Hydrogen bonding and molecular association in 2-(quinuclidinium)-butyric acid bromide hydrate studied by X-ray diffraction, DFT calculations, FTIR and NMR spectroscopy, and potentiometric titration

Journal of Molecular Structure 975 (2010) 357–366

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Hydrogen bonding and molecular association in 2-(quinuclidinium)-butyric acid bromide hydrate studied by X-ray diffraction, DFT calculations, FTIR and NMR spectroscopy, and potentiometric titration Z. Dega-Szafran *, A. Katrusiak, M. Szafran, P. Barczyn´ski ´ , Poland Faculty of Chemistry, Adam Mickiewicz University, ul. Grunwaldzka 6, 60-780 Poznan

a r t i c l e

i n f o

Article history: Received 6 April 2010 Received in revised form 6 May 2010 Accepted 6 May 2010 Available online 12 May 2010 Keywords: Quinuclidine betaine derivatives Hydrogen bonds X-ray diffraction DFT calculations Spectroscopic methods Potentiometric titration

a b s t r a c t The structure of 2-(quinuclidinium)-butyric acid bromide hydrate (QNBuH2OHBr, 3) has been determined by X-ray diffraction, DFT calculations and characterized by FTIR and NMR spectroscopy. Crystals of 3 are monoclinic, space group P21. The water molecule interacts with the carboxylic group of 2-(quinuclidinium)-butyric acid and with the bromide anion by the COOH  OH2 and HOH  Br hydrogen bonds of 2.575(3) and 3.293(2) Å, respectively. The structures of monomer (4) and dimeric cation (5) of the title complex have been optimized by the B3LYP/6-31G(d,p) approach, yielding conformations consistent with this in the crystal. The solid-state FTIR spectra of 3 and its deuterated analogue have been measured and compared with the theoretical spectrum of 4. The assignments of the observed and predicted bands have been proposed. The molecule of 3 has a chiral center at the C(9) atom, which is responsible for the nonmagnetically equivalence of the a-ring and C(11)H2 methylene protons in 1H NMR spectrum. The values of pKa of quinuclidinium-acetate (quinuclidine betaine), 2-(quinuclidinium)-propionate and 2-(quinuclidinium)-butyrate have been determined by the potentiometric titration of their hydrohalides. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Betaines are inner salts (zwitterionic compounds) in which the positively charged nitrogen atom is separated by at least one methylene group from the negatively charged carboxylate group [1]. In betaines, the positively charged nitrogen atom is inert as a hydrogen-bonding center, whereas the carboxylate group is basic, and can interact with different proton-donors. Betaines form the 1:1 and 2:1 complexes with inorganic and organic acids. Some of them display interesting physical properties like phase transitions with ferroelectric, antiferroelectric and ferroelastic behavior [2–7]. Betaines found many of applications in industry and cosmetology [1,8]. Quinuclidine (1-azabicyclo[2.2.2]octane) is a stronger base (pKa = 11.15) than piperidne and has poorer steric requirements compared to triethylamine [9,10]. The Menschutkin reaction results in formation of a variety of quaternary quinuclidinium salts. Recently, we have studied the structures of quinuclidine betaine hydrate (quinuclidinium-acetate inner salt, QNB) [11], its hydrochloride, QNBHCl [12] and 2-(quinuclidinium)-propionic acid bromide hydrate, QNPrH2OHBr [13]. The latter one can be treated as a homolog of QNBHCl. The methyl group (R) is a substituent in the typical of betaines N+–CH(R)COO group forming a

* Corresponding author. Tel.: +48 61 8291216; fax: +48 61 8291505. E-mail address: [email protected] (Z. Dega-Szafran). 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.05.004

chiral center. In this work we extend the study over the synthesis and crystal structure of another homolog with ethyl group, the complex of 2-(quinuclidinium)-butyrate with hydrobromic acid (Scheme 1). Its optimized structure is calculated at the B3LYP/631G(d,p) level of theory and the infrared and NMR spectra are measured. The effect of the alkyl chain in the N+–CH(R)COO group on the pKa values is determined by the potentiometric titration.

2. Experimental 2.1. Synthesis To 4.7 g of quinuclidine dissolved in 30 cm3 diethyl ether, a portion of 8.24 g of (±)ethyl 2-bromobutyrate dissolved in 30 cm3 of diethyl ether was slowly dropped on cooling and stirring. The reaction mixture was kept for two weeks at 10 °C. The precipitate was filtered off and washed with diethyl ether. Ethyl 2-(quinuclidinium)-butyrate bromide (1, Scheme 1) was dried over P2O5; 93% yield, m.p. 178–180 °C. Ethyl 2-(quinuclidinium)-butyrate bromide (1) (7 g) was dissolved in water (100 cm3) and treated with an anion-exchange resin in its basic form (100 g, Amberlite IRA400), thus substituting the hydroxy ion for the bromide ion. After 1 h, when the Beilstein test for halide of the water layer was negative, the resin was eluted

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Br

N

CH3CH2 C COOC2H5 H

CH3 CH2

+ N CH COOCH2CH3 _ Br 1 IRA 410 (OH)

β γ 3

α

CH3 CH2

+ N CH COOH HOH .Br

_

HBr H2O

CH3 CH2

_ + N CH COO

2

Scheme 1. Synthesis of 2-(quinuclidinium)-butyric acid derivatives.

with water. Removal of water by a rotatory evaporator gave (4.2 g, 94%) a white solid powder of 2-(quinuclidinium)-butyrate inner salt (2), m.p. 210 °C. 2-(Quinuclidinium)-butyrate inner salt (2), was dissolved in the excess of 24% hydrobromic acid and the solution was evaporated to dryness under the reduced pressure. The residue was solved with water and evaporated again. The solid product of 2-(quinuclidinium)-butyrate hydrobromide (3) was recrystallized from acetonitrile, m.p. 183–184 °C. The elemental analysis has shown the presence of one water molecule. Analysis for: C11H22NO3Br: calcd.: 44.60%C; 7.49%H; 4.73%N. Found: 44.56%C; 7.57%H; 4.72%N. [a]D = 2.6° in water. The deuterated sample was prepared by threefold dissolving in D2O followed by evaporation of the excess of D2O and DHO under the reduced pressure and recrystallized from CH3OD.

