Effects of the nucleophile structure on the mechanisms of reaction of 1-chloro-2,4-dinitrobenzene with aromatic amines in aprotic solvents

Article abstract of DOI:10.1135/cccc19991583

The kinetics of reactions of 1-chloro-2,4-dinitrobenzene with aniline and several substituted aromatic amines, B, in toluene shows a quadratic dependence of the second-order rate constant, k_A, on [B], which is preserved even in the presence of increasing amounts of dimethylaniline, while the reaction with N-methylaniline shows a linear dependence of k_A vs [B]. All these results are interpreted by the "dimer nucleophile" mechanism, and confirmed by the effects of a non-nucleophilic hydrogen bond acceptor tertiary amine which show the relevance of the structure of the nucleophile and the role of mixed aggregates in defining the mechanisms of aromatic nucleophilic substitutions with amines in aprotic solvents.

Full text of DOI:10.1135/cccc19991583

Effects of the Nucleophile Structure
1583
EFFECTS OF THE NUCLEOPHILE STRUCTURE ON THE MECHANISMS
OF REACTION OF 1-CHLORO-2,4-DINITROBENZENE WITH AROMATIC
AMINES IN APROTIC SOLVENTS
a,
b1
b2
Norma Sbarbati NUDELMAN *, Cecilia E. Silvana ALVARO , Monica SAVINI ,
b3
b
Viviana NICOTRA and Jeannette YANKELEVICH
a
Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales,
Universidad de Buenos Aires, 1428 Buenos Aires, Argentina; e-mail: nudelman@qo.fcen.uba.ar
Departamento de Química, Facultad de Ingeniería, Universidad Nacional del Comahue, Neuquén,
b
1
2
Argentina; e-mail: salvaro@uncoma.edu.ar, msavini@uncoma.edu.ar,
3
vnicotra@uncoma.edu.ar
Received July 1, 1999
Accepted Septem ber 13, 1999
Dedicated to Professor Otto Exner on the occasion of his 75th birthday.
Th e kin etics of reaction s of 1-ch loro-2,4-din itroben zen e with an ilin e an d several substituted
arom atic am in es, B, in toluen e sh ows a quadratic depen den ce of th e secon d-order rate con -
stan t, k , on [B], wh ich is preserved even in th e presen ce of in creasin g am oun ts of
A
dim eth ylan ilin e, wh ile th e reaction with N-m eth ylan ilin e sh ows a lin ear depen den ce of
kA vs [B]. All th ese results are in terpreted by th e “dim er n ucleoph ile” m ech an ism , an d
con firm ed by th e effects of a n on -n ucleoph ilic h ydrogen bon d acceptor tertiary am in e
wh ich sh ow th e relevan ce of th e structure of th e n ucleoph ile an d th e role of m ixed aggre-
gates in defin in g th e m ech an ism s of arom atic n ucleoph ilic substitution s with am in es in
aprotic solven ts.
Key words: Arom atic nucleophilic substitutions; Aprotic solvents; Dim er nucleophile m echanism ;
Am in e aggregation states; Nucleoph ile structure; Reaction m ech an ism ; Reaction kin etics.
Th e solven t in wh ich an arom atic n ucleoph ilic substitution (S Ar) is carried
N
out plays a critical role in determ in in g th e reaction m ech an ism by con trol-
lin g th e degree of aggregation of reactan ts an d th e life-tim e of th e differen t
1
in term ediates th at can be form ed . Th us, th e n ature of th e solven t deter-
m in es wh eth er th e form ation or th e decom position of th e zwitterion ic in -
term ediate will be th e rate-determ in in g step2
,3
.
However, recen t studies on S Ar with n eutral n ucleoph iles (aliph atic an d
N
arom atic am in es) in aprotic solven ts h ave been ch aracterized by un usual
fin din gs, especially wh en th e secon d step is rate determ in in g1 . Th ese
,4,5
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
584
Nudelman et al.:
“
abn orm al” results are ch aracterized, am on g oth er features, by a th ird-order
depen den ce on am in e con cen tration , an d m ost of th em can be con sisten tly
explain ed by th e “dim er n ucleoph ile m ech an ism ” wh ich was previously de-
6
scribed .
