Vibrational spectroscopic investigation and conformational analysis of 1-cyclohexylpiperazine

Journal of Molecular Structure 975 (2010) 85–92

Contents lists available at ScienceDirect

Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc

Vibrational spectroscopic investigation and conformational analysis of 1-cyclohexylpiperazine Özgür Alver a,b,*, Cemal Parlak c a

Plant, Drug and Scientific Research Centre, Anadolu University, Eskisßehir, Turkey Department of Physics, Science Faculty, Anadolu University, Eskisßehir, Turkey c Department of Physics, Arts and Science Faculty, Dumlupınar University, Kütahya, Turkey b

a r t i c l e

i n f o

Article history: Received 8 February 2010 Received in revised form 31 March 2010 Accepted 31 March 2010 Available online 7 April 2010 Keywords: 1-Cyclohexylpiperazine Vibrational spectra Conformational analysis DFT

a b s t r a c t The possible stable conformers of 1-cyclohexylpiperazine (1-chpp) molecule were experimentally and theoretically studied by FT-IR and Raman spectroscopy in the region of 4000–200 cm1. The optimized geometric structures concerning to the minimum on the potential energy surface were investigated by B3LYP hybrid density functional theory method together with 6-31G(d) basis set. Comparison between the experimental and theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting vibrational wavenumbers and equatorial–equatorial (e–e) form is supposed to be the most stable form of 1-chpp molecule. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction

2. Experimental

1-Cyclohexylpiperazine (1-chpp) molecule has been part of many different scientific studies. For example, a series of 1-chpp and its derivatives were investigated as potent and selective antagonists of the human MC4, CCR4 receptors and potential myocardial imaging agents [1–4]. It has been also used to synthesize of potential analgesic agents and some of its derivatives have been studied in the cancer researches [5,6]. The B3LYP density functional model exhibits good performance on electron affinities, excellent performance on bond energies and reasonably good performance on vibrational frequencies and geometries of organic compounds [7–12]. A detailed quantum chemical investigation will aid in making assignments to the fundamental normal modes of 1-chpp and clarifying the obtained experimental results for this molecule. In this work, the stable conformers of 1-chpp have been studied within the framework of DFT. FT-IR and Raman spectra with the vibrational spectral assignments of 1-chpp have been reported. The vibrational wavenumbers and structural parameters have been also calculated for the most stable conformer at B3LYP level of theory using 6-31G(d) basis set.

A commercial sample of 1-chpp was purchased and used without further purification. FT-MIR spectrum (4000–400 cm1) of 1chpp was recorded KBr pellet technique using Perkin-Elmer FT-IR 2000 spectrometer at a resolution of 4 cm1. Far infrared spectrum was recorded with Bruker Optics IFS66v/s FTIR spectrometer with the resolution of 2 cm1 in the spectral region of 400–200 cm1. The Raman spectrum was obtained using a Bruker Senterra Dispersive Raman microscope spectrometer with 532 nm excitation from a 3B diode laser having 3 cm1 resolution in the spectral region of 3700–200 cm1.

* Corresponding author at: Plant, Drug and Scientific Research Centre, Anadolu University, Eskisßehir, Turkey. Tel.: +90 222 335 05 80/3668; fax: +90 222 320 49 10. E-mail address: [email protected] (Ö. Alver). 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.03.090

3. Calculations Many possible conformers could be proposed for 1-chpp but here the discussion was limited for e–e (equatorial–equatorial), e–a (equatorial–axial), a–a (axial–axial) and a–e (axial–equatorial) conformers of 1-chpp (Fig. 1), where the former represents NH while the latter stands for cyclohexyl ring. They are considered in axial and equatorial positions according to plane formed by C18, C20, C19 and C23 atoms of the title molecule. For the calculations, all four forms of 1-chpp were first optimized by B3LYP with 6-31G(d) basis set in the gas phase. The optimized geometric structures concerning to the minimum on the potential energy surface were provided by solving self-consistent field (SCF) equation iteratively. e–e and a–e conformations were found more stable than the other two forms and the energy difference between e–e (a–e) and

86

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92

Fig. 1. Possible stable conformers of 1-chpp.

e–a (a–a) are larger than 2.0 kcal/mol. Therefore, relative mole fractions of e–a and a–a conformers could be neglected. For the vibrational calculations, the vibrational frequencies of e–e and a–e forms of 1-chpp were calculated using the same method and the basis set under the keyword freq = raman. No imaginary frequencies were observed, therefore; none of the optimized structures are in transition state for the investigated forms. All the calculations were performed with Gaussian 03 program on a personal computer [13]. 4. Results and discussion 4.1. Geometrical structures

