nitroso

{{Main|Nitrosation}}

Nitroso compounds can be prepared by the reduction of nitro compounds{{cite journal| author = G. H. Coleman| author2 = C. M. McCloskey| author3 = F. A. Stuart | title = Nitrosobenzene | journal=Org. Synth.|volume = 25 | pages = 80| year = 1945 | doi=10.15227/orgsyn.025.0080}} or by the oxidation of hydroxylamines.{{OrgSynth|first1=A. |last1=Calder |first2=A. R. |last2=Forrester |first3=S. P. |last3=Hepburn |title=2-Methyl-2-nitrosopropane and Its Dimer |collvol=6 |collvolpages=803 |volume=52 |page=77 |prep=cv6p0803}}

Ortho-nitrosophenols may be produced by the Baudisch reaction. In the Fischer–Hepp rearrangement, aromatic 4-nitrosoanilines are prepared from the corresponding nitrosamines.

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Nitrosoarenes typically participate in a monomer–dimer equilibrium. The azobenzene N,N'-dioxide (Ar(^–O)N⁺=⁺N(O^–)Ar) dimers, which are often pale yellow, are generally favored in the solid state, whereas the deep-green monomers are favored in dilute solution or at higher temperatures. They exist as cis and trans isomers.{{cite journal|author1=Beaudoin, D. |author2=Wuest, J. D. |title=Dimerization of Aromatic C-Nitroso Compounds|journal=Chemical Reviews|year=2016|volume=116|issue=1 |pages=258–286|doi=10.1021/cr500520s|pmid=26730505}} The central "double bond" in the dimer in fact has a bond order of about 1.5.{{cite book|title=Nitrosation|first=D. L. H.|last=Williams|publisher=Cambridge University|location=Cambridge, UK|year=1988|isbn=0-521-26796-X|url=https://archive.org/details/nitrosation0000will|url-access=registration|page=36}}

When stored in protic media, primary and secondary nitrosoalkanes isomerize to oximes.{{cite journal |doi=10.1039/CS9770600001|title=Electrophilic C-nitroso-compounds|year=1977|last1=Kirby|first1=G. W.|journal=Chemical Society Reviews|volume=6|page=2|postscript=none}} (Tilden lecture). Some tertiary nitrosoalkanes also isomerize to oximes through C-C bond fission, particularly if the bond is electron-poor.{{sfn|Williams|1988|p=36}} Nitrosophenols and naphthols isomerize to the oxime quinone in solution, but reversibly; nitrosophenol ethers typically dealkylate to facilitate the isomerization. Nitroso tertiary anilines generally do not dealkylate in that way.{{sfn|Williams|1988|pp=59-61}}

Due to the stability of the nitric oxide free radical, nitroso organyls tend to have very low C–N bond dissociation energies: nitrosoalkanes have BDEs on the order of {{cvt|30|-|40|kcal/mol|kJ/mol|-1}}, while nitrosoarenes have BDEs on the order of {{cvt|50|-|60|kcal/mol|kJ/mol|-1}}. As a consequence, they are generally heat- and light-sensitive. Compounds containing O–(NO) or N–(NO) bonds generally have even lower bond dissociation energies. For instance, N-nitrosodiphenylamine, Ph₂N–N=O, has a N–N bond dissociation energy of only {{cvt|23|kcal/mol|kJ/mol|0}}.{{Cite book|title=Comprehensive Handbook of Chemical Bond Energies|last=Luo|first=Yu-Ran|publisher=Taylor and Francis|year=2007|isbn=9781420007282|location=Boca Raton, FL}}

Organonitroso compounds serve as a ligands giving transition metal nitroso complexes.{{cite journal |doi=10.1021/cr0000731 |title=Interactions of Organic Nitroso Compounds with Metals |date=2002 |last1=Lee |first1=Jonghyuk |last2=Chen |first2=Li |last3=West |first3=Ann H. |last4=Richter-Addo |first4=George B. |journal=Chemical Reviews |volume=102 |issue=4 |pages=1019–1066 |pmid=11942786 }}

Many reactions make use of an intermediate nitroso compound, such as the Barton reaction and Davis–Beirut reaction, as well as the synthesis of indoles, for example: Baeyer–Emmerling indole synthesis, Bartoli indole synthesis. In the Saville reaction, mercury is used to replace a nitrosyl from a thiol group.

C-nitroso compounds are used in organic synthesis as synthons in some well-documented chemical reactions such as hetero Diels-Alder (HDA), nitroso-ene and nitroso-aldol reactions.{{cite journal|author1=Bianchi, P. |author2=Monbaliu, J. C. M. |title=Three decades of unveiling the complex chemistry of C-nitroso species with computational chemistry|journal=Organic Chemistry Frontiers|year=2022|volume=9|pages=223–264|doi=10.1039/d1qo01415c}}

Image:Metal-nitrosyl-coordination-modes-2D.png

Nitrosyls are non-organic compounds containing the NO group, for example directly bound to the metal via the N atom, giving a metal–NO moiety. Alternatively, a nonmetal example is the common reagent nitrosyl chloride ({{chem2|Cl\sN\dO}}). Nitric oxide is a stable radical, having an unpaired electron. Reduction of nitric oxide gives the nitrosyl anion, {{chem2|NO-}}:

:{{chem2|NO + e- -> NO- }}

Oxidation of NO yields the nitrosonium cation, {{chem2|NO+}}:

:{{chem2|NO -> NO+ + e- }}

Nitric oxide can serve as a ligand forming metal nitrosyl complexes or just metal nitrosyls. These complexes can be viewed as adducts of {{chem2|NO+}}, {{chem2|NO-}}, or some intermediate case.

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• Nitrosamine, the functional group with the NO attached to an amine, such as R₂N–NO
• Nitrosobenzene
• Nitric oxide
• Nitroxyl

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{{Functional Groups}}

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{{Nitrogen compounds}}

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Category:Functional groups

Nitrosyl compounds