DFT, RAMAN AND FT-IR INVESTIGATIONS OF 1-CYCLOPENTYLPIPERAZINE Ö. BAĞLAYAN1, M.F. KAYA2, C. PARLAK2, Ö. ALVER1, M. ŞENYEL1 1 Physics Department, Science Faculty, Anadolu University, Eskişehir, 26470, Turkey 2 Department of Physics, Dumlupnar University, Kütahya, 43100, Turkey

ABSTRACT FT-IR and Raman spectra of 1-cyclopentylpiperazine (1cppp) have been experimentally reported in the region of 4000-50 cm−1. The optimized geometric parameters (bond lengths, bond and dihedral angles), conformational analysis, normal mode frequencies and corresponding vibrational assignments of 1cppp (C9H18N2) are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6−31+ +G(d,p) basis set. Furthermore, reliable vibrational assignments have been made on the basis of potential energy distribution (PED) and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 1cppp have been predicted.

ABSTRACT Calculations are employed for four different conformations of 1cppp both in gas phase and in solution. Solvent effects are investigated using chloroform and dimethylsulfoxide. All results indicates that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters, mole fractions of stable conformers, vibrational frequencies and assignments, IR and Raman intensities of 1cppp are solvent dependent.

INDEX 1-CYCLOPENTYLPIPERAZINE Experimental Study Infrared Spectrum Raman Spectrum Theoretical Study Vibrational Assignments Thermodynamics functions Homo-Lumo Orbitals Results

1-cyclopentylpiperazine(1cppp) Molecular Formula:C9H18N2 Molecular Weight:154.255 g/mol Boil Point : 105°C (11mm Hg) Density : 0.97 Mg/m3 Main hazards:Irritating to eyes, respiratory system and skin. Structure : Solid This molecule has 3N-6 vibrational modes. So, there are 3x29-6=81 vibrational modes.

1-cyclopentylpiperazine(1cppp)

It has been known that many piperazine derivatives are of great interest in pharmacy and notable successful drugs. 1cppp has been used in the construction of some drugs obtained for the treatment of viral disease, medical treatment and cancer. It has been also used for synthesis of anti-obesity agent, and antimicrobial agent.

Additionally, this molecule has been used for : imidazole-free histamine H3 receptor anti obesity agent treatment of viral disease pharmaceutical compositions useful for medical treatment antimicrobial agent tachykinin agent therapeutic compounds and their use in cancer

Experimental Study A commercial sample of 1cppp was purchased (Santa Cruz Biotechnology, ≥ % 98) and used without further purification. FT-MIR and FT-FIR spectra of 1cppp were recorded in the region of 4000-400 cm-1 and 400-10 cm-1 with Bruker Optics IFS66v/s FTIR spectrometer with the resolution of 2 cm-1. Raman spectrum was obtained using a Bruker Senterra Dispersive Raman microscope spectrometer with 532 nm excitation from a 3B diode laser having 3 cm-1 resolution in the spectral region of 4000-50 cm-1.

Experimental Study-Infrared Spectrum (MIR)

Experimental Study-Infrared Spectrum (FIR)

Experimental Study-Raman Spectrum

THEORETICAL STUDY All the calculations were performed by using Gaussian 09.A1 program on a personal computer and GaussView 5.0.8 was used for visualization of the structure and simulated vibrational spectra. PED calculations were carried out by the VEDA 4 (Vibrational Energy Distribution Analysis) program. Many possible conformers could be proposed for 1-cppp, but here the discussion was confined to e-e (equatorial-equatorial), e-a (equatorial-axial), a-a(axial-axial) and a-e (axial-equatorial) conformers of the title molecule where the former represents NH while the latter stands for cyclopentyl group.

Conformations of 1cppp (a-a & e-e)

Conformations of 1cppp (e-a & a-e)

THEORETICAL STUDY They are considered in axial and equatorial positions according to plane formed by C1, C2, C3 and C6 atoms of 1cppp. For the calculations, all four forms of 1cppp were first optimized in the gas phase, chloroform (chlf) and dimethylsulfoxide (dmso) at B3LYP level of theory using 6-31++G(d,p) basis set. The e-e and e-a conformations were found more stable than the other two forms. Therefore, for the vibrational calculations, the vibrational frequencies of e-a form of 1cppp were calculated by using the same method and basis set under the keyword freq = Raman, pop = full and then scaled by 0.955 (above 1800 cm-1) and 0.977 (under 1800 cm-1) for 6-31++G(d,p).

Optimized parameters and Mole fractions of three forms of 1cppp B3LYP / 6-31++G(d,p) e-e e-a a-a a-e Gas   ΔG (Hartree) -463.090892 -463.091297 -463.082971 -463.084252 Relative Stability (δΔG;kcal/mol) 0.25 5.22 4.42 Mole Fractions (%) 40 60 Molar Volume (cm3/mol) 149.137 119.361 124.608 116.328 Recommend a0 (Å) 4.79 4.48 4.54 4.45 Chloroform -463.094949 -463.094305 -463.087209 -463.087982 0.40 4.86 4.37 66 34 Dimethylsulfoxide -463.097010 -463.096238 -463.089288 -463.089975 0.48 4.85 4.14 69 31

Optimized geometric parameters for e-e form of 1-cppp in various medium.

Theoretical Spectrum (Gas IR-Raman)

Theoretical Spectrum (Chloroform IR-Raman)

Theoretical Spectrum (Dmso IR-Raman)

Thermodynamic parameters for e-e and e-a form of 1-cppp

Homo & Lumo Orbitals (Gas)

Homo & Lumo Orbitals (Chloroform)

Homo & Lumo Orbitals (Dmso)

Conclusion The experimental and theoretical vibrational investigations of 1cbpp are successfully performed by using FT-IR, Raman and quantum chemical calculations. Following results can be summarized: Results of energy calculations indicate that e-a form is the most stable conformer of 1cppp in gas phase whereas e-e form is the most stable conformer in dmso & chlrfm and the conformational energy barrier is dependent of the solvent. In generally, there are no significant changes in the geometric parameters when 1cppp in solvated. From lower to higher dielectric, the dipole moment increases and there are very significant shifts in vibrational frequencies due to dielectric medium. The frequency differences increase when going from non-polar to polar solvents.Solvent effects on vibrational intensities are considerable and they increase as one goes from lower to higher dielectric constant.

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