Table 1. According to the literature, experimental data on the geometric structure of 1-chpp is not available. However, some geometric parameters for piperazine and cyclohexene molecules were identified both experimentally and theoretically in previously reported studies [14,15]. Henceforth, the results were compared with data of piperazine and cyclohexene as given in Table 1. The calculated structural parameters for piperazine and cyclohexene in 1-chpp are similar to previously reported data (Table 1). The magnitude of dihedral angles, D(20;18;32;3) and D(32;3;4;5) for the optimized 1-chpp in the e–e form are found to be as 175.5° and 179.4°. Moreover, these dihedral angles are found as 175.3° and 179.8° for the a–e form of 1-chpp. The mole fractions of individual conformers can be calculated with the following equations: K T1

The optimized geometric parameters (bond lengths, bond and dihedral angles) calculated by B3LYP/6-31G(d) are listed in

K T2

K T3

a () b () c () d According to equilibrium given above,

87

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92 Table 1 Optimized geometric parameters of 1-chpp for four conformers calculated by B3LYP with 6-31G(d) basis set. Exp. piperazinea

Parameters

Exp. cyclohexylb

B3LYP/ 6-31G(d) e–e

a–e

e–a

a–a

0

Bond lengths (Å A) C3–H17 N32–C3 C4–C3 C3–C2 C4–C5 C5–C6 C6–C1 C1–C2 C2–C3 C–C C–N C–H C18–C20 C19–C23 C18–H21 C18–H22 C23–H28 C23–H29 N30–H31 Bond angles (°) N32–C3–C4 C4–C3–C2 N32–C3–C2 C3–C4–C5 C4–C5–C6 C5–C6–C1 C6–C1–C2 C3–C2–C1 N32–C3–H17 C4–C3–H17 C2–C3–C17 C–C–N C–N–C H–C–H C20–N30–C23 C18–N32–C19 C19–C23–N30 C18–C20–N30 C20–C18–N32 C23–C19–N32 H28–C23–H29 H21–C18–H22

1.000 1.476 1.515 1.509 1.517 1.516 1.516 1.522 1.509

a

1.111 1.482 1.545 1.541 1.536 1.533 1.533 1.538 1.541

1.100 1.466 1.549 1.543 1.539 1.535 1.535 1.537 1.543

1.100 1.466 1.549 1.543 1.539 1.535 1.535 1.537 1.543

1.530 1.528 1.108 1.092 1.097 1.107 1.018

1.536 1.534 1.112 1.093 1.096 1.098 1.021

1.539 1.537 1.100 1.094 1.097 1.107 1.018

1.542 1.541 1.104 1.095 1.098 1.098 1.022

1.540 1.467 1.110

112.2 112.9 112.8 110.2 112.0 111.4 110.5 110.3 102.5 107.3 108.4

110.0 108.9 112.9 112.8 111.5 110.4 112.3 112.3 109.6 108.2 107.0

110.0 108.9 113.1 112.8 111.4 110.4 112.3 112.2 109.5 108.2 107.0

117.1 110.0 111.0 111.8 111.7 111.0 111.6 112.0 105.0 106.8 106.4

117.0 109.9 111.1 111.7 111.6 111.1 111.6 111.8 104.9 106.9 106.3

110.1 108.9 109.2 109.7 110.5 111.1 108.0 107.9

109.7 109.0 113.7 114.3 110.5 111.2 107.6 107.3

111.1 111.8 108.4 108.8 114.0 114.2 107.6 107.3

109.9 112.1 113.0 113.4 114.0 114.3 107.2 106.5

179.4 56.5 54.5 54.5 55.8 179.4 175.5 179.4

179.8 56.4 54.4 54.5 55.8 68.2 175.3 179.7

177.3 55.5 54.8 54.7 55.6 177.4 97.4 177.3

176.8 55.5 54.6 54.7 55.8 67.2 97.3 176.8

110.4 109.0 109.1

Dihedral angles (°) N32–C3–C4–C5 C3–C4–C5–C6 C4–C5–C6–C1 C5–C6–C1–C2 C6–C1–C2–C3 C19–C23–N30–H31 C20–C18–N32–C3 C5–C4–C3–N32 b

1.111 1.481 1.545 1.542 1.536 1.533 1.533 1.538 1.542

176.6 53.6 55.5 56.4 56.2

Taken from Ref. [14]. Taken from Ref. [15].

