Density Functional Theory (DFT) Based GIAO Investigation of the Structural and NMR Spectroscopic Properties of (E)-4,6-Dibromo-3-methoxy-2-[((5-methylpyridin-2-yl)imino)methyl]phenol Schiff Base

Öz

In this study, the molecular geometry and nuclear magnetic resonance (NMR) spectroscopic properties of the Schiff base (E)-4,6-dibromo-3-methoxy-2-[((5-methylpyridin-2-yl)imino)methyl]phenol, prepared by ethanolic reflux condensation of 3,5-dibromo-2-hydroxy-6-methoxybenzaldehyde with 2-amino-5-methylpyridine, have been investigated within the framework of density functional theory (DFT). Geometry optimization and harmonic frequency analyses were carried out at the B3LYP/6-31G(d,p) level in the gas phase. ¹H and ¹³C isotropic magnetic shielding constants were computed at the same level using the GIAO (Gauge-Including Atomic Orbitals) approach with the polarizable continuum model (PCM) for chloroform. Theoretical chemical shifts were referenced to tetramethylsilane (TMS) calculated at the same level and solvent. Comparison with experimental CDCl₃ data yielded R²=0.995 and a mean absolute error (MAE)=0.28 ppm for ¹H, and R²=0.970, MAE=5.27 ppm for ¹³C (n=14); excluding the two bromine-substituted carbons (C4 and C6) gave R²=0.994 and MAE=3.88 ppm. The systematic deviations for C–Br atoms were rationalized within the framework of the heavy atom on light atom (HALA) effect. A strong intramolecular O–H···N hydrogen bond (N···H = 1.650 Å) was identified, in agreement with both the strongly deshielded OH proton at 15.88 ppm and the imine proton at 9.705 ppm. The HOMO–LUMO energy gap was found to be 3.84 eV; the spatial localization of the frontier molecular orbitals, global reactivity descriptors and the molecular electrostatic potential map have been used to characterize the electronic structure of the title compound.

Anahtar Kelimeler

• Schiff base
• Density functional theory
• GIAO NMR
• Hydrogen bond
• HOMO–LUMO
• MEP

Destekleyen Kurum

Sinop University

Proje Numarası

EĞTF-1901-13.02

Etik Beyan

The authors declare that ethical rules are followed in all preparation processes of this study. In the case of a contrary situation, Avrasya University Science and Engineering Journal has no responsibility, and all responsibility belongs to the study's authors. This study was carried out within the scope of the scientific research project coded EĞTF-1901-13.02 supported by Sinop University.

(E)-4,6-Dibromo-3-metoksi-2-[((5-metilpiridin-2-il)imino)metil]fenol Schiff Bazının Yapısal ve NMR Spektroskopik Özelliklerinin Yoğunluk Fonksiyoneli Teorisi (DFT) Çerçevesinde GIAO Yaklaşımıyla İncelenmesi

Öz

Bu çalışmada, (E)-4,6-dibromo-3-metoksi-2-[((5-metilpiridin-2-il)imino)metil]fenol Schiff bazının moleküler geometrisi ve nükleer manyetik rezonans (NMR) spektroskopik özellikleri yoğunluk fonksiyoneli teorisi (DFT) kapsamında ele alınmıştır. Geometri optimizasyonu ve harmonik frekans analizi B3LYP/6-31G(d,p) seviyesinde gaz fazında yürütülmüş; ¹H ve ¹³C izotropik manyetik kalkanlama sabitleri aynı seviyede GIAO (Gauge-Including Atomic Orbitals) yöntemiyle, kloroform ortamı için polarizable continuum model (PCM) kullanılarak hesaplanmıştır. Hesaplanan kimyasal kaymalar, tetrametilsilan (TMS) referans molekülünün aynı seviyede ve aynı solvent ortamında elde edilen kalkanlama değerleri kullanılarak türetilmiştir. Deneysel CDCl₃ verileriyle karşılaştırılan teorik kaymalar; ¹H için R²=0,995 ve ortalama mutlak hata (MAE)=0,28 ppm, ¹³C için (n=14) R²=0,970 ve MAE=5,27 ppm; brom-bağlı karbonlar (C4 ve C6) hariç tutulduğunda ise R²=0,994 ve MAE=3,88 ppm korelasyonu vermiştir. Bromür sübstitüentli karbonlarda gözlenen sapmalar HALA (heavy atom on light atom) etkisiyle açıklanmıştır. Optimize yapıda 1,650 Å N···H mesafesindeki molekül içi O–H···N hidrojen bağı, 15,88 ppm değerindeki deneysel OH protonuyla uyumlu bulunmuş; 9,705 ppm değerindeki güçlü perdesizleşmiş azometin protonu da bu hidrojen bağının bağımsız bir spektroskopik göstergesi olarak değerlendirilmiştir. HOMO–LUMO enerji aralığı 3,84 eV olarak hesaplanmış; sınır moleküler orbitallerin moleküldeki delokalizasyon karakteri, küresel reaktivite parametreleri ve moleküler elektrostatik potansiyel haritası birlikte tartışılmıştır.

Anahtar Kelimeler

• Schiff bazı
• Yoğunluk fonksiyoneli teorisi
• GIAO NMR
• Hidrojen bağı
• HOMO–LUMO
• MEP

Destekleyen Kurum

Sinop Üniversitesi

Proje Numarası

EĞTF-1901-13.02

Etik Beyan

Bu çalışmanın tüm hazırlanma süreçlerinde etik kurallara uyulduğunu yazarlar beyan eder. Aksi bir durumun tespiti hâlinde Avrasya Üniversitesi Fen ve Mühendislik Bilimleri Dergisi’nin hiçbir sorumluluğu olmayıp, tüm sorumluluk çalışmanın yazarlarına aittir. Bu çalışma Sinop Üniversitesi desteği ile EĞTF-1901-13.02 kodlu bilimsel araştırma projesi kapsamında yapılmıştır.

Kaynakça

1. Alaşalvar, C., Soylu, M. S., Güder, A., Albayrak, Ç., Apaydın, G., & Dilek, N. (2014a). Crystal structure, DFT and HF calculations and radical scavenging activities of (E)-4,6-dibromo-3-methoxy-2-[(3- methoxyphenylimino)methyl]phenol. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 125, 319–327. https://doi.org/10.1016/j.saa.2014.01.104
2. Alaşalvar, C., Soylu, M. S., Güder, A., Albayrak, Ç., Apaydın, G., & Dilek, N. (2014b). Molecular structure, quantum mechanical calculation and radical scavenging activities of (E)-4,6-dibromo-2-[(3,5- dimethylphenylimino)methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-[(2,6- dimethylphenylimino)methyl]-3-methoxyphenol compounds. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 130, 357–366. https://doi.org/10.1016/j.saa.2014.03.069
3. Albayrak, Ç., Kaştaş, G., Odabaşoğlu, M., & Büyükgüngör, O. (2013). Existence of a resonance hybrid structure as a result of proton tautomerism in (±)-(E)-4-bromo-2-[(2,3-dihydroxypropylimino)methyl]phenol racemate. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 120, 201–207. https://doi.org/10.1016/j.saa.2013.10.022
4. Becke, A. D. (1993). Density-functional thermochemistry. III. The role of exact exchange. The Journal of Chemical Physics, 98(7), 5648–5652. https://doi.org/10.1063/1.464913
5. Cheeseman, J. R., Trucks, G. W., Keith, T. A., & Frisch, M. J. (1996). A comparison of models for calculating nuclear magnetic resonance shielding tensors. The Journal of Chemical Physics, 104(14), 5497–5509. https://doi.org/10.1063/1.471789
6. Cohen, M. D., Schmidt, G. M. J., & Flavian, S. (1964). Topochemistry. Part VI. Experiments on photochromy and thermochromy of crystalline anils of salicylaldehydes. Journal of the Chemical Society, 2041–2051. https://doi.org/10.1039/JR9640002041
7. Cozzi, P. G. (2004). Metal-Salen Schiff base complexes in catalysis: practical aspects. Chemical Society Reviews, 33(7), 410–421. https://doi.org/10.1039/B307853C
8. Demircioğlu, Z., Albayrak, Ç., & Büyükgüngör, O. (2014). Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 128, 748–758. https://doi.org/10.1016/j.saa.2014.02.186B.

9. Da Silva, C. M., da Silva, D. L., Modolo, L. V., Alves, R. B., de Resende, M. A., Martins, C. V. B., & de Fátima, Â. (2011). Schiff bases: A short review of their antimicrobial activities. Journal of Advanced Research, 2(1), 1–8. https://doi.org/10.1016/j.jare.2010.05.004
10. Ditchfield, R. (1974). Self-consistent perturbation theory of diamagnetism: I. A gauge-invariant LCAO method for N.M.R. chemical shifts. Molecular Physics, 27(4), 789–807. https://doi.org/10.1080/00268977400100711
11. Domingo, L.R., & Perez P. (2011) The nucleophilicity N index in organic chemistry. Org. Biomol. Chem., 9, 7168-7175.
12. Frisch, M. J., Trucks, G. W., Schlegel, H. B. Et al., (2004). Gaussian 03, Revision E.01. Gaussian, Inc., Wallingford CT.
13. Hadjoudis, E., & Mavridis, I. M. (2004). Photochromism and thermochromism of Schiff bases in the solid state: structural aspects. Chemical Society Reviews, 33(9), 579–588. https://doi.org/10.1039/B303644H
14. Hehre, W. J., Ditchfield, R., & Pople, J. A. (1972). Self-consistent molecular orbital methods. XII. Further extensions of Gaussian-type basis sets for use in molecular orbital studies of organic molecules. The Journal of Chemical Physics, 56(5), 2257–2261. https://doi.org/10.1063/1.1677527
15. Kaupp, M., Malkina, O. L., Malkin, V. G., & Pyykkö, P. (1998). How do spin-orbit-induced heavy-atom effects on NMR chemical shifts function? Validation of a simple analogy to spin-spin coupling by density functional theory (DFT) calculations on some iodo compounds. Chemistry – A European Journal, 4(1), 118–126. https://doi.org/10.1002/(SICI)1521-3765(199801)4:1<118::AID-CHEM118>3.0.CO;2-6
16. Lee, C., Yang, W., & Parr, R. G. (1988). Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density. Physical Review B, 37(2), 785–789. https://doi.org/10.1103/PhysRevB.37.785
17. Lodewyk, M. W., Siebert, M. R., & Tantillo, D. J. (2012). Computational prediction of ¹H and ¹³C chemical shifts: A useful tool for natural product, mechanistic, and synthetic organic chemistry. Chemical Reviews, 112(3), 1839–1862. https://doi.org/10.1021/cr200106v
18. Murray, J. S., & Politzer, P. (2011). The electrostatic potential: an overview. WIREs Computational Molecular Science, 1(2), 153–163. https://doi.org/10.1002/wcms.19
19. Parr, R. G., & Pearson, R. G. (1983). Absolute hardness: companion parameter to absolute electronegativity. Journal of the American Chemical Society, 105(26), 7512–7516. https://doi.org/10.1021/ja00364a005
20. Parr, R. G., Szentpály, L. v., & Liu, S. (1999). Electrophilicity index. Journal of the American Chemical Society, 121(9), 1922–1924. https://doi.org/10.1021/ja983494x
21. Schiff, H. (1864). Mittheilungen aus dem Universitätslaboratorium in Pisa: Eine neue Reihe organischer Basen. Justus Liebigs Annalen der Chemie, 131(1), 118–119. https://doi.org/10.1002/jlac.18641310113
22. Tomasi, J., Mennucci, B., & Cammi, R. (2005). Quantum mechanical continuum solvation models. Chemical Reviews, 105(8), 2999–3094. https://doi.org/10.1021/cr9904009
23. Vícha, J., Novotný, J., Komorovsky, S., Straka, M., Kaupp, M., & Marek, R. (2020). Relativistic Heavy-NeighborAtom Effects on NMR Shifts: Concepts and Trends Across the Periodic Table. Chemical Reviews, 120(15), 7065–7103. https://doi.org/10.1021/acs.chemrev.9b00785
24. Wolinski, K., Hinton, J. F., & Pulay, P. (1990). Efficient implementation of the gauge-independent atomic orbital method for NMR chemical shift calculations. Journal of the American Chemical Society, 112(23), 8251– 8260. https://doi.org/10.1021/ja00179a005