2.2. Measurements The crystals for X-ray measurements were grown by slow evaporation of acetonitrile solution of the title compound. The crystal structure of 2-(quinuclidinium)-butyric acid bromide hydrate (3) was determined by X-ray diffraction, measured with a KUMA KM-4 CCD diffractometer [14,15]. The structure was solved by direct methods using SHELXS-97 [16] and refined on F2 by full-matrix least-squares with SHELXL-97 [17]. The hydrogen atoms were located from the molecular geometry (dCH = 0.97 Å, Uiso depending on Ueq of their carriers: Uiso = 1.2Ueq for methylene and methine groups, and Uiso = 1.3Ueq for the methyl group), except for proton H(1) and the H-atoms of the water molecule. Proton H(1) was located in the difference Fourier map, but was not refined; its Uiso = 1.2Ueq of O(1). The hydrogen atoms of the water molecule were located from the Fourier map and were refined, but their Uiso was set to 1.3Ueq of O(1W). The crystal data, details of data collection and structure refinement are given in Table 1, and the final atomic coordinates are listed in Table 2. The complete set of structural parameters in CIF format is available as an Electronic Supplementary Publication from the Cambridge Crystallographic Data Centre (CCDC 771867). FTIR spectra were measured on a Bruker IFS 66v/S instrument in Nujol and Fluorolube suspensions using KBr plates. Each spectrum consisted of 64 scans. NMR spectra were recorded on a Bruker Advance DRX spectrometer operating at 600.31 and 150.75 MHz for 1H and 13C, respectively. The spectra were measured in D2O relative to internal standard of 3-(trimethylsilyl)propionic-d4 acid sodium salt. The 2D 1 H–13C (HETCOR) spectrum was obtained with the standard Bruker software.

Table 1 Crystal data and structure refinement for 2-(quinuclidinium)-butyric acid bromide hydrate (3). Empirical formula Formula weight Temperature Wavelength Crystal system Space group

C11H22BrNO3 296.21 293(2) K 0.71073 Å Monoclinic P21

Unit cell dimensions a b c b Volume Z Calculated density Absorption coefficient F(0 0 0) Crystal size h range for data collection (°) Max/min indices h, k, l Reflections collected/unique hMax (°)/completeness (%) Refinement method Data restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2rI] R1/R2 indices (all data) Absolute structure parameter Largest diff. peak and hole

6.8095(3) Å 10.1615(5) Å 10.0406(6) Å 101.523(5)° 680.75(6) Å3 2 1.445 g/cm3 3.014 mm1 308 0.11  0.09  0.07 mm 2.88–29.24 7/9, 13/13, 13/13 6703/3156 [R(int) = 0.0303] 29.24/93.5 Full-matrix least-squares on F2 3156/4/151 1.000 R1 = 0.0296, wR2 = 0.0617 0.0387/0.0628 0.022(9) 0.341 and 0.238e Å3

Table 2 Atomic coordinates (104) and equivalent isotropic displacement parameters (Å2  103) for 2-(quinuclidinium)-butyric acid bromide hydrate (3). Ueq is defined as one third of the trace of the orthogonalized Uij tensor. Uiso are given for the Hatoms. Atom

x

y

z

Ueq/Uiso

N(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) O(1) O(2) O(1W) Br(1) H(2A) H(2B) H(3A) H(3B) H(4A) H(5A) H(5B) H(6A) H(6B) H(7A) H(7B) H(8A) H(8B) H(9A) H(11A) H(11B) H(12A) H(12B) H(12C) H(1) H(1W) H(2W)

1180(3) 2538(4) 1482(5) 546(4) 1845(5) 757(4) 202(5) 675(4) 2281(4) 3384(5) 951(5) 2182(6) 2267(3) 5068(4) 3711(5) 4411(1) 2950 3732 2303 1287 1198 2164 3091 473 1609 711 1462 285 1878 3308 132 62 1305 3051 2972 2942 4480(50) 3840(60)

553(2) 637(3) 1861(3) 1502(3) 885(3) 262(3) 482(4) 770(3) 1779(3) 1555(3) 2993(2) 4240(4) 1061(2) 1904(3) 636(3) 2429(1) 764 487 2295 2466 2283 1541 578 52 1036 828 280 1482 1018 1987 2925 3033 4985 4208 4319 965 1290(30) 274(15)

7731(2) 8006(3) 7371(4) 6492(3) 7394(3) 8189(3) 5474(3) 6199(3) 8390(3) 9852(3) 8322(3) 8552(4) 10,647(2) 10,216(3) 13,182(2) 14,233(1) 8979 7637 6817 8080 6030 8020 6837 9151 8056 4933 4867 5987 5881 7865 9007 7439 8507 9432 7865 11,414 13,820(30) 13,550(40)

32(1) 50(1) 60(1) 48(1) 56(1) 40(1) 53(1) 46(1) 39(1) 46(1) 48(1) 65(1) 61(1) 85(1) 83(1) 50(1) 60 60 72 72 58 67 67 48 48 64 64 55 55 46 57 57 97 97 97 73 108 108