K T1 ¼ Nb =Na ; K T2 ¼ Nc =Nb ; K T3 ¼ Nd =Nc and Na þ Nb þ Nc þ Nd ¼ 1 can be written, where K T1 ; K T2 and K T3 are conformational equilibrium constants between a, b, c and d forms, Na , Nb , N c and N d are mole fractions of conformers a, b, c and d.

1 ; Nb 1 þ K T1 þ K T1 K T2 þ K T1 K T2 K T3 K T1 ¼ ; Nc 1 þ K T1 þ K T1 K T2 þ K T1 K T2 K T3 K T1 K T2 ¼ ; Nd 1 þ K T1 þ K T1 K T2 þ K T1 K T2 K T3 K T1 K T2 K T3 ¼ ; 1 þ K T1 þ K T1 K T2 þ K T1 K T2 K T3

Na ¼

K T ¼ edDG=RT ; R ¼ 1:987  103 kcal=mol  K;T ¼ 298  K and dDG ¼ DGb  DGa [16]. Regarding the calculated free energies for the gas phase, the following mole fractions were obtained: Na = 0.546 (e–e), Nb = 0.449 (a–e), Nc = (3.287)103 (e–a) and Nd = (2.232)103 (a–a). Based on the calculations, the e–e form is also the most stable and the most abundant conformer in the gas phase. Regarding the calculated free energies for gas phase, e–e form is more stable than a–e by 0.115 kcal/mol, e–a by 3.03 kcal/mol and a–a by 3.26 kcal/mol. The e–a and a–a forms could be neglected for calculation of equilibrium constant since their energy differences are larger than 2 kcal/mol. Consequently, 1-chpp in the gas phase prefers e–e and a–e forms with preference of 54.6% and 44.9%, respectively. Since Na and Nb are larger than Nc and Nd, approximate mode descriptions were determined considering e–e conformer.

88

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92

Table 2 The measured IR and Raman wavenumbers (cm1) for 1-chpp molecule together with the data for piperazine and cyclohexene molecules. Ass.a

Piperazinea

Ass.b

IR

R

N–H str. CH2 a-str. – – – – m11(au), m28(bu) CH2 str. – – m12(au), m29(bu) CH2 str. + CH2 a-str. – – – m30(bu) CH2 scissor m13(au) CH2 scissor

3225 s – – – – – 2940 s – – 2827 vs – – – 1455 s 1446 sh

– 3225 s – – – – – – – 2832 s – –

– CH2 wagging – m14(au) CH2 wagging – – – CH2 twist m15(au) CH2 twist – – – CH2 twist – m16(au) Ring str

– 1414 sh – – 1369 m – – – – 1266 s – – – – – 1132 vs –

– – CH2 rock m17(au) CH2 rock – – – m33(bu) ring str. – m34(bu) CH2 wagging – – CH2 rock m18(au) ring str. – – – – m35(bu) ring band – Ring band Ring band Ring band – – m19(au) ring band m36(bu) ring band – – –

– – – 1084 m – – – 1000 m – 962 m – – – 833 s – – – – 591 s – – – – – – 317 s 272 vs – – –

m31(bu) CH2 wagging

1455 m 1446 s

– –

m23 m1 –

m24 m2 –

m4 m5 – –

m7 m7 m28 m29

– 1393 w

–

m12 + m42 m12 + m42 –

m9 m10 m31 1297 vs

–

m32 m11 –

m12 1184 vs

– –

m13 1123 m 1119 s

–

– – 1109 vs

m14 –

m15 –

m35 – –

866 vs 836 vs – – – – – – 481 w 448 vw 404 w – – – – – – –

m16 m37 m17 m38 m18 m40+m42 – –

m40 – –

m20 m41 m21 – – –

m22 – – –

Cyclohexeneb

1-chpp

IR

R

IR

R

– – 3061 m 3019 s 2982 m 2958 w 2930 vs 2893 sh 2858 s 2836 s – – 1461 m 1454 m 1445 m

3284 m – – – – 2958 sh 2926 vs – 2851 s 2825 sh – 2753 w 1473 sh – 1451 s

– – – – 2976 sh 2960 s 2921 s 2891 w 2851 vs 2833 sh 2769 w – 1473 sh 1466 m 1448 vs

1442 s – 1393 sh 1390 w – 1353 w – 1321 m – 1265 w 1242w – 1225 m – – 1137 m –

– – 3063 w 3021 s 2986 w 2960 w 2937 s – 2866 m 2839 m – – – – 1449 w 1432 s – – – – – 1354 vw 1342 vw – – 1269 w 1245 m – 1225 vw – – 1141 vw –

