The influence of steric effects on the kinetics and mechanism of SNAr reactions of 1-phenoxy-nitrobenzenes with aliphatic primary amines in acetonitrile

Article abstract of DOI:10.1002/poc.3687

Rate constants are reported for the reactions of 1-phenoxy-dinitrobenzenes, 3, 1-phenoxy-dinitrotrifluoromethylbenzenes, 4, with n-propylamine, and 1-methylheptylamine in acetonitrile as solvent. The results are compared with results reported previously f

Full text of DOI:10.1002/poc.3687

Received: 13 October 2016
DOI 10.1002/poc.3687
Revised: 29 November 2016
Accepted: 9 January 2017
R E S E A R C H A R T I C L E
The influence of steric effects on the kinetics and mechanism of
SNAr reactions of 1‐phenoxy‐nitrobenzenes with aliphatic primary
amines in acetonitrile
Chukwuemeka Isanbor
Chemistry Department, University of Lagos,
Abstract
Lagos, Nigeria
Rate constants are reported for the reactions of 1‐phenoxy‐dinitrobenzenes, 3, 1‐
Correspondence
Chukwuemeka Isanbor, Chemistry Department,
University of Lagos, Lagos, Nigeria.
Email: cisanbor@unilag.edu.ng
phenoxy‐dinitrotrifluoromethylbenzenes, 4, with n‐propylamine, and 1‐
methylheptylamine in acetonitrile as solvent. The results are compared with results
reported previously for n‐butylamine, pyrrolidine, and piperidine. Decreasing ring
activation leads to lower values of k1 for nucleophilic attack although this may be
mediated by reduced steric congestion around the reaction centre. Specific steric
effects, leading to rate retardation, are noted for the ortho‐CF3 group. In general,
reactant‐bearing ortho‐CF3 group were subject to base catalysis irrespective of the
amine nucleophile and values of kAm/k−1 are reduced as the size of the amine get
bulkier. This is likely to reflect increases in values of k−1 coupled with decreases
in values of kAm as the proton transfer from zwitterionic intermediates to catalysing
amine becomes less thermodynamically favourable.
KEYWORDS
aliphatic amines, nucleophilic aromatic substitution, steric effects, substituent effects
1
|
INTRODUCTION
substituent, other factors have been considered, such as the
steric inhibition of resonance,[6] the field effect,[7] and the
intermolecular hydrogen bonds.[8,9] Generally, steric effects
are not linearly dependent in various reactions[10] but rather
vary nonlinearly with the substituent, becoming suddenly
appreciable at its certain size. The universal scales of steric
effect therefore have no physical applicability and little prac-
ticability only in combination with other parameters. In this
respect, steric effect differs from inductive and also from
resonance effects.[11]
In activated aromatic nucleophilic substitution reactions
(SNAr) involving nitroaryl ethers, considerable attention has
been attached to the observation of base catalysis by primary
and secondary amines and its significance.[1–4] The overall
mechanism of these reactions is given in Scheme 1, where
EWG denotes a generalized substituent.
The presence or absence of base catalysis exerted by the
nucleophile itself or by an externally added base has played
an important role in deciding whether formation or decompo-
sition of the intermediate complex is rate limiting.[5] While
the factors affecting the incidence of base catalysis have been
extensively discussed and in most cases substantiated experi-
mentally, only meagre attention has been given to the effects
of ortho substitution in the substrate. This may be due to
complications arising from ortho effect of most substituents.
