Nitrogen and Oxygen Centered Radicals

549 Pages·2004·5.743 MB·English

by  H. Fischer (auth.), H. Fischer (eds.)

General introduction 1
I General introduction
H. Fischer

A Definition and substances

In the context of these tables the term free radical means a chemically stable or transient paramagnetic
atomic or molecular species which derives its paramagnetism from a single, unpaired valence shell
electron. Following this definition the tables cover
a) atoms and atomic ions in ground and excited 2S and 2P states,
b) diatomic and linear polyatomic molecules in 2Σ and 2Π states,
c) polyatomic molecules and molecular ions which arise or may be thought to arise from the break of a
single bond of a diamagnetic molecule or molecular ion,
d) mono-(tri-, penta-, etc.) – negative or – positive ions of neutral organic or inorganic compounds.
Not classified as free radicals are atoms or molecules in ground or excited electronic states with
multiplicities larger than two (e.g. O, 3P; O , 3Σ; N, 4S; molecules in excited triplet states), transition
2
metal ions and their complexes deriving their paramagnetism exclusively or mainly from d- and f-
electrons and charge transfer complexes. However, a number of polyatomic molecular species which do
not fulfill the above definition are included because their properties closely resemble those of structurally
closely related free radicals. These are
e) metal(0) complexes and clusters,
f) high spin polyradicals with electron exchange or dipolar couplings not greatly exceeding the Zeeman
or hyperfine interactions, triplet carbenes and poly-carbenes,
g) selected transition metal complexes deriving their paramagnetism from free radical ligands and the
electrons of the center atom.
The volumes cover only compounds with unambiguously verified or at least very plausibly assumed
structures. Papers which only state the presence of free radicals in a sample and do not give detailed
structures nor magnetic properties are not reviewed. Also not covered are publications which deal
exclusively with other topics than experimental determinations of magnetic properties of free radicals.
Such work may however be mentioned in footnotes or as further references at the appropriate places.
The ordering of the substances into subclasses is given in the general table of contents. The ordering
within the subclasses is explained, where not self explanatory, in the introductions to the individual
chapters.
The literature was considered mainly for the period of 1985 to 2001. The earlier literature was covered
in: Magnetic Properties of Free Radicals, Landolt-Börnstein, New Series, Group II, Vol. 1, Berlin:
Springer, 1965; Landolt-Börnstein, New Series, Group II, Vols. 9a–9d2, Berlin: Springer, 1977–80;
Landolt-Börnstein, New Series, Group II, Vols. 17a–17h, Berlin: Springer, 1986–90. Further information
on free radicals is also found in: Radical Reaction Rates in Liquids, Landolt-Börnstein, New Series,
Group II, Vols. 13a–13e, Berlin: Springer, 1984–85; Landolt-Börnstein, New Series, Group II, Vols. 18a–
18e2, Berlin: Springer, 1994–97.

B Magnetic properties

The magnetic properties of most free radicals can conveniently be represented by parameters describing
their interaction with an external magnetic field and the intra-molecular hyperfine interactions, i.e. the
parameters g and aλ of the Spin-Hamiltonian

H = µB B0 g S – Σ µN gNλ B0 Iλ + Σ S aλ Iλ
λ λ

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New Series II/26C
2 General introduction
where µB, µN, B0, g, S, gNλ, aλ, Iλ are the Bohr magneton, the nuclear magneton, the magnetic induction,
the g-tensor of the radical, the electron spin operator, the nuclear g-factor of nucleus λ, the hyperfine
coupling tensor of nucleus λ, and the spin operator of nucleus λ, respectively.
g is symmetric and the mean value of its diagonal elements

3
Σ
g = 1/3 g
ii
i=1

is called the isotropic g-factor. For many radicals g deviates only slightly from the g-factor of the free
electron

g = 2.002319304386(20) .
e

aλ, the hyperfine coupling tensor, describes the dipolar and contact interaction between the electron
spin momentum and the nuclear spin momentum of nucleus λ of the radical. aλ is most often also
symmetric and the mean value