Th e n ature an d exten t of solute–solven t in teraction s can alter th e proper-
7
8,9
ties of th e n ucleoph ile . It is well kn own
th at am in es un dergo self-
association givin g rise to aggregates of various stoich iom etries; th e predom -
in atin g aggregate is usually a dim er with typical form ation con stan t of
–
1
3
0
.1–1 m ol dm . Th e n ucleoph ile dim er is form ed because of th e kn own
ability of prim ary an d secon dary am in es to in teract th rough h ydrogen
bon ds. A n on -n ucleoph ilic tertiary am in e could act as a h ydrogen bon d ac-
ceptor (HBA) toward th e n ucleoph ile, form in g a m ixed aggregate providin g
th at th e n ucleoph ilic am in e is less basic th an th e previous on e. Th e m ixed
dim er would th en be a better n ucleoph ile th an th e pure dim er, as it was re-
1
0
cen tly reported
.
In order to search in to th e exten t of th is n ew m ech an ism , kin etic an d
spectroph otom etric studies on th e reaction of 1-ch loro-2,4-din itroben zen e
with an ilin e an d substituted an ilin es in an aprotic solven t such as toluen e,
h ave been carried out. Th e effects of th e structure of th e n ucleoph ile, its
self-aggregation states, an d th e form ation of m ixed aggregates on th e rates
of reaction are exam in ed.
EXPERIMENTAL
Reagen ts an d Solven ts
An ilin e (Fluka), p-toluidin e (Fluka), 2,4-dim eth ylan ilin e (Fluka), N-m eth ylan ilin e (Fluka) an d
N,N-dim eth ylan ilin e (Fluka) were kept overn igh t over potassium h ydroxide, distilled over
zin c powder an d th en over sodium ; both distillation s were carried out un der n itrogen at re-
duced pressure; p-an isidin e (Fluka) was purified to con stan t m eltin g poin t by
1
1
recrystallization with toluen e (m .p. 56–57 °C, ref.
ben zen e (Sigm a) was crystallized twice from absolute eth an ol (m .p. 52–53 °C, ref. gives
2–53 °C). Toluen e was kept over sodium wire for several days, an d distilled twice over
gives 57 °C). 1-Ch loro-2,4-din itro-
1
2
5
1
3
sodium . N-(2,4-din itroph en yl)an ilin e (m .p. 155–156 °C, ref. gives 155–156 °C) was pre-
pared from 1-ch loro-2,4-din itroben zen e an d an ilin e followin g th e procedure reported
1
4
for N-(2,4-din itroph en yl)-2-m eth oxyan ilin e . N-(2,4-Din itroph en yl)-2,4-dim eth ylan ilin e
1
3
(
1
m .p. 156–157 °C), N-(2,4-din itroph en yl)-N-m eth ylan ilin e (m .p. 165–167 °C, ref. gives
1
3
66–167 °C), N-(2,4-din itroph en yl)-p-toluidin e (m .p. 132–134 °C, ref. gives 136–137 °C)
1
1
an d N-(2,4-din itroph en yl)-p-an isidin e (m .p. 133–134 °C, ref. gives 133–134 °C) were pre-
pared by th e sam e procedure14. Th e solven ts were purified as already described15 an d stored
in special vessels wh ich allow delivery with out air con tam in ation .
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Effects of the Nucleophile Structure
1585
An cillary Spectroph otom etric Measurem en ts
UV-VIS spectra of th e substrate an d products, of various m ixtures of both com poun ds with
an ilin e an d with substituted an ilin es at several am in e con cen tration s were recorded in a
Sh im adzu spectroph otom eter. UV spectra of con trol solution s of th e substitution products
in toluen e con tain in g various am oun ts of th e am in es were recorded, an d th e absorption co-
efficien ts determ in ed at λ = 450 n m wh ere th e reagen ts are tran sparen t un der th ese con di-
tion s. All th e solution s were foun d to obey Beer’s law.
Kin etic Procedures
Kin etic run s were perform ed by th e m eth ods previously reported12 followin g th e appearan ce
of th e reaction product at λ = 450 n m . In all cases pseudo-first-order kin etics were observed.
Pseudo-first-order rate con stan ts, k , were obtain ed by th e least-squares m eth od as th e slope
ψ
of th e depen den ce [ln (A∞ - A )/A ] again st tim e, wh ere A is th e absorban ce of th e reaction
t
∞
∞
m ixture m easured at “in fin ity” (m ore th an ten h alf-lives); th e secon d-order rate con stan ts,
kA, were obtain ed by dividin g kψ by th e am in e con cen tration s. Th e rate con stan ts were re-
producible to ±2%. No correction s for expan sion were applied to th e con cen tration values.
