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\begin{document}

\title{Gas-Phase Smiles Rearrangement of ortho-Nitro-substituted Diaryliodonium
Cations and Their Mechanistic Insights}



\author[1]{Haoyang Wang}%
\author[2]{Wu-Zhi Wei}%
\author[3]{Cheng Pan}%
\author[1]{Ling Lin}%
\author[3]{Jianwei Han}%
\affil[1]{Chinese Academy of Sciences Shanghai Institute of Organic Chemistry}%
\affil[2]{University of Shanghai for Science and Technology}%
\affil[3]{East China University of Science and Technology}%


\vspace{-1em}



  
  \date{May 25, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
\textbf{Rationale}: Diaryliodonium salts are useful electrophilic
reagents in organic chemistry, finding extensive applications in
arylations and photo-induced polymerizations. However, the comprehensive
mechanistic investigations, particularly concerning the mass
spectrometric behaviors of diaryliodonium salts, are relatively scarce
in the literatures. \textbf{Methods}: Diaryliodonium salts could be
readily ionized in ESI-MS to give {[}Ar \textsuperscript{1}-I
\textsuperscript{+}-Ar \textsuperscript{2}{]}, and the high-resolution
ESI-MS/MS experiments were conducted to investigate their gas-phase
chemical reactions. \textbf{Results}: Investigations on ESI-MS/MS of
{[}Ar \textsuperscript{1}-I \textsuperscript{+}-Ar
\textsuperscript{2}{]} revealed two major fragmentation patterns: 1)
Reductive elimination resulting the diaryl coupling product ion {[}Ar
\textsuperscript{1}-Ar \textsuperscript{2}{]} \textsuperscript{+*} by
the loss of I. 2) Generating aryl cations {[}Ar \textsuperscript{1}{]}
\textsuperscript{+} or {[}Ar \textsuperscript{2}{]} \textsuperscript{+}
through cleavage of the C--I bonds. We unrevealed that the introduction
of NO \textsubscript{2} into Ar \textsuperscript{2} of {[}Ar
\textsuperscript{1}-I \textsuperscript{+}-Ar \textsuperscript{2}{]}
could lead to an unexpected fragmentation ion {[}Ar
\textsuperscript{1}O{]} \textsuperscript{+} in MS/MS, arising from an
O-atom transfer process from NO \textsubscript{2} to Ar
\textsuperscript{1}. Particularly, when NO \textsubscript{2} was
\emph{ortho}-positioned to the iodine in Ar \textsuperscript{2}, the
{[}Ar \textsuperscript{1}O{]} \textsuperscript{+} sometimes exhibited
dominant behavior. \textbf{Conclusions}: Comprehensive ESI-MS/MS studies
and theoretical calculations provided strong support for the O-atom
transfer mechanistic pathway: {[}Ar \textsuperscript{1}-I
\textsuperscript{+}-( \emph{o}-NO \textsubscript{2}-Ar
\textsuperscript{2}){]} initially underwent a Smiles rearrangement to
the intermediate {[}Ar \textsuperscript{1}-O-( \emph{o}-NO-Ar
\textsuperscript{2}I){]} \textsuperscript{+}, which subsequently
dissociated to {[}Ar \textsuperscript{1}O{]} \textsuperscript{+} or {[}
\emph{o}-NO-Ar \textsuperscript{2}I{]} \textsuperscript{+*}. Herein, we
proposed an unexpected '' \emph{ortho}-effect'' in the gas-phase
fragmentation reaction of {[}Ar \textsuperscript{1}-I
\textsuperscript{+}-( \emph{o}-NO \textsubscript{2}-Ar
\textsuperscript{2}){]}, in which the crucial determinant factor for the
aryl migration was identified as the Smiles rearrangement reaction.%
\end{abstract}%



\sloppy


\textbf{Gas-Phase Smiles Rearrangement of \emph{ortho}-Nitro-substituted
Diaryliodonium Cations and Their Mechanistic Insights}

Wu-Zhi Wei\textsuperscript{1, 2}, Cheng Pan\textsuperscript{3}, Ling
Lin\textsuperscript{2}, Jianwei Han\textsuperscript{3,*}, Hao-Yang
Wang\textsuperscript{2,*}

\textsuperscript{1}School of Materials and Chemistry, University of
Shanghai for Science and Technology, Shanghai, People's Republic of
China

\textsuperscript{2}Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, Shanghai, People's Republic of China

\textsuperscript{3}Key Laboratory for Advanced Materials and Feringa
Nobel Prize Scientist Joint Research Center, Department of Fine
Chemistry and Institute of Fine Chemicals, School of Chemistry and
Molecular Engineering, East China University of Science and Technology,
Shanghai, People's Republic of China

Correspondence:

Jianwei Han, Key Laboratory for Advanced Materials and Feringa Nobel
Prize Scientist Joint Research Center, Department of Fine Chemistry and
Institute of Fine Chemicals, School of Chemistry and Molecular
Engineering, East China University of Science and Technology, Shanghai,
200237, People's Republic of China. Email: jianweihan@ecust.edu.cn

Hao-Yang Wang, Shanghai Institute of Organic Chemistry, Chinese Academy
of Sciences, Shanghai, 200032, People's Republic of China. Email:
haoyangwang@sioc.ac.cn

\textbf{Rationale} : Diaryliodonium salts are useful electrophilic
reagents in organic chemistry, finding extensive applications in
arylations and photo-induced polymerizations. However, the comprehensive
mechanistic investigations, particularly concerning the mass
spectrometric behaviors of diaryliodonium salts, are relatively scarce
in the literatures.

\textbf{Methods} : Diaryliodonium salts could be readily ionized in
ESI-MS to give
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]},
and the high-resolution ESI-MS/MS experiments were conducted to
investigate their gas-phase chemical reactions.