3
Σ
aλ = 1/3 aii, λ
i=1

is called the isotropic hyperfine coupling constant or splitting parameter. If a radical contains several
nuclei which interact there are several tensors aλ. In general their principal axes do not coincide, nor do
they with the principal axes of g.
For polyatomic radicals in the gas phase the above Spin-Hamiltonian does not apply and four
magnetic hyperfine coupling constants a, b, c, d are needed to describe the interaction between a nuclear
and the electron spin. These are defined and explained in the introduction to the tables on inorganic
radicals.
Polyradicals and certain radicals on transition metal complexes have N unpaired electrons located on
different molecular segments k. Their Spin-Hamiltonian is

N N
H = µB Σ B0 gk Sk + J Σ Sk Sl + S D S + Σ Σ Sk aλ k Iλ k
k l>k=1 k=1 λ

where the nuclear Zeeman terms are omitted and

S = Σ Sk .
k

J is the electron exchange parameter and D the zero-field splitting tensor. D is symmetric and
traceless, i.e.

3
Σ D = 0
ii
i=1

and consequently the two zero-field splitting parameters

D = 3/2 D
33

E = 1/2 (D – D )
11 22
Landolt Börnstein

New Series II/26C
General introduction 3
completely determine the tensor. J determines the energy separation of different spin states of the N-Spin
System. For N = 2

J = E – E
triplet singlet

and for N = 3

3/2 J = E – E .
quartet doublet

Further information on the description of N-electron spin systems are found in the introductions to the
appropriate chapters.
There are many experimental techniques in both continuous wave or pulse forms for the determination
of the Spin-Hamiltonian parameters g, aλ, J, D, E. Often applied are Electron Paramagnetic or Spin
Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-
Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing
effects of Chemically Induced Dynamic Nuclear or Electron Polarization (CIDNP, CIDEP), Optical
Detection of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser
Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (µSR). The
extraction of data from the spectra varies with the methods, the systems studied and the physical state of
the sample (gas, liquid, unordered or ordered solid). For the detailed procedures the reader is referred to
the original literature and the monographs (D) listed below. Further, effective magnetic moments µ of
eff
free radicals are often known from static susceptibilities. In recent years such determinations are rare, but
they may be mentioned in the tables. A list of references covering the abundant earlier literature is found
in: Magnetic Properties of Free Radicals, Landolt-Börnstein, New Series, Group II, Vol. 1, Berlin:
Springer, 1965, Vols. 9a–9d2, Berlin: Springer, 1977–80 and Vols. 17a–h, Berlin: Springer, 1986–90.

C Arrangements of the tables

For the display of the data the volumes are divided into chapters on specific classes of compounds. These
are prepared by authors who are experts in these fields. Each chapter is headed by an introduction which
specifies the coverage, the ordering of substances, details of the data arrangement, the special general
literature and special abbreviations, if necessary. The tables are followed by the references belonging to
the individual entries. A small overlap between chapters has been allowed for reasons of
comprehensiveness and consistency. An index of all substances appears at the end of the last subvolume
of the series.
Within the individual chapters the data are arranged in columns in a manner, which, as far as possible,
holds for all chapters:
The first column (Substance) describes the structure of the species. It contains the gross formula
including charge and, where appropriate, information on the electronic state. Whenever possible a
structural formula is also given or a reference to a structural formula displayed elsewhere.
The second column (Generation/Matrix or Solvent/Method/T [K]) briefly describes the method of
generation of the species, the matrix or solvent in which it was studied, the experimental technique
applied to obtain the magnetic properties and the temperature for which the data are valid in Kelvin. 300
normally means an unspecified room temperature.
The third column contains the magnetic properties. For radicals it is headed g-Factor, a-Value [mT],
and the information on g is given first where available. If only one value is listed it is the isotropic g-
factor. If four values are listed the first three are the principal elements of g, the fourth denoted by “is:” is
the mean value. For axially symmetric g occasionally only the two principal elements and the isotropic g
are listed. These entries are followed by the information on the hyperfine interactions. It states the nuclei
by their chemical symbols, a left upper index denoting the isotope, if necessary. Numbers preceding the
chemical symbols note the number of equivalent nuclei, i.e. 3H means three equivalent 1H nuclei. Right
hand indices of the symbols or information given in parentheses point to positions of the nuclei in the
structural formulae. The a-values are displayed following the symbols. If only one value is given it is the
Landolt Börnstein
New Series II/26C
4 General introduction
isotropic part of the coupling tensor. If four values are listed the first three are the principal values of a,
the fourth denoted by “is:” is the isotropic part. Signs are given if they are known. Errors are quoted in
parentheses after the values in units of the last digit quoted for the value.
In the tables on high spin systems the third column also gives the available information on the
exchange and zero-field parameters J, D and E, and the heading is changed accordingly. Further, in some
tables where liquid-crystal data are reported column five may give besides the isotropic coupling constant
a the shift ∆a caused by the partial alignment. It is related to the elements of a by