– 1403 vw 1385 w – 1370 w 1337 m – 1319 m 1305 m 1274 m 1257 sh – 1223 m – 1185 w 1158 sh 1137 s

– – – – – 1343 m – – 1297 s – 1258 m – 1204 w 1193 vs 1185 sh 1158 m –

– – 1072 vw – 1062 w – 1038 ms – – 960 vw 916 s 903 m 878 s – 808 w – – 641 w – – – 455 m – – – – – – – ––

– – 1075 mw – 1066 m – 1034 m – – 967 vw – 906 w 881 m 828 vs 813 w – – 644 w – – 495 w 454 w 397 m – – – 285 w – – –

1122 m 1104 m 1085 vw 1072 w 1065 w 1052 w 1033 m 1021 m 1000 vw 977 m 925 w – 891 m 850 s 808 w 785 w 769 w 638 m 549 s 501 w – 470 vw – 391 m 374 w 355 w 285 w 270 w 263 w –

1122 w – 1077 m – 1052 m – 1034 m 1022 m – 972 vw – – 856 w 845 s 808 vs 786 w 771 vs – – – 470 vs 429 m – – – – 291 w 277 w 266 w 238 w

a,b

Taken from Refs. [17] and [18], respectively. v: very, s: strong, m: medium, w: weak, vw: very weak, sh: shoulder, br: broad.

4.2. Vibrational studies of 1-chpp Up to our knowledge, the vibrational assignments of 1-chpp in the region of 4000–200 cm1 have not been reported in the literature. 1-chpp (C10H20N2) consists of 32 atoms, so it has 90 normal

vibrational modes and it belongs to the point group C1 with only identity (E) symmetry operation. It is difficult to determine 1chpp’s vibrational assignments in the observed spectrum due to its low symmetry. All the experimental and theoretical vibrational modes obtained in this study are given in Tables 2 and 3. The

89

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92 Table 3 Comparison of the experimental and calculated vibrational wavenumbers (cm1) of 1-chpp. Mode

m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 m13 m14 m15 m16 m17 m18 m19 m20 m21 m22 m23 m24 m25 m26 m27 m28 m29 m30 m31 m32 m33 m34 m35 m36 m37 m38 m39 m40 m41 m42 m43 m44 m45 m46 m47 m48 m49 m50 m51 m52 m53 m54 m55 m56 m57 m58 m59 m60 m61 m62 m63 m64 m65 m66 m67

Approximate mode descriptionsa

NH str C(18)–H2 a-str C(4;19)–H2 a-str C(2;4)–H2 a-str C(2;4)–H2 a-str C(20;23)–H2 a-str C(20;23)–H2 a-str C(1;5;6)–H2 a-str C(5;6)–H2 a-str C(1;5)–H2 a-str C(4;5)–H2 s-str C(1;2)–H2 s-str C(1;2;5;6)–H2 s-str C(1;2;6)–H2 s-str C(1;2;5;6)–H2 s-str C(18;19;20;23)–H2 s-str C(18;20;23)–H2 s-str C(18;19;20;23)–H2 s-str C(18;19;20)–H2 s-str C(3)–H str C(1;2;4;5;6)–H2 sciss C(18;19;20;23)–H2 sciss C(18;19;20;23)–H2 sciss C(1;2;4;5;6)–H2 sciss C(1;2;4;18;19;20;23)–H2 sciss C(1;2;4;6;18;19;20;23)–H2 sciss C(4;5;6)–H2 sciss C(1;5;18;19;20;23)–H2 sciss C(1;2;4;5;19)–H2 sciss C(20;23)–H2 wag + CNH(31) bend C(18;19;20;23)–H2 wag + C(18;20) str + C(19;23) str + NCH(17) bend C(18;19;20;23)–H2 wag + NCH(17) bend C(1;2;4;5)–H2 wag + NCH(17) bend CH2 wag (Cyc-ring) + C(18;19)–H2 wag + CCH(17) bend CH2 wag (Cyc-ring) + C(18)–H2 wag + C(2)C(3)H(17) bend CCC a-str (cyc-ring) CH2 wag (cyc-ring) + CCH(17) bend + CCC a-str (Cyc-ring) CH2 wag (cyc-ring) + C(2)C(3)H(17) bend + C(18;19)–H2 wag C(1;2) str + C(4;5) str + CH2 wag (cyc-ring) + C(2)C(3)H(17) bend C(2;20;23)–H2 wag + C(18;19)–H2 twist + CNH(31) C(2;23)–H2 wag + C(1)–H2 twist + NCH(17) C(4)–H2 wag + C(5;18;19)–H2 twist + NCH(17) C(18;19;20;23)–H2 twist + C(3)–H bend C(4;18;19;20;23)–H2 twist + C(3)–H bend C(1;2;4;5;6)–H2 twist + C(3)–H bend C(1;2;4;5;6;18)–H2 twist + C(3)–H bend CH2 twist (cyc + pp) + C(3)–H bend CH2 twist (cyc + pp) + C(3)–H bend + N(30)–H bend C(18;19;20;23)–H2 twist C(1;5;20;23)–H2 twist + C(2;4)–H wag + C(6)–H2 def. cyc-ring bend + CH2 rock (cyc) CN(30)C str + C(20;23)–H2 wag N(32)C(3) str + C(19)–H2 twist + C(18)–H2 def + CN(32)C bend C(18)N(32)C(19) str + CH2 def (cyc + pp) C(18;19;20;23)–H2 rock + N(32)C(3) str. + ring bend (pp) C(1;2;4;5;6)–H2 twist + C(3)–H bend C(2;4;6)–H2 twist + ring str (cyc) CH2 rock (pp) + N(32)–H bend Ring str (pp) + CH2 def (pp) + N(32)–H bend C(6)–H2 wag + C(1;5)–H2 twist + C(3)–H bend Ring str (cyc) Ring str (cyc + pp) + N(32)C(3) str ring str (cyc + pp) + N(32)C(3) str Ring str (cyc + pp) Ring str (cyc + pp) Ring str (cyc + pp) + N(32)C(3) str + N(30)–H bend Ring str (cyc) + N(30)–H bend Ring str (cyc) + CH2 rock (cyc)