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The pKa values of quinuclidinium-acetate (quinuclidine betaine, QNB), 2-(quinuclidinium)-propionate (QNPr) and 2-(quinuclidinium)-butyrate (2, QNBu) have been determined by titrating 0.01 M aqueous solutions of their hydrohalides with 0.1 M KOH. The solutions were prepared by weighing hydrohalides directly into a tarred titration vessel and adding the appropriate volumes of water to achieve the desired concentrations. The volume of the solution was determined by weighing the vessel and its contents to the nearest milligram. The potentiometric titrations were carried out at 25 ± 0.5 °C in the atmosphere of purified argon, using a pH-meter N517 (Mera-Tronic) equipped with a glass combined electrode OSH-10-10 (Metron). The instrument was calibrated with at least two standard buffers before and after each titration and its accuracy was 0.01 pH unit. For details see Refs. [18,19]. 2.3. DFT calculations The DFT calculations were performed with the GAUSSIAN-03 program package [20]. The calculations employed the B3LYP exchange–correlation functional, which combines the hybrid exchange functional of Becke [21,22] with the gradient-correlation functional of Lee et al. [23] and the split-valence polarized 631G(d,p) basis set [24]. The magnetic isotropic shielding constants were calculated with the standard GIAO/B3LYP/6-31G(d,p) (GaugeIndependent Atomic Orbital) approach. 3. Results and discussion 3.1. Crystal structure of 3 2-(Quinuclidinium)-butyrate inner salt (2) forms a complex with hydrobromic acid and water molecule. It crystallizes in monoclinic space group P21. Molecular structure of 2-(quinuclidinium)butyric acid bromide hydrate, QNBuH2OHBr, 3, with the anisotropic displacement ellipsoids and atom labeling scheme is shown in Fig. 1. Bond lengths and selected bond and torsion angles are listed in Table 3. Similarly as in 2-(quinuclidinium)-propionic acid bromide hydrate (QNPrH2OHBr) [13], the carboxylate group is protonated and as a proton-donor it forms a hydrogen bond to the oxygen atom of the water molecule by the O(1)–H  O(1 W)

Fig. 1. The symmetry-independent part of the 2-(quinuclidinium)-butyric acid bromide hydrate crystal structure (3). The thermal ellipsoids have been drawn at the 50% probability level. The hydrogen bonds have been indicated by the dashed lines.

Table 3 Experimental and calculated, by the B3LYP/6-31G(d,p) approach, bond lengths (Å), bond and torsion angles (°) for 2-(quinuclidinium)-butyric acid bromide hydrate (3 and 4). Parameters Bond lengths N(1)–C(2) C(2)–C(3) C(3)–C(4) C(4)–C(5) C(5)–C(6) N(1)–C(6) C(4)–C(7) C(7)–C(8) N(1)–C(8) N(1)–C(9) C(9)–C(11) C(11)–C(12) C(9)–C(10) C(10)–O(1) C(10)–O(2) N(1)  Br(1) Bond angles N(1)–C(2)–C(3) C(2)–C(3)–C(4) C(3)–C(4)–C(5) C(4)–C(5)–C(6) C(5)–C(6)–N(1) C(2)–N(1)–C(6) C(2)–N(1)–C(8) C(8)–C(7)–C(4) C(7)–C(4)–C(3) C(7)–C(4)–C(5) N(1)–C(8)–C(7) C(6)–N(1)–C(8) C(2)–N(1)–C(9) C(6)–N(1)–C(9) C(8)–N(1)–C(9) C(10)–C(9)–N(1) C(11)–C(9)–N(1) C(11)–C(9)–C(10) C(9)–C(11)–C(12) O(1)–C(10)–C(9) O(2)–C(10)–O(1) O(2)–C(10)–C(9) Torsion angles N(1)–C(2)–C(3)–C(4) C(2)–C(3)–C(4)–C(5) C(3)–C(4)–C(5)–C(6) C(4)–C(5)–C(6)–N(1) C(2)–N(1)–C(6)–C(5) C(6)–N(1)–C(2)–C(3) C(2)–C(3)–C(4)–C(7) C(2)–N(1)–C(8)–C(7) C(6)–N(1)–C(8)–C(7) C(4)–C(7)–C(8)–N(1) C(7)–C(4)–C(5)–C(6) C(8)–N(1)–C(6)–C(5) C(3)–C(4)–C(7)–C(8) C(8)–N(1)–C(2)–C(3) C(5)–C(4)–C(7)–C(8) C(9)–N(1)–C(2)–C(3) C(9)–N(1)–C(6)–C(5) C(9)–N(1)–C(8)–C(7) C(2)–N(1)–C(9)–C(11) C(6)–N(1)–C(9)–C(11) C(8)–N(1)–C(9)–C(11) C(2)–N(1)–C(9)–C(10) C(6)–N(1)–C(9)–C(10) C(8)–N(1)–C(9)–C(10) N(1)–C(9)–C(11)–C(12) C(10)–C(9)–C(11)–C(12) N(1)–C(9)–C(10)–O(1) N(1)–C(9)–C(10)–O(2) C(11)–C(9)–C(10)–O(1) C(11)–C(9)–C(10)–O(2)

X-ray (3) 1.515(3) 1.512(4) 1.527(4) 1.521(4) 1.520(4) 1.510(3) 1.506(5) 1.527(5) 1.524(3) 1.534(3) 1.524(4) 1.511(5) 1.527(4) 1.307(4) 1.186(4)

B3LYP (4) 1.535 1.541 1.535 1.536 1.545 1.530 1.536 1.547 1.521 1.547 1.534 1.536 1.548 1.313 1.219 4.120

111.0(2) 110.3(3) 108.7(3) 110.4(2) 110.7(2) 109.1(2) 107.8(2) 110.4(2) 108.2(3) 107.9(3) 110.4(2) 107.5(2) 110.0(2) 114.1(2) 108.1(2) 113.4(2) 113.8(2) 109.7(2) 111.4(3) 114.2(3) 124.9(3) 120.7(3)