\textbf{Results} : Investigations on ESI-MS/MS of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
revealed two major fragmentation patterns: 1) Reductive elimination
resulting the diaryl coupling product ion
{[}Ar\textsuperscript{1}-Ar\textsuperscript{2}{]}\textsuperscript{+*} by
the loss of I. 2) Generating aryl cations
{[}Ar\textsuperscript{1}{]}\textsuperscript{+} or
{[}Ar\textsuperscript{2}{]}\textsuperscript{+} through cleavage of the
C--I bonds. We unrevealed that the introduction of
NO\textsubscript{2}into Ar\textsuperscript{2} of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
could lead to an unexpected fragmentation ion
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} in MS/MS, arising from
an O-atom transfer process from NO\textsubscript{2} to
Ar\textsuperscript{1}. Particularly, when NO\textsubscript{2}
was\emph{ortho} -positioned to the iodine in Ar\textsuperscript{2}, the
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} sometimes exhibited
dominant behavior.

\textbf{Conclusions} : Comprehensive ESI-MS/MS studies and theoretical
calculations provided strong support for the O-atom transfer mechanistic
pathway: {[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} initially underwent a
Smiles rearrangement to the intermediate
{[}Ar\textsuperscript{1}-O-(\emph{o}
-NO-Ar\textsuperscript{2}I){]}\textsuperscript{+}, which subsequently
dissociated to {[}Ar\textsuperscript{1}O{]}\textsuperscript{+} or
{[}\emph{o} -NO-Ar\textsuperscript{2}I{]}\textsuperscript{+*}. Herein,
we proposed an unexpected ''\emph{ortho} -effect'' in the gas-phase
fragmentation reaction of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]}, in which the crucial
determinant factor for the aryl migration was identified as the Smiles
rearrangement reaction.

\textbf{Key Words:} Smiles Rearrangement, Nitro-substituted
Diaryliodonium salts, ESI-MS/MS, O-atom transfer reaction

\textbf{1 Introduction}

Hypervalent iodine compounds (HICs) possess remarkable advantageous
characteristics, including facile synthesis, low toxicity, and
environmental friendliness, making them versatile tools in a wide range
of organic reactions, such as functionalizations, rearrangements,
aryl-coupling and cyclization reactions.\textsuperscript{1-3} The
notable feature of HICs is its ability to exhibit similar reactivity to
the transition metal reagents due to the changes in valence states,
thereby providing cost-effective alternatives to expensive
organometallic catalysts and toxic heavy metal-based
oxidants.\textsuperscript{4,5} Within this category of HICs,
diaryliodonium salts, also referred to as
diaryl-\selectlanguage{greek}λ\selectlanguage{english}\textsuperscript{3}-iodines following IUPAC
nomenclature,\textsuperscript{6} stand out as a unique class of HICs
renowned for their utility as highly electrophilic arylating reagents
under mild reaction conditions.\textsuperscript{7} Apart from their
synthetic applications, diaryliodonium salts play a significant role in
semiconductor photolithography. For instance, the
bis(4-(1,1-dimethylethyl)phenyl)iodonium salt is a type of useful ionic
photoacid generators (PAGs). Additionally, the aryliodonium salts find
widespread usage in photo-redox catalysis and serve as cationic
photo-initiators in polymerization reactions, contributing to the
production of diverse materials such as adhesives, coatings, composites,
dental materials.\textsuperscript{8-11}

In 1983, Gross et al. pioneered the use of mass spectrometry to
investigate the gas-phase reaction between benzene radical cations and
alkyl iodides, leading to the proposal of the
C\textsubscript{9}H\textsubscript{13}I\textsuperscript{+}intermediate.\textsuperscript{12}
Six years later, the same group described the six fragmentation
processes involving iodonium radical cations.\textsuperscript{13} In
1989, Busch et al. employed fast atom bombardment (FAB) and secondary
ion mass spectrometry (SIMS) to provide further
insights.\textsuperscript{9,10} Then, in 1992, Busch group combined FAB
with semi-empirical calculations to examine iodonium salts and pointed
out that \emph{ortho} -hindered iodonium salts lacked the rearrangement
process.\textsuperscript{11} In 1995, Sam et al. made significant
contributions by employing electrospray ionization mass spectrometry to
investigate the oxidation of PhIO in methanol.\textsuperscript{14} In
1999, Ochiai et al. made a noteworthy discovery concerning the
dimerization of iodine(III) reagents using FAB.\textsuperscript{15}
Additionally, Silva and colleagues conducted detailed studies on the
disproportionation reaction of (diacetoxyiodo)benzene (DAIB) in
acetonitrile and methanol by employing high-resolution ESI-MS/MS
techniques.\textsuperscript{16,17} Our group intercepted and
characterized the transient reactive \selectlanguage{greek}α-λ\selectlanguage{english}\textsuperscript{3}-iodine alkyl
acetophenone intermediate using ESI-MS/MS, thus validating the reaction
mechanism proposed by Ochiai.\textsuperscript{18} Rissanen's group
dedicated to explore the role of iodonium ions in supramolecular
chemistry.\textsuperscript{19-22} Niu et al. identified the
photoproducts of bis(4-tert-butylphenyl)iodonium salts using GC-MS and
proposed a mechanism for the photolytic reaction.\textsuperscript{8}

The Smiles rearrangement is an intramolecular nucleophilic aromatic
substitution, in which the aryl group transfers within an aromatic ring
to an adjacent carbon atom.\textsuperscript{23} It is becoming
increasingly recognized that the gas-phase Smiles rearrangement is not
confined to the classical five-membered ring transition state. For
examples, both Wang and Pan proposed transition states of six-membered
rings, supported by theoretical
calculations.\textsuperscript{24-28}Additionally, Pan's group
highlighted that carbon monoxide (CO) could be eliminated through a
three-membered ring transition state.\textsuperscript{29} Concerning the
extrusion of sulfur dioxide (SO\textsubscript{2}), Lu and Irikura
suggested that this process occurred through a five-membered ring
transition state.\textsuperscript{30,31} In this case, Li proposed a
three-membered ring pathway.\textsuperscript{32} Wu et al. proposed a
Smiles rearrangement involving a four-membered ring, providing an
explanation for the loss of formaldehyde (H\textsubscript{2}CO)
following this skeletal rearrangement.\textsuperscript{33}

