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{{Short description|Chemical group (NH2)}} |
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{{About|the neutral compound|other compounds with the formula NH<sub>2</sub> but different charges|Azanide|and|Nitrenium ion}} |
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{{Redirect|Amidogen|the chemical compound also called amidogen|Ammonia}} |
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{{Chembox |
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{{Chembox |
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| Name = |
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| ImageFileL1 = Amino radical.svg |
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| ImageFileR1 = Amino-radical-3D-vdW.png |
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| verifiedrevid = 448993879 |
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| SystematicName = Azanyl<ref name = "aminyl (CHEBI:29318)">{{Cite web|url = https://www.ebi.ac.uk/chebi/searchId.do?chebiId=29318|title = aminyl (CHEBI:29318)|work = Chemical Entities of Biological Interest (ChEBI)|location = UK|publisher = European Bioinformatics Institute|at = IUPAC Names}}</ref> (substitutive)<br /> |
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| SystematicName = Azanyl<ref name = "aminyl (CHEBI:29318)">{{Cite web|url = https://www.ebi.ac.uk/chebi/searchId.do?chebiId=29318|title = aminyl (CHEBI:29318)|work = Chemical Entities of Biological Interest (ChEBI)|location = UK|publisher = European Bioinformatics Institute|at = IUPAC Names}}</ref> (substitutive)<br /> |
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Dihydridonitrogen(•)<ref name = "aminyl (CHEBI:29318)" /> (additive) |
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Dihydridonitrogen(•)<ref name = "aminyl (CHEBI:29318)" /> (additive) |
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| OtherNames = Amidogen; Amino radical |
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| Section1 = {{Chembox Identifiers |
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| IUPACName = Azanyl; Aminyl |
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| CASNo = 13770-40-6 |
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| Section1 = {{Chembox Identifiers |
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| PubChem = 123329 |
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| PubChem _Ref = {{Pubchemcite|correct|pubchem}} |
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| CASNo_Ref = {{cascite|correct|??}} |
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| CASNo = 13770-40-6 |
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| ChemSpiderID = 109932 |
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| PubChem = 123329 |
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| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |
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| ChEBI = 29318 |
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| ChemSpiderID = 109932 |
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| ChEBI_Ref = {{ebicite|correct|EBI}} |
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| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |
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| SMILES = |
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| ChEBI = 29318 |
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| ChEBI_Ref = {{ebicite|correct|EBI}} |
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| StdInChI = 1S/H2N/h1H2 |
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| SMILES = |
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| StdInChI_Ref = {{stdinchicite|correct|chemspider}} |
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| StdInChI = 1S/H2N/h1H2 |
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| StdInChIKey = MDFFNEOEWAXZRQ-UHFFFAOYSA-N |
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| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |
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| StdInChI_Ref = {{stdinchicite|correct|chemspider}} |
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| StdInChIKey = MDFFNEOEWAXZRQ-UHFFFAOYSA-N |
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| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |
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}} |
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| Section2 = {{Chembox Properties |
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| Section2 = {{Chembox Properties |
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| Formula = {{Chem|NH|2}}<sup>•</sup> |
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| Formula = {{Chem|NH|2}}<sup>•</sup> |
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| MolarMass = 16.0226 g mol<sup>-1</sup> |
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| MolarMass = 16.0226 g mol<sup>−1</sup> |
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| ExactMass = 16.018724069 g mol<sup>-1</sup> |
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| Section3 = {{Chembox Thermochemistry |
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| Section3 = {{Chembox Thermochemistry |
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| DeltaHf = 190.37 kJ mol<sup>-1</sup> |
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| DeltaHf = 190.37 kJ mol<sup>−1</sup> |
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| Entropy = 194.71 J K<sup>-1</sup> mol<sup>-1</sup>}} |