110.64 109.71 109.12 110.01 110.31 108.26 107.75 109.20 108.59 108.73 111.10 109.42 109.39 112.78 109.13 109.85 114.64 111.64 110.78 112.60 126.65 120.75

7.1(4) 62.1(4) 54.0(4) 6.7(4) 61.8(3) 53.8(3) 54.9(4) 54.5(3) 63.0(3) 7.0(4) 63.1(3) 54.8(3) 62.8(3) 62.6(3) 54.7(3) 179.7(3) 174.7(2) 173.3(2) 172.7(2) 49.7(3) 69.9(3) 46.3(3) 76.7(3) 163.7(2) 161.5(3) 70.2(3) 52.9(3) 132.3(3) 75.6(3) 99.2(3)

5.60 55.49 61.69 4.51 56.29 62.61 62.88 62.88 54.61 6.43 56.61 60.88 55.77 55.63 62.85 174.14 177.47 178.44 174.99 54.46 67.36 48.34 72.19 165.99 170.55 63.74 84.13 95.67 44.20 136.01

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of 2.575(3) Å (Table 4). The interaction between the carboxylate group and the water molecules in quinuclidine betaine hydrate (quinuclidinium-acetate, QNB), according the COO(1)  H2O distance of 2.731(1) Å [11], is weaker than between the carboxylic group and water molecules in QNPrH2OHBr [13] and QNBuH2OHBr. In 3 the water molecule interacts with the bromide anion through the O(1 W)–H(2)  Br hydrogen bond of 3.293(2) Å. The main difference between the complex investigated and QNPrH2OHBr [13] is the arrangement of molecules in the crystal structure. The ions and water molecules are hydrogen-bonded into sheets parallel to the crystal planes (1 0 0), as illustrated in Fig. 2. In the network of hydrogen bonds in such a sheet, each cation is bonded to a water molecule, which in turn is H-bonded to two Br anions. Each of these Br ions is further H-bonded to another water molecule, forming a chain along the crystal direction [0 1 0]. The bromide anion is additionally involved in the C(9)– H  Br contacts with the C(9)  Br distance of 3.877(2) Å (Table 4), which enclose a motif of eight-membered hydrogen-bonded cyclamers within the sheets (eight ions and molecules form one cyclamer, where twenty atoms are involved, as shown in Fig. 2). The piperidinium rings in the quinuclidinium moiety of the complex investigated have distorted-boat conformations; three N(1)–CH2–CH2–C(4) ethylene bridges assume similar torsion angles of about 7° and the same sign, which is characteristic of a propeller conformation of quinuclidine (Table 3). Analogous propeller conformation was observed in the other quinuclidinium betaine derivatives [12,13,25–27], and DABCO (1,4-diazabicyclo[2.2.2]octane) derivatives [28–34], whereas the N–C–C–C and N–C–C–N torsion angles are equal or close to 0° in quinuclidine betaine hydrate [11] and DABCO mono-betaine hydrate [35].

Fig. 2. The autostereographic projection [47] of the 2-(quinuclidinium)-butyric acid bromide hydrate structure (3) viewed down the [1 0 0] direction. Hydrogen bonds OH  O, OH  Br and the shortest of the C(9)H  Br contacts have been indicated by the dashed lines.

3.2. DFT calculations The structures of 2-(quinuclidinium)-butyric acid bromide hydrate as monomer (4) and the dimeric cation (5) built of two 2(quinuclidinium)-butyric acids molecules, two water molecules and one bromide anion, were optimized by the B3LYP/6-31G(d,p) approach (Fig. 3). The X-ray geometry of 3 was used as a starting point for calculations. Their energies and dipole moments are given in Table 4. The bond lengths, bond and torsion angles of 4 are listed in Table 3. There are no significant differences between the crystal and optimized structures, except the geometries of the carboxylic

Table 4 Experimental and calculated, by the B3LYP/6-31G(d,p) approach, hydrogen bond dimensions (Å and °) for 2-(quinuclidinium)-butyric acid bromide hydrate (3, 4 and 5).

3

4c

5d

D–H  A

d(D–H)

d(H  A)

d(D  A)

<(D–H  A)

X-ray O(1)–H(1)  O(1 W) O(1 W)–H(2 W)  Br(1) O(1 W)–H(1 W)  Br(1)a C(9)–H(9)  Br(1)b

0.82 0.99(3) 1.00(4) 0.98

2.31 2.31(3) 2.35(3) 2.92

2.575(3) 3.293(2) 3.303(2) 3.877(2)

163 173(3) 161(3) 167

B3LYP/6-31G(d,p) O(1)–H(1)  O(1 W) O(1 W)–H(2 W)  Br(1) C(2)–H  Br(1)

1.057 1.007 1.093

1.455 2.147 2.580

2.496 3.129 3.495

167.13 164.51 140.7

O(1)–H(1)  O(1 W) O(1W)–H(2W)  Br(1) O(1W0 )–H(1W0 )  Br(1) O(10 )–H(10 )  O(1W0 )

1.020 0.998 0.996 1.048

1.597 2.193 2.187 1.483

2.586 3.179 3.158 2.518

161.88 169.16 164.57 168.25

Symmetry codes: a 1  x, y  0.5, 3  z. b 1  x, y  0.5, 2  z. c E (HF) = 3284.6103496 a.u.; l = 11.89 D for 4 (monomer). d E (HF) = 3997.3382196 a.u.; l = 6.06 D for 5 (dimeric cation).

groups (Table 3) and the hydrogen bonds lengths (Table 4). In monomer 4 the O(1)–H  O(1W) hydrogen bond is shorter than in the crystal 3 and cation 5, while the O(1W)–H  Br distances in 4 and 5 are comparable. However, the 2-(quinuclidinium)-butyric acid molecules in 5 are not equivalent. The bromide anion assumed the position much closer to the one positively charged nitrogen atom than to the other; the N  Br distances are 4.25 and 6.02 Å.