\textbf{Scheme 1} Schematics illustrating. (\textbf{a} ) Mass
spectrometric behaviors of nitroarenes in EI-MS: \emph{ortho} effect
of\emph{o} -nitrotoluene and rearrangement of nitrobenzene; (\textbf{b}
) Our previous work: the gas-phase rearrangement reaction from
{[}CF\textsubscript{3}-I\textsuperscript{+}-Ph{]} to
{[}PhCF\textsubscript{3}{]}\textsuperscript{+*} by loss of I;
(\textbf{c} ) This work: gas-phase reduction elimination of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
to aryl coupling product ion of
{[}Ar\textsuperscript{1}-Ar\textsuperscript{2}{]}\textsuperscript{+*}with
loss of an iodine atom and the generation of O-atom transfer product ion
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} from
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} in ESI-MS/MS.

The \emph{ortho} effect and rearrangement of nitroarenes in EI-MS have
previously been investigated (\textbf{Scheme 1a}
),\textsuperscript{34,35} and we have studied on gas-phase
intramolecular aryltrifluoromethylation of
phenyl(trifluoromethyl)iodonium cation via loss of an iodine atom
(\textbf{Scheme 1b} ).\textsuperscript{36} However, our recent findings
have unveiled that the introduction of NO\textsubscript{2} to
diaryliodonium salts had introduced an entirely new dimension to the
fragmentation patterns, resulting in the unexpected O-atom transfer
product ion {[}Ar\textsuperscript{1}O{]}\textsuperscript{+} from
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} (\textbf{Scheme 1c} ).
Surprisingly, the exploration of the fragmentation patterns of
nitro-substituted diaryliodonium cations was limited in the literature.
Hence, we comprehensively investigated various diaryliodonium cations
using high-resolution electrospray ionization tandem mass spectrometry
(ESI-MS/MS) and provided mechanistic insights into the understanding of
their gas-phase reactions through theoretical calculations. The research
results would be beneficial for the research for the chemical and mass
spectrometric studies of these diaryliodonium salts.

\textbf{2 EXPERIMENTAL}

\textbf{2.1 Chemicals and Reagents}

Methanol and dichloromethane (DCM) were purchased from Merck KGaA
(Darmstadt, Germany). All of the samples were provided by Jianwei Han
research group at East China University of Science and Technology,
Shanghai. The preparation methods could be referred to relevant
articles.\textsuperscript{37-39} Some structures of the diaryliodonium
salts (\textbf{M} ) were given in \textbf{Scheme 2} , while the rest
structures were shown in \textbf{Scheme S1} , and they were labeled for
convenience as \textbf{1} to \textbf{54} . Salts \textbf{24} ,
\textbf{33}and \textbf{34} contained OTs\textsuperscript{--} as counter
anion, the rest diaryliodonium salts contained OTf\textsuperscript{--}
as counter anion. DCM was a suitable aprotic solvent for preparing the
solution of diaryliodonium salts. In most cases, the diaryliodonium
salts were dissolved in DCM to prepare the sample solution at
concentration of 1\textasciitilde{}10 \selectlanguage{greek}µ\selectlanguage{english}g/mL for mass spectrometric
analysis.

\textbf{Scheme 2} Chemical structures of some diaryliodonium salts
(\textbf{1} \textasciitilde{}\textbf{16} ) in this study, Mes =
mesitylene.

\textbf{2.2 Mass Spectrometry}

The high-resolution ESI-MS and subsequent high-resolution ESI-MS/MS
experiments were performed on a Q Exactive HF Orbitrap mass spectrometer
(Thermo Fisher Scientific Inc., Waltham, MA, USA) equipped with a
standard ESI interface. Nitrogen was used as the sheath gas, auxiliary
gas and collision gas. The basic ESI conditions were: spray voltage,
3500 V; capillary temperature, 275 \selectlanguage{ngerman}°C; probe heater temperature, 300 °C;
sheath gas flow rate, 35 arbitrary units; auxiliary gas flow rate, 10
arbitrary units; while the selected collision energy depended on the
dissociation capability of the precursor ions. Data acquisition and
analysis were carried out with the Xcalibur software package (version
4.2.47, Thermo Scientific).

\textbf{3 RESULTS AND DISCUSSION}

\textbf{3.1 The general fragmentation patterns of diaryliodonium
cations}

Firstly, we studied some representative diaryliodonium salts (\textbf{1}
\textasciitilde{}\textbf{4} , structures were shown in\textbf{Scheme 2}
). These diaryliodonium salts could be easily ionized by loss of
OTf\textsuperscript{--} to give diaryliodonium cations {[}\textbf{M}
--OTf{]}\textsuperscript{+} in the form of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
and their ESI-MS/MS were shown in \textbf{Figure 1} . According to the
previous reports and our studies of these
spectra,\textsuperscript{13,36,40} we proposed two major fragmentation
patterns of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
cations: 1) Reductive elimination\textsuperscript{10-13,36} to give
diaryl coupling product ions
{[}Ar\textsuperscript{1}-Ar\textsuperscript{2}{]}\selectlanguage{english}\textsuperscript{+*} by
loss of an iodine atom, followed by the generation of further fragment
ions from these species. Such gas-phase reductive elimination
rearrangement reaction was similar to our previous finding of the
process from {[}CF\textsubscript{3}-I\textsuperscript{+}-Ph{]}
at\emph{m/z} 273 to {[}PhCF\textsubscript{3}{]}\selectlanguage{english}\textsuperscript{+*}
at\emph{m/z} 146 by loss of an iodine atom in ESI-MS/MS of
{[}CF\textsubscript{3}-I\textsuperscript{+}-Ph{]};\textsuperscript{36}2)
The C--I bond cleavage to produce aryl cations
{[}Ar\textsuperscript{1}{]}\textsuperscript{+} or
{[}Ar\textsuperscript{2}{]}\textsuperscript{+}, which might further give
{[}Ar\textsuperscript{1}+H\textsubscript{2}O{]}\textsuperscript{+} or
{[}Ar\textsuperscript{2}+H\textsubscript{2}O{]}\textsuperscript{+} and
{[}Ar\textsuperscript{1}+N\textsubscript{2}{]}\textsuperscript{+} or
{[}Ar\textsuperscript{2}+N\textsubscript{2}{]}\textsuperscript{+} adduct
ions,\textsuperscript{41} along with their respective fragment ions.
This type fragmentation has also be found in the in ESI-MS/MS of
{[}CF\textsubscript{3}-I\textsuperscript{+}-Ph{]}, in which C--I bond
cleavage of {[}CF\textsubscript{3}-I\textsuperscript{+}-Ph{]}
at\emph{m/z} 273 gave rise to {[}Ph{]}\textsuperscript{+} at \emph{m/z}
77 or {[}PhI{]}\selectlanguage{english}\textsuperscript{+*} at \emph{m/z} 204 by loss of
CF\textsubscript{3}.\textsuperscript{36}