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| Entropy = 194.71 J K<sup>−1</sup> mol<sup>−1</sup>}} |
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| Section4 = |
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The '''azanyl''' radical, '''{{Chem|NH|2}}<sup>•</sup>''', is the neutral form of the ] ] ({{Chem|NH|2|-}}). Azanyl ] are highly reactive and consequently short lived; however, they form an important part of radical chemistry. In sufficiently high concentration, azanyl dimerises to form ]. |
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In ], the '''amino radical''', '''{{chem2|*NH2}}''', also known as the '''aminyl''' or '''azanyl''', is the neutral form of the ] ({{chem2|NH2-}}). Aminyl ]s are highly ] and consequently short-lived, like most radicals; however, they form an important part of ] chemistry. In sufficiently high ], amino radicals ] to form ]. While {{chem2|NH2}} as a ] is common in nature, forming a part of many compounds (e.g. the ]s), the radical cannot be isolated in its free form.<ref name="die.net">{{cite web|url=http://dictionary.die.net/amidogen |archive-url=https://archive.today/20130221094825/http://dictionary.die.net/amidogen |url-status=dead |archive-date=February 21, 2013 |title=Amidogen |author=die.net |access-date=May 16, 2012 }}</ref> |
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== References == |
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== Synthesis == |
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===Reaction 1: Formation of amino radical from ammonia=== |
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Amino radicals can be produced by reacting ] with ammonia in irradiated aqueous solutions. This reaction is formulated as a hydrogen abstraction reaction.<ref name="NetaMaruthamuthu1978">{{cite journal|last1=Neta|first1=P.|last2=Maruthamuthu|first2=P.|last3=Carton|first3=P. M.|last4=Fessenden|first4=R. W.|year=1978|title=Formation and reactivity of the amino radical|journal=The Journal of Physical Chemistry|volume=82|issue=17|pages=1875–1878|doi=10.1021/j100506a004|issn=0022-3654}}</ref> |
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{{Reflist}} |
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:{{chem2 | NH3 + '''*'''OH -> '''*'''NH2 + H2O }} |
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The rate constant (''k<sub>1</sub>'') for this reaction was determined to be {{val|1.0|e=8|u=M<sup>−1</sup> s<sup>−1</sup>}}, while the parallel reaction of OH with {{chem|NH|4|+}} was found to be much slower. This rate was redetermined by using two-pulse ] competition methods with ] and thiocyanate ions at pH 11.4. A value of ''k''<sub>1</sub> = {{nowrap|(9 + 1){{e|7}} M<sup>−1</sup> s<sup>−1</sup>}} was obtained from both systems. While in acidic solution, the corresponding reaction of {{chem2|*OH}} with {{chem2|NH4+}} is too slow to be observed by pulse radiolysis. |
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===Reaction 2: Formation of amino radical from hydroxylamine=== |
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The amino radical may also be produced by reaction of ] with ] ({{chem2|NH2OH}}). Several studies also utilized the redox system of {{chem2|]\sNH2OH}} for the production of amino radicals using electron paramagnetic resonance (ESR) spectroscopy and polarography.<ref name="NetaMaruthamuthu1978" /> |
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:{{chem2 | Ti^{III} + NH2OH -> Ti^{IV} + '''*'''NH2 + HO- }} |
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===Reaction 3: Formation of amino radical from ammoniumyl=== |
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Reduction of hydroxylamine by e<sup>−</sup>(aq) has also been suggested to produce the amino radical in the following reaction.<ref name="NetaMaruthamuthu1978" /> |
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:{{chem2 | '''*'''NH3+ <-> '''*'''NH2 + H+ }} |
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The reactivity of the amino radical in this reaction is expected to be pH dependent and should occur in the region of pH 3–7. |
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== Properties == |
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=== Electronic states === |
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The amino radical has two characteristic electronic states: |
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] |
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The more stable electronic state is <sup>2</sup>B<sub>1</sub>, where the unpaired electron is in the p-orbital perpendicular to the plane of the molecule (π type radical). The high energy electronic state, <sup>2</sup>A<sub>1</sub>, has the two electrons in the p-orbital and the unpaired electron in the sp<sup>2</sup> orbital (σ type radical).<ref name="NIST">{{Cite web |url=https://webbook.nist.gov/cgi/cbook.cgi?ID=C13770406&Mask=6FF |title=Amino Radical |date=2017 |work=NIST Chemistry WebBook |publisher=National Institute of Science and Technology |access-date=15 June 2018}}</ref><ref name="KoenigHoobler1974">{{cite journal |last1=Koenig |first1=T. |last2=Hoobler |first2=J. A. |last3=Klopfenstein |first3=C. E. |last4=Hedden |first4=G. |last5=Sunderman |first5=F. |last6=Russell |first6=B. R. |title=Electronic configurations of amido radicals |journal=Journal of the American Chemical Society |volume=96 |issue=14 |year=1974 |pages=4573–4577 |issn=0002-7863 |doi=10.1021/ja00821a036}}</ref> |