3.3. Infrared spectra 3.3.1. Experimental FTIR spectra The experimental solid-state FTIR spectra of 2-(quinuclidinium)-propionic acid bromide hydrate (3) and its deuterated analogue are shown in Fig. 4a. According to the crystal structure (Table 4) there are two hydrogen bonds of different strength, with the O(1)–H  O(W) distance of 2.575(3) Å and O(W)–H  Br distance of 3.293(2) Å. There are several bands in the 3600– 1900 cm1 region attributed to the mO–H vibrations, which shift to lower wavenumbers after deuteration. The weaker O(W)–H  Br hydrogen bond is manifested in the spectrum as a strong band at 3489 cm1 region, while the stronger COOH  OH2 hydrogen bond as broad bands in the 2710–2000 cm1 region. The strong band at 1724 cm1, attributed to the mC@O vibration, confirms that the proton is transferred from hydrobromic acid to the carboxylate group of 2-(quinuclidinium)-butyrate. In the FTIR spectrum of quinuclidine betaine hydrochloride the mC@O band at 1728 cm1 was observed [12]. In the finger-print region the difference between the protonated and deuterated species is significant and corresponds to the in-plane and out-of-plane OH and OD vibrations (Table 5).

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Fig. 3. The optimized structures by the B3LYP/6-31G(d,p) approach of 2-(quinuclidinium)-butyric acid bromide hydrate monomer 4 and dimeric cation 5.

Absorbance

1,5

(a)

1,0

0,5

0,0

Intensity

80

(b)

60 40 20 0

Intensity

80

(c)

60 40 20 0 3600

3000

2400

1800

1500

1200

900

600

-1

Wavenumbers (cm ) Fig. 4. Infrared spectra of 2-(quinuclidinium)-butyric acid bromide hydrate, (a) solid-state FTIR spectrum of (3), dashed line denoted spectrum of deuterated sample, (b) calculated by the B3LYP/6-31G(d,p) scaled spectrum of 4, (c) calculated by the B3LYP/6-31G(d,p) scaled spectrum of the deuterated species of 4.

3.3.2. Calculated spectra of 4 The infrared spectra calculated by the B3LYP/6-31G(d,p) approach of the optimized structure of 4 and its deuterated analogue

are shown in Fig. 4b and c. There are 108 bands in the 4000–0 cm1 region; their intensities vary from 0.1 to 1960 KM/mol (Table 5). The most intensive bands are attributed to the mO–H  Br,

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Table 5 Experimental and calculated frequencies (cm1) for 2-(quinuclidinium)-butyric acid bromide hydrate and its deuterated analogue; A, intensity in KM/mol. 3 (H)

4 (H)

mexp

mcalc

3489 3326

3818

46.6

3665

3165 3163 3146 3142 3136 3126 3120 3115 3112 3105 3101 3094 3092 3091 3069 3065 3062 3057 3056 3053 2287

10.4 15.4 15.2 22.0 16.0 1213 4.4 3.8 5.9 21.8 11.5 64.3 32.1 45.7 10.3 91.1 44.6 36.3 44.9 20.6 1958.1

3038 3036 3020 3016 3010 3000 2995 2990 2987 2980 2976 2970 2968 2967 2944 2942 2939 2934 2933 2930 2195

3191

2984

2960

2942

2886 2746 2525 2000 1725 1558 1492 1464

1454

1417 1384

1358 1347 1329 1322 1307

1270 1257 1239 1208

1122 1102 1071 1046 1027

975 939 928

858 839

1801 1664 1562 1544 1522 1520 1517 1514 1509 1504 1497 1488 1444 1434 1430 1414 1397 1389 1376 1372 1369 1364 1353 1346 1336 1327 1318 1292 1281 1278 1249 1243 1219 1165 1151 1140 1111 1075 1066 1057 1051 1040 1004 982 967 950 936 931

m

a scaled

A

261.4 63.4 23.5 17.3 8.2 6.3 14.2 4.6 14.4 0.7 2.1 1.5 14.2 1.7 5.2 4.1 2.7 7.1 67.1 22.7 6.1 12.4 12.5 0.2 56.6 16.8 25.1 50.6 40.1 113.1 6.1 6.9 1.4 0.9 0.1 0.6 20.4 9.7 2.3 6.0 0.7 2.7 1.9 0.1 8.4 6.1 10.3 0.4

1728 1597 1499 1482 1461 1459 1456 1453 1448 1443 1437 1428 1386 1376 1372 1357 1341 1333 1320 1317 1314 1309 1298 1292 1282 1273 1265 1240 1229 1226 1199 1193 1170 1118 1104 1094 1066 1032 1023 1014 1008 998 963 942 928 912 898 893

Assignments

b

mOH mOH masCH2 masCH2 masCH2 masCH2 masCH3 mO–H  Br msCH3 masCH2 masCH2 masCH2 mC–H msCH2, mC–H msCH2, mC–H msCH2 msCH2 msCH2 msCH2 msCH2 msCH2 msCH2 mCOOH  OH2 mCOOH  OH2 mCOOH  OH2 masCOO, dCOOH  OH2 dHOH dCOOH  OH2 Sciss CH2 Sciss CH2 dCH3 Sciss CH2 dCH3 Sciss CH2 Sciss CH2 Sciss CH2 Sciss CH2 Sciss CH2 dCH3 dCH3, wag CH2 Wag CH2 Wag CH2 Wag CH2 dCOOH  OH2, msCOO, wag CH2 Twist CH2 Wag CH2 Wag CH2, twist CH2 Twist CH2 Twist CH2 msCOO, twist CH2 Wag CH2, twist CH2 dC–H, twist CH2 dCOOH, dOH, dCH3, twist CH2 dCOOH  OH2, dHOH, twist CH2 dCOOH  OH2, dHOH dC–H, twist CH2 dC–H, twist CH2 Twist CH2 Twist CH2 dC–H, rock CH2 dC–H, rock CH2 dC–H, rock CH2, rock CH3 mC–C, mC–N mC–C Rock CH2 cC–H, rock CH2 mC–C, mC–N mC–C, mC–N Rock CH2 Rock CH2, cCH3, mC–N cCH3, ring Skeleton Ring