Taking the MS/MS of {[}\textbf{1} --OTf{]}\textsuperscript{+} as an
illustrative example, we observed that the reductive elimination of
{[}Ph-I\textsuperscript{+}-Ph{]} gave diaryl coupling product ion
biphenyl\selectlanguage{english}\textsuperscript{+*} at \emph{m/z} 154 rather than
I\selectlanguage{english}\textsuperscript{+*} at \emph{m/z} 127. This divergence could be
attributed to the significantly higher ionization energy of iodine
(10.45 eV) compared to biphenyl (8.16 eV).\textsuperscript{42}Meanwhile,
C--I bond cleavage of {[}Ph-I\textsuperscript{+}-Ph{]} produced
{[}Ph{]}\textsuperscript{+} at \emph{m/z} 77, along with
{[}Ph+H\textsubscript{2}O{]}\textsuperscript{+} at \emph{m/z} 95 and
{[}Ph+N\textsubscript{2}{]}\textsuperscript{+} at \emph{m/z} 105.
Notably, we did not observe the formation of
{[}PhI{]}\selectlanguage{english}\textsuperscript{+*} at \emph{m/z} 204, which could be
attributed to the higher ionization energy of PhI (8.72 eV) in
comparison to the phenyl radical (8.32
eV).\textsuperscript{42}Therefore,
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
predominantly formed diaryl coupling product ions and aryl cations in
ESI-MS/MS. The two principal fragmentation pathways of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
originating from diaryliodonium salts (\textbf{1}
\textasciitilde{}\textbf{4} ) were depicted in \textbf{Scheme 3} . The
structural assignments for fragment ions were supported by accurate mass
measurements (see in \textbf{Table S1} \textasciitilde{}\textbf{S3} ).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 1} High-resolution ESI-MS/MS of {[}\textbf{M}
--OTf{]}\textsuperscript{+}: (\textbf{a} ) \textbf{1} , (\textbf{b} )
\textbf{2} , (\textbf{c} ) \textbf{3} and (\textbf{d} )\textbf{4} .

\textbf{Scheme 3} Proposed fragmentation patterns of {[}\textbf{M}
--OTf{]}\textsuperscript{+}: (\textbf{a} ) \textbf{1} , (\textbf{b} )
\textbf{2} , (\textbf{c} ) \textbf{3} and (\textbf{d} )\textbf{4} .

When we examined diaryliodonium salt \textbf{4} with introduction of a
nitro group into Ar\textsuperscript{2}, We not only observed fragment
ions consistent with the processes outlined in \textbf{Scheme 3} but
also identified novel types of fragment ions:
{[}\emph{\textsuperscript{t}}
Bu-C\textsubscript{6}H\textsubscript{4}O{]}\textsuperscript{+}at
\emph{m/z} 149 and {[}\emph{p}
-NO-C\textsubscript{6}H\textsubscript{4}I{]}\textsuperscript{+*}at
\emph{m/z} 233 in the ESI-MS/MS of {[}(\emph{p}
-\emph{\textsuperscript{t}}
Bu-C\textsubscript{6}H\textsubscript{4})-I\textsuperscript{+}-(\emph{p}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} at
\emph{m/z} 382 (\textbf{Figure 1d} and \textbf{Scheme 3} ). These
findings strongly suggested the involvement of a gas-phase O-atom
transfer reaction from the nitro group to the aryl moiety in the
ESI-MS/MS of {[}(\emph{p} -\emph{\textsuperscript{t}}
Bu-C\textsubscript{6}H\textsubscript{4})-I\textsuperscript{+}-(\emph{p}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]}. It could
be attributed to the presence of a nitro group in Ar\textsuperscript{2}
of the diaryliodonium cations.

\textbf{3.2. Gas-phase rearrangements of nitro-substituted
diaryliodonium cations}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 2} High-resolution ESI-MS/MS of {[}\textbf{M}
--OTf{]}\textsuperscript{+}: (\textbf{a} ) \textbf{5} , (\textbf{b} )
\textbf{6} , (\textbf{c} ) \textbf{7} and (\textbf{d} )\textbf{8} .

\textbf{Scheme 4} Proposed rearrangement patterns of {[}\textbf{M}
--OTf{]}\textsuperscript{+} of salts\textbf{5}
\textasciitilde{}\textbf{7} .

