SEPARAZIONE E CARATTERIZZAZIONE DI COMPOSTI ORGANICI

Module CARATTERIZZAZIONE STRUTTURALE DI COMPOSTI ORGANICI E LABORATORIO (Modulo 2)

The course aims to provide students with the basic knowledge and methodology necessary for the interpretation of infrared (IR), ultraviolet-visible (UV-Vis) and nuclear magnetic resonance (NMR) spectra. At the end of the course, the student will be able to carry out a complete structural and stereochemical characterization of organic molecules using spectra (NMR, MS, UV, IR) in an integrated way.

Regarding the so-called Dublin Descriptors, the learning outcomes of the course are:

D1 - Knowledge and understanding: The student must demonstrate mastery of the basic knowledge of modern spectroscopic investigation methods as well as the ability to understand the fundamental characteristics of the spectra supplied by each substance (NMR, IR, UV, and MS).

D2 - Ability to apply knowledge and understanding: The student must show the ability to apply the acquired knowledge and the ability to identify a molecule through the combined analysis of the spectra obtained with the various techniques. He must be able to simulate the spectra of new molecules and be able to decide which methods are most useful to solve a particular structural problem.

D3 - Independent judgment: students must be able to design and conduct experiments independently. At the end of the course, they will know how to interpret the collected data in a coherent, critical, and correct way, correlating them to the appropriate theories. At the end of the course, they will have to know how to formulate hypotheses and discard the incorrect ones.

D4 - Communication skills: The student must be able to communicate his/her knowledge and his/her interpretative ability of the various spectra to specialists and not with adequate language.

D5 - Learning skills: students will be able to solve a problem of structural identification autonomously, showing the ability to face it through applying the skills acquired during the course.

Information for students with disabilities and/or SLD
To guarantee equal opportunities and in compliance with the laws in force, interested students can ask for a personal interview to plan any compensatory and/or dispensatory measures, based on the didactic objectives and specific needs.

The course is structured to allow the acquisition of the indispensable tools for a straightforward interpretation of spectroscopic data aimed at the structural characterization of compounds of biological, pharmaceutical, and nutritional interest.

The course is organized into lectures, classroom exercises, and laboratory activities. The course is divided into 6 credits (CFU): 4 of frontal teaching, 1 of excercises, and 1 of laboratory.

During the exercises (1 CFU), guided analyses of IR, MS, UV, mono, and bidimensional NMR spectra will be performed to identify an unknown organic molecule. The interpretation of the spectral data is carried out by the teacher interactively with the students.

Instead, the laboratory part (1 CFU) aims to complete the training course provided by the whole class. During the hours of this part of the course, practical exercises will be developed aimed at acquiring the NMR, IR, UV and mass spectra and subsequent interpretation of the relative spectral data.

Should teaching be carried out in mixed mode or remotely, it may be necessary to introduce changes concerning previous statements in line with the program planned and outlined in the syllabus.

Basic knowledge of mathematics and physics. Good knowledge of the structure and reactivity of organic compounds.

Attendance in the course is compulsory, with the student having to attend at least 70% of the total course hours for both face-to-face
lectures and laboratory classes (see teaching regulations section 3.1)

Introduction

Importance of spectroscopic techniques in organic chemistry. Regions of the electromagnetic spectrum and corresponding spectroscopic techniques.

Ultraviolet and visible spectroscopy (UV-VIS)
Introduction and fundamental concepts. Analysis and interpretation of UV-VIS spectra: characteristic bands and absorption intensity. Main chromophores.
Exercises.

Infrared spectroscopy (IR)
Introduction and fundamental concepts. Analysis and interpretation of IR spectra. Characteristic absorptions of the main functional groups of organic molecules. Exercises.

Introduction to nuclear magnetic resonance spectrometry (NMR)
Magnetic properties of nuclei. Energy levels and population of nuclei immersed in a magnetic field. Downgrading processes. Pulse and Fourier transform NMR spectroscopy (PFT-NMR). NMR spectrometers.

1H NMR spectra
Chemical shift. Screen constant and its components. Inductive effects, diamagnetic anisotropy, electric field; effects of intermolecular relationships on the chemical shift. Protons on oxygen and nitrogen atoms. Signal intensity. Spin-spin coupling.
Scalar and dipolar couplings. Zero-order and 1st order systems. Chemical equivalence and magnetic equivalence. 2nd order systems. Exercises.

