Alkyl nitrites, structure

Aminopyrazolo[3,4-d]pyrimidines 257 were converted into the corresponding 4-aryl substituted derivatives 259 via treatment with alkyl nitrites and boiling in aromatic solvent. The isomer distribution of 259 prepared by these route was that predicted for a radical intermediate (ortho, meta, and para). The structure of isomers was established by H-NMR. Unusual fragmentation products were isolated these probably result from collapse of the radical intermediate 258 (83JOC4605). Methylation of 257 takes place at either N-1 or N-2. Further methylation affords methylamino derivatives structures of the products were established by C-NMR as well as by chemical methods (75JOC1822). 

Doyle, M. P., Pickering, R. A., daConcei5ao, J. (1984). Structural effects in alkyl nitrite oxidation of human hemoglobin. J. Biol. Chem. 259, 80-87. 

Alkyl nitrites, which are readily prepared by reaction of the corresponding alcohols with nitrosyl chloride in pyridine, absorb UV in two regions - a broad band centered at ca. 210 nm (e 1000-1700) and a structured band at ca. 360-380 nm... 

The first absorption band of simple alkyl nitrites occurs in the region 3200-4400 A and displays considerable fine structure it appears to be related to an n - n transition of the non-bonding nitrogen electrons to the antibonding n group orbital of the double bond system . A second stronger absorption, has a maximum around 2200-2300 A (n, a transition). The major photodissociative process in alkyl nitrites is the homolytic cleavage of the O-N bond to form NO and alkoxy radicals which are usually vibrationally and/or electronically excited. 

Hindered rotation occurs on the NMR time scale for numerous other systems with partial double bonds, including carbamates, thioamides, enamines, nitrosamines, alkyl nitrites, diazoketones, aminoboranes, and aromatic aldehydes. Formal double bonds can exhibit free rotation when alternative resonance structures suggest partial single bonding. The calicene 5-5, for example, has a barrier to rotation about the central bond of only 20 kcal mol . ... 

Alkyl nitrites exhibit a weak band (fmax - 80) with fine structure (nearly six or seven well defined maxima) in the region of 370 rn/x12. The fine structure... 

Only the last method, developed by Rapoport s group [95], is a versatile, chemoselective, and high-yielding. The method is accomplished by adding an alkyl nitrite (2 eq.) to a cold acetone solution of a Pschorr s amine substrate (1 eq.) and sulfuric acid (2 eq.) followed by sodium iodide. Here the iodide serves as a one-electron reductant, which converts an aryldiazonium salt to an aryl radical [95,96]. Then, the fast intramolecular arylation takes place with formation of the phenanthrene structure. While the older Pschorr methods gave very low yields, often under 20%, the Rapoport s method introduced significant improvements as the yields were 45-71% [95]. For example, polymethoxy compound 52 was converted to phenanthrene 53 in 71% yield [95], respectively. Scheme 22. 

The absorption regions of the alkyl nitrites overlaps well the distribution of solar flux within the lower troposphere see figure IX-H-1. The characteristic band structure that appears in each spectrum, like that in HONO, originates from the excitation to the different vibrational energy levels (an N-O stretching mode, V2) in the Si excited state. Like HONO, the alkyl nitrites (RONO) photodissociate readily to form free radicals RONO+hv RO+NO, that can drive the chemistry that results in ozone generation within the troposphere. The alkyl nitrites (RONO) are often used as convenient sources of alkoxy radicals (RO) in laboratory experiments. 

As indicated above, the data for cross sections of the higher alkyl nitrites available today are not highly accurate. However, these are given in graphical form in figure IX-H-5 and in tabular format in table IX-H-3. The banded structure characteristic of all of the alkyl nitrites reflects the excitation to the different vibrational bands that involve largely the stretching motion in the RON—O bond of the excited Si state. 

The reactions of alkyl sulfonates with superoxide ion and with nitrite ion directly afford the corresponding inverted alcohols. - Although displacement by superoxide ion has been successfully utilized in prostaglandin chemistry, elimination again takes place to some extent, depending on the structures of the substrates. In the reaction with nitrite ion, ketone and nitroalkane are also formed. The inversion of cyclopentanol derivatives via tosylates has been studied by the use of various methods involving displacement by benzoate, nitrite ion and superoxide ion as well as the diethyl azodicarboxylate (DEAD)-PhsP procedure, where varied amounts of elimination products are invariably formed. ... 

This tautomerism is suggested by the fact that by the interaction of metal nitrites with alkyl halides two series of compounds are obtained, the nitrites-in which the NO2 group is attached to carbon through an O atom—and the nitro compounds, in which there is a direct N—C link. From i.r. studies of nitrous acid gas it is concluded that there is no evidence for the existence of form (a) and that the two isomers of (b) exist in comparable amounts, the trans isomer being rather more stable. The structure (c) has been assigned to the trans isomer. 

Another type of reaction may be mentioned here, which, while not oxidation-reduction, shows some of the possibilities in the way of relative oxidizing potentials of different atoms, or the relative aflSnities of the atoms for valence electrons. Silver nitrite ind sodiuiii nitrite when treated with an alkyl halide give different products. With the former, a nitro compound is obtained mainly with the latter a nitrite predominates. While according to the older views, this would point to different structures for the two nitrites, according to the principles developed in this book, the explanation of these differences involves tautomerism and several chemical equilibria. The reaction may be given in general terms as follows ... 

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