Nitrous oxide resonance

Perhaps the best known oxide of nitrogen is N20, commonly called nitrous oxide or laughing gas. Nitrous oxide is frequently used as an anesthetic, particularly in dentistry. It is also the propellant gas used in whipped cream containers N20 is nontoxic, virtually tasteless, and quite soluble in vegetable oils. The N20 molecule, like all those in Figure 21.6, can be represented as a resonance hybrid. 

Procedure (ii). Make certain that the instrument is fitted with the correct burner for an acetylene-nitrous oxide flame, then set the instrument up with the calcium hollow cathode lamp, select the resonance line of wavelength 422.7 nm, and adjust the gas controls as specified in the instrument manual to give a fuel-rich flame. Take measurements with the blank, and the standard solutions, and with the test solution, all of which contain the ionisation buffer the need, mentioned under procedure (i), for adequate treatment with de-ionised water after each measurement applies with equal force in this case. Plot the calibration graph and ascertain the concentration of the unknown solution. 

A double-beam atomic absorption spectrophotometer should be used. Set up a vanadium hollow cathode lamp selecting the resonance line of wavelength 318.5 nm, and adjust the gas controls to give a fuel-rich acetylene-nitrous oxide flame in accordance with the instruction manual. Aspirate successively into the flame the solvent blank, the standard solutions, and finally the test solution, in each case recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil. 

Resonance occurs only between structures with the same arrangement of atoms. For example, although we might be able to write two hypothetical structures for the dinitrogen oxide (nitrous oxide) molecule, NNO and NON, there is no resonance between them, because the atoms lie in different locations. 

Linus Pauling, Proc. Nat. Acad. Set., 18, 293 (1932). Examples of molecules which resonate among several Lewis structures are given in this paper. Further discussion of the nitrous oxide molecule is given in a later note, Linus Pauling, ibid., July, 1932. 

The investigation of methyl azide, methyl nitrate, and fluorine nitrate by electron diffraction is shown to lead to configurations of the molecules corresponding in each case to resonance between two important valence-bond structures. The unimportance of a third otherwise reasonable structure for these molecules as well as for nitrous oxide is ascribed to instability due to the presence of electric charges of the same sign on adjacent atoms. It is shown that the differ-... 

The oxides of nitrogen that have been well characterized are described in Table 14.4. Nitrous oxide (m.p. -91 °C, b.p. -88 °C) is a 16-electron triatomic molecule having a linear structure. Three resonance structures can be drawn for this molecule as follows ... 

One easily understood mechanism for changes in lifetime is collisional quenching (Figure 10.3). A variety of substances act as quenchers, including oxygen, nitrous oxide, heavy atoms, Cl , and amines, to name a few. By consideration of the lifetime in the absence (to) and presence (r) of collisional quenchers (no resonance energy... 

The discussion in Section 1-3 about the element of arbitrariness in the concept of resonance may be recalled at this point with reference to the nitrous oxide molecule and the other molecules that are described in this chapter as resonating among several valence-bond structures. It is not necessary that the structures A, B, and C be used as the basis of discussion of the nitrous oxide molecule. We might say instead that the molecule cannot be satisfactorily represented by any single valence-bond structure, and abandon the effort to correlate its structure and properties with those of other molecules. By using valence-bond structures as the basis for discussion, howrever, with the aid of the concept of resonance, we are able to account for the properties of the molecule in terms of those of other molecules in a straightforward and simple way. It is for this practical reason that we find it convenient to speak of the resonance of molecules among several electronic structures. 

In Section 6-1 nitrous oxide was considered to resonate among three structures Ay B, and C, which are so similar in nature as to contribute about equally to the normal state of the molecule. There is, however, a fourth structure, D, that must be discussed ... 

It is analogous to the fourth structure for carbon dioxide, which has the same number of electrons as nitrous oxide, and might be of importance for the latter molecule also. Resonance among the four structures, contributing equally, leads to the values N—N = 1.15AandN—0 = 1.11 A that is, to an N—O distance smaller than the N—N distance, which is contrary to observation 18 N—N = 1.126 A, N—N = 1.186 A. The observed values are those expected for resonance among the first three structures. 

A less obvious result of this criterion is that when contributing structures differ in bond angle, resonance will be reduced. Consider, for example, the following hypothetical resonance for nitrous oxide. 

Resonance is by no means restricted to organic molecules. The following sets of valence-bond structures represent the hybrid structures of nitrate ion, NO30, carbonate ion, CO320, and nitrous oxide, NaO. These are only representative examples. We suggest that you check these structures carefully to verify that each member of a set conforms to the general rules for resonance summarized above. 

PROBLEM 7.12 Called "laughing gas," nitrous oxide (N2O) is sometimes used by dentists as an anesthetic. Given the connections N-N-0 draw two electron-dot resonance structures for N2O. 

Nitrous oxide is a good example of a molecule that shows resonance. The structure on the left in Figure 7.6 has two double bonds, with two lone pairs on each of the distal atoms. The structure on the right has a triple bond. Neither structure fully describes nitrous oxide, nor does either structure actually exist. The real nitrous oxide molecule is a resonance hybrid of the two Lewis structures. 

The nitrous oxide molecule can be considered to be a resonance hybrid between the structures ... 

An HgCdTe layer 2, comprising photodiodes 3, is formed on a first side of a CdTe substrate 11. The detector is bonded to a silicon chip 7 by a flip-chip process. A reflection preventive film is formed on a second side, opposite to the first side, of the CdTe substrate. The film is formed by a cyclotron resonance plasma CVD method by introducing nitrogen, nitrous oxide and silane as reaction gas. The thickness of the film is selected so that the reflectivity is minimized for radiation having a wavelength to be detected by the photodiodes. 

Copper is invariably determined by AAS in a lean air-acetylene flame, using the main resonance line at 324.7 nm. The detection limit is generally around 10 ng ml-1, which is marginally better than that generally achievable by flame AFS, and comparable to that reported for AES using a carefully optimized nitrous oxide-acetylene flame.2 Provided samples are not excessively diluted, this value is adequate for many practical applications in environmental analysis, such as the measurement of plant copper concentration or EDTA- or DTPA-extractable copper in soils. Interferences are rare, and unlikely to be a problem from concomitant elements present in most environmental samples, but matrix matching is still advisable. The sensitivity is inadequate for the direct determination of copper in natural water samples, for which a suitable preconcentration technique must be employed.1,23,24... 

For nitrous oxide, N20, two equally acceptable structures can be drawn. By the resonance treatment the true structure of this molecule should be intermediate in character between structures A and B. Thus, the nitrogen-to-nitrogen bond distance... 

The inherent sensitivity of double resonance methods has led to studies of transition metal and rare earth compounds which would be difficult with more conventional methods. In chapter 10 we described the study of rotational transitions of the FeO molecule by Endo, Saito and Hirota [46] using a conventional ffee-space absorption cell, and by Allen, Ziurys and Brown [47] who used a high-temperature oven to study the reaction between iron vapour and nitrous oxide. We also mentioned, however, that a comprehensive study had been made by Krockertskothen, Knockel and Tiemann [48] using a double resonance technique which we now describe in detail. Allen, Ziurys and Brown [47] combined the data from different experiments to produce the best analysis. 

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