Exp. IRb

Exp. Rb

3284 m 2976 sh

2958 sh

2960 s

2926 vs

2921 s 2891 w

2851 s

2851 vs

2825 sh

2833 sh 2769 w

2753 w 1473 sh 1473 sh

1451 s

1466 m

1451 s 1403 vw

1448 vs

1385 w 1370 w 1337 m

1343 m

1319 m

1305 m 1274 m

1297 s

1257 sh

1258 m

1223 m

1204 w 1193 vs 1185 sh 1158 m

1185 w 1158 sh 1137 s 1122 m 1104 m 1085 vw 1072 w 1065 w 1052 w 1033 m 1021 m 1000 vw 977 m 925 w

1122 w 1077 m

1052 m 1034 m 1022 m 972 vw

891 m 856 w

Scaled wavenumbers

B3LYP/6–31G(d)

ma

mb

e–e

(cm1)

(cm1)

3336 2988 2982 2957 2954 2939 2938 2938 2932 2932 2905 2894 2890 2886 2885 2818 2811 2803 2793 2760 1488 1486 1478 1474 1469 1469 1466 1463 1461 1451 1407

a–e

Freq.

IIR

IR

Freq.

IIR

IR

3297 2980 2974 2956 2955 2954 2953 2938 2933 2932 2912 2907 2906 2894 2891 2886 2885 2768 2754 2749 1488 1481 1474 1470 1469 1466 1462 1462 1453 1401 1396

3493 3129 3123 3096 3093 3078 3077 3076 3070 3070 3042 3030 3026 3022 3021 2951 2944 2935 2925 2890 1539 1537 1529 1524 1519 1519 1516 1513 1511 1501 1455

3.32 27.49 48.58 54.52 17.14 43.48 61.41 60.45 69.64 58.62 27.49 24.48 19.52 18.15 24.90 206.59 18.59 30.87 39.76 41.48 0.82 0.38 13.18 5.09 3.69 2.80 1.59 0.28 0.16 1.20 3.99

188.72 75.81 87.35 43.04 47.11 137.14 109.22 100.35 178.03 89.66 54.27 23.83 40.97 141.70 63.07 39.35 24.03 218.57 8.49 35.44 1.61 11.61 0.93 0.86 0.58 5.11 17.00 42.72 11.99 4.85 2.99

3452 3120 3114 3095 3094 3093 3092 3077 3071 3070 3049 3044 3043 3030 3027 3022 3021 2898 2884 2879 1539 1532 1524 1520 1519 1516 1512 1512 1503 1499 1444

3.56 34.42 52.20 87.70 22.61 34.63 5.13 63.23 67.42 55.67 44.48 41.99 26.94 24.13 20.90 18.29 18.29 165.55 21.62 25.41 0.76 3.19 5.55 4.83 2.58 1.37 4.03 2.82 6.35 0.18 1.43

78.72 80.80 117.00 57.20 97.15 99.43 24.03 88.17 199.26 81.07 147.83 37.65 55.61 26.33 35.52 171.97 171.97 141.86 15.40 14.98 1.92 6.95 0.64 4.49 4.35 19.48 13.65 15.89 2.09 28.38 0.67

1395 1381 1361 1358

1385 1371 1361 1358

1443 1428 1407 1404

3.19 5.92 0.20 13.84

2.34 2.63 5.01 5.91

1432 1418 1407 1404

13.39 1.28 0.41 9.00

0.76 5.93 5.63 6.89

1353 1345 1339

1354 1343 1340

1399 1391 1385

5.75 4.33 0.43

4.45 4.82 0.23

1400 1389 1386

7.69 11.17 0.08

4.90 5.93 0.14

1333 1316 1310 1302 1271 1265 1260 1248 1236 1198 1182 1146 1136 1134 1116 1103 1071 1067 1055 1048 1033 1020 1015 969 914 910 894 882 880

1338 1325 1315 1308 1286 1268 1264 1255 1241 1198 1175 1152 1145 1130 1111 1108 1170 1068 1035 1021 1013 1012 1002 965 913 907 896 881 879

1379 1361 1355 1347 1314 1308 1303 1291 1278 1239 1222 1185 1175 1173 1154 1141 1108 1103 1091 1084 1068 1055 1050 1002 945 941 925 912 910

46.21 7.03 7.07 7.85 8.35 5.41 5.78 2.75 7.02 0.84 0.27 0.39 13.16 46.84 32.20 15.45 0.37 1.11 1.26 17.47 0.29 5.12 5.52 14.08 0.32 2.91 1.26 3.68 1.00

1.00 6.16 6.16 28.37 0.70 16.94 10.65 2.77 3.66 17.98 1.17 2.73 3.92 6.77 3.94 3.08 1.46 0.14 0.18 13.02 4.00 8.49 2.17 0.91 1.25 0.10 5.63 1.82 0.44

1384 1370 1360 1353 1330 1311 1307 1298 1283 1239 1215 1191 1184 1169 1149 1146 1107 1104 1070 1056 1048 1047 1036 998 944 938 927 911 909

4.40 0.75 1.23 7.53 18.42 14.00 10.59 1.21 8.56 1.05 11.80 13.17 28.79 14.12 28.90 39.57 0.44 0.45 0.01 0.65 5.07 7.09 6.45 21.36 0.07 4.64 7.88 5.11 1.60

2.63 15.60 7.81 7.16 14.46 5.83 15.16 1.68 5.28 10.42 3.87 3.04 4.43 3.78 7.98 2.32 1.68 0.12 4.81 17.20 0.25 0.57 3.11 2.05 0.97 1.64 2.48 0.73 0.97

(continued on next page)

90

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92

Table 3 (continued) Mode

m68 m69 m70 m71 m72 m73 m74 m75 m76 m77 m78 m79 m80 m81 m82 m83 m84 m85 m86 m87

Approximate mode descriptionsa

Exp. IRb

Ring str (pp) + CH2 rock (pp) Ring str (cyc) + C(6)–H2 rock Ring breath (cyc) + ring str (pp) + N(30)–H bend ring breath (cyc) + ring str (pp) + N(30)–H bend Ring str (cyc) + CH2 rock (cyc) Ring str (cyc) + CH2 rock (cyc) + N(30)–H bend + CN(32)C str Ring bend (cyc) + N(30)–H bend + C(3)C(4)C(5) bend Ring bend (cyc + pp) + CN(30)C def. Ring bend (cyc + pp) Ring bend (cyc + pp) Ring bend (cyc + pp) + C(19)N(32)C(3) bend + C(19)N(32)C(18) bend Ring bend (cyc) Ring bend (pp) Ring bend (cyc + pp) Ring bend (cyc + pp) Ring bend (cyc + pp) + C(19)N(32)C(3) bend + C(19)N(32)C(18) bend N(32)C(3) str Ring bend (pp) Ring bend (cyc) C(19)N(32)C(3) bend + C(19)N(32)C(18) bend

850 s 808 w 785 w 769 w 638 m 549 s

Exp. Rb

845 s 808 vs 786 w 771 vs

470 vs 470 vw

429 m 391 m 374 w 355 w 285 w

263 w

291 w 277 w 266 w 238 w

Scaled wavenumbers

B3LYP/6–31G(d)

ma

mb

e–e

(cm1)

(cm1)

846 839 798 793 775 767 605 515 471 463 451

839 822 806 792 775 762 605 525 476 467 449

875 868 825 820 802 793 626 533 487 479 466

0.14 5.26 89.93 26.96 0.15 1.11 11.65 15.01 0.10 2.48 4.83

1.15 7.83 1.58 1.57 1.24 10.34 0.25 3.82 1.76 0.91 1.62

868 850 834 819 802 788 626 543 492 482 464

8.34 0.53 133.24 2.09 1.95 25.00 7.27 1.74 2.19 0.70 0.68

7.65 1.25 4.85 1.26 1.07 8.77 0.38 2.11 2.25 0.91 1.85

426 408 374 342 283

427 406 374 343 285

441 422 386 354 293

0.06 0.16 0.21 1.05 3.25

2.09 0.32 1.08 0.25 0.20

442 420 386 355 295

0.30 4.91 2.43 3.91 5.92

2.22 0.32 1.06 0.07 0.36

277 255 219 191

275 245 219 191

286 264 227 198

1.14 1.00 0.17 0.86

3.37 0.47 0.02 0.04

284 253 227 198

0.69 0.09 0.08 0.21

4.24 0.20 0.05 0.15

Freq.

a–e IR

IIR

Freq.

IIR

IR

a,b

Dual scaling factors were used, 0.955 above 1800 cm1, 0.967 under 1800 cm1 [7]. ma, mb: Scaled calculated wavenumbers for e–e and a–e conformers, respectively. IIR and IR: Infrared intensities (km/mole) and Raman activities (Å4/amu), Exp.: Experimental, Freq.: Frequency, str: stretching, bend: bending, sciss: scissoring, twist: twisting, wag: wagging, s: symmetric, a: antisymmetric, breath.: breathing, def.: deformation. a Our vibrational frequency assignment on the basis of DFT calculations. b Our experimental IR and Raman wavenumbers.

assignments of the vibrational modes of the title molecule are provided by animation option of the GaussView package program for the B3LYP/6-31G(d) level of calculation. Using the animation we identified vibrational motions of the studied molecule. The vibrational assignments for the free 1-chpp are tabled in accordance with the vibrational assignments of piperazine [17] and cyclohexene [18] (Table 2). The similar approach was adopted for the vibra-

tional assignments of several previous studies [10,11]. The measured IR and Raman wavenumbers for the free 1-chpp together with the data for piperazine and cyclohexene are given in Table 2. NH stretching band of 1-chpp is due to piperazine group. The free piperazine has a main NH band at 3225 cm1, (3276 cm1) in the infrared spectrum [17]. While NH band of 1-chpp was observed at 3284 cm1 in the IR spectrum (Fig. 2), no NH band observed in

Fig. 2. FT-IR spectrum of 1-chpp.

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92

91

Fig. 3. Raman spectrum of 1-chpp.

the Raman spectrum which refers to low polarizability of NH in 1chpp for the powder form (Fig. 3). NH stretching mode was calculated at 3493/3452 cm1 (e–e/a–e), (Fig. 4). CH2 antisymmetric and

symmetric stretching of 1-chpp were observed at 2976 cm1 (R), 2960/2958 cm1 (R/IR), 2926/2921 cm1 (IR/R) and 2891 cm1 (R), 2851 cm1 (R, IR), 2833/2825 cm1 (R/IR), 2769 cm1 (R), respectively. The theoretically calculated values for these antisymmetric and symmetric CH2 vibrations are (e–e/e–a), 3123/ 3114 cm1, 3078/3093 cm1, 3070/3071 cm1 and 3042/ 3049 cm1, 3022/3030 cm1, 2951/3022 cm1, 2935/2898 cm1, respectively (Fig. 4). The band experimentally observed at 2753 cm1 (IR) is attributed to CH stretching vibrations arising mainly from cyclohexyl ring which is theoretically calculated as 2890/2898–2879 cm1. The fundamental CH2 vibrations which are scissoring, wagging and rocking appear in the expected frequency region 1600–800 cm1 [19]. We made measurements in the frequency region 1600–200 cm1. These vibrations have revealed to be mixed CH2 wagging, CH2 twisting, CH2 rocking, NH bending, ring stretching and ring bending. The bands appeared at 1451 cm1 (IR) and 1448 cm1 (R) are mainly due to CNH bending vibrations calculated as 1501 cm1 (e–e) and 1499 cm1 (a–e). The bands at 1122 cm1 and 549 cm1 are mainly arisen from CN(32) stretching CN(30)C deformation which are theoretically calculated at (e–e/a–e), 1173/1149 cm1 and 533/543 cm1. As can be seen from Table 3 that NH stretching mode and four modes with number 16, 17, 18, 19 all of which associated with piperazine show remarkable sensitivities to the conformation, while the remaining all normal modes show either weak or almost insensitive to the conformational structure.

