PHYSICAL METHODS IN ORGANIC CHEMISTRY
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- Versione italiana
- Academic year
- 2022/2023
- Teacher
- PAOLO MARCHETTI
- Credits
- 6
- Didactic period
- Secondo Semestre
- SSD
- CHIM/06
Training objectives
- The knowledge that characterize the course relate to the use of Infrared spectroscopy , 1-H and 13 C-NMR and Mass spectrometry . The final aim consists in the acquisition of the ability to identify the structure of an unknown organic compound by use of the main spectroscopic techniques ( IR , 1-H and 13-C NMR and MS) . Moreover, the course will also enable the student to acquire the basis in order to follow with profit the course of Analisi Qualitativa del Farmaco (4th year of degree in CTF).
Prerequisites
- The student must have successfully frequented the courses of Chimica Generale and Inorganica and Chimica Organica I. The knowledge that must have been already acquired regard chemical bond, the valence of the atoms, the concept of hybridization and electronegativity . As regards organic compounds, it is essential to know the functional groups and the concepts of isomerism, conformation and stereochemistry.
Course programme
- Energy and electromagnetic spectrum. Units: wavelength and frequency. Elemental analysis and molecular formula calculation. Hydrogen deficiency index in molecules with or without nitrogen.
Nuclear Magnetic Resonance Spectroscopy. Magnetic properties of common nuclei. Spin quantum numbers and population densities of nuclear spin states. Absorption of energy. Fundamental NMR’s and Boltzamann's equations. Saturation condition and T1 time. The NMR spectrometers: magnet types and parameters optimization for a good resolution.
Proton NMR spectra (1H-NMR). Chemical shifts: shielding and local diamagnetic shielding. The concept of chemical and NMR equivalences. Numbers of hydrogen atoms in a molecule: integration of the signals. Protons on heteroatoms: the acidity concept in NMR, exchangeable protons, hydrogen bond, experiment with deuterated water. Magnetic anisotropy. Spin-spin coupling: J constant and (n+1 rule). Geminal, vicinal and long range constant values. Simple and multiple coupling. Spectra of mono- and bi-substituted aromatic rings. First and second order spectra. Coupling of H-1 with other common nuclei. Decoupling and nOe experiments. Chiral centers and NMR spectra.
C-13 NMR spectra. Coupled and decoupled 1H-13C spectra. DEPT. Heteronuclear coupling with F-19 and P-31. Examples.
Infrared Spectroscopy. Uses of infrared spectrum. Mulecular vibrations: stretching and bending modes. Hook's law. Dispersive and FT-IR instruments. GC-IR. Costs. Sampling techniques. Identification of functional groups with particular attention to the carbonyl group and to the parameters that shift absorption from standard value. Use of the digital finger zone. Examples.
Mass Spectrometry. Basic principles. Electron-impact spectrometer. Low and high resolution instruments. The mass spectrum: base peak and molecular ion. Natural abundance and isotopes. M+1 and M+2 peaks. Molecular weight determination with low and high resolution instruments. Use of the Beynon tables. Fragmentation processes in electron-impact ionization: basic rules. Alternative tecniques to electron-impact ionization: soft ionization (Chemical ionization, FAB, MALDI). GC-MS, MS-MS. Main fragmentation of functional groups. Examples.
Combined structure problems: examples. Identification of a unknown compound. Didactic methods
- Theoretical lectures (5 credits, 40 hours) combined as follow: 2.5 credits (20 hours) of NMR, 1.2 credits (9 hours) of IR, 1.3 credits (11 hours) of MS. Combined structure problems at the end of course (1 credit, 8 hours). The presence during the last 8 hours of exercises is essential for getting through the final test.
Learning assessment procedures
- The final test consists of an oral examination based on a combined structure problem. IR, 1H- and 13C-NMR and MS spectra of an unknown compound are given to the student that must:
1st, determine the molecular weight of the unknown molecule by interpretation of the mass spectrum.
2nd, write the molecular formula by counting hydrogen and carbon atoms in NMR spectra and detecting the functional groups in IR spectra. This step constitutes the minimum goal to be able to access the second part of the exam with the following operations.
3rd, calculate hydrogen deficiency.
4rd, taken into consideration NMR and IR spectra, elencate radicals and functional groups of the unknown compound.
5th, using signals multeplicity in 1H-NMR and valuating DEPT or coupled C-13 spectra, propose one or more probable structures.
6th, confirm the exact structure with MS spectra. Reference texts
- - A copy of the slides used by the teacher during the lessons. The latter are sufficient to pass the final test with full marks.
Any supporting books:
1. D. L. Pavia, G. M. Lampman, G. S. Kriz, Jr - Introduction to spectroscopy Saunders College Eds. (2nd Ed.)
2. R. M. Silverstein, F. X. Webster - Identificazione spettroscopica di composti organici. Casa Ambrosiana Editrice. 2a Ed. italiana su settima americana.
3. L. D. Field, S. Sternhell, J. R. Kalman. - Organic structure from spectra. John Wiley and Sons Ed.