3 (D)

4 (D)

mexp

mcalc

A

mscaleda

Assignmentsb

2817

2778 3165 3164 3146 3142 3136 2272 3120 3115 3112 3105 3101 3094 3092 3091 3069 3066 3062 3057 3056 3054

34.3 11.7 18.9 9.4 22.7 15.7 686.0 5.2 2.7 5.4 20.0 10.6 40.3 51.1 10.6 17.6 68.2 37.8 21.8 40.7 21.4

2667 3038 3037 3020 3016 3010 2181 2995 2990 2987 2980 2976 2970 2968 2967 2946 2943 2939 2934 2933 2931

1830

373.1

1757

1643 1213 1153 1544 1522 1520 1517 1514 1509 1504 1498 1488 1443 1434 1431 1414 1397 1390 1384 1373 1369 1365 1353 1346 1340 1327 1318 1290 1212 933 1249 1243 1220 1172 1150 1139 1110 1075 1066 1057 1051 1039 1003 982 967 949 936 930

885.8 28.3 12.5 7.4 8.2 6.0 15.1 6.0 14.5 1.7 5.1 1.4 6.1 0.3 4.3 6.6 3.7 25.9 83.1 4.4 1.9 4.3 10.0 0.1 34.5 10.3 11.4 0.8 28.3 96.7 4.5 3.2 1.9 9.1 8.1 0.6 15.6 11.1 2.4 8.0 1.4 2.2 2.2 0.1 8.1 5.2 8.5 7.4

1577 1164 1106 1482 1461 1459 1456 1453 1448 1443 1438 1428 1385 1376 1373 1357 1341 1334 1328 1318 1314 1310 1298 1292 1286 1273 1265 1238 1164 895 1199 1193 1171 1125 1104 1093 1065 1032 1023 1014 1008 997 962 942 928 911 898 895

mOD masCH2 masCH2 masCH2 masCH2 masCH3 mO–D  Br msCH3 masCH2 masCH2 masCH2 mC–H msCH2, mC–H msCH2, mC–H msCH2 msCH2 msCH2 msCH2 msCH2 msCH2 msCH2 mCOOD  OD2 mCOOD  OD2 mCOOD  OD2 masCOO, dCOOD  OD2

3029

2150 2997

2980

2960

2953 2935

2879 2150 1998 1370 1725

1494 1467 1457 1445

1416 1397 1381 1371 1346 1331

1314 1301

1267 1260

1203 1137 1126 1091 1072 1049 1032 1011 985 968 943 930 923 915 904

dDOD dCOOD  OD2 Sciss CH2 Sciss CH2 Sciss CH2 dCH3 Sciss CH2 dCH3 Sciss CH2 Sciss CH2 Sciss CH2 Sciss CH2 Sciss CH2 dCH3 dCH3, wag CH2 Wag CH2 Wag CH2 Wag CH2 Twist CH2 Wag CH2 Wag CH2, twist CH2 Twist CH2 Twist CH2 msCOO Twist CH2 Wag CH2 Wag CH2, twist CH2 dDOD dCOOD  OD2, dDOD msCOO, twist CH2 Twist CH2 Twist CH2 dCOOD  OD2, dDOD dC–H, rock CH2 dC–H, rock CH2 dC–H, rock CH2, rock CH3 mC–C, mC–N mC–C Rock CH2 cC–H, rock CH2 mC–C, mC–N mC–C, mC–N Rock CH2 Rock CH2, cCH3, mC–N cCH3, ring Skeleton Ring

363

Z. Dega-Szafran et al. / Journal of Molecular Structure 975 (2010) 357–366 Table 5 (continued) 3 (H)

4 (H)

mexp

mcalc

830 817

914 869 851 835 829 817 815 800 791 695 663 604 550 536 535 480 432 417 411 390 333 326 307 269 257 249 210 188 176 166 111 107 98 86 84 62 53 37

780 735 666 616

533 430 415 406

a

A 3.6 4.5 43.7 15.8 238.6 2.3 2.1 18.0 12.4 2.7 6.4 17.6 58.8 0.8 0.9 3.8 28.4 19.8 42.8 65.4 1.3 0.8 0.3 1.0 1.7 17.3 30.2 1.0 1.1 1.8 1.5 3.3 1.5 11.1 2.2 0.5 1.6 0.7

3 (D)

4 (D)

mscaleda

Assignmentsb

mexp

mcalc

A

mscaleda

Assignmentsb

877 834 816 801 795 784 782 768 759 667 636 579 528 514 513 460 414 400 394 374 319 312 294 258 246 239 201 180 168 159 106 102 94 82 80 59 50 35

Skeleton, cCOO Skeleton Rock CH2 Rock CH2 cHOH, cCOOH  OH2 Ring Ring cHOH, cCOOH cHOH, cCOOH  OH2 cHOH, skeleton Skeleton cHOH, skeleton cHOH Skeleton Skeleton Skeleton cHOH, skeleton cHOH, ring cHOH, ring cHOH, skeleton Skeleton Skeleton Skeleton Skeleton Skeleton Skeleton cCOOH  OH2 Ring Skeleton Skeleton Ring cOH  Br Skeleton cHOH Skeleton Skeleton Skeleton Skeleton

855 837 817 789 595 789 776 756

908 867 850 835 656 817 815 612 794 786 687 589 417 536 535 479 297 417 413 385 333 326 307 268 257 245 201 185 173 165 111 107 97 84 81 61 53 36

5.8 3.4 27.9 7.8 9.3 1.9 2.3 44.4 8.4 34.0 1.5 131.6 42.6 1.8 0.2 2.2 35.8 42.6 11.2 36.8 1.4 0.7 0.3 1.5 1.7 16.4 31.3 1.2 0.8 1.5 1.6 3.6 1.4 1.8 10.5 0.3 1.6 0.7

871 832 816 801 630 784 782 762 754 659 629 587 400 514 513 459 409 400 396 369 319 312 294 285 257 246 235 192 177 166 158 106 93 80 77 58 50 34

Skeleton, cCOO Skeleton Rock CH2 Rock CH2 Skeleton, cCOO Skeleton Rock CH2 Rock CH2 cDOD, cCOOD  OD2 cDOD, cCOOD Skeleton cDOD, cCOOD cDOD Skeleton Skeleton Skeleton Skeleton cDOD Ring Skeleton Skeleton Ring Skeleton Skeleton Skeleton Skeleton OD  Br Skeleton Skeleton Ring Skeleton Skeleton Ring Skeleton cDOD Skeleton Skeleton Skeleton

679 643

448 432

Scaling factor = 0.96 [38]. m – stretching, d – in-plane, c – out-of-plane, sciss – scissoring, wag – wagging, twist – twisting, rock – rocking.

b

Table 6 Experimental 1H and 13C chemical shifts (dexp, ppm, in D2O) for 2-(quinuclidinium)-butyrate derivatives 1, 2 and 3 and calculated by the GIAO/B3LYP/6-31G(d,p) approach average magnetic isotropic shieldings (r) and predicted chemical shifts (dpred) for 4. Atoma

1

Ester 1

Inner salt 2

Hydrobromide 3

Hydrobromide 4

dexp

dexp

dexp

dpred

rcalcb

H

a-ax a-eq b

c C(9)–H C(11)–H C(11)–H C(12)–H3 OCH2 CH3

3.45 3.74 2.00 2.20 3.90 1.95 2.14 0.96 4.37 1.34

3.36 3.73 1.96 2.17 3.36 1.77 1.96 0.94 – –

3.43 3.73 1.99 2.18 3.64 1.86 2.06 0.96 – –

2.47 4.65 2.17 1.93 2.49 1.43 2.15 1.15 – –

29.1643 ± 0.1399 26.4797 ± 1.4269 29.5343 ± 0.9132 29.8212 29.1374 30.4322 29.5575 30.7777 ± 0.2308 – –

56.56 26.15 22.13 78.11 21.69 11.32 170.92 66.61 11.96

55.92 26.28 21.94 82.37 21.91 12.47 175.04 – –

56.40 26.31 22.07 79.65 21.88 12.29 173.36 – –

56.37 26.82 22.93 82.88 21.77 11.94 160.46 – –

136.0073 ± 3.5701 165.0999 ± 1.4048 168.9313 109.8988 170.0664 179.7511 33.5217 – –

13

C

a b

c C(9) C(11) C(12) C(10)OO OCH2 CH3 a b

For numbering of atoms see Scheme 1 and Fig 1. Coefficients for the equation d = a + br have been determined by the linear regression.

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mCOOH  OH2, mC@O, dOH, cCOOH  OH2 and cO–H vibrations and

3.4. NMR spectra

appear at 3818, 3126, 2287, 1801, 1376, 1278, 829 cm1. The Gauss View 3.0 program [36] was used for visual animation and for inspecting the normal modes description. The proposed assignments are given in Table 5. Seven CH2 groups are responsible for the large number of the stretching and bending C–H vibrations in the theoretical spectrum, which often overlap the stretching and bending O–H vibrations and hamper the interpretation of the spectrum. However, the almost equivalent methylene groups in the quinuclidinium ring reduce the number of the CH2 vibrations in the experimental spectrum. Generally, the number of IR bands in the experimental spectrum is much lower that that in the theoretical IR spectrum, because some of them are weak, degenerated, coalesced or fall outside the observed range [37]. Additionally the experimental and theoretical spectra are different, because the experimental values are anharmonic, while a harmonic approximation was used for the computation of frequencies. The experimental spectrum was recorded for the solid state compound, while the computed spectrum was that of the isolated molecule. After correcting these discrepancies by scaling the calculated wavenumbers with a 0.96 factor [38], the experimental spectrum is much better reproduced (Fig. 4b and c).

The 1H and 13C chemical shifts for three 2-(quinuclidinium)butyrate derivatives: ester 1, inner salt 2 and hydrobromide 3 are listed in Table 6. The carbon atoms directly bonded to the quaternary nitrogen atom are denoted as a, the further ones as b and c (Scheme 1). The atoms of the N+CH(C2H5)COOR substituent are numbered as shown in Fig. 1. The proton chemical shifts assignments were based on the 2D (COSY) experiments, where the proton–proton connectivity is observed through the off-diagonal peaks in the counter plot. The 2D heteronuclear shift-correlated contour maps (HETCOR) were used to identify resonance signals in the 13C NMR spectra [39]. There are no significant differences in the chemical shifts of the ring protons and carbons in the spectra of compounds 1, 2 and 3, and the resonance signals of b and c-protons in the 1H NMR spectra of the 2-(quinuclidinium)-acetate derivatives [11,12,25–27]. However, when the alkyl group (R) is introduced to the N+CHR–COO substituent, two signals attributed to the a-protons are observed in the 1H NMR spectrum. These multiplets are separated by ca. 0.3 ppm. Similarly, as in the 2-(quinuclidinium)-propionic acid hydrobromide hydrate [13] and in the N-methylpiperidine betaine complexes [40], the axial protons are

C(12)H3

β

α-ax

α-eq

γ C(9)H C(11)H2

3.8

3.6

3.4

3.2

3.0 2.8

2.6

2.4

2.2

2.0

1.8 1.6

1.4

1.2

1.0 ppm

1

Fig. 5. H NMR spectrum for 2-(quinuclidinium)-butyric acid bromide hydrate (3) in D2O.

Chemical shifts (ppm)

3,5

150

3,0 2,5

100

2,0 50

1,5 1,0 26

(a) 27

(b) 28

29

30

31

50

100

150

Magnetic isotropic shielding tensors (ppm) Fig. 6. The experimental chemical shifts (d) of 2-(quinuclidinium)-butyric acid bromide hydrate (3) in D2O versus the magnetic isotropic shielding constants (r) from the GIAO/B3LYP/6-31G(d,p) calculations for 4; (a) 1H dexp = 26.1951–0.8136rH, r = 0.8766 and (b) 13C dexp = 194.5088–1.0157rC, r = 0.9978.

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more shielded than the equatorial ones [41]. The C(11)H2 methylene protons in the group attached to the chiral center at C(9) are non-magnetically equivalent (diastereotopic protons) [42] and in the 1H NMR spectrum two multiplets, separated by ca. 0.2 ppm, are observed (Fig. 5). Such an effect has been observed by Binsch and a heuristic mathematical model for its explanation has been proposed [43]. In the 1H NMR spectrum of 2 one of the resonance signal of C(11)–H2 protons overlaps the resonance signal of b-protons, while these resonance signals are well resolved in the 1H NMR spectra of 1 and 3. The resonance signal of the C(9)–H proton appears as a doublet and its chemical shift depends on the adjacent substituent (Table 6). The chemical shifts assignments for 3 are confirmed by the calculated magnetic shieldings for 4 by the GIAO/B3LYP/6-31G(d,p) approach (Table 6). The relations between the experimental 1H and 13C chemical shifts and average magnetic shielding constants (r) are usually linear and described by the equation: dexp = a + brcalc [44,45]. The data in Table 6 and Fig. 6 show that the agreement between the experimental chemical shifts (dexp) and the magnetic isotropic shielding constants (r) is much better for 13C than for 1H. The coefficients a and b are used to calculate the predicted 1H and 13C chemical shifts (Table 6). The protons are located on the periphery of the molecule and thus are more susceptible to intermolecular solvent–solute effects than the carbon atoms [46]. Additionally, some C(a)–H  Br contact in the isolated molecule 4 (Table 4) can be responsible for the above discrepancy in the magnetic isotropic shielding constants (Table 6). 3.5. Potentiometric measurements The pKa values of quinuclidinium-acetate (QNB, quinuclidine betaine), 2-(quinuclidinium)-propionate (QNPr) and 2-(quinuclidinium)-butyrate (2, QNBu) have been determined by the potentiometric titration of their hydrohalides with KOH (Scheme 2). The constant Ka corresponds to the dissociation of the carboxylic group of the cation. The potentiometric titration curves are shown in

R + N CH COOH

R _ + + N CH COO + H

Ka

R = H, CH 3, CH2CH3

14 12

pH

10 8 6 4 2 0

a b

Compounds

pKa

Quinuclidine Quinuclidinium-acetate 2-(Quinuclidinium)-propionate 2-(Quinuclidinium)-butyrate N-methylpiperidine betaine

11.15a 1.59 ± 0.03 1.32 ± 0.02 0.92 ± 0.04 1.91 ± 0.02b

From Ref. [9]. From Ref. [19].

Fig. 7. The pKa values given in Table 7 are compared with these of quinuclidine [9] and N-methylpiperidine betaine [19]. The alkyl group in the N+–CH(R)COO substituent decreases the pKa values. 4. Conclusions In 2-(quinuclidinium)-butyric acid bromide hydrate (3) the water molecule is engaged in two hydrogen bonds with the COOH group and the bromide anion of 2.575(3) and 3.293(2) Å, respectively, and links them into chains. The B3LYP/6-31G(d,p) approach reproduces well the structures of monomer (4) and hydrogen bond distances in the dimeric cation (5) built of two 2-(quinuclidinium)butyric acid molecules, two water molecules and one bromide anion. The mOH  O and mOH  Br bands in the FTIR spectrum confirm that the OH  O hydrogen bond is stronger than the OH  Br bond. The tentative assignments of the bands are based on the spectrum calculated by the B3LYP/6-31G(d,p) methods. The 1H NMR spectra of QNBu derivatives (1–3) show that protons at the carbon atoms attached to the quaternary nitrogen atom are non-equivalent. The C(11)H2 methylene protons in the group attached to the chiral center at C(9) are non-magnetically equivalence (diastereotopic protons) and two signals at ca. 1.8 and 2.0 ppm are observed. The ethyl group in the N+–CH(R)COO substituent decreases the basicity of QNBu (2). Acknowledgement DFT calculations were performed at the Poznan´ Supercomputing and Networking Centre. References

Scheme 2. The dissociation of the quinuclidinium-alkanocarboxylic acid cation.

0

Table 7 pKa values in water at 25 °C.

2

4

Titrant, ml

6

8

Fig. 7. The potentiometric titration curves for quinuclidinium-acetate hydrochloride (d), 2-(quinuclidinium)-propionate hydrobromide (s) and 2-(quinuclidinium)-butyrate hydrobromide (4).

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