5. Conclusion

Fig. 4. Calculated FT-IR (a) and Raman (b) spectra of 1-chpp for e–e conformer.

We performed the experimental and the theoretical vibrational analysis of 1-chpp for the first time. The structural parameters, IRRaman frequencies and intensities–activities of vibrational bands of 1-chpp were calculated with B3LYP methods and 6-31G(d) basis set for e–e and a–e conformers. In order to make a comparison with experimental wavenumbers, we calculated root mean square deviation (RMSD) based on the calculation. The following rmsd values were obtained: 15.00 cm1 (e–e, IR), 15.44 cm1 (e–e, R), 17.27 cm1 (a–e, IR) and 20.00 cm1 (a–e, R). Based on the gas phase energy calculations and the obtained experimental–theoretical rmsd results indicate that is the most stable conformer of the 1-chpp molecule. Any differences observed between the experimental and the calculated wavenumbers could be due to the fact that the calculations have been performed for single molecule in

92

Ö. Alver, C. Parlak / Journal of Molecular Structure 975 (2010) 85–92

the gaseous state contrary to the experimental values recorded in the presence of intermolecular interactions. Henceforth, the assignments made at B3LYP/6-31++G(d, p) level of theory with only reasonable deviations from the experimental values seem feasible. References [1] J.A. Tran, J. Pontillo, M. Arellano, B.A. Fleck, F.C. Tucci, D. Marinkovic, C.W. Chen, J. Saunders, A.C. Foster, C. Chena, Bioorg. Med. Chem. Lett. 15 (2005) 3434. [2] F.C. Tucci, N.S. White, S. Markison, M. Joppa, J.A. Tran, B.A. Fleck, A. Madan, B.P. Dyck, J. Parker, J. Pontillo, L.M. Arellano, D. Marinkovic, W. Jiang, C.W. Chen, K.R. Gogas, V.S. Goodfellow, J. Saunders, A.C. Foster, C. Chen, Bioorg. Med. Chem. Lett. 15 (2005) 4389. [3] J. Lu, D. Kong, Z. Yang, S. Yang, W. Fan, H. Jia, X. Wang, Appl. Radiat. Isot. 65 (2007) 1134. [4] K. Yokoyama, N. Ishikawa, S. Igarashi, N. Kawano, K. Hattori, T. Miyazaki, S. Ogino, Y. Matsumoto, M. Takeuchi, M. Ohta, Bioorg. Med. Chem. 16 (2008) 7021. [5] W. Malinka, P. S´wia˛tek, B. Filipek, J. Sapa, A. Jezierska, A. Koll, Il Farmaco 60 (2005) 961. [6] N.A. Colabufo, F. Berardi, M. Contino, S. Ferorelli, M. Niso, R. Perrone, A. Pagliarulo, P. Saponaro, V. Pagliarulo, Cancer Lett. 237 (2006) 83. [7] K. Balcı, S. Akyüz, Vib. Spectrosc. 48 (2008) 215.

[8] A.P. Scott, L. Radom, J. Phys. Chem. 100 (1996) 16502. [9] J.B. Foresman, A. Frisch, Exploring Chemistry with Electronic Structure Methods, Second ed., Gaussian Inc., Pittsburgh, 1996. [10] Ö. Alver, C. Parlak, M. Sß enyel, Spectrochim. Acta A 67 (2007) 793. [11] Ö. Alver, C. Parlak, M. S ß enyel, J. Mol. Struct. 923 (2009) 120. [12] A.D. Becke, J. Chem. Phys. 98 (1993) 5648. [13] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery, J.T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. AlLaham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03 Revision C.02 Gaussian Inc., Pittsburgh PA, 2003. [14] A. Yokazeki, K. Kuchitsu, Bull. Chem. Soc. Jpn. 44 (1971) 2352. [15] A. Karayel, S. Özbey, G. Çapan, J. Mol. Struct. 841 (2007) 118. [16] D. Hür, A. Güven, J. Mol. Struct. (Theochem). 583 (2002) 1. [17] P.J. Hendra, D.B. Powell, Spectrochim. Acta 18 (1962) 299. [18] J. Haines, D.F.R. Gilson, Can. J. Chem. 67 (1989) 941. [19] D. Vedal, O.H. Ellestad, P. Klaboe, G. Hagen, Spectrochim. Acta 32A (1976) 877.