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Nitrogen centered compounds, such as amines, are ] in nature. This character is also seen in amino radicals, which can be considered to be nucleophilic species.<ref name="NIST" /><ref name="KoenigHoobler1974" /> |
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=== Spectral properties === |
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The amino radical only exhibits a very low optical absorption in the visible region (''λ''<sub>max</sub> = 530 nm, ''ε''<sub>max</sub> = {{nowrap|81 M<sup>−1</sup> s<sup>−1</sup>}}), while its absorption in the UV (<260 nm) is similar to that of OH. Due to this, it is impractical to determine the rate of reaction of the amino radical with organic compounds by following the decay of the amino radical. |
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== Reactivity == |
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In general, amino radicals are highly reactive and short lived; however, this is not the case when reacted with some organic molecules. Relative reactivities of the amino radical with several organic compounds have been reported, but the absolute rate constants for such reactions remain unknown. In reaction 1, it was hypothesized that the amino radical might possibly react with NH<sub>3</sub> more rapidly than OH and might oxidize {{chem|NH|4|+}} to produce the amino radical in acid solutions, given that radicals are stronger oxidants than OH. In order to test this, ] and ] radical anions were used. The sulfate and phosphate radical anions were found to react more slowly with NH<sub>3</sub> than does the amino radical and they react with ammonia by hydrogen abstraction and not by electron transfer oxidation.<ref name="NetaMaruthamuthu1978" /> |
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When the amino radical is reacted with ] ions, the rate constant is very low and only a weak absorption in the UV spectra is observed, indicating that amino radicals do not react with benzene rapidly. ], on the other hand, was found to react more rapidly with the amino radical. In experiments at pH 11.3 and 12, using 1.5 M NH<sub>3</sub> and varying concentrations of phenol between 4 and 10 mM, the formation of the phenoxyl radical absorption was observed with a rate constant of {{nowrap|(3 + 0.4){{e|6}} M<sup>−1</sup> s<sup>−1</sup>}}. This reaction can produce phenoxyl radicals via two possible mechanisms:<ref name="NetaMaruthamuthu1978" /> |
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# Addition to the ring followed by elimination of NH<sub>3</sub>, or |
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# Oxidation by direct electron transfer |
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] |
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While the amino radical is known to be weakly reactive, the recombination process of two amino radicals to form ] appears to be one of the fastest. As a result, it often competes with other NH<sub>2</sub> reactions. |
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:NH<sub>2</sub> + NH<sub>2</sub> → N<sub>2</sub>H<sub>4</sub> |
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At low pressures, this reaction is the fastest and therefore the principal mode of NH<sub>2</sub> disappearance.<ref name=KheSoulingnac1977>{{cite journal |last1=Khe |first1=P. V. |last2=Soulignac|first2=J. C.|last3=Lesclaux |first3=R. |title=Pressure and temperature dependence of amino radical recombination rate constant |journal=The Journal of Physical Chemistry |date=1977 |volume=81 |issue=3 |pages=210–214 |doi=10.1021/j100518a006}}</ref> |
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== See also == |
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* ] |
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* ] |
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* ] |
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* ] (dimer) |
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== References == |
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{{Reflist}} |
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==Further reading== |
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* {{Cite journal|last=Davies|first=P|date=2008|title=Detection of the amino radical NH<sub>2</sub> by laser magnetic resonance spectroscopy|journal=The Journal of Chemical Physics|volume=62|issue=9|pages=3739–3742|doi=10.1063/1.430970}} |
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* {{Cite journal|last=Buttner|first=T|date=2005|title=A stable aminyl radical metal complex|pmid=15653498|journal=Science|volume=307|issue=5707|pages=235–8|doi=10.1126/science.1106070|bibcode=2005Sci...307..235B|s2cid=6625217}} |
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* {{Cite journal|last=John|first=Seely|date=1977|title=Temperature and Pressure Dependence of the Rate Constant for the HO<sub>2</sub> + NO Reaction|journal=The Journal of Physical Chemistry|volume=81|issue=10|pages=210–214|doi=10.1021/jp952553f}} |
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* {{Cite journal|last=Koenig|first=Hoobler|title=Electronic configurations of amino radicals|journal=Journal of the American Chemical Society|volume=96|issue=14|pages=4573–4577|doi=10.1021/ja00821a036|year=1974}} |
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{{Molecules detected in outer space}} |
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{{Inorganic-compound-stub}} |
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] |
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] |