∆a = 2/3 Σ O a
ij ji
i, j

where O are the elements of the traceless ordering matrix. For the extraction of the parameters from the
ij
spectra the original literature and the introduction to the individual chapters should be consulted. Finally,
for radicals observed in the gas phase the third column lists the hyperfine coupling constants a, b, c, d.
The general unit of a-values in column three is milli-Tesla (mT) with the occasional and well founded
exception of Mc/s (MHz) for a few cases. The original literature often quotes coupling constants in Gauss
and the conversion is

1 mT = 10 Gauss = 28.0247 (g/g) Mc/s .
e

For the interaction energy terms J, D and E the unit cm–1 is used with 1 cm–1 = c –1 · 1 c/s where c is the
0 0
vacuum light velocity.
The fourth column (Ref./Add. Ref.) lists the reference from which the data of the former columns are
taken. This reference may be followed by additional but secondary references to the same subject. All
references belonging to one chapter are collected in a bibliography at the end of this chapter, and the
respective pages are referred to at the top of each page.
Throughout the chapters footnotes give additional information or explanations. A list of general
symbols and abbreviations are found at the end of each subvolume and the last subvolume contains an
index.

Landolt Börnstein

New Series II/26C
General introduction 5
D Monographs, reviews and important conference proceedings

67Atk Atkins, P.W., Symons, M.C.R.: The Structure of Inorganic Radicals, Amsterdam: Elsevier,
1967.
67Ays Ayscough, P.B.: Electron Spin Resonance in Chemistry, London: Methuen, 1967.
67Car Carrington, A., McLauchlan, A.D.: Introduction to Magnetic Resonance, Harper International,
1967.
67Ger Gerson, F.: Hochauflösende ESR-Spektroskopie, Weinheim: Verlag Chemie, 1967.
67Poo Poole, C.P., Jr.: Electron Spin Resonance, New York: Interscience, 1967.
68Alg Alger, R.S.: Electron Paramagnetic Resonance, New York: Interscience, 1968.
68Kai Kaiser, E.T., Kevan, L.: Radical Ions, New York: Interscience, 1968.
70Sch Scheffler, K., Stegmann, H.B.: Elektronenspinresonanz, Berlin, Heidelberg, New York:
Springer, 1970.
72Ges Geschwind, S. (ed.): Electron Paramagnetic Resonance, New York: Plenum Press, 1972.
72McL McLauchlan, K.A.: Magnetic Resonance, Oxford: Clarenden Press, 1972.
72Muu Muus, L.T., Atkins, P.W. (eds.): Electron Spin Relaxation in Liquids, New York: Plenum
Press, 1972.