Apart from the simple steric effect owing to a bulky
We have reported a detailed kinetic study of the reaction
of
4‐substituted‐1‐chloro‐2,6‐dinitrobenzenes,
1,
6‐
substituted‐1‐chloro‐2,4‐dinitrobenzenes, 2, and some of the
corresponding 1‐phenoxy derivatives, 3 and 4, with n‐
butylamine, pyrrolidine, and piperidine in acetonitrile as
solvent. Values of k1, the rate constant for nucleophilic
attack at the 1‐position, increase with increasing ring
activation but may be reduced by steric repulsion at the
reaction centre, which increases in the order Cl < OPh
and n‐butylamine < pyrrolidine ~ piperidine. Also, we
have extended[12] the study to the reaction of a series of
This study is dedicated to the memory of late Emeritus Professor Thomas
Anthony Emokpae in honour of his immense contributions to the understand-
ing of the mechanism of SNAr Reactions.
J Phys Org Chem. 2017;e3687.
wileyonlinelibrary.com/journal/poc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.3687

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ISANBOR
as 2‐octylamine) are reported. The results are compared with
those reported for the same substrates with n‐butylamine in
acetonitrile.[12]
SCHEME 1 EWG, electron withdrawing groups
2
| RESULTS AND DISCUSSION
1‐chloro‐nitrobenzenes, 1‐fluoro‐nitrobenzenes, and 1‐phenoxy‐
nitrobenzenes activated by CF3 or CN groups or by ring
nitrogen with n‐butylamine, pyrrolidine, or piperidine in
acetonitrile. Our results showed that the decreased ring
activation in the nitroaryl ethers or pyridyl ethers leads to
reductions in values of kAm/k−1 resulting in greater suscepti-
bility to base catalysis.[12] Rate constants k1 for nucleophilic
attack are also reduced, but steric effects due to repulsion
between the incoming nucleophile and ortho substituents
are less evident. Specific rate‐retarding effects of an ortho‐
CF3 group were observed.
The reactions of parent molecules 3 and 4 with n‐
propylamine and 1‐methylheptylamine in acetonitrile gave
the expected products of substitution of phenoxide respec-
tively in >95% yield. Kinetic measurements were made
spectrophometrically with the concentration of amine in large
excess of the parent concentration, ca 5.0 × 10−5 to
1 × 10−4 mol dm−3, and first‐order kinetics were observed.
Previous studies[13–15] in dimethyl sulfoxide (DMSO) have
shown that substitution may be preceded by the formation,
under kinetic control, of adducts resulting from attack at
unsubstituted ring positions. An example for 4f is shown in
Scheme 2. The values of the equilibrium constant for such
processes depend on the degree of ring activation and also
on the solvent. Thus, in acetonitrile, the values for the reac-
tion in Scheme 2 are ca 104 smaller than in DMSO.[13–15]
The dominant factor here is likely to be the greater ability
of DMSO than of acetonitrile to solvate the ionic reaction
products.[9]
The reaction of 4f with amines such as pyrrolidine and n‐
butylamine in acetonitrile was shown[12] to yield the substitu-
tion products without the observation of the adduct
analogous to 5. Similarly, in the present investigation, substi-
tution proceeded smoothly to give first‐order kinetics without
the observation, in spectroscopically measurable concentra-
tions, of transient species analogous to 5 or other intermedi-
ates on the substitution pathway. Values of kObs, the
first‐order rate constant, are assembled in Tables 1 and 2.