RESULTS AND DISCUSSION
Effect of the Nucleophile Structure
Th e rates of th e reaction s of 1-ch loro-2,4-din itroben zen e, DNClB, with an i-
lin e, p-m eth ylan ilin e, p-an isidin e, 2,4-dim eth ylan ilin e an d N-m eth ylan ilin e
in toluen e at 40 °C were determ in ed at am in e con cen tration s ran gin g from
–
3
0
.25 to 3.0 m ol dm . In all th e reaction s studied, quan titative form ation of
th e N-(2,4-din itroph en yl)an ilin e was observed an d pseudo-first-order con -
dition s were used th rough out th is work. Th e determ in ed pseudo-first- an d
secon d-order rate con stan ts are given in Table I. Th e secon d-order rate con -
stan ts, k , were foun d to in crease rapidly with am in e con cen tration , [B]; th e
A
plots of k vs [B] (Fig. 1) sh ow a quadratic depen den ce for th e reaction s of
A
th e prim ary an ilin es. If th e quotien t k /[B] is plotted again st [B] (n ot
A
sh own ), a straigh t lin e is obtain ed, con sisten t with a th ird-order kin etic
law, with respect to th e am in e, as it h as been previously observed for oth er
arom atic n ucleoph ilic substitution s with am in es in aprotic solven ts1,14,16
.
On th e oth er h an d, th e reaction of 2,4-DNClB with N-m eth ylan ilin e sh ows
a strictly lin ear depen den ce of k vs [B] (n ot sh own ).
A
Th e classic two-step base-catalyzed S Ar with am in es, B, follows a
N
th ird-order kin etic law. Th e overall secon d-order rate con stan t, k , derived
A
by stan dard steady-state approxim ation h as th e form of Eq. (1)
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
586
Nudelman et al.:
B
k k + k k [B]
1
2
1
3
kA =
,
(1)
B
k−1 + k + k [B]
2
3
wh ich cam e from th e addition –elim in ation m ech an ism depicted in Eq. (2)
for n eutral n ucleoph iles (am in es, alcoh ols, water) an d n itro-activated aro-
1
,2
m atic substrates
.
k3 [B]
k2
k1
(
2)
S +
B
[SB]
Products
k-1
Equation (1) predicts a straigh t lin e for th e plot of k vs [B] or a down -
A
ward curvature. But several S Ar reaction s with am in es in aprotic solven ts
N
studied in th e last years exh ibit an upward curvature, th is kin etic beh aviour
bein g in terpreted by th e m ech an ism sh own in Eqs (3) an d (4) wh ere a dimer
(
B:B) of th e n ucleoph ile attacks th e substrate, S, form in g th e in term ediate,
SB , a th ird m olecule of am in e assistin g th e decom position step. Th e tran si-
2
TABLE I
a
Reaction s of 1-ch loro-2,4-din itroben zen e, DNClB, with substituted an ilin es in toluen e at 40 °C
[
An ilin e], m ol dm –3
06kψ, s–1
0.50
1.00
1.20
1.20
1.00
0.73
0.73
0.50
4.32
8.64
1.01
0.179
0.177
1.01
0.111
0.110
2.00
5.20
2.98
14.0
1
1
0.32
0 k , s m ol–1 dm 3
6
–1
0.64
2.60
4.70
3.00
A
[
4-Meth ylan ilin e], m ol dm –3
06kψ, s–1
0.50
2.00
1
1
0.16
4.28
17.20
5.73
0 k , s m ol–1 dm 3
6
–1
0.32
2.14
A
[
4-Meth oxyan ilin e], m ol dm –3
06kψ, s–1
0.25
0.75
1.00
1
1
1.05
11.68
15.57
1.51
27.63
27.63
1.99
0 k , s m ol–1 dm 3
6
–1
4.20
A
[
2,4-Dim eth ylan ilin e], m ol dm –3
06kψ, s–1
0.520
0.054
0.104
0.498
0.035
0.070
2.50
1
0.431
0.286
1.51
0.794
0.399
2.01
1.526
0.610
2.51
0 k , s m ol–1 dm 3
6
–1
1
A
[
N-m eth ylan ilin e], m ol dm –3
06kψ, s–1
1
1
0.234
0.155
0.382
0.190
0.59
0 k , s m ol–1 dm 3
6
–1
0.235
A
a
DNClB] = 2.00 · 10–4 m ol dm –3, b [DNClB] = 5.12 · 10–4 m ol dm –3
[
.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Effects of the Nucleophile Structure
1587
tion states in Eq. (4) are h igh ly zwitterion ic an d th e extra am in e m olecule
sh ould h elp to stabilize th e developin g ch arge in th e n on polar solven ts.