Based on the observation of O-atom transfer product ion
{[}\emph{\textsuperscript{t}}
Bu-C\textsubscript{6}H\textsubscript{4}O{]}\textsuperscript{+}at
\emph{m/z} 149 from nitro-substituted diaryliodonium cation
{[}\textbf{4} --OTf{]}\textsuperscript{+}, we extended to more
diaryliodonium cations with salts \textbf{5}
\textasciitilde{}\textbf{7}as shown in \textbf{Scheme 1} , and the
spectra of the salts\textbf{5} \textasciitilde{}\textbf{7} with nitro
substituent in different position (\emph{ortho} , \emph{meta} and
\emph{para} ) of Ar\textsuperscript{2} were depicted in \textbf{Figure
2a} \textasciitilde{}\textbf{c} . To our delight,
{[}Mes-I\textsuperscript{+}-(NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]}
from salts \textbf{5} \textasciitilde{}\textbf{7} all exhibited the
O-atom transfer product ion {[}MesO{]}\textsuperscript{+} at\emph{m}
/\emph{z} 135 with high abundances in their respective MS/MS. As a
comparison, we also tested cations from salt \textbf{8} simultaneously
(\textbf{Figure 2d} ). However, the product ion
{[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135 could not be
observed in the MS/MS of {[}Mes-I\textsuperscript{+}-Mes{]} at\emph{m/z}
365. The accurate mass measurements (in \textbf{Table S1} and\textbf{S2}
) supported our explanations. These results collectively demonstrated
that the introduction of a nitro group into Ar\textsuperscript{2} of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
could give rise to new type fragmentation ions
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} by O-atom transfer
process from the nitro group in Ar\textsuperscript{2} to
Ar\textsuperscript{1} in ESI-MS/MS of nitro-substituted diaryliodonium
cations.

Most importantly, when the nitro group was in \emph{ortho} -position of
Ar\textsuperscript{2}, the fragmentation ion
{[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135 dominated the
tandem mass spectrum of {[}Mes-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}\emph{-} C\textsubscript{6}H\textsubscript{4}){]} at
\emph{m} /\emph{z} 368 from salt \textbf{5} , with only a minimal
presence of {[}Mes{]}\textsuperscript{+} at \emph{m/z} 119
(\textbf{Figure 2a} ). Two possible reaction pathways were proposed for
the gas-phase O-atom transfer rearrangement of {[}\textbf{5}
--OTf{]}\textsuperscript{+} (\textbf{Scheme 4} ):\emph{path} (\textbf{a}
) Smiles rearrangement via a six-membered ring transition state (TS
\textbf{5a} ) to intermediate \textbf{5b}{[}Mes-O-(\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I){]}\textsuperscript{+}, which
finally dissociated to {[}MesO{]}\textsuperscript{+} at\emph{m}
/\emph{z} 135; \emph{path} (\textbf{b} ) Cleavage of the C--I bond to
form another transition state (TS \textbf{5a} ) and ion-neutral
intermediate \textbf{5d} , which could directly give to
{[}Mes{]}\textsuperscript{+} at \emph{m/z} 119 or further lead to
intermediate \textbf{5b} and finally forming
{[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135 (\textbf{Scheme
4} ). Due to the distance problems, the
{[}Mes-I\textsuperscript{+}-(\emph{m}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} and
{[}Mes-I\textsuperscript{+}-(\emph{p}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} from salt
\textbf{6} or \textbf{7} might follow a stepwise process involving
ion-neutral intermediates {[}Mes\textsuperscript{+} \& (\emph{m}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}I){]} or
{[}Mes\textsuperscript{+} \& (\emph{p}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}I){]} to
generate the intermediate \textbf{6b}{[}Mes-O-(\emph{m}
-NO-C\textsubscript{6}H\textsubscript{4}I){]}\textsuperscript{+}or
\textbf{7b}{[}Mes-O-(\emph{p}
-NO-C\textsubscript{6}H\textsubscript{4}I){]}\textsuperscript{+},
respectively. These intermediates ultimately resulted in the O-atom
transfer product ion {[}MesO{]}\textsuperscript{+} at \emph{m}
/\emph{z}135 (here Ar\textsuperscript{1} = Mes) with loss of neutral
species {[}\emph{m} -NO-C\textsubscript{6}H\textsubscript{4}I{]} or
{[}\emph{p} -NO-C\textsubscript{6}H\textsubscript{4}I{]} (\textbf{Scheme
4} ).

\textbf{3.3 Gas-Phase Smiles Rearrangement of \emph{ortho}-nitro
diaryliodonium cations}

In order to clearly explain the gas-phase O-atom transfer reaction
mechanism of {[}Mes-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} from salt
\textbf{5} to the dominating fragment ion {[}MesO{]}\textsuperscript{+},
we further studied the tandem mass spectra of some
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} cations
with different Ar\textsuperscript{1} from salts\textbf{9}
\textasciitilde{}\textbf{12} (shown in \textbf{Scheme 1} ) and these
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} cations
all exhibited the oxygen-atom transfer product ions
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} by loss of neutral
{[}\emph{o} -NO-Ar\textsuperscript{2}I{]} (shown in \textbf{Figure 3} ).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 3} High-resolution ESI-MS/MS of {[}\textbf{M}
--OTf{]}\textsuperscript{+}: (\textbf{a} ) \textbf{9} , the\emph{inset}
showed an expanded view of {[}PhO{]}\textsuperscript{+} at\emph{m}
/\emph{z} 93, (\textbf{b} ) \textbf{10} , (\textbf{c} ) \textbf{11}and
(\textbf{d} ) \textbf{12} .

To our surprise, the fragment ion {[}\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I{]}\textsuperscript{+*}at
\emph{m} /\emph{z} 233 appeared in the ESI-MS/MS of
{[}C\textsubscript{6}H\textsubscript{5}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-C\textsubscript{6}H\textsubscript{4}){]} at
\emph{m/z} 326 from salt \textbf{9} . Meanwhile, this same fragment ion
{[}\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I{]}\textsuperscript{+*}at
\emph{m} /\emph{z} 233 was also observed in the ESI-MS/MS of
{[}\textbf{10} --OTf{]}\textsuperscript{+} and {[}\textbf{11}
--OTf{]}\textsuperscript{+} (\textbf{Figure 3} ). The structural
assignments for fragment ions were supported by accurate mass
measurements (in \textbf{Table} \textbf{S1} and \textbf{S2} ). The
fragment ion {[}\emph{o}
-NO-Ar\textsuperscript{2}I{]}\textsuperscript{+*} was proposed to be the
counterpart product ion of gas-phase O-atom transfer reaction from nitro
to Ar\textsuperscript{1} due to the charge transfer between the neutral
{[}\emph{o} -NO-Ar\textsuperscript{2}I{]} with
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+}. All these result
supposed that the O atom in the
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} originated from the
nitro group of Ar\textsuperscript{2} to Ar\textsuperscript{1}.
Consequently, the fragment ions {[}\emph{\textsuperscript{t}}
Bu-C\textsubscript{6}H\textsubscript{4}O{]}\textsuperscript{+}at
\emph{m/z} 149 and {[}\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I{]}\textsuperscript{+*}at
\emph{m/z} 233 in the MS/MS of {[}\textbf{4} --OTf{]}\textsuperscript{+}
at \emph{m/z} 382 (\textbf{Figure 1d} and \textbf{Scheme 3} ) could be
attributed to the gas-phase O-atom transfer reaction from the nitro
group in Ar\textsuperscript{2} to Ar\textsuperscript{1}.

\textbf{Scheme 5} Proposed rearrangement patterns of {[}\textbf{M}
--OTf{]}\textsuperscript{+} of salts\textbf{9}
\textasciitilde{}\textbf{11} .\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

\textbf{Figure 4} High-resolution ESI-MS/MS of {[}\textbf{M}
--OTf{]}\textsuperscript{+}: (\textbf{a} ) \textbf{13} , (\textbf{b} )
\textbf{14} , (\textbf{c} ) \textbf{15} and (\textbf{d} )\textbf{16} .

However, the formation of product ions
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} from
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}\emph{-} Ar\textsuperscript{2}){]} cations could not
be simply rationalized by a one-step bond cleavage process. All the
experimental results suggested that in the case of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]}, a Smiles rearrangement
initially occurred, with the O-atom from the nitro group attacking the
C\textsubscript{(ipso)} position of Ar\textsuperscript{1}I via a
six-membered ring transition state, leading to the formation of the
intermediate {[}Ar\textsuperscript{1}-O-(\emph{o}
-NO-Ar\textsuperscript{2}I){]}\textsuperscript{+}. This transformation
was accompanied by the reduction of the iodine (III) species to the
corresponding iodine (I) species, which ultimately dissociated to
produce {[}Ar\textsuperscript{1}O{]}\textsuperscript{+}(such as
{[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135 in MS/MS of
{[}\textbf{5} --OTf{]}\textsuperscript{+}, as shown in \textbf{Scheme 4}
and Figure \textbf{2a} ). This dissociation was achieved through the
loss of neutral {[}\emph{o} -NO-Ar\textsuperscript{2}I{]} or the
generation of {[}\emph{o}
-NO-Ar\textsuperscript{2}I{]}\textsuperscript{+*} by the loss of
Ar\textsuperscript{1}O\textsuperscript{*}. The ESI-MS/MS of
{[}\textbf{M} --OTf{]}\textsuperscript{+} (\textbf{M} =\textbf{13}
\textasciitilde{}\textbf{22} shown in \textbf{Figure
4a\textasciitilde{}d} and \textbf{S13} \textasciitilde{}\textbf{S22} )
exhibited striking similarity to the MS/MS of {[}\textbf{5}
--OTf{]}\textsuperscript{+}, all prominently featuring
{[}MesO{]}\textsuperscript{+} at \emph{m/z} 135 as the dominant fragment
ion. Therefore, this unexpected ''\emph{ortho} effect'' observed in the
gas-phase fragmentation reaction of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} cations could likely be
attributed to the Smiles rearrangement induced by the \emph{ortho}
effect of the nitro group.

\textbf{3.4 Computations for gas phase rearrangements of nitro
diaryliodonium cations}

To shed insight to the reaction mechanisms of nitro diaryliodonium
cations, density functional theory (DFT) calculations were performed
with the Gaussian 16 package.\textsuperscript{43} The geometries were
fully optimized at the M062x/Def2-TZVP level in gas
phase,\textsuperscript{44,45} and harmonic vibration frequency
calculations confirmed that the optimized structures were either minima
(no imaginary vibrations) or transition states (only one imaginary
vibration). The Gibbs free energies were given in kcal/mol and
geometrical coordinates could be referred to the supporting information.

The schematic potential energy surface and the optimized structures of
reactive species in ESI-MS/MS of {[}\textbf{5}
--OTf{]}\textsuperscript{+} resulting from the theoretical calculations
were shown in \textbf{Figure 5} . Two paths of {[}\textbf{5}
--OTf{]}\textsuperscript{+} were considered, including\emph{path}
(\textbf{a} ): the Smiles rearrangement via a six-membered ring
transition state (\textbf{IAr2-\emph{o}-TS1} ); and
\emph{path}(\textbf{b} ): the cleavage of the C--I bond to form another
transition state (\textbf{IAr2-\emph{o}-TS3} ). The distance between
C\textsubscript{(ipso)} and I, C\textsubscript{(ipso)} and O atom of
nitro group in \textbf{IAr2-\emph{o}-TS1} were 3.130 and 2.436 \selectlanguage{ngerman}Å, which
were both smaller than that of \textbf{IAr2-\emph{o}-TS3} (4.367 and
4.589 Å, respectively). These results suggested that Smiles
rearrangement of {[}\textbf{5} --OTf{]}\textsuperscript{+} could
facilely occur via a six-membered ring transition state
(\textbf{IAr2-\emph{o}-TS1} ), leading to the formation of the
intermediate \textbf{IAr2-\emph{o}-INT1} .

\textbf{Figure 5} Schematic of potential energy surface and the
optimized structures of reactive species in ESI-MS/MS of {[}\textbf{5}
--OTf{]}\textsuperscript{+} (\textbf{IAr2-\emph{o}-R} ). The Gibbs free
energies were given in kcal/mol.