For all the reactions, the UV‐visible spectra (in dilute and
in more concentrated solution) at the completion of the mea-
sured process were identical to those of authentic samples of
Reactions of the titled compounds have been performed
to see how wide spread the influence of the ortho‐CF3 group
exerts on the reaction’s pathways in SNAr reactions. Herein,
the results of the kinetic studies in acetonitrile of the reactions
of a selection of nitro‐activated aryl phenyl ethers 3 and 4
with n‐propylamine and 1‐methylhepthylamine (also named
SCHEME 2
TABLE 1 Kinetic results for reaction of phenyl‐2,6‐dinitrophenyl ether 3a, phenyl‐2,4‐dinitrophenyl ether 3b, 4‐phenoxy‐3,5‐dinitrotrifluoromethylbenzene 4a, and
2‐phenoxy‐3,5‐dinitrotrifluoromethylbenzene 4b with n‐propylamine in acetonitrile at 25°C
kObs/10−3 s−1
kObs/10−4 s−1
kObs/10−3 s−1
kObs/10−3 s−1
(n‐Propylamine)/mol dm−3
3a
3b
4a
4b
0.001
0.002
0.003
0.004
0.005
0.006
0.01
4.2
0.35
1.12
2.15
3.38
4.90
6.12
11.5
8.92
13.67
18.27
22.75
28.48
1.39
1.38
0.015
0.02
4.17
5.58
8.08
4.16
5.63
8.53
11.5
14.6
0.03
0.04
0.05

ISANBOR
3 of 7
TABLE 2 Kinetic results for reaction of phenyl‐2,6‐dinitrophenyl ether 3a, phenyl‐2,4‐dinitrophenyl ether 3b, 4‐phenoxy‐3,5‐dinitrotrifluoromethylbenzene 4a,
and 2‐phenoxy‐3,5‐dinitrotrifluoromethylbenzene 4b with 1‐methylheptylamine in acetonitrile at 25°C
kObs/10−4 s−1
kObs/10−5 s−1
kObs/10−3 s−1
kObs/10−4 s−1
(1‐Methylheptylamine)/mol dm−3
3a
3b
4a
4b
0.001
0.002
0.004
0.006
0.01
0.015
0.03
0.06
0.1
0.65
1.43
3.27
5.16
0.08
0.28
0.95
2.05
5.20
0.82
2.05
4.43
7.59
23.80
0.61
1.58
3.30
6.03
17.70
0.3
the substitution products 8 dissolved in the reaction medium.
representative rapid spectrum scan is shown in
K1kAm½Amꢀ
kA ¼
(2)
kAm
k−1
A
1 þ
½Amꢀ
Figure 1a. Our results are best interpreted by Scheme 3.
Making the usual[12] assumption that the zwitterionic
adduct 6 may be treated as a steady‐state intermediate (when
the amine acts both as the nucleophile and as the catalysing
base) leads to Equation 1.
kA¼ K1kAm½AmꢀþK1k2
(3)
For the reactions of the nitroaryl ethers reactants 3a, 3b, and
4a with n‐propylamine and 1‐methylheptylamine, plots of kobs
,
the first‐order rate constant against the amine concentration,
were essentially linear with null intercept. A representative plot
of kobs vs (n‐propylamine) is shown in Figure 1b. Thus, values
of the second‐order rate constant, kA, obtained from the slopes
were independent of the amine concentration. This corresponds
to the condition k2 + kAm[Am] > > k−1 so that kA = k1. This is
not unexpected as base catalysis with primary aliphatic amine
nucleophiles has been found in a fewer cases[16–18] where fac-
tors such as the nature of the electrophilic substrate and the sol-
vent contribute to a lowering of the ratio k2/k−1. Before
discussing these data, results for 4b will be reported.
kobs
k1ðk2þkAm½AmꢀÞ
kA ¼
¼
(1)
½Amꢀ k‐1þk2þkAm½Amꢀ
The general reaction scheme for the amine substitution of
1‐phenoxy compounds 3 and 4 shown in Scheme 3 indicates
the possibilities for product formation by an amine (base)
catalysed, kAm, or uncatalysed k2 pathways. However, here,
base catalysis, as argued previously,[12–15,9] is indicative of
rate‐limiting proton transfer from the zwitterionic intermedi-
ates 6, rather than general acid catalysis of phenoxide
expulsion. Hence, Equation 1 applies. Limiting forms,
where K1 = k1/k−1, are Equation 2, when the uncatalysed
pathway may be neglected, and Equation 3, when the condi-
tion k−1 > > k2 + kAm[Am] applies.
For the reactions with n‐propylamine and 1‐
methylheptylamine of 4b carrying an ortho‐CF3 substituent,
the plot of kA versus (amine), shown (Figure 2), was curvilinear
downwards. Values, in Table 3, gave a good fit with Equation 2.