72Swa Swartz, H.M., Bolton, J.R., Borg, D.C.: Biological Applications of Electron Spin Resonance,
New York: Wiley, 1972.
72Wer Wertz, J.E., Bolton, J.R.: Electron Spin Resonance, New York: McGraw-Hill, 1972.
73Ath Atherton, N.M.: Electron Spin Resonance, Theory and Applications, New York: Halsted,
1973.
73Buc Buchachenko, A.L., Wassermann, A.L.: Stable Radicals, Weinheim: Verlag Chemie, 1973.
73Koc Kochi, J.K. (ed.): Free Radicals, New York: Wiley, 1973.
73Nor Norman, R.O.C., Ayscough, P.B., Atherton, N.M., Davies, M.J., Gilbert, B.C. (eds.): Electron
Spin Resonance, Specialist Periodical Reports, London: The Chemical Society, 1973ff.
73Pak Pake, G.E., Estle, T.L.: The Physical Principles of Paramagnetic Resonance, 2nd ed., Reading:
Benjamin, 1973.
74Car Carrington, A.: Microwave Spectroscopy of Free Radicals, London: Academic Press, 1974.
77Box Box, H.C.: Radiation Effects, ESR and ENDOR Analysis, New York: Academic Press, 1977.
77Muu Muus, L.T., Atkins, P.W., McLauchlan, K.A., Pedersen, J.B. (eds.): Chemically Induced
Magnetic Polarization, Dordrecht: Reidel, 1977.
77Ran Ranby, B., Rabek, J.F.: ESR Spectroscopy in Polymer Research, Berlin: Springer, 1977.
78Har Harriman, J.E.: Theoretical Foundations of Electron Spin Resonance, New York: Academic
Press, 1978.
78Sli Slichter, C.P.: Principles of Magnetic Resonance, Berlin: Springer, 1978.
78Sym Symons, M.C.R.: Chemical and Biochemical Aspects of Electron Spin Resonance
Spectroscopy, New York: van Nostrand-Reinhold, 1978.
79Dor Dorio, M.M.. Freed, J.H. (eds.): Multiple Electron Resonance Spectroscopy, New York:
Plenum Press, 1979.
79Kev Kevan, L., Schwartz, R.: Time Domain Electron Spin Resonance, New York: Wiley, 1979.
79Shu Shulman, R.G. (ed.): Biological Applications of Magnetic Resonance, New York: Academic
Press, 1979.
80Ber Bertini, I., Drago, R.S.: ESR and NMR of Paramagnetic Species in Biological and Related
Systems, Hingham: Kluver Boston, 1980.
80Gor Gordy, W.: Theory and Applications of Electron Spin Resonance, New York: Wiley, 1980.
80Ily Il’yasov, A.V., Kargin, Yu.M., Morozova, I.D.: EPR Spectra of Organic Radical Ions,
Moscow: Nauka, 1980.
80Mol Molin, Yu.N., Salikhov, K.M., Zamaraev, K.I.: Spin-Exchange – Principles and Applications
in Chemistry and Biology, Berlin: Springer-Verlag, 1980.
82Sch Schweiger, A.: Structure and Bonding, Vol. 51: Transition Metal Complexes: Electron
Nuclear Double Resonance of Transition Metal Complexes with Organic Ligands, Berlin:
Springer-Verlag, 1982.