2
Th e kin etic law is given by Eq. (5) wh ere K = [B:B]/[B] stan ds for th e am in e
0
self-association con stan t.
K
2
B
B:B
(3)
(4)
k3 [B]
k1
k-1
[
SB2]
S + B:B
Products
k2
2
k k K[B] + k k K[B]
1
2
1
3
kA =
(5)
k−1 + k + k [B]
2
3
Th e presen t results can be in terpreted in term s of “dim er n ucleoph ile”
m ech an ism in wh ich a dim eric aggregate of th e am in e, (B:B) is con sidered
to attack th e substrate in th e first step17 (Eqs (3)–(5)).Th e dim er m ech an ism
does n ot preclude attack by free am in e wh ich is sim ultan eously operatin g.
A wh ole kin etic treatm en t wh ich in volves th e classic (m on om er) an d th e
6
n ew (dim er) m ech an ism was subsequen tly reported .
3
0
6
5
2
2
5
0
4
1
1
5
0
3
2
5
0
1
0
0
.0
0.5
1.0
1.5
2.0
2.5
3.0
Amine], mol dm
–
3
[
FIG. 1
Overall secon d-order rate con stan ts, k , for th e reaction of 1-ch loro-2,4-din itroben zen e with :
A
❐
4-m eth oxyan ilin e, ❐ an ilin e, ❐ 4-m eth ylan ilin e an d ❐ 2,4-dim eth ylan ilin e in toluen e at
4
0 °C, as a fun ction of am on e m olar con cen tration
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
588
Nudelman et al.:
Th ere is eviden ce th at a h igh er basicity of th e am in es supports th eir
dim erization , th e dim er bein g m ore reactive because of its h igh er
1
8–20
don icity
secon d-order rate con stan t an d a greater curvature in th e plot of k vs [B],
. Wh en 4-m eth oxyan ilin e is used as n ucleoph ile, a greater
A
(
Fig. 1), were observed. In order to evaluate th e m agn itude of th e curvature,
th e experim en tal values were fitted to a secon d-degree polyn om ial fun c-
tion . Th e quadratic coefficien ts an d stan dard deviation s (SD) for all
n ucleoph iles are sh own in Table II. Th ese data in dicate th at th e quadratic
coefficien ts, except for N-m eth ylan ilin e, are sign ifican tly differen t from
zero.
Wh en 2,4-dim eth ylan ilin e is used, th e secon d-order rate con stan ts are
con siderably sm aller th an for an ilin e at an y con cen tration , in spite of its
expected greater n ucleoph ilicity; th e quadratic coefficien t is also m uch less
relevan t th an for th e oth er an ilin es. Th ese results are con sisten t with th e
“
dim er n ucleoph ile” m ech an ism an d can be easily explain ed by decreased
dim erization due to th e steric h in dran ce produced by th e m eth yl group at
th e ortho position .
For th e reaction of DNClB with N-m eth ylan ilin e in toluen e, th e plot of
kA vs [N-m eth ylan ilin e] (n ot sh own ) sh ows a clear lin ear depen den ce with a
zero in tercept, wh ich can be properly described by Eqs (1) an d 2, wh ere th e
spon tan eous decom position of th e zwitterion ic in term ediate is n egligible.
Th is kin etic beh aviour differen t from th at observed with th e oth er n ucleo-
ph iles (Table I), is con sisten t with wh at could be expected for th e N-alkyl-
an ilin es, con siderin g th at th ey un dergo less self-association th an an ilin e.