(A)
(B)
FIGURE 1 A, It shows a UV‐Vis rapid scans (at 5 minutes interval for 1 hour and after several hours) for the reaction mixtures of 5.0 × 10−5 M of 4b with 1.0 × 10−3
(n‐propylamine) in acetonitrile. B, This shows a representative plot of the first‐order rate constant, kObs, against (n‐propylamine, PA) for the reactions with 4a
M

4 of 7
ISANBOR
SCHEME 3
FIGURE 2 This shows a representative plot of
the second‐order rate constant, kA, against (n‐
propylamine, PA) for the reaction with 4b (the
inset of Figure 2 shows a linear plot of 1/kA,
against 1/(n‐propylamine, 1/PA) used to obtained
the rate coefficients displayed in Table 3)
A previous result for the same compound with n‐butylamine
has shown that this curvature is indicative of general base catal-
ysis by the reaction with DABCO, a nonnucleophilic base.[12]
for k1 of n‐propylamine
>
n‐butylamine
>
1‐
methylheptylamine for the less‐activated compounds 3a and
3b. In contrast, for the more activated compounds 4a and
4b, the reactivity ratios in k1 are in the order of n‐
butylamine ≈ n‐propylamine > 1‐methylheptylamine. The
reactivity ratios in the values of k1(n‐propylamine)/k1(1‐
methylheptylamine) are 33 (3a), 48 (3b), 5.3 (4a), and 17
(4b). Previous[11,12] results with a set of secondary and pri-
mary amines with the same compounds have shown a
2.1 | Comparisons of the rate constants, k1, for
nucleophilic attack
The results in Table 3 involving nucleophilic attack at a ring
carbon carrying phenoxy nucleofuge show a reactivity order
TABLE 3 Summary of resultsa for reaction of 3 and 4 with aliphatic primary amines in acetonitrile at 25°C
Substrate, R
n‐propylamine
n‐butylamineb
1‐methylheptylamine
3a 4‐H
k1/dm3 mol−1 s−1
k1/dm3 mol−1 s−1
k1/dm3 mol−1 s−1
k1/dm3 mol−1 s−1
0.27 (1)
2.9 × 10−2 (1)
4.8 (1)
4.7 × 10−2 (0.17)
4.9 × 10−3 (0.17)
5.6 (1.17)
8.1 × 10−3 (0.03)
6.0 × 10−4 (0.02)
0.9 (0.19)
3b 6‐H
4a 4‐CF3
4b 6‐CF3
1.70 (1)
2.0 (1.18)
9.7 × 10−2 (0.06)
k
Am/k−1 dm3 mol−1
K1kAm/dm6 mol−2 s−1
245 (1)
220 (0.9)
87 (0.36)
417 (1)
450 (1.08)
8.45 (0.02)
aValues in parentheses are the reactivities for a given compound relative to that for n‐propylamine; for example, k1(n‐butylamine)/k1(n‐propylamine) and
k1(1‐methylheptylamine)/k1(n‐propylamine).
bValues available from previous studies.[12]

ISANBOR
5 of 7
reactivity order for k1 of pyrrolidine > piperidine > n‐
butylamine. This is the order commonly found in nucleo-
philic substitution reactions[1–4] and reflects the relative
basicities of the amines in acetonitrile; pKa values,[19] for
the protonated amines, are pyrrolidine 19.58, piperidine
18.92, and n‐butylamine 18.26. The superior reactivity of
the secondary amines has also been attributed[20] to
favourable ion‐induced dipole interactions in the transition
state between the partially positively charged nitrogen moiety
and the polarisable alkyl substituents attached to it. The pKa
values in water for n‐propylamime, n‐butylamine, and n‐
heptylamine are similar (approximately 10.66),[21] and in ace-
tonitrile, the pKa value of 18.22 for n‐propylamine is compa-
rable with n‐butylamine. However, pKa value in acetonitrile
of 1‐methylheptylamine is not available in the literature, but
it is also expected to be of comparable value to these primary
aliphatic amines. Hence, in the present study, the superior
reactivity of n‐butylamine and n‐propylamine over the lon-
ger‐chain aliphatic amine, 1‐methylheptyamine, is not attrib-
utable to the differences in their basicities but stemmed from
unfavourable steric hindrance to nucleophilic attack due to
the 1‐methyl group in the heptylamine nucleophile.