The energy barrier for the Smiles rearrangement of
\emph{path}(\textbf{a} ) via a six-membered ring transition state
(\textbf{IAr2-\emph{o}-TS1} ) was only 22.7 kcal/mol and 9.5 kcal/mol
less than the energy required for the C--I bond cleavage energy barrier
of \textbf{IAr2-\emph{o}-TS3} (36.0 kcal/mol). Furthermore, the Smiles
rearrangement from the hypervalent iodine(III)
complex\textbf{IAr2-\emph{o}-R} to the iodane(I)
intermediate\textbf{IAr2-\emph{o}-INT1} (-14.9 kcal/mol) was exothermic,
but the C--I bond cleavage to product complex
\textbf{IAr2-\emph{o}-INT3} (30.0 kcal/mol, which might give
{[}Mes{]}\textsuperscript{+} at \emph{m/z}119) was endothermic. Thus,
according to \textbf{Figure 5} , the Smiles rearrangement process of
\emph{path} (\textbf{a} ) formed {[}Mes-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}\emph{-} C\textsubscript{6}H\textsubscript{4}){]}
(\textbf{IAr2-\emph{o}-R} ) to the intermediate
{[}Ar\textsuperscript{1}-O-(\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I){]}\textsuperscript{+}(\textbf{IAr2-\emph{o}-INT1}
) via \textbf{IAr2-\emph{o}-TS1} was a favorable reaction pathway both
kinetically and thermodynamically. Then, the N--O bond cleavage of
intermediate {[}Ar\textsuperscript{1}-O-(\emph{o}
-NO-C\textsubscript{6}H\textsubscript{4}I){]}\textsuperscript{+}(\textbf{IAr2-\emph{o}-INT1}
) gave {[}MesO{]}\textsuperscript{+} at\emph{m} /\emph{z} 135 by loss of
neutral {[}\emph{o} -NO-C\textsubscript{6}H\textsubscript{4}I{]}
(\textbf{IAr2-\emph{o}-INT2} ) via transition
state\textbf{IAr2-\emph{o}-TS2} (energy barrier of only 12.4 kcal/mol).
Such calculation results supported our hypothesis proposed for
\emph{path}(\textbf{a} ) \textbf{IAr2-\emph{o}-R} to
intermediate\textbf{IAr2-\emph{o}-INT1} via Smiles rearrangement and
finally produced {[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135
with N--O bond cleavage of intermediate \textbf{IAr2-\emph{o}-INT1} .

Meanwhile, the C--I bond cleavage to product
complex\textbf{IAr2-\emph{o}-INT3} (30.0 kcal/mol) might produce the
intermediate \textbf{IAr2-\emph{o}-INT4} (-10.2 kcal/mol) in
\emph{path}(\textbf{b} ) and such process was exothermic. The N--O bond
cleavage of intermediate \textbf{IAr2-\emph{o}-INT4} might also give
{[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z} 135 and neutral
{[}\emph{o} -NO-C\textsubscript{6}H\textsubscript{4}I{]}
(\textbf{IAr2-\emph{o}-INT5} ) via transition
state\textbf{IAr2-\emph{o}-TS4} (energy barrier of only 14.4 kcal/mol).
The structures of the active species involved in the steps
from\textbf{IAr2-\emph{o}-INT3} to \textbf{IAr2-\emph{o}-INT5} were same
as those in the process from \textbf{IAr2-\emph{o}-INT1}
to\textbf{IAr2-\emph{o}-INT2} , but the species with same structures had
minor differences in relative energies due to the different spatial
configurations in the finally optimized structures.

\textbf{Figure 6} Schematic of potential energy surface and the
optimized structures of reactive species in ESI-MS/MS of {[}\textbf{6}
--OTf{]}\textsuperscript{+} (\textbf{IAr2-\emph{m}-R} ). The Gibbs free
energies were given in kcal/mol.

The \emph{path} (\textbf{b} ) of C--I bond cleavage process proposed for
{[}\textbf{5} --OTf{]}\textsuperscript{+} was unfavorable than Smiles
rearrangement of \emph{path} (\textbf{a} ) (\textbf{Figure 5} ).
However, the Smiles rearrangement via O-attacking was not accessible for
{[}\textbf{6} --OTf{]}\textsuperscript{+} and {[}\textbf{7}
--OTf{]}\textsuperscript{+} due to their distances between
C\textsubscript{(ipso)} and O atom of nitro group. Therefore, the
stepwise processes involved ion-neutral complexes were considered for
the explanation of the unexpected fragment ion
{[}MesO{]}\textsuperscript{+} at \emph{m/z} 135 in ESI-MS/MS of
{[}\textbf{6} --OTf{]}\textsuperscript{+} and {[}\textbf{7}
--OTf{]}\textsuperscript{+}. The schematic potential energy surface and
the optimized structures of reactive species in MS/MS of {[}\textbf{6}
--OTf{]}\textsuperscript{+} and {[}\textbf{7}
--OTf{]}\textsuperscript{+} resulting from the theoretical calculations
were shown in \textbf{Figure 6} and \textbf{7} . Theoretical
calculations showed that {[}\textbf{6} --OTf{]}\textsuperscript{+} and
{[}\textbf{7} --OTf{]}\textsuperscript{+} dissociated via similar
mechanism as the \emph{path} (\textbf{b} ) of C--I bond cleavage process
proposed for {[}\textbf{5} --OTf{]}\textsuperscript{+}, which was
unfavorable than Smiles rearrangement of \emph{path} (\textbf{a} )
(\textbf{Figure 5} ). However, the Smiles rearrangement via O-attacking
was not accessible for {[}\textbf{6} --OTf{]}\textsuperscript{+} and
{[}\textbf{7} --OTf{]}\textsuperscript{+} , due to the fact that the
distances between C\textsubscript{(ipso)} and O atom of nitro group
in\textbf{IAr2-\emph{m}-R} and \textbf{IAr2-\emph{p}-R} were 4.783 and
7.265 Å, respectively, which were both much longer than that
of\textbf{IAr2-\emph{o}-R} (3.007 Å).