For th is reason th e attack by th e “dim er n ucleoph ile” is n ot relevan t. Con -
TABLE II
Quadratic coefficien t of th e polyn om ial equation for th e reaction of DNClB with an ilin e an d
a
substituted an ilin es in toluen e at 40 °C
Nucleoph ile
Quadratic coefficien t
SD
An ilin e
0.2302
0.7043
19.714
0.0141
–0.0218
0.0572
0.1383
4.6299
0.0041
0.0126
4
4
2
-Meth ylan ilin e
-Meth oxyan ilin e
,4-Dim eth ylan ilin eb
N-Meth ylan ilin eb
a
DNClB] = 2.00 · 10–4 m ol dm –3, b [DNClB] = 5.12 · 10–4 m ol dm –3
[
.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Effects of the Nucleophile Structure
1589
sisten t with th is in terpretation , th e reaction with N-m eth ylan ilin es are
slower th an with an ilin e, in spite of th eir in creased basicity, pK = 9.21 an d
b
2
1
pK = 9.40, respectively .
b
Effect of HBA Additive
Abun dan t eviden ce of th e effect of m ixed aggregates of th e am in e n ucleo-
ph ile an d HBA additives on th e rates of S NAr h as been accum ulated in
N
1
,22,23
recen t years
. Th e en h an cem en t effect of th e HBA additives is in trin si-
cally in volved in th e “dim er n ucleoph ile” m ech an ism , an d it is also in ter-
preted by th e m on o–h etero-con jugate m ech an ism developed by Hirst
1
2
3,24
.
Th e in fluen ce of N,N-dim eth ylan ilin e, DMA, a good HBA, was studied by
m easurin g th e rate depen den ce with th e an ilin e con cen tration at various
fixed [DMA] values; th e secon d-order rate con stan ts are given in Table III.
Addition of DMA to th e reaction m ixture in creases th e reaction rate at all
th e an ilin e con cen tration s studied, an d th e quadratic depen den ce of
k with [B] (Fig. 2), is preserved even in th e presen ce of [DMA] as h igh as
A
–
3
0
.8 m ol dm . Th e plots of k vs [DMA] at fixed [an ilin e] (n ot sh own ) are
A
lin ear with n o zero in tercepts, an d th e slope is alm ost 2 for th e reaction
with 2 M an ilin e. Form ation of th e m ixed dim er, Ph (CH ) N···H NPh ,
3
2
2
wh ich com petes with th e pure dim er, is th ough t to be respon sible for th e
rate in crease. Sch em e 1 sh ows th e overall reaction picture wh ich in volves
th e m on om er, th e dim er an d th e m ixed aggregate m ech an ism s. An aggre-
TABLE III
Secon d-order rate con stan ts, 10 kA, s–1 m ol–1 dm , in th e reaction of 1-ch loro-2,4-din itro-
6
3
a
ben zen e, DNClB , with an ilin e, B, in th e presen ce of N,N-dim eth ylan ilin e, DMA, in toluen e
at 40 °C
[
An ilin e], m ol dm –3
1.00
[
DMA], m ol dm –3
0
.50
2.00
0
0
0
0
0
.100
.200
.300
.505
.804
0.178
0.206
0.228
0.260
0.316
0.397
0.461
0.513
0.646
0.834
0.789
0.921
1.078
1.40
1.93
a
DNClB] = 5.12 · 10–4 m ol dm –3
[
.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
590
Nudelman et al.:
NRH2
X
H
k3 B
k2
NO2
NHR
k1
X
NO2
.
+
RH2N...H NHR
[
P NHR2] + XH
k-1
B:B
NO2
X
NO2
K2
K1
B
B
NHR
NO2
.
NO2
NH2R
NO2
k4
X
k5
+
RNH2
+ X
k-4
B
NO2
X
NO2
NO2
P
K3 DMA
DMA K4
R3N
NO2
H
k7
R3N...H NHR
NHR
NO2
.
3
[P NR ] + XH
+
X
k-7
k8
DMA:B
NO2
k9,DMA
NO2
SCHEME 1
3
2
.0
.5
2
1
.0
.5
1
0
.0
.5
0
.0
0
.0
0.5
1.0
1.5
2.0
Aniline], mol dm
2.5
–
3
[
FIG. 2
Overall secon d-order rate con stan ts, k , for th e reaction of 1-ch loro-2,4-din itroben zen e with
A
–3
an ilin e in th e presen ce of N,N-dim eth ylan ilin e, DMA, in toluen e at 40 °C. [DMA] in m ol dm
0.1, ❐ 0.2, ❐ 0.3, ❐ 0.5, ❐ 0.8
:
❐
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Effects of the Nucleophile Structure
1591
gate between th e product, P, an d th e am in e, depicted as [P·NHR ], is
2
sh own in th e sch em e, sin ce we h ave recen tly reported kin etic an d spectro-
1
2
scopic eviden ce of th e form ation of such type of aggregates . In th e pres-
en t case, th e form ation of a m olecular com plex between P an d DMA,
1
2
[
P·NR ], was also detected by th e procedure already described , th e slope
3
of plot of th e “excess” of th e absorban ce of th e product in th e presen ce of
2
differen t am oun ts of DMA bein g 0.049 (r = 0.9951).