Landolt Börnstein
New Series II/26C
6 General introduction
83Car Carrington, A., Hudson, A., McLauchlan, A.D.: Introduction to Magnetic Resonance, 2nd ed.,
New York: Chapman and Hall, 1983.
83Poo Poole, C.P.: Electron Spin Resonance, 2nd ed., New York: Wiley, 1983.
83Wal Walker, D.C.: Muon and Muonium Chemistry, Cambridge: Cambridge University Press,
1983.
83Wel Weltner, W., Jr.: Magnetic Atoms and Molecules, New York: van Nostrand-Reinhold, 1983.
84Kok Kokorin, A.I., Parmon, V.N., Shubin, A.A.: Atlas of Anisotropic EPR Spectra of Nitric Oxide
Biradicals, Moscow: Nauka, 1984.
84Sal Salikhov, K.M., Molin, Yu.N., Sagdeev, R.Z., Buchachenko, A.L.: Spin Polarization and
Magnetic Effects in Radical Reactions, Amsterdam: Elsevier, 1984.
85Dal Dalton, L.R. (ed.): EPR and Advanced EPR Studies of Biological Systems, Boca Raton: CRC
Press, 1985.
85Ily Il’yasov, A.V., Morozova, I.D., Vafina, A.A., Zuev, M.B.: EPR Spectra and Stereochemistry
of Phosphorous-Containing Free Radicals, Moscow: Nauka, 1985.
85Kir Kirmse, R., Stach, J.: ESR-Spectroskopie, Anwendungen in der Chemie, Berlin: Akademie-
Verlag, 1985.
86Wer Wertz, J.E., Bolton, J.R.: Electron Spin Resonance: Elementary Theory and Practical
Applications, New York: Chapman and Hall, 1986.
88Kur Kurreck, H., Kirste, B., Lubitz, W.: Electron Nuclear Double Resonance Spectroscopy of
Radicals in Solution, Weinheim: VCH Verlagsgesellschaft, 1988.
88Rod Roduner, E.: The Positive Muon as Probe in Free Radical Chemistry, Berlin: Springer-Verlag,
1988.
88Wau Waugh, J.S. (ed.): Advances in Magnetic Resonance, Vol. 12, San Diego: Academic Press,
1988.
89Hof Hoff, A.J. (ed.): Advanced EPR, Applications in Biology and Biochemistry, Amsterdam:
Elsevier, 1989.
90Pla Platz, M.S. (ed.): Kinetics and Spectroscopy of Carbenes and Biradicals, New York: Plenum,
1990.
91IHa I’Haya, Y.J. (ed.): Spin Chemistry, Tokyo: The Oji International Conference on Spin
Chemistry, 1991.
92Bag Bagguley, D.M.S. (ed.): Pulsed Magnetic Resonance: NMR, ESR and Optics, a Recognition
of E.L. Hahn, Oxford: Oxford University Press, 1992.
94Wei Weil, J.A., Bolton, J.R., Wertz, J.E.: Electron Paramagnetic Resonance: Elementary Theory
and Practical Applications, New York: Wiley, 1994.
95Low Lowe, D.J. (ed.): ENDOR and EPR of Metalloproteins, Berlin: Springer-Verlag, 1995.
95Sut Sutcliffe, L.H. (ed.): Electron Spin Resonance, the Fiftieth Anniversary of Zavoiski’s
Discovery of Electron Resonance Spectroscopy (in Magn. Reson. Chem 33 (1995) Spec.
Issue), Chichester: Wiley, 1995.
96Bre Brey, W.S. (ed.): Magnetic Resonance in Perspective: Highlights of a Quarter Century, San
Diego: Academic Press, 1996.
96Hen Henry, Y., Guissani, A., Ducastel, B. (eds.): Nitric Oxide Research from Chemistry to
Biology: EPR Spectroscopy of Nitrosylated Compounds, Berlin: Springer-Verlag, 1996.
96Sal Salikhov, K.M. (ed.): Magnetic Isotope Effect in Radical Reactions, Vienna: Springer-Verlag,
1996.
98Eat Eaton, G.S., Eaton, S.S., Salikhov, K.M. (eds.): Foundations of Modern EPR, Singapore:
World Scientific, 1998.
98Nag Nagakura, S., Hayashi, H.; Azumi, T. (eds.): Dynamic Spin Chemistry, Tokyo: Kodansha
Ltd., 1998.
99Poo Poole, C.P.: Handbook of Electron Spin Resonance, Vol. 2, Secausus: AIP, 1999.
00Ber Berliner, L.J., Eaton, G.R., Eaton, S.S. (eds.): Distance Measurements in Biological Systems
by EPR, New York: Plenum, 2000.
01Sch Schweiger, A., Jeschke, G.: Principles of Pulse Electron Paramagnetic Resonance
Spectroscopy, Oxford: Oxford University Press, 2001.

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New Series II/26C
Ref. p. R1] 9 Nitrogen-centered monoradicals, biradicals and high-spin nitrenes 7
9 Nitrogen-centered monoradicals, biradicals
and high-spin nitrenes
F.A. Neugebauer