For compounds 3a and 4a, the reactivity ratios in the
values of k1, 4a/3a, are 18 and 112 for n‐propylamine and
1‐methylheptylamine, respectively. The corresponding ratios
for 4b/3b are 58 and 162 for n‐propylamine and 1‐
methylheptylamine, respectively. It is interesting to note that
these reactivity ratios in the rate of nucleophilic attack is
lower for compounds 4a/3a (where the steric situation at
the 1‐position is constant) compared with 4b/3b, where 4b
is carrying a 6‐CF3 group rather than hydrogen atom at the
6‐position. These observed reactivity differences stem from
an increase in activation in the ring rather than steric effect
due to a change in the substituent group. However, a compar-
ison of the reactivity of 4a/4b gave a ratio of 2.8 for n‐
propylamine or n‐butylamine and 9 for 1‐methylheptylamine.
This is an evidence of increased steric effects due to 6‐CF3
group in 4b, which is more severe due to the methyl group
close to the reaction centre in the reaction with 1‐
methylheptylamine. This is in accord with our previous
results that the reactivity ratio for 4a/4b in the rate of nucle-
ophilic attack increases with increasing bulk of the attacking
amine.[12] The steric effects of the CF3 group in nucleophilic
substitutions have been noted previously,[22] and its size has
been estimated to be comparable to that of an isopropyl
group.[23] Recent calculations[24] have shown that these
effects may derive in part from electrostatic repulsions
between the local negative charge on the trifluoromethyl
group and the bulky nucleophiles. This repulsion from the
trifluoromethyl, CF3, group has been shown[24] to be stronger
than that from the nitro group because of the presence of the
more electronegative fluorine atom and the bigger size of the
CF3 group. Although the x‐ray structure[24,12] of 4b does not
indicate any particularly large effects in the parent molecule,
but kinetic results suggest that sterically, the effect of an
ortho‐CF3 group on nucleophilic attack is greater than that
of a nitro group. Thus, the current investigation reinforces
the idea that the CF3 group is sterically more demanding than
the NO2 group.
2.2 | Base catalysis
The incidence of base catalysis depends on the value of the
ratio kAm/k−1; the lower the value, the greater the likelihood
of base catalysis being observed.[13–15,25] The only com-
pound in this study that is subject to catalysis is 4b in all its
reactions with the amines. This is likely to be due to a
low value for kAm due to repulsion between the ortho‐
CF3 group in the zwitterion and the catalysing amine.
There is good evidence[26–28] that with strongly activated
substrates such as 3 and 4, the zwitterionic intermediates,
6, are more acidic than the corresponding ammonium ion,
RR’H2N+, so that the proton transfer process, kAm, will
be in the thermodynamically “downhill” direction. Hence,
values of kAm may approach the diffusion limit but are
known to be strongly influenced by steric factors. Thus,
values are considerably decreased by steric congestion
around the 1‐position[28,29] and have been found to
decrease with bulkier amine nucleophiles.[11,12,28,29] It must
be noted that steric factors on kAm differ from those
involved in nucleophilic attack at the 1‐position, k1, and
relate to hindrance of the approach of an amine molecule
to the zwitterionic intermediates 6 to allow proton transfer
to occur.
Interestingly, that the reactions with 4b are the only reac-
tion with all amines where base catalysis is observed is a
further evidence for the large “steric” effect of the ortho‐
trifluoromethyl substituent, probably involving electrostatic
repulsion by the CF3 group of the amine base catalyst.
Evidence from our report showed that values of kAm/k−1
tend to increase with increasing electron withdrawal by the
4‐substituent in the reactions of phenoxy compounds, 3, car-
rying various substituent groups in the para position where
the steric situation around the 1‐position is similar. Since
values of kAm are likely to be unchanged, these increases
may be attributed to decreases in values of k−1 as the zwitter-
ionic intermediates, 6, become more thermodynamically sta-
ble. It is interesting to observe from Table 3 that the values of
kAm/k−1 in the reactions with 4b decrease by a factor of ca 3
for n‐propylamine (or n‐butylamine) to 1‐methylheptylamine.
The lower value of kAm/k−1 for 4b as the size of the nucleo-
phile increases again reflects the large “steric” effects of the
6‐CF3 substituent.
It is also intriguing to recall that the reactions with the
phenyl ethers 3 and 4 with aliphatic secondary amines, pyr-
rolidine, and piperidine are all base catalysed whereas it is
only in the reactions with 4b that such catalysis was observed
with all 3 aliphatic primary amines. Here, catalysis involves
rate‐limiting proton transfer from the zwitterionic intermedi-
ates, 6, to base. An additional factor to be considered in

6 of 7
ISANBOR
differentiating the mechanism of SNAr reactions with the
amines is intramolecular hydrogen bonding in the zwitter-
ionic intermediates, 6, between an N‐H proton and an
ortho‐nitro group. The presence of such hydrogen bonding,
affecting the proton to be transferred, has been used[3,4] as
an argument to explain differences in reactivity between pri-
mary and secondary amines. In the case of primary amines,
there will always be one nonhydrogen‐bonded proton avail-
able for transfer thus reducing the susceptibility to base catal-
ysis. We have recently shown by Density functional theory
(DFT) studies[24] that such hydrogen bond with either the
NO2 or the CF3 groups may exist for compounds 4a and 4b
in the transition state leading to the substitution products with
aniline. However, this investigation as in our previous stud-
ies[12] has not found evidence for such hydrogen bonding as
the differentiating factor in the dichotomy of the reactions
involving 4a and 4b with a range of primary aliphatic amines
and secondary amines of comparable basicities. In the present
work, the rather similar susceptibilities to base catalysis with
4b, of which contains an ortho‐nitro and trifluoromethyl
groups, and the observation of base catalysis in the reaction
with both aliphatic primary and secondary amines affirm that
such hydrogen bonding is not a major factor.
3‐positions or 4‐positions of the anilines have only small ste-
ric effects, alkyl substituents at the 2‐position may result in
considerable reductions in reactivity.[31] These effects are
more pronounced for the base‐catalysed pathway, and in
2,6‐dimethylaniline, the uncatalysed decomposition of the
zwitterionic intermediate, 10, takes all the reaction flux.
The results from this study and our previous work[12, 26, 32]
show that all phenyl trinitrophenyl ethers are sterically strained
structures. Hence, steric hindrance to the steps involved in
nucleophilic aromatic substitution by amine nucleophiles
may become a major factor in controlling the rate‐determining
step in the substitution process when
i. the electrophile carries a bulky ortho‐substituent group.
In this case, specific rate‐retarding effects of an ortho‐
CF3 group are observed.
ii. both entering amine and leaving groups carries 2 ortho‐
substituent groups. This often results in an uncatalysed
substitution.[30,31]
iii. N‐substitution in the amine nucleophile[29,32] results in
considerable reduction in reactivity due to steric hin-
drance to the entrance of nucleophile in the formation
of zwitterionic intermediate. The deactivating effect of
N‐CH3 has been observed to be slightly higher than that
of 2,6‐dimethyl group in aniline nucleophiles.