Th e wh ole an alytical expression for k is sh own in a con den sed way in
A
Eq. (6), wh ere B an d DMA stan d for an ilin e an d N,N-dim eth ylan ilin e,
respectively.
2
kA = k [B] + k [B] + k [B] [DMA] + k [DMA]
(6)
a
b
c
d
Several reaction s were carried out to test Eq. (6); th e four con stan ts could
be determ in ed wh ich are given in Eq. (7). Th e n egative param eters in
Eq. (7) are n egligible an d m ean in gless, for th is reason , by puttin g th e
restriction k = k = 0, Eq. (7) was sim plified to Eq. (8), wh ich sh ows th at
b
d
th e rate con stan t for th e m ixed-aggregate is m ore th an twice th at of th e
m on om er.
2
kA = 0.336 [B] – 0.017 [B] + 0.957 [B] [DMA] – 0.0296 [DMA]
(7)
(8)
kA = 0.307 [B] + 0.76 [B] [DMA]
Table IV gives th e observed k for differen t [an ilin e] an d [DMA] as well as
A
th e k ’s calculated from Eqs (7) an d (8). Th ese results sh ows th at Eqs (7) an d
A
(
8) h old in th e wh ole con cen tration s ran ge studied. As sh own in Table IV,
th e secon d-order rate con stan ts given by Eq. (8) agree satisfactorily with th e
experim en tal kA.
Conclusions
Th e presen t results con firm th at association of am in es in aprotic solven ts
plays an im portan t role in defin in g th e m ech an ism s of arom atic
n ucleoph ilic substitution s in aprotic solven ts. Th e n ucleoph ile structure is
crucial: prim ary arom atic am in es are pron e to react by th e “dim er
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
592
Nudelman et al.:
n ucleoph ile” m ech an ism , wh ile secon dary am in es can react in th e
m on om eric state. Steric effects in th e substituted an ilin e n ear th e reaction
cen tre cause a decrease in th e dim er rate con stan t wh ile m ixed-aggregation
of th e n ucleoph ile with H-bon d acceptor, a n on -n ucleoph ilic am in e, sh ows
a con siderable in crease in th e rate, con sisten tly with wh at can be expected
with in th e “dim er n ucleoph ile” m ech an ism fram ework.
TABLE IV
Experim en tal an d calculated secon d-order rate con stan ts, 10 k , s m ol–1 dm , in th e reac-
6
–1
3
A
a
tion of 2,4-din itroben zen e, DNClB , with an ilin e in th e presen ce of N,N-dim eth ylan ilin e,
DMA, in toluen e at 40 °C
a
1
06k
A
[
An ilin e]
[DMA]
m ol dm
–
3
–3
m ol dm
(
exp)
(calc)b
(calc)b,c
0
1
2
.5
.0
.0
0.100
0.178
0.206
0.228
0.260
0.316
0.182
0.200
0.219
0.256
0.312
0.191
0.229
0.267
0,.345
0.462
0
0
0
0
.200
.300
.505
.812
0.105
0.393
0.461
0.513
0.646
0.834
0.389
0.452
0.518
0.663
0.841
0.387
0.459
0.535
0.702
0.907
0
0
0
0
.200
.300
.520
.789
0.100
0.789
0.921
1.078
1.400
1.930
0.767
0.929
1.091
1.423
1.907
0.766
0.918
1.070
1.381
1.836
0
0
0
0
.200
.300
.505
.804
a
DNClB] = 5.12 · 10–4 m ol dm –3. b Calculated from Eq. (6). c Calculated with restriction : kb
[
=
kd = 0.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Effects of the Nucleophile Structure
1593
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Collect. Czech. Chem. Commun. (Vol. 64) (1999)