Physical and Chemical Properties of NO

NO is a colorless gas at room temperature and pressure (boiling point, -151.7°C at 1 atm). Its maximum solubility in water is similar to that of pure oxygen, 2-3 mM. It is a fairly nonpolar molecule which would be expected to freely diffuse through membranes. Certainly, one of the most unique and outstanding chemical features of NO is that it is a paramagnetic (radical) species. Using the most basic bonding description, the Lewis dot formalism, it is immediately evident that NO has an unpaired electron (Fig. 

Although much of the chemistry of NO is dominated by the fact that it is a radical (discussed in Section III), it does not possess the type of reactivity normally associated with other radicals. For example, unlike other carbon, oxygen-, or nitrogen-centered radicals, NO does not even have the tendency to dimerize. That is, at standard temperature and pressure, NO tends to remain in the monomeric form. This lack of dimerization has been attributed to the fact that overall bonding does not increase when two NO molecules interact (Ragsdale, 1973). Thus, the formal bond order in NO is 2.5, while the bond order for ONNO is 5. 

The redox relationship of NO with other nitrogen oxides is shown in Fig. 3. As indicated, NO occupies a central and unique position in this redox scheme. The two-electron oxidation of ammonia (NH3) generates hydroxylamine (NH2OH) and a further two-electron oxidation of hydroxyl-amine generates nitroxyl (HNO). NO can then be generated by a single- 

FIGURE 3 Redox scheme for the nitrogen oxides. Values in parentheses represent the formal nitrogen oxidation state. 

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Table l-E-4. Comparison of the physical and chemical properties of No. 1 and No. 2 diesel fuels with those of the hiofuel, methyl esters prepared from soy oil (from Canakci, 2005)... 

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