9.1 Introduction

9.1.1 General remarks

In continuation of Chap. 5 in Landolt-Börnstein, New Series, Vol. II/17c, the literature has been surveyed
beginning with the year 1987 (except the references published in Vol. II/17c) and ending in 2001. Data of
the year 2001 may be not complete. The references of nitrenes, these species have not been covered yet,
start from 1962. Main sources for references have been “Chemical Abstracts”, the specialist periodical
reports “Electron Spin Resonance” (The Royal Society of Chemistry, London), and the bibliographies of
the surveyed references.
Sections 9.2–9.10 list uncharged nitrogen-centered radicals of the basic structure
.
R N R
(R represents hydrogen, carbon, or a heteroatom)
and σ-type radicals of the general structures
. . .
+ _
R C N R N N R C N O
2 2 .
The notation of proton positions in the radical structure follows the usual way. Contrary to common
practice, however, the same notation is also used for heavier atoms (C, N, O, P, etc.). The central atom is
defined X :
z
. .
C C C C N O C C N O
α z α β β α z
Hε Hδ Hγ Hβ Hγ Hγ
.
Section 9.11 gives data of nitrogen-centered biradicals for the period 1986–2001 including a few
examples with different kinds of radical centers one being nitrogen (R1N•⋅⋅⋅⋅⋅C•R2R3, R1N•⋅⋅⋅⋅⋅N(O•)R2,
R1N•⋅⋅⋅⋅⋅O•). This section continues Landolt-Börnstein, New Series, Vol. II/17h, Sect. 21.3 “Nitrogen-
centered polyradicals”.
In addition, high spin mono- and polynitrenes, the nitrogen analogues of carbenes, have been taken
up. Their data are compiled in Sect. 9.12 (for reviews see [71Was1], [95Lah1], [96Fuk1]).
Analogous to organic polyradicals, high spin mono- and polynitrenes are molecules with N unpaired
electrons, which are described by the spin Hamiltonian in the introduction, Sect. IB, of this volume. The
spin Hamiltonian, derived by Reitz and Weisman [60Rei1], is based on a particular model of the
electronic structure of polyradicals. The authors assume, that a polyradical with N unpaired electrons can
be divided into N segments. To each segment proper spatial and spin functions are assigned. The electron
spin operator S(k) refers to segment k. It is assumed that the corresponding spatial function vanishes at
segment j ≠ k and the overlap may be neglected.
The zero-field splitting parameters D and E characterize the magnetic dipole interaction of the
unpaired electrons in the absence of an external field ([73Ath1], [83Poo1], [85Kir1], [86Wer1]).
D provides information on the mean distance r of the unpaired electrons in biradicals and on the amount
Landolt-Börnstein
New Series II/26C
8 9.1 Introduction [Ref. p. R1
of delocalization in nitrenes with a conjugated π system. The symmetry parameter E measures the
difference of the magnetic dipole interaction along the x and y axes and allows to estimate the bond angle
at the nitrene center. The z axis is defined along the rotational axis. In molecules with high symmetry, e.g.
in a linear nitrene, the value of E is zero due to cancellation of the x and y terms:
D ∝ [(r2 − 3 z2)/r5] ~ 1/r3 , E ∝ [(y2 − x2)/r5] .
Transverse field muon spin rotation (FT-µSR) has enabled the study of a wide range of organic
radicals, formed by addition of the light hydrogen isotope muonium (Mu ≡ µ+e−) to unsaturated
molecules during irradiation with positive muons (µ+). Muon-electron hyperfine coupling constants are
related to the radical structures in the same way as corresponding hydrogen-electron couplings of
analogous H-substituted radicals. Reduction of a(Mu) by the muon/proton relative magnetic moments,
µµ/µp = 3.1833, gives a(Mu)⋅µp/µµ values [in the tables Mu(µp/µµ)], which can be compared with a(H)
data of hydrogen in equivalent positions. Furthermore, avoided-level-crossing muon spin resonance
(ALC-µSR) allows the determination of other nuclear hyperfine coupling constants, e.g. a(H), a(D),
a(13C), a(F).