3
| CONCLUSION
These results provide an interesting example of how the
ortho‐CF3 substituent group in the substrate may give rise
to a change in the nature of the rate‐determining step in the
substitution pathway. Steric effects appear to be less impor-
tant in the determining the value of k1, the rate constant for
nucleophilic attack. However, it can, in the case of aromatic
substrates bearing ortho‐CF3 compounds, slow the rate con-
stants for intermolecular proton transfer to a catalysing base.
The result is, for an SNAr reactions in dipolar aprotic solvents
with primary aliphatic amines and aromatic substrates, which
are not prone to catalysis, a change from an ortho‐NO2 to the
ortho‐CF3 substituent often changes the pathway from
uncatalysed to wholly base‐catalysed reaction. A situation
attributed to steric‐induced change in the rate‐determining
step in SNAr reactions.
The observed reactivity differences and the change in
mechanism from uncatalysed to catalysed reaction observed
from a change in the reaction of 4a to 4b with these primary
aliphatic amines are adequately explained in steric factors,
which result in decreases in the value of kAm in the order n‐
propylamine > n‐butylamine ≫ 1‐methylheptylamine. This
is in contrast to the situation in which there is severe steric
hindrance in the nucleofuge or the entering nucleophile.
Our previous report[30] on the kinetic studies for the reactions
with aniline in acetonitrile of a series of ‐phenyl 2,4,6‐
trinitrophenyl ethers (X = H, 2‐, 3‐, 4‐CH3, 2,4‐, 2,6‐
(CH3)2, 2‐, 3‐, 4‐NO2, 2,4‐, 2,6‐(NO2)2) and x‐ray crystal
structures for X = H, 2,6‐(CH3)2 and 2,6‐(NO2)2 provided
evidence for steric crowding around the 1‐position of these
molecules. With the 2,4‐dinitro derivative, the uncatalysed
reaction could compete with the base‐catalysed pathway
but the reactions with the 2,6‐dinitro derivative (X = 2,6‐
(NO2)2) was uncatalysed, as the steric hindrance to intermo-
lecular proton transfer from the zwitterion, 9, to base was
sufficient to make the base‐catalysed pathway insignificant
relative to the k2 pathway. Similarly, the reactions of 2,4‐
dinitrophenyl‐2,4,6‐trinitrodiphenyl ethers with 12 ring‐
substituted anilines showed that although substituents at the
4
| EXPERIMENTAL
The compounds, 3 and 4 and the corresponding amine substi-
tution products, were available from previous work.[12]
Amines and acetonitrile were the purest available commercial
samples. Kinetic measurements were made spectrophotomet-
rically at the absorption maxima of the products using Varian
Cary 50 or 100 UV‐Vis spectrophotometers. Rate constants

ISANBOR
7 of 7
[15] M. R. Crampton, S. D. Lord, J. Chem. Soc., Perkin Trans. 2 1997, 369.
were measured at 25°C under pseudo–first‐order condi-
tions with substrate concentrations of 1 × 10−4 to
1 × 10−5 mol dm−3 and were calculated by standard methods.
Values are precise to 3%.
[16] S. M. Chiacchiera, J. O. Singh, J. D. Anunziata, J. J. Silber, J. Chem. Soc.,
Perkin Trans. 2. 1987, 987.
[17] W. Eggiman, P. Schmid, H. Zollinger, Helv. Chim. Acta 1975, 58, 527.
[18] N. S. Nudelman, Patai’s Chemistry of Functional Groups, Chapter 26,
Chichester, England 1996, 1215.
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How to cite this article: Isanbor C. The influence of
steric effects on the kinetics and mechanism of SNAr
reactions of 1‐phenoxy‐nitrobenzenes with aliphatic
primary amines in acetonitrile. J Phys Org Chem.
2017;e3687. https://doi.org/10.1002/poc.3687
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T. A. Emokpae, C. Isanbor, Eur. J. Org. Chem. 2007, 1378.
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