LYP with 6-31G* basis sets) predict greatly different bond lengths. The HF values are too short by up to 0.19 Angstrom, the MP2 values are too long by up to 0.08 Angstrom and the B3LYP method reproduces all bond lengths very well. Only a very limited number of gas phase structures of covalent nitrites MO-NO has been reported. In these compounds the N-O bond length varies from 1.397(6) Angstrom in HONO to 1.572(21) Angstrom in (CF3)(2)NO-NO. Again the B3LYP method reproduces these bond lengths better than HF or MP2 approximations. A possible exception, however, may be CIONO, where the MP2 approximation reproduces the estimated experimental value better than the B3LYP method. (C) 2002 Elsevier Science B.V. All rights reserved.