13C NMR spectra
Theory. Spin decoupling (double resonance). Broadband heteronuclear decoupling. Overhauser nuclear effect (NOE). Heteronuclear NOE. Controlled decoupling (Gated decoupling). Exercises.

1H NMR spectra and molecular structure
Equivalence, symmetry and chirality. Pairs of omotopic, enantiotopic and diasterotopic protons. Effects of a chiral centre. Virtual coupling. Coupling constants: structure and stereochemistry. Homonuclear couplings: geminal, vicinal and long-distance. Double homonuclear resonance 1H-1H. Overhauser effect difference spectrometry (NOE). Solvent effect and shift reagents. Exercises.

NMR in dynamic processes
Conformational equilibrium and chemical equilibrium. Fast exchange and slow exchange. NMR spectra at variable temperature. Eyring equation. NMR spectra of compounds containing "mobile" hydrogens.

Advanced experiments and 2D NMR
Advanced one-dimensional experiments: evolution time and mixing time. Evolution of magnetization in AX, AX2 and AX3 systems. J-modulation. DEPT Spectra. 1D-TOCSY Spectra. Two-dimensional NMR experiments (2D NMR). Homonuclear correlation spectra. Analysis of 1H-1H COSY and 1H-1H TOCSY spectra. 1H-1H NOESY and ROESY experiments and spectra analysis. Heteronuclear correlation spectra. Analysis of 1H-13C COZY spectra (HETCOR) and long-distance heteronuclear correlation 1H-13C (HMBC). Exercises.

NMR spectra of heteronuclei
15N NMR spectra: characteristics, chemical shift region, constants 1H-15N.
19F NMR spectra: characteristics, chemical shift region, constants 1H-19F. 31P NMR spectra: characteristics, chemical shift region, constants 1H-31P. Multinuclear couplings.

Protein-ligand interactions
Interactions with small ligands. Diffusion limited systems, KD, equations. Chemical exchange: slow and fast exchange. Time scales and chemical exchange. In vitro screening. Experiments for NMR characterization: WaterLOGSY, STD, DOSY.

Hints of solid-state NMR (HR-MAS NMR)

Classroom exercises
Guided analysis of spectra (NMR, MS, UV, IR); integrated use of the studied spectroscopic techniques and development of problems of determination of the structure of organic molecules.

Laboratory
Identification of unknown molecules by NMR, MS, UV and IR analysis
Simulation analysis of the metabolic profile of fruits and plant extracts by 1H NMR

1. R.M. Silverstein, F.X. Webster e D.J. Kiemle, Spectrometric Identification of Organic Compounds,” John Wiley & Sons
2. A. Randazzo, “Guida pratica alla interpretazione degli spettri NMR” Loghìa Publishing
3. L.D. Field, S. Sternhell, J.R. Kalman, “Organic Structures From Spectra” IV Edizione, John Wiley and Sons (Chichester New York Brisbane Toronto Singapore)
4. M. Hesse, H. Meier, B. Zeeh, Spectroscopic Methods in Organic Chemistry, Published by Thieme
5. Educational material made available on www.studium.unict.it

The examination is designed to ascertain:

1. The acquisition of the course's basic concepts and the ability to link them with each other and with the experiments carried out in the laboratory.
2. The ability to clearly expound the concepts using scientific language appropriately.
3. The ability to use and quantitatively interpret experimental data by applying the concepts and methodologies acquired during the course.

The end-of-course examination consists of a written test and an oral test. The written test, lasting 2 hours, consists of solving even a partial solution of a structural determination problem based on the interpretation of one- and two-dimensional NMR, MS, UV and IR spectra.

Oral interview: verification of learning outcomes.

The learning verification (written and oral tests) may also be conducted electronically if the conditions require it.

The student's ability to tackle (at least in part) the resolution of a problem of determining the structure of an organic molecule based on MS, IR, UV, and NMR spectra is considered essential.

Sample questions: Spectroscopic analysis of organic compounds exhibiting OH groups; 1HNMR: Screen constant and chemical shift due to diamagnetic anisotropy; