Conformational control ofN-methyl-N,N'-diacylhydrazines by noncovalent carbon bonding in solution

Article abstract of DOI:10.1039/d0cc00943a

In recent years, some X-ray structural and computational evidence has emerged for noncovalent carbon bonding (C-bond). However, evidence of C-bonds in solution is limited. Herein, from the conformational analyses of strategically designedN-methyl-N,N'-dia

Full text of DOI:10.1039/d0cc00943a

View Article Online
View Journal
ChemComm
Chemical Communications
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: B. K. Sarma, J. K.
R. Deka, B. Sahariah, K. Baruah and A. K. Bar, Chem. Commun., 2020, DOI: 10.1039/D0CC00943A.
Volume 54
This is an Accepted Manuscript, which has been through the
Number
January 2018
Pages 1-112
1
4
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Chemical Communications
rsc.li/chemcomm
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
S. J. Connon, M. O. Senge et al.
Conformational control of nonplanar free base porphyrins:
towards bifunctional catalysts of tunable basicity
rsc.li/chemcomm

Please do not adjust margins
Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/D0CC00943A
COMMUNICATION
Conformational control of N-methyl-N,N-diacylhydrazines by
noncovalent carbon bonding in solution†
Jugal Kishore Rai Deka,a Biswajit Sahariah,a Kalpita Baruah,a Arun Kumar Barb and Bani Kanta
Received 00th January 20xx,
Accepted 00th January 20xx
Sarma*c
DOI: 10.1039/x0xx00000x
radicals10 or -electrons11. The C-bond is a subset of much
broader and well-studied tetrel bonds12, a noncovalent bonding
between electron donors and the group 14 elements (Si, Ge and
Sn). C-bond, like any other tetrel bond, is regarded as a -hole
interaction between the region of positive electrostatic
potential (-hole) in the sp3 carbon moiety (X−C) and the
negative electrostatic potential of an electron rich site (Y). From
the orbital interaction point of view, C-bond (X−C···Y) can be
regarded as the electron delocalization between a lone pair or
filled or partially filled  orbital of Y and the vacant * orbital of
the C-X bond.
In recent years, some X-ray structural and computational evidence
have emerged for noncovalent carbon bonding (C-bond). However,
evidence of C-bonds in solution is limited. Herein, from the
conformational analyses of strategically designed N-methyl-N,N'-
diacylhydrazines, we for the first time show that C-bonds can be
modulated to control the conformational preferences of small
molecules in solution. We show that unusual N(amide)C-X
noncovalent carbon bonding interactions stabilize the trans-cis (t-
c) amide bond rotamers of N-methyl-N,N-diacylhydrazines over
the expected trans-trans (t-t) rotamers.
The presence of the C-bond is now recognized in small
molecules,13 proteins14 and protein-ligand complexes15.
However, the existing evidence of C-bonds is based on the
crystallographic and computational studies. Although carbon-
centered, three-center, four-electron tetrel bond, [N−C−N]+ ,
were studied by capturing a carbenium ion with a bidentate
Lewis base,16 to the best of our knowledge, there has been no
study of C-bond in solution involving neutral carbon donors.
Moreover, it is not known if C-bond can affect the
conformational properties of molecules in solution. In this
paper, we report the conformational control of N-methyl-N,N'-
diacylhydrazines in solution by an unusual N(amide)C C-bond.
In a recent report, Frontera and co-workers used X-ray
crystallography and theoretical calculations to show that C-
bonds can stabilize the cis conformation in acylhydrazones
(Figure 1A).17 Inspired by this study, we have chosen N-methyl-
N,N'-diacylhydrazines 1-8 (Figure 1B) to investigate the
possibility of C-bonding. Based on our previous study with
unsubstituted N,N'-diacylhydrazines4a, we predict the NH-
Noncovalent interactions involving carbon atoms are exciting
due to the ubiquity of carbon in both chemistry and biology.
Carbonyl-carbonyl (COCO) nO → * interactions1 involving sp2
carbons have gained a lot of attention in recent years, especially
in the stabilization of small molecules,2 -helices3, polyproline
II helices4 and collagen triple helices.5 Various orientation
dependent modes of COCO interactions were also recently
discovered.6 Although COCO interactions were initially
thought of as dipolar interactions,7 it is now accepted that these
interactions are predominantly n → * in nature where a lone
pair (n) of the oxygen atom of one carbonyl group is delocalized
over the π* orbital of the another carbonyl group.8 However,
relatively less is known about sp3 carbon-mediated
“noncovalent carbon bonding” (C-bond)9, commonly
represented as X−C···Y, where X−C is the carbon bond donor
fragment and Y is the carbon bond acceptor. In C-bonds, C-bond
“donor” means the electron deficient sp3 carbon (C−X) moiety
(* orbital) and C-bond “acceptor” means the electron rich
group (Y). The C-bond acceptor can be lone pair of electrons,9
amide
bond
in
N-methyl-N,N-diacylhydrazines
to
predominantly exist in the trans geometry (H―N―C=O ~ 180°),
due to steric reasons. However, N-methylation should enhance
the cis-trans isomerization of the other amide bond bearing the
NMe group. In such a scenario, the presence of a tetrahedral
carbon at the R2 position may facilitate C-bonding with either O
or N of the NH-amide group and stabilize the cis conformations
of the NMe-amides in 1-8 (Figure 1C).
a. Department of Chemistry, School of Natural Sciences, Shiv Nadar University,
Dadri, Uttar Pradesh 201314, India
b. Department of Chemistry, Indian Institute of Science Education and Research
(IISER) Tirupati, Tirupati 501507, India
c. New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research
(JNCASR), Jakkur, Bangalore 560064, India
†Electronic Supplementary Information (ESI) available: [Experimental details, 1D and
2D NMR studies, concentration dependent NMR studies, IR studies and DFT results.
See DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
COMMUNICATION
Journal Name
O
Table 1. Amide bond rotamers of N-methyl-N,N'-diacylhydrazines 1-8. In
View Article Online
O
R1
H
the abbreviated rotamer description (t-t and t-c), the first letter indicates the
DOI: 10.1039/D0CC00943A
(A)
R1
N
R2
N
N
nN
conformation of the NH-amide bond and the second letter is for the NMe-
amide bond. C.G. = crystal geometry.

N
H
H
H
O
H
trans
H
cis
R2
Comp
R1
Ph
Ph
R2
t-t (%)
23
21
12
13
21
37
40
42
t-c (%)
77
79
88
87
79
63
60
58
C.G.
t-c
t-c
-
t-c
t-c
t-c
t-c
t-c
R1
1
2
3
4
5
6
7
8
(B)
R1
, R1 = Ph, R2 = CH3
, R1 = Ph, R2 = C2H5
, R1 = Ph, R2 = CF3
, R1 = 4-NMe2-Ph, R2 = CH3
, R1 = 4-OMe-Ph, R2 = CH3
, R1 = 4-CF3-Ph, R2 =CH3
, R1 = 4-CN-Ph, R2 = CH3
, R1 = 4-NO2-Ph, R2 = CH3
1
2
3
4
5
6
7
8
CH3
C2H5
CF3
CH3
CH3
CH3
CH3
CH3
H
H
N
N
N
O
N
R2
O
H3C
Ph
H3C
R2
O
4-NMe2-Ph
4-OMe-Ph
4-CF3-Ph
4-CN-Ph
4-NO2-Ph
trans-trans (t-t)
trans-cis (t-c)
R1
R1
R1
(C)
H
H
H
N
N
O
H
N
N
O
N
N
O
O
H
X
H
X
H
X
or
H3C
H3C
H3C
H
O
cis
O
H
trans
cis

nN

nO
Figure 1. (A) C-bonding in the cis geometry of acylhydrazones. (B) Trans-trans
(t-t) and trans-cis (t-c) rotamers of N-methyl-N,N-diacylhydrazines 1-8. (C)
Proposed C-bonding in 1-8 through amide nitrogen and amide carbonyl oxygen.
The solution NMR studies of compound 1 (R1 = Ph, R2 = CH3)
revealed the NH-amide bond to be in trans-conformation in
CDCl3 (20 mM) whereas isomerization of the amide bond near
the NMe group having relatively smaller acyl substituent (R2 =
CH3) produced a rotameric mixture of t-c (77%) and t-t (23%) of
1 (Table 1). Changing the acyl substituent on the NMe-amide
bond to CH2CH3 (2) and CF3 (3) further increased the percentage
of the t-c rotamer to 79% and 88%, respectively (Table 1),
probably due to the increase in the size of the acyl substituent
(steric effect) or due to increase in the strength of C-bond from
1 to 3 with increase in electron withdrawing capacity of R2. In
agreement with the NMR studies, theoretical calculations at
M06-2X/6-311+G(2d,p) level of theory also indicated that the
rotamer stability of 1-3 decreases in the order t-c > t-t > c-c > c-
t with the NH-amide bond in the trans and the NMe-amide bond
in the cis form in the most stable t-c rotamer (Table S8-S10). The
cis-trans isomerization barrier of the NMe amide bond in these
molecules is ~25 kcal.mol-1 (Figure S18). Both compounds 1 and
2 crystallized in the t-c form with twisted geometries (Figure 2)
around the N―N bonds [C―N―N―C ~ 90] 18, which support
our solution NMR interpretations. Short noncovalent HN···CH3
and HN···CH2CH3 distances [1, N···C = 2.710 Å and 2, N···C =
2.722 Å] in the crystal structure of 1 and 2 and almost linear
N···C―C angle in 2 [N···C―C = 173.4°] indicated the possibility
of nN → σ*C―H/C interactions in them (Figure 2).
Natural Bond Orbital (NBO)19 analyses of the t-c rotameric
form of 1-3 revealed the presence of nN → σ*C―X noncovalent
interaction between the NH-amide nitrogen lone pair (nN) and
the σ* orbitals of C―X (X = H, C or F) bonds of the acyl
substituent on the NMe-amide group (Figure 3A, Table 2). As
expected, due to the presence of electron withdrawing group at
R2, compound 3 showed higher NBO stabilization energy E2(nN
→ σ*C―X) than 1 and 2. Similarly, electron donating group at R1
increased E2(nN → σ*C―X) in 4 but electron withdrawing group
at R1 decreased E2(nN → σ*C―X) in 8 compared to that of 1 having
no such electron donating or withdrawing substituents in the
aryl ring. Non-Covalent Interaction (NCI)20 analyses also showed
Figure 2. Crystal structures of (A) 1 and (B) 2 (C) Crystal packing of 1 via
intermolecular N―H···O=C hydrogen bonds.
the presence of weak interactions between the amide nitrogen
and the acyl carbon atoms (Figure S17). These nN→ σ*C―X
interactions are quite unusual as the lone pair of electrons of
the nitrogen atoms in the N-methyl-N,N'-diacylhydrazines
should be in conjugation with the carbonyl groups and,
therefore, are supposed to be unavailable for such nN → σ*
interactions. We also observed weak CO···CO nO → π*
interactions in 1 wherein the NH-amide carbonyl group acts as
the donor and the NMe-amide carbonyl group acts as the
acceptor of electrons (Figure 3B). However, CO···CO nO → π*
interactions were absent in 2 and 3. We also did not observe
any nO→ σ*C―X in 1-3. Therefore, we believe that the nN → σ*C―X
interactions are the major contributors to the stabilization of
the t-c rotamers of 1-3. Moreover, while such nN → σ*C―X and
nO → σ*C―X interactions are not possible in the t-t rotamer, the
CO···CO nO → π* interactions should still be intact in the t-t
rotamer (Figure 3C-D). Geometry optimization using explicit
water molecules at M06-2X/6-311+G(2d,p) level of theory
followed by NBO calculations of the t-c rotamers of 1-4 and 8
showed little effect of solvent on the carbon bonding
interactions (Table S14).
Theoretical calculations, solution NMR studies and solid-
state structures indicated t-c to be the most stable rotamer of
1-3, which is quite unexpected in absence of C-bond as methyl
group is not bulky enough to exert such dramatic effect on the
amide bond geometry. This can be rationalized by comparing
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 4
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
bond in 1(CH2)-3(CH2) suggests a lesser role of CVOie·w··CArOticlne →Onlπin*e
DOI: 10.1039/D0CC00943A
interactions in stabilizing the t-c form. Interestingly, MeN-
CO···CH2 nN → σ* interactions were found to stabilize the trans
amide bonds in 1(CH2)-3(CH2) (Table S13).
Spectroscopic signature of nN → σ*C―X interactions in 1-3 is
1
evident in the deshielding of H and shielding of 13C and 19F
signals of R2 (CH3, C2H5 and CF3) relative to those of 1(CH2)-
3(CH2) (Table 3). We expect the carbon atoms of CH3, CH2 (of
C2H5) and CF3 groups in 1-3 to be shielded due to gain in electron
density via nN (amide) → σ* delocalization. Accordingly, the 13
C
signals of 1-3 are upfield shifted relative to their CH2 isostere
analogues 1(CH2)-3(CH2), respectively (Table 3). Although
earlier studies21 predicted deshielding of C-bond donor carbon
atoms, upfield shift of 13C signals were also observed in carbon-
centered, three-center, four-electron tetrel bond, [N−C−N]+ of
carbenium ions with bidentate Lewis base.16 In compound 1, the
donation of electrons from the amidic nitrogen lone pair to
antibonding σ*C-H orbital should elongate the C―H bond of the
CH3 group at R2, which should deshield the protons compared
to that of 1(CH2) where no such electron donation is present.
We clearly observed deshielding of the CH3 protons in 1 (2.12
Figure 3. (A) nN → σ*C―H interaction in the t-c rotamer of 1. (B) CO···CO nO → π*
interaction in the t-c rotamer of 1. (C)-(D) Reciprocal CO···CO n → π* interaction
in the t-t rotamer of 1.
Table 2. NBO second-order perturbation energies for nN → σ*C―X and CO···CO ppm) compared to that of 1(CH2) (2.00 ppm). In 2, due to higher
nO → π* interactions in the t-c rotamer of 1-4 and 8.
electronegativity of carbon compared to hydrogen, the increase
in electron density in the C2H5 group via nN (amide) → σ*
donation is shared by both the ethyl carbon atoms, which make
the CH2 and CH3 carbon atomsshielded. However, like 1, the CH2
hydrogen atoms are deshielded in 2 compared to 2(CH2). In 3,
the electronegative fluorine atoms withdraw electron density
more towards themselves and thus the 19F signals are more
shielded in 3 than in 3(CH2).
Comp
R1
R2
E2
E2
n → π*
n → σ*
kcal·mol-1
kcal·mol-1
0.31
NP
1
2
3
4
8
Ph
Ph
Ph
CH3
C2H5
CF3
CH3
CH3
0.81
0.79
1.52
0.86
NP
NP
0.30
4-NMe2-Ph
4-NO2-Ph
0.78
Table 3. 1H, 13C and 19F NMR values of the acyl substituent on the NMe-amide
bond of 1-3 and 1(CH2)-3(CH2) and N―H stretching of the NH-amide of 1-3.
Comp
1H
(ppm)
2.12
2.00
2.41 (CH2)
13C
(ppm)
20.6
21.2
25.5 (CH2)
8.95 (CH3)
26.1 (CH2)
9.41 (CH3)
116.1
19F
(ppm)
-
-
-
NH Stret.
(cm-1)
O
O
O
O
N
O
N
O
N
1
1(CH2)
2
3248
Me
Me
Me
CH3
C2H5
CF3
3200
3154
1(CH2)
2(CH2)
t = 83%
3(CH2)
t = 77%
t = 85%
2(CH2)
2.18 (CH2)
-
Figure 4. Chemical structures of 1(CH2)-3(CH2) and % of their tMe-N-C=O rotamer.
3
-70.9
-69.2
3(CH2)
116.5
the NMe amide bond geometries of 1-3 with that of 1(CH2)-
3(CH2) (Figure 4) where the NH group is replaced by a CH2
isostere. Unlike 1-3, the NMe-amide bonds in 1(CH2)-3(CH2)
predominantly adopted the trans-conformation (Me-N-C=O
~180) in CDCl3 (20 mM), which indicate that the steric effect
exerted by N-methylation cannot account for the predominant
cis-geometry observed for the NMe-amide bond in the 1-3.
These observations also support that absence of such nN → σ*
stabilization in 1(CH2)-3(CH2), the cis-form of the NMe-amide
bond is less stable than the trans-form. It should be noted that
1(CH2)-3(CH2) have two carbonyl (CO) groups at identical
positions as that of 1-3 and possibility of CO···CO n→π*
interactions to stabilize the t-c form. However, the lower
stability of the cis-form than the trans-form of the NMe-amide
At high concentration, 1-3 are expected to associate via
intermolecular N―H···O=C hydrogen bonding (Figure 2C).
Increase in the strength of nN → σ*C―X interaction should
strengthen these N―H···O=C hydrogen bonds and, therefore,
decrease the N-H stretching frequency. For neat solid samples
of 1-3, we observed a band below 3300 cm-1, which could be
assigned to the N―H stretching of the major t-c rotamer
associated strongly by N―H···O=C hydrogen bonds. As
expected, we observed decrease in N―H frequencies from 1 to
3 (Table 3) with increase in nN → σ*C―X interactions.
To investigate if the nN → σ* interactions can be modulated
to affect the rotamer population in solution; we studied
compounds 1 and 4-8 with a CH3 group at R2 and aryl groups
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Journal Name
substituted with various electron donating and withdrawing Acknowledgements
substituents at R1 to modulate the donor ability of the NH-
View Article Online
DOI: 10.1039/D0CC00943A
This project was funded by Early Career Research Grant
(ECR/2015/000337) from Science and Engineering Research
Board (SERB), Department of Science and Technology (DST),
Government of India and Shiv Nadar University (SNU). We
acknowledge the MAGUS supercomputing facility at SNU.
amide nitrogen atom. Electron donating substituent at the 4-
position of the aryl ring (R1) should decrease HN―CO
delocalization in the NH-amide, make the NH nitrogen lone pair
more available for nN → σ*C―H interaction and, hence, stabilize
the t-c rotamer whereas electron withdrawing groups at R1
should have an opposite effect. Accordingly, we observed that
the population of t-c rotamer gradually decreased from 4 to 8
(Table 1). Excellent correlation was observed between the
Hammett parameter σP of the substituent at the 4-position of
the aryl group at R1 and the change in the t-c rotamer
population in solution (Figure 5A), suggesting important roles of
nN → σ*C―H interactions in the stabilization of the t-c rotamer.
Notes and references
1.
a) R. W. Newberry and R. T. Raines, Acc. Chem. Res., 2017, 50, 1838-
1846; b) S. K. Singh and A. Das, Phys. Chem. Chem. Phys., 2015, 17,
9596-9612.
2.
a) R. W. Newberry and R. T. Raines, ACS Chem. Biol., 2014, 9, 880–883;
b) R. W. Newberry, B. VanVeller, I. A. Guzei, and R. T. Raines, J. Am.
Chem. Soc., 2013, 135, 7843–7846; c) A. Choudhary, K. J. Kamer and R.
T. Raines, J. Org. Chem., 2011, 76, 7933–7937.
3.
a) R. W. Newberry, G. J. Bartlett, B. VanVeller, D. N. Woolfson, and R. T.
Raines, Protein Sci., 2014, 23, 284–288; b) G. J. Bartlett, R. W. Newberry,
B. VanVeller, R. T. Raines and D. N. Woolfson, J. Am. Chem. Soc., 2013,
135, 18682–18688; c) G. J. Bartlett, A. Choudhary, R. T. Raines and D. N.
Woolfson, Nat. Chem. Biol., 2010, 6, 615–620; d) C. Fufezan, Proteins
2010, 78, 2831–2838.
4.
5.
a) A. Rahim, P. Saha, K. K. Jha, N. Sukumar and B. K. Sarma, Nat. Comm.
2017, 8, 78; b) M. P. Hinderaker, and R. T. Raines, Protein Sci. 2003, 12,
1188-1194.
a) F. A. Etzkorn, R. I. Ware, A. M. Pester and D. Troya, J. Phys. Chem. B,
2019, 123, 2, 496-503; b) M. L. DeRider, S. J. Wilkens, M. J. Waddell, L.
E. Bretscher, F. Weinhold, R. T. Raines and J. L. Markley, J. Am. Chem.
Soc. 124, 2497–2505; c) L. E. Bretscher, C. L. Jenkins, K. M. Taylor, M. L.
DeRider and R. T. Raines, J. Am. Chem. Soc. 2001, 123, 777-778.
B. Sahariah and B. K. Sarma, Chem. Sci., 2019, 10, 909- 917.
a) F. R. Fischer, P. A. Wood, F. H. Allen and F. Diederich, Proc. Natl Acad.
Sci. USA 2008, 105, 17290–17294; c) R. Paulini, K. Müller, and F.
Diederich, Angew. Chem. Int. Ed., 2005, 44, 1788–18058.
a) K. J. Kamer, A. Choudhary, and R. T. Raines, J. Org. Chem., 2013, 78,
2099–2103; b) A. Choudhary, D. Gandla, G. R. Krow, and R. T. Raines, J.
Am. Chem. Soc., 2009, 131, 7244–7246.
Figure 5. (A) Hammett correlation between the substituent at 4-position of the aryl
ring at R1 and the percentage of the t-c and t-t rotamers observed in CDCl3 (20
mM). (B) Increase in the percentage of the t-c rotamer with increase in the
concentrations of N-methyl-N,N'-diacylhydrazines from 1 mM to 100 mM in CDCl3.
6.
7.
As hydrogen bond donation makes an amide nitrogen lone
pair more available22, we envisaged that intermolecular
N―H···O=C hydrogen bonding in 1-8 (seen in crystal packing) in
concentrated solution could enhance the nN → σ*C―X
interactions, which should be reflected in the increase in their
t-c rotamer population in solution. We carried out
concentration dependent 1H NMR studies of 1 and 4-8 as their
minor rotamers were detectable at low concentrations. We
observed consistent increase in their t-c rotamer population
with increase in concentration (Figure 5B) in CDCl3. As can be
expected, compounds 1(CH2) and 9 (N,N'-dimethylated version
of 1) that lacked NH hydrogens did not show concentration
dependent change in rotamer populations.
In conclusion, we have shown the stabilization of the t-c
rotameric form of N-methyl-N,N'-diacylhydrazines due to
noncovalent C-bonding interactions in solution. We have also
demonstrated that it is possible to control of the population of
the t-c rotamers in solution by modulating these C-bonds. The
C-bonds described here are quite unusual as the electron
donation occurs from an amide nitrogen atom, whose lone pair
of electrons is supposed be conjugated with the carbonyl group.
We envisage that such C-bonds could play important roles in
other N―N bond containing molecules as well, especially in aza-
oligomers such as azapeptides, azapeptoids and their N-methyl
derivatives that have N,N'-diacylhydrazine units embedded in
their structure.
8.
9.
D. Mani and E. Arunan, Phys. Chem. Chem. Phys., 2013, 15, 14377–
14383.
10.
Q. Li, X. Guo, X. Yang, W. Li, J. Cheng and H. -B. Li, Phys. Chem. Chem.
Phys., 2014, 16, 11617−11625.
11.
12.
D. Mani and E. Arunan, J. Phys. Chem. A., 2014, 118, 10081−10089.
A. Bauzá, T. J. Mooibroek and A. Frontera, Angew. Chem., Int. Ed., 2013,
52, 12317–12321; Angew. Chem., 2013, 125, 12543–12547.
S. P. Thomas, M. S. Pavan and T. N. Guru Row, Chem. Commun., 2014,
50, 49–51.
13.
14.
V. R. Mundlapati, D. K. Sahoo, S. Bhaumik, S. Jena, A. Chandrakar and
H. S. Biswal, Angew. Chem., Int. Ed., 2018, 57, 16496 –16500.
A. Bauzá and A. Frontera, Crystals., 2016, 6, 26/21–26/13.
A. Karim, N. Schulz, H. Andersson, B. Nekoueishahraki, A. -C. C. Carlsson,
D. Sarabi, A. Valkonen, K. Rissanen, J. Grafenstein, S. Keller and M.
15.
16.
́
17.
18.
M. M. Naseer, M. Hussain, A. Bauz, K. M. Lo and A. Frontera,
ChemPlusChem., 2018, 83, 881–885.
(a) C. H. Reynolds and R. E. Hormann, J. Am. Chem. Soc., 1996, 118,
9395-9401; (b) T. Ottersen, Acta Chem. Scand., 1978, 32a, 127-131; (c)
T. Ottersen, Acta Chem. Scand., 1974, 28a, 1145-1149.
E. D. Glendening, A. E. Reed, J. E. Carpenter and F. Weinhold, NBO
Version 3.1.
19.
20.
21.
22.
E. R. Johnson, S. Keinan, P. M. –Sánchez, J. C. –García, A.J. Cohen and
W. yang, J. Am. Chem. Soc., 2010, 132, 6498-6506.
a) S. Scheiner, J. Phys. Chem. A., 2018, 122, 39, 7852-7862; b) S. A.
Southern and D. L. Bryce, J. Phys. Chem. A., 2015, 119, 49, 11891-11899.
M. J. Deetz, J. E. Fahey and B. D. Smith, J. Phys. Org. Chem., 2001, 14,
463-467.
Conflicts of interest
There are no conflicts to declare.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins