1H and 13C NMR spectra, structure and physicochemical features of phenyl acridine-9-carboxylates and 10-methyl-9-(phenoxycarbonyl) acridinium trifluoromethanesulphonates - alkyl substituted in the phenyl fragment

Article abstract of DOI:10.1016/j.saa.2010.10.029

The ¹H and ¹³C NMR spectra of twelve phenyl acridine-9-carboxylates - alkyl-substituted in the phenyl fragment - and their 10-methyl-9-(phenoxycarbonyl)acridinium salts dissolved in CD₃CN, CD₃OD, CDCl₃

Full text of DOI:10.1016/j.saa.2010.10.029

Spectrochimica Acta Part A 78 (2011) 401–409
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
1H and 13C NMR spectra, structure and physicochemical features of phenyl
acridine-9-carboxylates and 10-methyl-9-(phenoxycarbonyl)acridinium
trifluoromethanesulphonates – alkyl substituted in the phenyl fragment
K. Krzymin´ ski∗, P. Malecha, B. Zadykowicz, A. Wróblewska, J. Błaz˙ ejowski
Faculty of Chemistry, University of Gdan´sk, J. Sobieskiego 18, 80-952 Gdan´sk, Poland
a r t i c l e i n f o
a b s t r a c t
The 1H and 13C NMR spectra of twelve phenyl acridine-9-carboxylates – alkyl-substituted in the phenyl
fragment – and their 10-methyl-9-(phenoxycarbonyl)acridinium salts dissolved in CD3CN, CD3OD, CDCl3
and DMSO-d6 were recorded in order to examine the influence of the structure of these compounds and
the properties of the solvents on chemical shifts and 1H–1H coupling constants. Experimental data were
compared with 1H and 13C chemical shifts predicted at the GIAO/DFT level of theory for DFT(B3LYP)/6-
31G** optimised geometries of molecules, as well as with values of 1H chemical shifts and 1H–1H coupling
constants, estimated using ACD/HNMR database software to ensure that the assignment was correct. To
investigate the relations between chemical shifts and selected structural or physicochemical characteris-
tics of the target compounds, the values of several of these parameters were determined at the DFT or HF
levels of theory. The HOMO and LUMO energies obtained at the HF level yielded the ionisation potentials
and electron affinities of molecules. The DFT method provided atomic partial charges, dipole moments,
LCAO coefficients of pz LUMO of selected C atoms, and angles reflecting characteristic structural features
of the compounds. It was found that the experimentally determined 1H and 13C chemical shifts of certain
atoms relate to the predicted dipole moments, the angles between the acridine and phenyl moieties,
and the LCAO coefficients of the pz LUMO of the C atoms believed to participate in the initial step of
the oxidation of the target compounds. The spectral and physicochemical characteristics of the target
compounds were investigated in the context of their chemiluminogenic ability.
Article history:
Received 9 June 2010
Received in revised form 9 September 2010
Accepted 1 October 2010
Keywords:
Phenyl acridine-9-carboxylates
10-Methyl-9-(phenoxycarbonyl)acridinium
cations
1H and 13C NMR spectroscopy
Structure
Physicochemical features
Spectral versus structural or
physicochemical characteristics
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
capable of reacting with the relevant fragments of molecules of bio-
logical importance. Such compounds, known as chemiluminescent
Acridinium cations alkyl-substituted at the endocyclic nitro-
gen atom and containing electron-attracting substituents at C9
(Scheme 1) demonstrate chemiluminogenic features in reaction
with oxidants (H2O2, peroxidases) in alkaline media [1–7]. The oxi-
dation of these entities, initiated by the attack of peroxide anions
(e.g. OOH−) on C9, gives rise to electronically excited 10-alkyl-
9-acridinones, whose relaxation is accompanied by the emission
of light. The efficiency of chemiluminescence, reaching a level of
a few percent is affected by the presence of nucleophilic species
competing with oxidants for substitution at C9 [8–10]. The above-
mentioned features exhibited by acridinium chemiluminogenic
indicators can be utilised in the assay of oxidants or nucleophiles
[4,5,9–11]. Acridinium chemiluminogens can also be linked via
a spacer (e.g. alkyl chain) to an active group (e.g. succinimidyl)
labels, are widely used in chemical, biological, medical and envi-
ronmental analyses [4–6,8,11–17]. For these reasons, acridinium
chemiluminogens have been objects of interest for several years
[3,7,9,18,19].
This publication focuses on the NMR spectra of twelve
10-methyl-9-(phenoxycarbonyl)acridinium
trifluoromethane-
sulphonates, alkyl substituted in the phenyl fragment, that we
think are interesting as chemiluminogenic indicators, and their
precursors
– phenyl acridine-9-carboxylates (Scheme 1). To
our knowledge no systematic NMR investigations and quan-
tum chemistry studies on this interesting group of compounds
have been carried out so far. Undertaking these investigations
thus opens up possibilities for gathering NMR data for acri-
dinium chemiluminogens, for their thorough interpretation
with the aid of computationally predicted characteristics, for
determining their structural and physicochemical characteris-
tics, and for discovering the relations between the spectral and
physicochemical features of the molecules. This knowledge may
∗
Corresponding author. Tel.: +48 58 523 5467; fax: +48 58 523 5472.
E-mail address: karolk@chem.univ.gda.pl (K. Krzymin´ ski).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.10.029

402
K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
17
16
17
O
16
O
O
O
15
15
R
R
8
9
8
9
1
1
14
13
11
14
13
11
12
7
6
7
6
2
3
2
3
10
N+
12
N
10
5
4
5
4
R1
I
II
R=
R1=
23
22
20
23
23
23
22
20
22
20
22
20
26
24
25
18
18
18
18
21
21
21
21
CH3
CH3
CH3
24
19
19
24
19
19
C
H C
3
H C
1A
2A
3A
2
24
H C
3
CH
26
3
CH
25
3
27
28
25
25
CH3
CH3
CH3
1
2
4
3
25
CH
4A
5A
6A
3
23
22
23
19
23
22
22
22
23
24
CH
25
26
18
26
18
21
18
18
21
21
21
3
CH3
CH3
CH3
19
20
24
C
20
19
20
20
25
H C
3
19
H C
3
8A
7A
9A
CH
24
3
24
H C
CH
27
3
3
26
27
26
26
CH3
CH3
CH3
5
6
7
8
25
H C
3
26
H C
25
CH
11A
10A
12A
3
3
3
23
23
23
22
20
22
22
20
23
19
22
20
25
25
CH
18
18
18
18
21
21
21
21
CH
3
3
19
20
19
19
H C
3
CH
24
CH
H C
3
3
24
24
24
9
12
10
11
Scheme 1. Canonical structures of phenyl acridine-9-carboxylates (I) and 10-methyl-9-(phenoxycarbonyl)acridinium cations (II); the numbering of the
atoms is indicated. Names of the compounds: 1, phenyl acridine-9-carboxylate; 2, 2-methylphenyl acridine-9-carboxylate; 3, 2-ethylphenyl acridine-9-
I
–
carboxylate; 4, 2-isopropylphenyl acridine-9-carboxylate; 5, 2-tert-butylphenyl acridine-9-carboxylate; 6, 3-methylphenyl acridine-9-carboxylate; 7, 4-methylphenyl
acridine-9-carboxylate; 8, 2,5-dimethylphenyl acridine-9-carboxylate; 9, 2,6-dimethylphenyl acridine-9-carboxylate; 10, 3,4-dimethylphenyl acridine-9-carboxylate;
11, 3,5-dimethylphenyl acridine-9-carboxylate; 12, mesityl acridine-9-carboxylate; II
– 1A, 10-methyl-9-(phenoxycarbonyl)acridinium; 2A, 10-methyl-9-[(2-
methylphenoxy)carbonyl]acridinium; 3A, 9-[(2-ethylphenoxy)carbonyl]-10-methylacridinium; 4A, 9-[(2-isopropylphenoxy)carbonyl]-10-methylacridinium; 5A, 9-[(2-
tert-butylphenoxy)carbonyl]-10-methylacridinium; 6A, 10-methyl-9-[(3-methylphenoxy)carbonyl]acridinium; 7A, 10-methyl-9-[(4-methylphenoxy)carbonyl]acridinium;
8A, 9-[(2,5-dimethylphenoxy)carbonyl]-10-methylacridinium; 9A, 9-[(2,6-dimethylphenoxy)carbonyl]-10-methylacridinium; 10A, 9-[(3,4-dimethylphenoxy)carbonyl]-10-
methylacridinium; 11A, 9-[(3,5-dimethylphenoxy)carbonyl]-10-methylacridinium; 12A, 9-[(mesityloxy)carbonyl]-10-methylacridinium.
occur helpful in evaluating the practical utility of this group of
compounds.
N,N-diethylethanamine and a catalytic amount of N,N-dimethyl-4-
pyridinamine (room temperature, 15–25 h, anhydrous conditions).
The crude esters were subsequently flushed with HCl, NaHCO3 and
NaCl solutions and purified by column chromatography (station-
ary phase: Silica Gel 60 (Merck), mobile phase: cyclohexane/ethyl
acetate = 1/1–3/2, v/v) (yield 60–90%). The purity and identity of
the phenyl acridine-9-carboxylates was checked by TLC (using
the above-described stationary and mobile phase) and elemen-
tal analysis [20]. The structures of some of the compounds were
determined by X-ray diffractometry [21,22].
2. Methods
2.1. Materials
The compounds were synthesised in the manner described else-
where [12,18]. Briefly, acridine-9-carboxylic acid was converted
into 9-(chlorocarbonyl)acridinium chloride by being refluxed
with excess thionyl chloride (yield ca 92%). Next, portions of
the acyl chloride were stirred with a stoichiometric amount of
the appropriate phenol in dichloromethane in the presence of
To obtain 10-methyl-9-(phenoxycarbonyl)acridinium trifluo-
romethanesulphonates, the above-mentioned esters were quater-
narised using methyl trifluoromethanesulphonate (fivefold molar

Table 1
Structural and physicochemical features of phenyl acridine-9-carboxylates (1–12) and 10-methyl-9-(phenoxycarbonyl)acridinium cations (1A–12A).
Compound no.
(Scheme 1)
Methoda
Angle (◦)
Dipole moment
(D)
Energy (eV)
Relative partial
charge of
Relative atomic
partial charge
at
LCAO
coefficient of
the pz LUMO at
substituent at
C9c
N10···C9–C15
Ab
Bb
Cb
LUMO
HOMO
C9
C15
Mulliken
MEP fit
Mulliken
MEP fit
Mulliken
MEP fit
C9
C15
1
2
Theor
Theor
X-ray
Theor
X-ray
Theor
Theor
Theor
Theor
Theor
X-ray
Theor
Theor
Theor
Theor
Theor
X-ray
Theor
X-ray
Theor
X-ray
Theor
Theor
X-ray
Theor
Theor
X-ray
Theor
Theor
Theor
Theor
Theor
X-ray
178.4
177.8
177.7(1)
177.6
178.3(1)
178.5
177.3
178.4
178.4
178.4
178.3(1)
177.9
178.4
178.4
177.8
178.5
178.0(1)
178.2
175.6(1)
178.3
176.6(1)
178.0
177.4
177.8(1)
178.4
178.6
172.1(1)
178.4
177.8
178.8
177.6
177.7
1.2
1.3
0.4(1)
1.2
2.2(1)
1.3
1.3
1.2
1.2
1.2
2.2(1)
0.9
1.1
1.2
0.8
6.1
2.3(1)
6.2
4.8(1)
6.4
3.4(1)
6.6
6.5
0.7(1)
6.2
6.1
3.5(1)
6.3
6.3
6.1
6.2
6.3
51.4
51.2
58.0(1)
51.2
52.1(1)
50.4
51.3
51.5
51.5
51.1
52.1(1)
47.6
51.3
51.6
47.4
61.4
77.0(1)
60.7
87.8(1)
60.9
66.2(1)
60.0
60.1
60.7(1)
61.2
61.0
83.1(1)
60.4
59.9
60.3
63.0
60.1
85.4
81.4
30.0(1)
82.8
61.7(1)
76.5
77.7
81.8
87.0
81.4
61.7(1)
60.2
83.8
80.4
60.6
82.9
15.6(1)
76.1
28.5(1)
78.4
20.8(1)
78.9
73.1
66.1(1)
84.6
86.3
3.0(1)
76.5
48.8
84.8
76.3
49.2
1.99
1.81
0.871
0.871
−7.646
−7.619
−0.098
−0.092
0.091
0.105
0.018
0.018
−0.164
−0.215
0.515
0.528
0.734
0.756
0.291
0.279
0.083
0.087
3
1.79
0.843
−7.646
−0.095
0.114
0.018
−0.194
0.531
0.782
0.274
0.088
4
5
6
7
8
1.89
1.86
2.09
2.41
2.06
0.871
0.816
0.898
0.898
1.252
−7.646
−7.619
−7.619
−7.619
−7.782
−0.095
−0.087
−0.096
−0.095
−0.089
0.098
0.092
0.109
0.097
0.096
0.017
0.016
0.019
0.019
0.016
−0.206
−0.152
−0.224
−0.172
−0.187
0.517
0.545
0.516
0.515
0.530
0.727
0.728
0.749
0.735
0.730
0.277
0.254
0.291
0.291
0.268
0.081
0.096
0.081
0.081
0.086
9
1.69
2.59
2.45
2.05
0.871
1.252
1.252
0.871
−3.537
−7.646
−7.755
−7.755
−7.619
−11.455
−0.089
−0.092
−0.092
−0.159
0.018
0.110
0.126
0.111
0.017
0.019
0.019
0.016
0.095
−0.194
−0.259
−0.203
−0.208
−0.201
0.529
0.516
0.516
0.530
0.511
0.748
0.774
0.748
0.744
0.695
0.270
0.291
0.287
0.270
0.314
0.084
0.079
0.079
0.084
0.026
10
11
12
1A
−0.075
0.181
2A
3A
−3.510
−3.537
−11.292
−11.238
0.025
0.027
0.201
0.216
0.097
0.094
−0.222
−0.238
0.515
0.529
0.689
0.753
0.307
0.303
0.023
0.031
4A
5A
−3.510
−3.483
−11.183
−11.238
0.025
0.042
0.178
0.152
0.093
0.097
−0.221
−0.197
0.517
0.535
0.666
0.602
0.296
0.294
0.028
0.031
6A
7A
−3.510
−3.483
−11.156
−11.047
0.022
0.023
0.208
0.194
0.095
0.094
−0.273
−0.223
0.513
0.513
0.733
0.707
0.315
0.313
0.024
0.025
8A
9A
10A
11A
12A
−3.292
−3.510
−3.265
−3.265
−3.483
−11.020
−11.129
−10.993
−11.102
−10.993
0.029
0.031
0.027
0.026
0.035
0.216
0.186
0.206
0.209
0.204
0.096
0.094
0.095
0.094
0.094
−0.226
−0.188
−0.247
−0.285
−0.204
0.517
0.522
0.514
0.514
0.522
0.702
0.648
0.724
0.719
0.672
0.297
0.299
0.314
0.311
0.298
0.024
0.028
0.024
0.024
0.026
178.1(1)
4.7(1)
72.4(1)
18.6(1)
a
Theor – DFT; X-ray: 2 – Ref. [22], 3 – Ref. [21], 8 – Ref. [21], 1A – Ref. [26], 2A – Ref. [23], 3A – Ref. [25], 5A – Ref. [24], 7A – Ref. [27], 9A – Ref. [18].
A, between the mean planes delineated by C1, C2, C3, C4, C9, N10, C11, C12 (right-hand half of the acridine nucleus) and C5, C6, C7, C8, C9, N10, C13, C14 (left-hand half of the acridine nucleus); B, between the mean plane
b
of the acridine nucleus (delineated by C1, C2, C3, C4, C5, C6, C7, C8, C9, N10, C11, C12, C13, C14) and the plane delineated by C15, O16, O17; C, between the mean plane of the acridine nucleus and the mean plane of the phenyl
moiety (C18, C19, C20, C21, C22, C23).
c
Represents the sum of the relative partial charges of all the atoms in the phenoxycarbonyl fragment.

404
K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
Table 2
1H chemical shifts (in ppm) for phenyl acridine 9-carboxylates (1–12) and 10-methyl-9-(phenoxycarbonyl)acridinium cations (1A–12A).
b
a
Compd no (Scheme 1)
Method
Solvents
Hydrogen atom number
1/8
2/7
3/6
4/5
19
20
21
22
23
1
Exp
Theor
DMSO-d
8.29
8.63/8.67
8.60
8.34
8.70/8.69
8.60
8.32
8.73/8.68
8.60
8.28
8.97/9.71
8.60
8.34
8.75/8.74
8.60
8.36
9.09/8.87
8.60
8.64
9.07/9.00
8.95
8.63
9.42/8.99
8.95
8.60
9.05/9.15
8.95
8.59
9.49/9.19
8.95
8.62
9.15/9.18
8.95
8.60
9.39/9.21
8.94
7.84
7.71/7.72
7.74
7.82
7.73/7.72
7.74
7.87
7.73/7.71
7.74
7.86
7.80/7.82
7.74
7.82
7.74/7.73
7.74
7.86
7.76/7.75
7.73
8.19
8.33/8.33
7.46
8.18
8.37/8.35
7.46
8.22
8.33/8.32
7.46
8.22
8.40/8.43
7.46
8.17
8.34/8.30
7.46
8.24
8.36/8.33
7.48
8.00
7.92/7.92
7.72
7.99
7.93/7.93
7.72
8.01
7.93/7.93
7.72
8.00
7.96/7.97
7.72
7.99
7.93/7.93
7.72
8.00
7.93/7.93
7.71
8.57
8.73/8.72
7.95
8.57
8.75/8.75
7.95
8.57
8.72/8.72
7.95
8.57
8.76/8.76
7.95
8.56
8.72/8.72
7.95
8.58
8.74/8.72
7.95
8.32
8.44/8.42
8.48
8.32
8.42/8.45
8.48
8.35
8.42/8.45
8.48
8.33
8.46/8.46
8.48
8.33
7.47/7.44
8.48
8.33
8.45/8.42
8.47
8.95
8.36/8.38
8.47
8.96
8.38/8.38
8.47
8.98
8.38/8.36
8.47
8.98
8.38/8.39
8.47
8.98
8.39/8.37
8.47
8.99
8.37/8.36
8.45
7.65
7.08
7.20
7.61
7.50
7.39
7.53
7.32
7.20
7.47
7.36
7.50
7.56
7.35
7.62
7.53
7.54
6.72
7.01
7.08
6.75
7.66
7.74
7.39
7.50
7.71
7.20
7.53
7.59
7.50
7.59
7.64
7.62
7.56
7.78
6.72
7.14
7.33
6.75
7.45
7.37
7.25
7.36
7.29
7.03
7.40
7.32
7.09
7.42
7.28
7.18
7.37
7.34
7.25
7.61
7.60
7.39
7.48
7.44
7.18
7.50
7.46
7.11
7.45
7.39
7.18
7.48
7.47
7.36
7.01
7.00
6.75
7.66
7.88
7.39
7.47
7.62
7.18
7.49
7.71
7.11
7.48
7.62
7.18
7.52
7.72
7.36
7.14
7.18
6.75
7.65
8.11
7.20
7.78
7.91
7.00
7.72
7.92
7.12
7.70
7.20
7.26
7.79
7.89
7.27
6
6
6
6
6
6
6
6
6
6
6
6
gaseous
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
Exp
Theor
Comput
2
DMSO-d
gaseous
3
DMSO-d
gaseous
4
DMSO-d
gaseous
5
DMSO-d
gaseous
12
1A
2A
3A
4A
5A
12A
DMSO-d
gaseous
DMSO-d
gaseous
7.77
7.10
7.20
7.50
7.77
7.25
7.39
7.75
7.03
7.44
7.70
7.09
7.48
7.67
7.18
7.41
7.71
7.25
7.77
8.32
7.20
7.86
7.12
7.00
7.89
8.08
7.12
7.90
7.07
7.26
7.99
7.92
7.27
DMSO-d
gaseous
DMSO-d
gaseous
DMSO-d
gaseous
DMSO-d
gaseous
DMSO-d
gaseous
a
Hydrogen atom number
24
25
a
26
27
a
28
a
a
b
c
b
c
a
b
c
b
c
b
c
1.22
2.28
2.33
2.73
2.89
2.64
3.19
2.98
3.49
2.14
2.10
1.60
1.21
0.88
2.33
1.24
1.28
1.33
1.22
0.83
1.49
2.36
2.09
2.34
0.93
2.45
2.05
2.56
1.00
1.32
0.59
2.09
1.24
1.43
1.33
1.22
0.89
1.49
2.36
2.26
2.34
2.19
1.50
1.58
1.58
1.22
0.66
1.49
1.49
2.15
1.79
1.00
2.31
1.94
2.22
4.97
4.64
4.22
2.43
2.65
2.33
2.71
2.37
2.64
3.17
3.20
3.49
2.88
4.39
2.84
2.64
2.72
4.66
2.42
4.97
4.67
4.22
1.17
1.00
1.26
1.24
1.48
1.33
1.22
1.28
1.49
2.33
2.36
2.22
4.67
1.18
1.82
0.85
2.16
4.36
0.61
1.42
1.21
2.67
4.97
4.64
4.22
1.25
1.69
1.33
1.22
0.76
1.49
2.41
1.92
2.34
4.40
1.86
1.51
2.10
4.66
1.63
1.01
1.93
4.97
4.64
4.22
1.22
1.64
1.49
4.99
4.61
4.22
4.40
1.62
4.68
4.65
1.03
4.38
4.99
4.67
4.22
4.41
4.65
2.41
2.61
2.34
2.35
2.84
a
Identical with the carbon atom number to which it is attached (Scheme 1).
Exp – experimental values; Theor – values predicted at the DFT/GIAO level of theory; Comput – values calculated for isolated molecules using ACD/HNMR software.
b

K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
405
Table 3
13C chemical shifts (in ppm) for phenyl acridine 9-carboxylates (1–12) and 10-methyl-9-(phenoxycarbonyl)acridinium cations (1A–12A).
Compd no. (Scheme 1)
Methoda
Medium
Carbon atom number
1/8
2/7
3/6
4/5
9
11/14
12/13
148.0
1
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
Theor
Exp
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
DMSO-d6
gaseous
124.8
128.2
131.0
129.6
135.3
131.9
134.4
131.9
135.1
131.9
135.1
134.0
134.5
132.2
135.0
131.6
147.5
153.6
147.5
154.4
147.4
154.0
147.3
155.2
147.1
154.2
146.1
154.9
121.3
122.1/122.0
124.6
122.2/122.0
124.4
121.8/122.2
124.4
122.8/121.3
124.6
122.0/121.9
124.7
122.9/122.2
127.5
128.7/128.7
128.0
129.3/128.8
127.8
128.8/128.5
127.7
129.5/128.0
127.9
128.8/128.9
127.8
129.6/128.4
122.9/122.4
128.3
122.4/122.9
128.2
123.0/122.5
128.2
122.2/122.8
128.3
122.6/123.0
128.3
122.4/123.0
129.8
125.0/125.4
130.6
124.8/125.3
130.6
125.0/125.5
130.6
124.9/125.4
130.4
125.0/125.3
130.5
124.7/125.4
124.1/123.8
130.9
123.8/124.1
130.9
124.1/123.8
130.9
124.0/124.1
130.9
123.8/124.2
130.9
123.7/124.0
139.2
136.9/137.2
139.9
137.2/137.0
139.9
136.9/137.2
139.9
137.2/137.0
139.7
136.9/137.2
139.8
137.0/137.0
126.9/127.3
129.8
127.3/127.0
129.7
127.0/127.3
129.8
127.4/127.3
129.8
127.4/127.0
129.9
127.4/127.0
119.9
111.8/111.6
120.8
111.9/111.7
120.8
111.8/111.6
120.8
111.8/111.9
120.8
111.8/111.6
120.9
111.7/111.6
120.8/121.1
121.7
144.4/144.3
148.2
2
120.2/120.8
121.4
144.4/144.4
148.0
3
120.9/120.2
121.4
144.4/144.4
148.0
4
119.3/120.4
121.7
144.2/144.5
148.2
5
120.2/120.7
121.7
144.4/144.4
148.1
12
1A
2A
3A
4A
5A
12A
120.2/121.5
122.3
144.4/144.5
141.9
120.5/120.4
123.1
137.2/137.2
142.7
119.8/121.1
123.2
137.3/137.4
142.7
120.7/120.6
123.1
137.2/137.2
142.7
119.8/120.6
123.2
137.1/137.1
142.7
120.8/120.6
123.3
137.2/137.2
142.7
Theor
120.6/121.0
137.1/137.1
Carbon atom number
15
18
19
20
21
22
23
24
25
26
27
28
165.5
160.0
165.0
159.9
165.5
160.3
165.6
163.5
165.1
160.4
164.9
159.6
164.3
156.0
163.9
156.6
164.1
156.2
164.2
159.2
163.9
156.4
163.4
156.7
150.0
146.8
140.5
145.7
148.1
145.3
147.2
148.3
148.6
146.2
145.8
144.2
149.5
146.5
148.9
145.3
148.4
145.3
147.5
146.0
149.1
145.9
147.6
143.2
121.9
115.2
148.6
125.6
135.3
131.2
139.7
134.9
140.5
136.1
135.8
128.0
121.8
113.9
128.2
126.9
135.8
130.2
140.2
134.9
140.9
135.5
129.9
126.5
130.0
126.9
120.1
127.3
120.2
127.0
120.4
127.1
120.8
126.6
120.5
129.4
131.4
127.5
124.5
128.2
124.8
128.2
124.7
128.0
124.7
127.9
124.6
137.2
136.8
130.0
123.7
126.5
121.5
129.9
121.6
127.2
122.4
127.3
121.4
129.7
124.9
130.1
125.6
132.5
124.1
128.4
123.4
128.6
124.0
128.2
123.2
130.7
126.8
121.9
117.7
127.5
117.9
122.4
118.2
122.4
119.7
123.8
119.5
129.4
126.7
121.8
115.7
123.0
115.2
123.1
116.4
123.2
116.9
124.3
117.7
129.8
124.5
124.0
123.8
126.0
127.4
125.7
127.2
126.9
127.5
123.1
129.7
125.4
130.1
125.9
132.5
128.7
130.9
127.6
128.1
129.2
128.5
125.1
130.7
127.2
29.9
19.2
22.7
28.5
26.7
41.2
34.1
38.8
17.2
20.2
40.5
37.4
16.9
19.6
23.3
28.1
27.4
40.2
34.9
39.0
18.0
19.8
14.3
17.4
22.9
21.9
30.0
28.5
20.3
21.8
22.9
23.0
30.0
31.5
17.2
19.2
30.0
28.3
40.5
37.2
15.0
17.7
23.7
21.5
30.9
28.8
21.0
21.8
40.6
37.4
40.6
24.0
30.9
28.4
18.0
18.7
37.4
30.9
30.8
39.7
37.3
40.4
37.4
a
Exp – experimental values; Theor – values predicted at the DFT/GIAO level of theory.
excess) in dry dichloromethane containing catalytic amounts of
2,6-di-tert-butylpyridine (room temperature, 3–4 h). The crude
acridinium salts were purified by repeated precipitation from
ethanolic solution using excess of diethyl ether (yield 85–92%). The
purity and identity of the compounds was confirmed by HPLC and
MS [20]. The structure of some of the salts was determined by X-ray
diffractometry [18,23–27].
compound was dissolved in 0.7 ml of CD3CN, CD3OD, CDCl3 or
DMSO-d6 (Aldrich), while for the 13C experiments 10–15 mg of sam-
ples were dissolved in the same solvents. The chemical shifts were
referenced to tetramethylsilane (TMS). The homonuclear 1H–1H
two-dimensional correlation spectra were obtained using the
standard COSY pulse sequence [28]. The one-bond heteronuclear
(1H–13C) correlation diagrams and the long-range heteronuclear
(1H–13C) correlation spectra were respectively recorded by gHSQC
and gHMBC pulse field gradient techniques [28].
2.2. Spectra
1H and 13C NMR spectra were recorded at room temperature
on a Varian Unity 500 Plus operating at a proton frequency of
500 MHz and a carbon frequency of 125 MHz or on a Varian Mer-
cury 400BB spectrometer operating at 400 MHz and 100 MHz, for
1H and 13C, respectively. For the 1H experiments, 5–7 mg of each
2.3. Calculations
Unconstrained geometry optimisations of the isolated entities
(Scheme 1) were carried out at the Hartree–Fock [29] or density
functional theory (DFT) [30] levels using gradient techniques [31]

406
K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
and the 6-31G** basis set [29,32]. The DFT calculations were carried
out with the B3LYP functional, in which Becke’s non-local exchange
[33,34] and the Lee–Yang–Parr correlation functionals [35] were
applied. After completion of each optimisation, the Hessian (second
derivatives of the energy as a function of nuclear coordinates) was
calculated and checked for positive definiteness to assess whether
the structures were true minima [29,30]. DFT dipole moments of
neutral molecules, HF LUMO and HOMO energies, DFT Mulliken
partial charges [36], and DFT LCAO coefficients of the pz LUMO of the
entities investigated were extracted directly from data files after
geometry optimisations. MEP fitted charges at the DFT level were
those reproducing the molecular electrostatic potential around
molecules [37]. 1H and 13C magnetic shielding tensors (ꢀ) for DFT
optimised structures of I and II, and tetramethylsilane (TMS) as ref-
erence, were obtained following the gauge-including atomic orbital
(GIAO) approach [38–40] at the DFT (gaseous phase) or DFT/PCM
(liquid phase; PCM – Polarised Continuum Model in which UAHF
radii were used to model the molecular cavity [41,42]) levels. The
differences between the isotropic magnetic shielding tensors of
nuclei in TMS and the entity studied (ꢀTMS–ꢀentity) were consid-
ered to be relevant chemical shifts [38]. The calculations were done
on computers of the Tri-City Academic Network Computer Centre
in Gdan´ sk (TASK) using the GAUSSIAN 03 program package [43].
The angles in Table 1 were obtained using a program written by
ourselves [44]. 1H chemical shifts and 1H–1H coupling constants
were estimated using the ACD/HNMR database Predictor version
4.5 [45].
3.2. Physicochemical properties
The dipole moments of phenyl acridine-9-carboxylates, varying
between 1.7 and 2.6 D (Table 1), reflect the non-uniform distribu-
tion of electron density in molecules. This non-uniform distribution
may be caused by charge separation between the acridine and phe-
noxycarbonyl fragments. Indeed, the sum of the Mulliken atomic
partial charges indicates that the phenoxycarbonyl fragment gains
negative charge, which in turn implies a deficiency of this charge
at the acridine moiety, whereas the sum of MEP fitted charges
suggests the reverse situation. Be that as it may, the latter char-
acteristics do explain the existence of the dipole moment in phenyl
acridine-9-carboxylates.
According to Koopmans’ theorem [47] (which does not apply to
the density functional formalism [48]), the negative energies of the
lowest unoccupied (LUMO) and highest occupied (HOMO) molec-
ular orbitals respectively approximate the electron affinity and the
first ionisation potential of a molecule [49,50]. These characteristics
are typical of acridine-based derivatives [51]. The LUMO–HOMO
energy gap is equal to ca 8.6 eV in the case of phenyl acridine-
9-carboxylates and 7.7 eV in the case of the cations. Both these
latter values are similar, which indicates that the separation of the
respective energy levels in I and II is comparable.
Oxidation
of
10-methyl-9-(phenoxycarbonyl)acridinium
cations leading to chemiluminescence is most probably initiated
by an attack of OOH− on either C9 or C15 [3–5,7,20]. The charge
at these sites may thus be one of the factors determining the
primary substitution and the subsequent secondary processes. The
negative charge deficiency in II is passed on mostly the acridine
fragment. This fragment should therefore attract OOH− above all.
However, Mulliken population analysis and the MEP fit approach
predict a substantial negative charge deficiency at C15 in both
phenyl acridine-9-carboxylates and the cations derived from
them (Table 1). In contrast, the Mulliken method predicts a small
negative charge deficiency at C9, while the MEP fit approach unex-
pectedly gives an excess of negative charge at this atom – although
the latter approach is commonly considered to be more appropri-
ate for predicting atomic charge distribution in molecules. Despite
these discrepancies, charge distribution analysis suggests that the
favoured site for OOH− substitution is C15. On the other hand, the
LCAO coefficients of the pz LUMO of C9 are on average 3.3 times
higher for phenyl acridine-9-carboxylates and 11.8 times higher
for 10-methyl-9-(phenoxycarbonyl)acridinium cations than the
values of this coefficient for C15. Since the LCAO coefficients of the
pz LUMO, according to the Frontier Orbital Theory, can be regarded
as a measure of susceptibility to OOH− substitution, it may well be
C9 and not C15 that is attacked by this anion [52]. The values of the
LCAO coefficient are much higher for cations than for the corre-
sponding neutral molecules, which means that the former should
much more easily undergo substitution by OOH− and subsequent
oxidation. The above conclusions also arise from an analysis of the
LUMO distribution shown in Fig. 2S (Supplementary Material).
The analysis of the relations between 1H and 13C chemical shifts
and physicochemical parameters of I and II (Scheme 1) was carried
out using Statistica 8.0 software [46].
3. Results and discussion
3.1. Structural features
The DFT structures of phenyl acridine-9-carboxylates and their
derivatives, 10-methyl-9-(phenoxycarbonyl)acridinium cations
(Fig. 1S in the Supplementary Material), correspond quite well
to the X-ray structures of some of the compounds investigated
(Table 1). Both DFT and X-ray structural data demonstrate that
the endocyclic N atom, the C atom in position 9 and the C atom
of the carboxy group are aligned almost linearly in I and II, i.e. the
N10· · ·C9–C15 angle is only slightly smaller than the straight angle.
This indicates that the C atom of the carboxy group is deflected
only slightly from the plane defined by the acridine moiety. The
right- and left-hand halves of the acridine nucleus remain at an
angle which does not exceed 2.2◦ in I but is usually >6◦ in II
(Table 1, column A). This means that the geometry of the major-
ity of cations is of the ‘butterfly’ type. The angle between the mean
plane of the acridine nucleus and the plane delineated by the car-
boxy group varies between 47◦ and 52◦ in neutral molecules and
from 59◦ to 63◦ in cations, according to DFT structural data (Table 1,
column B). The values of this angle are thus higher in the latter
entities. In the crystal structure, values of the angle between the
mean plane of the acridine nucleus and the plane given by the
carboxy group are more differentiated; in the 10-methyl-[9-(2-
methylphenoxy)carbonyl]acridinium cation the carboxy group is
almost perpendicular to the acridine moiety. The angle between
the mean planes of the acridine and phenyl rings varies between
60◦ and 87◦ in phenyl acridine-9-carboxylates and between 48◦
and 87◦ in the respective cations, according to DFT structural data
(Table 1, column C). The values of this angle in the crystal structure
differ somewhat more: they are as low as 15.6(1)◦ and 18.6(1)◦ in
1A and 12A respectively.
3.3. 1H NMR and 13C NMR spectra
Four solvents – CD3CN, CD3OD, CDCl3 and DMSO-d6 – of various
polarity, as well as electron-donor-acceptor and proton-donor-
acceptor ability [53] were selected to record the NMR spectra.
However, DMSO-d6 appeared to be the only solvent able to dis-
solve all the compounds in sufficient amounts to obtain spectra of
reasonable quality. The majority of spectra were therefore recorded
in this solvent. Table 2 and Table 1S (Supplementary Material) list
the experimentally determined and predicted 1H chemical shifts
for the compounds investigated. Examples of 1H spectra are given
in the Supplementary Material (Fig. 3S). Table 2S (Supplementary
Material) contains values of 1H–1H coupling constants obtained

K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
407
Fig. 1. 1H4/1H5 chemical shifts (DMSO-d6) versus dipole moments in I (upper
graph) and coefficients of the pz LUMO in II (lower graph).
Fig. 2. 13C9 chemical shifts (DMSO-d6) versus dipole moments in I (upper graph)
and 13C15 chemical shifts (DMSO-d6) versus dihedral angles between acridine and
phenyl moieties (Table 1, column C: Theor) in I and II (lower graph).
from experiments and computations. Solvents other than DMSO-d6
were used only with selected compounds 1, 2 and 1A, 2A.
Three groups of signals can be discerned in the 1H spectra of the
target compounds – due to H atoms in the acridine moiety (highest
chemical shifts), to aliphatic H atoms (lowest chemical shifts) and
to H atoms in the benzene ring (middle range of chemical shifts).
In all the phenyl acridine-9-carboxylates the H1/H8 and H4/H5
signals appear at higher chemical shifts than those derived from
H2/H7 and H3/H6. This effect is probably due to the off-shielding
influence of neighbouring O atoms of the –COO– fragment and
the endocyclic N atom respectively. The 1H chemical shifts of
H1/H8 are also the most obviously affected by phenyl ring sub-
stitution.
between the H atoms in the acridine and benzene rings range from
0.5 to 2.6 Hz. All the coupling constants reflect unique features of
the compounds investigated.
The 13C NMR spectra of phenyl acridine-9-carboxylates
and 10-methyl-9-(phenoxycarbonyl)acridinium cations (Table 3,
Table 3S and Fig. 4S in the Supplementary Material) display the
pattern typical of acridine derivatives (1C–9C and 11C–14C signals)
[44,51] and characteristic of a benzene ring (C18–C23 signals) [54].
The 13C chemical shifts of C15 always take higher values than those
of any other C atom. This is caused by the off-shielding influence
of the O atoms of the –COO– fragment. Also, the 13C NMR signals
of C9 and C18 are shifted towards lower fields due to the electron
withdrawing property of the –COO– fragment. The 13C signals of C
atoms of alkyl substituents in the benzene ring and the endocyclic
N atom appear at typically higher magnetic fields [54].
The positions of the signals in the 1H spectra do not depend
significantly on the solvent used. The reason for this is the absence
in the compounds investigated of atoms or groups of atoms that
might interact specifically with solvent molecules. It may, however,
be noted that the 1H signals of atoms in the acridine moiety of I
recorded in solvents of relatively high polarity (CD3CN or DMSO-d6)
are shifted towards lower fields in comparison to those measured
in solvent of relatively low polarity (CDCl3).
As the target compounds were poorly soluble in CD3CN, CD3OD
and CDCl3, the influence of the medium on 13C NMR characteristics
was limited to 1, 2, 1A and 2A. Even so, the data obtained show
that this influence is negligible and that each entity behaves in a
different way in a magnetic field.
The 1H spectra of 10-methyl-9-(phenoxycarbonyl)acridinium
cations show a pattern similar to those of the phenyl acridine-9-
carboxylates. However, all signals due to H atoms in the acridine
moiety of compounds 1A–12A move towards higher chemical
shifts in comparison with those characterising compounds 1–12.
This feature arises from the lowering of the electron density in
the acridine ring of compounds 1A–12A, especially around the
endocyclic N atom. The 1H signals attributed to the H atoms
of the benzene ring appear at similar positions in 10-methyl-
9-(phenoxycarbonyl)acridinium cations and the corresponding
phenyl acridine-9-carboxylates.
The theoretically predicted (DFT/GIAO) 1H and 13C chemical
shifts were applied consistently in the interpretation of experi-
mental data. The agreement between the above two sets of values
(Tables 2 and 3 and Tables 1S and 3S in the Supplementary Material)
is reasonable, given that they were obtained independently.
The computed (using ACD/HNMR software) 1H chemical shifts
(Table 2 and Table 1S in the Supplementary Material) and 1H–1H
coupling constants (Table 2S in the Supplementary Material) also
compare reasonably well with the experimental data. We thus
believe that the assignments were done correctly and that all
the values present a unique collection of data on the spectral
behaviour of phenyl acridine-9-carboxylates and their derivatives,
10-methyl-9-(phenoxycarbonyl)acridinium cations.
The 1H–1H coupling constants (Table 2S in the Supplementary
Material) display regularities that are typical of aromatic systems
[54]. The coupling constants for single bond interdependences lie in
the 6.0–8.8 Hz range in compounds 1–12. They are slightly higher
in the case of compounds 1A–12A: 6.6–8.9 Hz. The values of this
quantity for double, triple and quadruple bond interdependences

408
K. Krzymin´ski et al. / Spectrochimica Acta Part A 78 (2011) 401–409
3.4. Spectral versus structural and physicochemical features
NMR spectral investigations and quantum chemistry calcula-
tions provide useful data for the evaluation of properties, reactivity
and utility of a cognitively and practically important group of
compounds. This information, together with other data that we
expect to obtain from our ongoing investigations, should form a
useful basis for the rational design and application of 10-methyl-
9-(phenoxycarbonyl)acridinium salts.
The 1H and 13C chemical shifts of atoms H1, H4, H5, H8, C9, C15
and C18 were related to the values of all the quantities listed in
Table 1 in order to reveal possible linear dependences between
these characteristics. Figs. 1 and 2, and Table 4S (Supplemen-
tary Material) demonstrate the best found linear trends. The 1H4
and 1H5 chemical shifts tend to decrease with the dipole moments
of phenyl acridine-9-carboxylates and with the LCAO coefficients of
the pz LUMO of C9 of 10-methyl-9-(phenoxycarbonyl)acridinium
cations. The 13C9 chemical shifts increase as the dipole moments
of neutral molecules do so, whereas the 13C15 shifts increase with
the angle between the acridine and phenyl moieties of neutral
molecules and cations.
Multiparametric regression analysis revealed a few statistically
significant triparametric dependences between chemical shifts and
predicted physicochemical parameters of the compounds inves-
tigated. The relevant equations are given in the Supplementary
Material (Table 4S). It is evident that NMR spectral characteristics
are dependent on certain structural and physicochemical charac-
teristics of the compounds investigated.
Acknowledgements
This study was financed from the State Funds for Scien-
tific Research though Grant No. N204 123 32/3143 (contract No.
3143/H03/2007/32) of the Polish Ministry of Research and Higher
Education, for the period 2007–2010.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.10.029.
References
4. Conclusions
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