Aydin Demircan

Subtractive-FTIR spectroscopy to characterize organic matter in lignite samples from different depths.

Organic matter present in lignite samples collected from different depths (i.e. top, mid and bottom) of lignite source, Ilgın, Konya province, was examined by using subtractive-FTIR-ATR spectroscopy. FTIR spectra were recorded on (i) original samples, (ii) the samples dried at 105 °C and (iii) the samples acid-treated and dried. After a combustion process performed for each sample at 650 °C for 15 min, the spectra of samples were recorded and subtracted from the spectra of untreated samples. Hence, a software-based subtraction made it possible to acquire a representative spectra related with organic matter. As the contribution of the bands related with inorganic constituents in lignite samples were eliminated after spectrum-subtraction procedure, difference-spectra led analyzing the spectra related with organic matter in lignite samples, reasonably. Furthermore, the bands related with acidic functional groups, aromatic and aliphatic structures were analyzed on the basis of difference-spectra, easily. From the difference-spectra it was shown that an acid-treatment process under mild conditions caused shift in some specific bands related with carbonyl groups of carboxyls so that the band at around 1710 cm(-1) arisen, while the intensity of the band at around 1420 cm(-1) was diminished. Through the acid-treatment process, acidic groups in lignite samples from different depths were thought to be turned into similar forms by protonation and/or stripping of metal ions originally bonded. Difference-spectra acquired for acid-treated samples made it possible to evaluate the form of carboxylic acid groups present in the studied samples under specific environmental conditions. Hence, a facile and environmentally-friendly methodology was used to analyze organic matter in lignite by using FTIR spectra, and valuable information was acquired about the aliphatic, aromatic and acidic character of the studied lignite samples collected from different depths. The proposed methodology seems to be promising in acquiring approximate representative spectra for lignite organic matter by using little or no chemicals.

Structure and Vibrational Spectra of Tert -butyl N -(2-bromocyclohex-2-enyl)- N -(2-furylmethyl)carbamate

The molecular structure, conformational stability and vibrational frequencies of tert-butyl N-(2-bromocyclohex-2- enyl)-N-(2-furylmethyl)carbamate were investigated by utilizing the Hartree-Fock (HF) and density functional theory (DFT) ab initio calculations with 6-31G* and 6-31G** basis sets. The optimized bond length and angle values obtained by HF method showed the best agreement with the experimental values. Comparison of the observed and calculated fundamental vibrational frequencies indicated that B3LYP was superior to the scaled HF approach for molecular problems. Optimal uniform scaling factors calculated for the title compound are 0.899/0.904, 0.958/0.961 and 0.988/0.989 for HF, B3LYP, and BLYP (6-31G*/6-31G**), respectively.

A FACILE SYNTHESIS OF HETEROTRICYCLES FROM FURFURYLBROMOALKENES USING THERMAL IMDA CYCLO ADDITION

A variety of key precursors to the IMDA reaction of furan diene have been prepared via facile alkylation. Subsequently, rigid tricyclic compounds (2a-g) possessing oxygen, nitrogen, and sulfur has been synthesized by employing thermal intramolecular Diels-Alder reactions. These heterocyclic fused tricycles include a bromo quaternary carbon centre obtained stereoselectively with moderate yields (32-44 % overall).

Thermal intramolecular Diels-Alder reaction of furan; synthesis of nitrogen tetracycles, isobenzofuran and isobenzothiophene

Thermal intramolecular Diels–Alder (IMDA) reaction of furan cored compounds has been further investigated; a series of key precursors to the IMDA reaction of furan diene (9a–c) have been prepared via facile alkylation and protection. While the cycloaddition process for (10a–c) was afforded in hot toluene, a commercial microwave (2450 MHz) was used for the synthesis of (12a–b). Treatment of fused oxy- and thio-heterotricycles (12a–b) with borontrifluoride-etherate in dichloromethane at −78°C cleaved epoxy bridge and concomitant aromatisation gave the isobenzo-furan and thiophene (13a–b) in 72–76% yields respectively.

Preparation of tricyclic nitrogen heterocycle via Intramolecular Diels-Alder reaction

Preparation of rigid tricyclic nitrogen heterocycles under radicalic condition has been studied. Cyclisation is performed by Diels-Alder ring closure after radicalic hydrogenation. We did not observe any radicalic Cycloaddition / Fragmentation product 12. Tri-n-butyltin hydride (TBTH) and azobisisobutyronitrile were used in toluene or benzene to generate radicalic condition. Intramolecular Diels-Alder (IMDA) reaction on substituted furan species gave tricyclic heterocycle.

Structure and vibrational frequencies of 6-chloro-8-thia-1,4-epoxybicyclo[4.3.0]non-2-ene: density functional theory study

The Fourier transform infrared (FT-IR) spectrum of 6-chloro-8-thia-1,4-epoxybicyclo[4.3.0]non-2-ene has been recorded in the region 4000–525 cm− 1. The optimised geometry, frequency and intensity of the vibrational bands of the title compound have been calculated using the ab initio Hartree–Fock and the density functional theory method with 6-31G(d,p) and 6-311G(d,p) basis set levels. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The observed and the calculated frequencies are found to be in good agreement. The theoretical vibrational spectrum of the title compound were interpreted by means of potential energy distributions using VEDA 4 program.

tert-Butyl 3a-chloro-2-methyl­perhydro-2,6a-epoxy­oxireno[e]isoindole-5-carboxyl­ate

The intramolecular Diels–Alder (IMDA) reaction of furans is a widely utilized synthetic strategy among synthetic organic chemists (Lipshutz, 1986). This versatile tool is used in ring formation for the synthesis of natural products such as carbohydrates and other biologically active compounds (Bear et al., 2001), or as a chiral auxiliary (Andres et al., 1997). However, the facile retro-Diels–Alder reaction and the low reactivity of furan as a diene, as a result of its aromatic character, make the Diels–Alder reaction of furan one of the most difficult cycloadditions (Kappe et al., 1997). In a continuation of our systematic studies on IMDA cycloadditon of furans (Demircan & Parsons, 2002; Demircan et al., 2006; Koşar et al., 2006), we have recently synthesized the tetracyclic compound (II), by the epoxidation of the thermal IMDA cycloadduct (I). Epoxidation of (I) was performed under standard condition in dichloromethane at 273 K. The solid product was purified by flash column chromatography using hexane–ethyl acetate as an eluant solvent system.

(3aR*,6S*,7aR*)-7a-Chloro-6-methyl-2-(4-methyl­phenyl­sulfon­yl)-2,3,3a,6,7,7a-hexa­hydro-3a,6-ep­oxy-1H-isoindole

In the title compound, C16H18ClNO3S, the six-membered ring has a boat conformation. The two five-membered rings with the bridging O atom adopt envelope conformations, whereas the N-containing five-membered ring adopts a twisted conformation. In the crystal, C—H⋯O hydrogen bonds link the molecules into a three-dimensional network.

(3aR,6S,7aR)-7a-Bromo-2-methyl­sulfonyl-1,2,3,6,7,7a-hexa­hydro-3a,6-ep­oxy­isoindole

In the title compound, C9H12BrNO3S, the two tetrahydrofuran rings adopt envelope conformations, the pyrrolidine ring adopts a half-chair conformation and the six-membered ring is in a boat conformation. In the crystal, weak intermolecular C—H⋯O hydrogen bonds link the molecules into R 2 2(8) and R 2 2(14) rings along the b-axis direction.

(3aR,6S,7aR)-7a-Bromo-2-[(4-methyl-phen-yl)sulfon-yl]-1,2,3,6,7,7a-hexa-hydro-3a,6-ep-oxy-isoindole.

In the title compound, C15H16BrNO3S, the boat form of the six-membered ring is almost symmetrical with respect to the epoxy bridge. The two five-membered rings generated by the epoxy bridge of the six-membered ring adopt envelope conformations, whereas the N-containing five-membered ring adopts a twisted conformation. In the crystal, molecules are linked by C—H⋯O hydrogen bonds.