9.1.2 Arrangement of tables

The arrangement of the tables corresponds essentially to that of Chap. 5 in Vol. II/17c.The monoradicals
are divided into two major groups: Radicals which generally are of π-electronic structure (Sects. 9.2–9.8)
and σ-type radicals (Sects. 9.9–9.10). Data of nitrogen-centered biradicals are given in Sect. 9.11. The
section “High-spin mono- and polynitrenes” (Sect. 9.12) has been divided into the subsections
mononitrenes (Sect. 9.12.1), mononitrenes and additional radicals (Sect. 9.12.2), quinonoidal dinitrenes
(Sect. 9.12.3), dinitrenes (Sect. 9.12.4), and polynitrenes (Sect. 9.12.5). The quinonoidal dinitrenes
represent a link between nitrogen-centered biradicals and dinitrenes. In relation to their formal diiminyl
structure the quinonoidal dinitrenes could also have been taken up in the biradical section, Sect. 9.11.
Since in their generation primarily dinitrenes are formed followed by immediate spin pairing, these
species have been placed into the nitrene section, Sect. 9.12.
Most of these sections are further divided into subgroups of acyclic, monocyclic, and polycyclic
radicals. Within the substituents R, hydrogen precedes carbon and carbon precedes heteroatom. Carbon
substituents are arranged in the order: primary alkyl, secondary alkyl, tertiary alkyl, vinyl, aryl, cyano,
acyl, acyloxy, etc. Substituents with leading heteroatom are ordered alphabetically to the chemical
symbol, i.e. Al, B, Br, Cl, Co, F, Ga, Ge, I, Mn, N, O, P, Pb, Re, S, Se, Si, Sn, Te, etc.
For some radicals the magnetic properties have been determined for different molecular environments
or temperatures. In these cases the display of the data follows the order: gas phase, solution (with
increasing polarity of the solvent), matrix, single crystal, polycrystalline. For the same environment and
different temperatures they are arranged according to increasing temperatures.

Landolt-Börnstein
New Series II/26C
Ref. p. R1] 9 Nitrogen-centered monoradicals, biradicals and high-spin nitrenes 9
9.1.3 Abbreviations

General:

add. addition MNDO modified neglect of differential
ALC-µSR avoided-level-crossing muon overlap
spin resonance (µLCR) MO molecular orbital
AM1 Austin method 1 Mu muonium (µ+e−)
av average n neutron
ax axial NMR nuclear magnetic resonance
CI configuration interaction ox. oxidation
CIDNP chemically induced dynamic pH pH-value
nuclear polarization phot. photolysis
CNDO complete neglect of differential overlap PM3 parametric method 3
corresp. corresponding red. reduction
DFT density functional theory RT room temperature
e electron SCF self consistent field theory
E “entgegen” = opposite (anti) SOMO single occupied orbital
EIE ENDOR induced ESR (FSE) theor. theoretical
ENDOR electron nuclear double resonance TR-ESR time-resolved ESR
eq equatorial TRIPLE general and (or) special triple
ESEEM electron spin echo envelope resonance
modulation UHF unrestricted Hartree-Fock method
ESR electron spin resonance UV ultraviolet
eV electron volt v volume
FSE field swept ENDOR (EIE) wt weight
hfs hyperfine splitting X X-ray
HMO Hückel molecular orbital Z “zusammen” = together (syn)
INDO intermediate neglect of γ γ-radiation
differential overlap µ+ positive muon
irr. irradiation µLCR muon level-crossing resonance
is isotropic (ALC-µSR)
MINDO modified intermediate neglect µSR muon spin resonance
of differential overlap

Substances or part of substances:

ACN acetonitrile
DTBNB 3,5-di-tert-butyl-1-nitrosobenzene
dibenzo-18-crown-6 2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene
DME 1,2-dimethoxyethane
DMF N,N-dimethylformamide
DMSO dimethyl sulfoxide
DTBP di-tert-butyl peroxide
HMPTA hexamethylphosphoric triamide
kryptofix®222 1,10-diaza-4,7,13,16,21,24-hexaoxabicyclo[8.8.8]hexacosane
MTHF 2-methyltetrahydrofuran
TTBNB 2,4,6-tri-tert-butyl-1-nitrosobenzene
TBO• tert-butoxy radical
THF tetrahydrofuran
TMS tetramethylsilane
Landolt-Börnstein
New Series II/26C
9 Nitrogen-centered monoradicals, biradicals and high-spin nitrenes R1
9.13 References for 9

9.13.1 Review articles

60Rei1 Reitz, D.C., Weisman, S.I.: J. Chem. Phys. 33 (1960) 700–704.
71Was1 Wasserman, E.: Electron spin resonance of nitrenes. Prog. Phys. Org. Chem. 8 (1971) 319–
336.
73Ath1 Atherton, N.M.: Electron Spin Resonance, Theory and Applications, New York: Halsted,
1973.
83Poo1 Poole Jr., C.P.: Electron Spin Resonance, New York: John Wiley & Sons, 1983.
85Kir1 Kirmse, R., Stach, J.: In: ESR-Spektroskopie, Berlin: Akademie-Verlag, 1985.
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