\textbf{Figure 7} Schematic of potential energy surface and the
optimized structures of reactive species in ESI-MS/MS of {[}\textbf{7}
--OTf{]}\textsuperscript{+} (\textbf{IAr2-\emph{p}-R} ). The Gibbs free
energies were given in kcal/mol.

Therefore, the stepwise processes involved ion-neutral complexes were
considered for explanation of the unexpected fragment ion
{[}MesO{]}\textsuperscript{+} at \emph{m/z} 135 in ESI-MS/MS of
{[}\textbf{6} --OTf{]}\textsuperscript{+} and {[}\textbf{7}
--OTf{]}\textsuperscript{+}. The energy barriers for the formation of
\textbf{IAr2-\emph{m}-TS1} and \textbf{IAr2-\emph{p}-TS1}were 33.0 and
33.4 kcal/mol, respectively, which were both much higher than that of
\textbf{IAr2-\emph{o}-TS1} (22.7 kcal/mol). These results proved that
the Smiles rearrangement process in\textbf{IAr2-\emph{o}-TS1} was the
most favorable path to give {[}MesO{]}\textsuperscript{+} at \emph{m}
/\emph{z} 135. Therefore, such calculation results explained why the
fragmentation ion {[}MesO{]}\textsuperscript{+} at \emph{m} /\emph{z}
135 dominated the MS/MS of {[}Mes-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}\emph{-} C\textsubscript{6}H\textsubscript{4}){]}
from diaryliodonium salts (\textbf{5} and\textbf{13}
\textasciitilde{}\textbf{16} ) but only with tiny amount of
{[}Mes{]}\textsuperscript{+} at \emph{m/z} 119.

To test the generality of the fragmentation patterns we proposed in this
article, we further performed MS/MS experiments on cations from
salts\textbf{17} \textasciitilde{}\textbf{54} (structures shown
in\textbf{Scheme S1} ), and their tandem mass spectra and MS/MS data
were summarized in \textbf{Figure S17} \textasciitilde{}\textbf{S54}
and\textbf{Table S1} \textasciitilde{}\textbf{S4} . At the same time,
pseudo-MS\textsuperscript{3} experiments were performed in order to
assign the origin of some ions (\textbf{Figure
S55}\textasciitilde{}\textbf{S57} ). These results showed the
fragmentation ion {[}MesO{]}\textsuperscript{+} from {[}\textbf{M}
--OTf{]}\textsuperscript{+} (\textbf{M} =\textbf{17}
\textasciitilde{}\textbf{22} ) completely dominated the spectra
(\textbf{Figure S17} \textasciitilde{}\textbf{S22} ) and diaryliodonium
cations from salts\textbf{17} \textasciitilde{}\textbf{36} also
conformed well to the fragmentation patterns proposed in \textbf{Scheme
3} and \textbf{4} . The fragmentation patterns of cyclic diaryliodonium
cations from salts\textbf{37} \textasciitilde{}\textbf{54} were also
characterized by loss of an iodine atom (\textbf{Scheme 6} ,
\textbf{Figure S37} \textasciitilde{}\textbf{S54} ).

\textbf{Scheme 6} Proposed fragmentation patterns of {[}\textbf{M}
--OTf{]}\textsuperscript{+} from salts \textbf{37} ,\textbf{41} ,
\textbf{43} and \textbf{46} .

\textbf{4 CONCLUSIONS}

In summary, a total of 54 diaryliodonium cations were subjected to a
comprehensive study using high-resolution ESI-MS/MS, and their
fragmentation patterns were elucidated based on the accurate mass
measurements of the resulting fragment ions. Our investigations unveiled
that the incorporation of the nitro group into Ar\textsuperscript{2} of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-Ar\textsuperscript{2}{]}
could lead to an unexpected type of fragment ion
{[}Ar\textsuperscript{1}O{]}\textsuperscript{+} through an O-atom
transfer process from the nitro group to Ar\textsuperscript{1} in their
ESI-MS/MS. The particular case was the nitro group positioned in
the\emph{ortho} -position of Ar\textsuperscript{2} moiety of the
diaryliodonium salt. The theoretical calculations provided mechanistic
insights into the O-atom transfer rearrangements of\emph{ortho-}
nitro-substituted diaryliodonium cations which supported the occurring
of gas-phase Smiles rearrangement of
{[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} to the intermediate
{[}Ar\textsuperscript{1}-O-(\emph{o}
-NOAr\textsuperscript{2}I){]}\textsuperscript{+}, finally giving the
product ions {[}Ar\textsuperscript{1}O{]}\textsuperscript{+} or
{[}\emph{o} -NO\emph{-} Ar\textsuperscript{2}I{]}\selectlanguage{english}\textsuperscript{+*}.
This work would be useful for the structural characterization of
diaryliodonium cations by mass spectrometry, and the gas-phase Smiles
rearrangement of {[}Ar\textsuperscript{1}-I\textsuperscript{+}-(\emph{o}
-NO\textsubscript{2}-Ar\textsuperscript{2}){]} might offer valuable
insights for organic chemists for the design of new types of organic
reactions involving diaryliodonium salts.

\textbf{ACKNOWLEDGEMENTS}

The authors thank the financial support from National Natural Science
Foundation of China for (Grant Nos. 21772227) and Shanghai Institute of
Organic Chemistry (Grant Nos. E22ZZ61).

\textbf{CONFLICT OF INTEREST}

There are no conflicts to declare.

\textbf{AUTHOR CONTRIBUTIONS}

Wu-Zhi Wei: Mass spectrometric investigations and writing draft. Cheng
Pan: Compounds synthesis. Ling Lin: Theoretical calculations. Jianwei
Han: Methodology, experiment designs, revising and editing. Hao-Yang
Wang: Conceptualization, mechanism studies and supervision.

\textbf{DATA AVAILABILITY STATEMENT}

The data that support the findings of this study are available from the
corresponding author upon reasonable request.

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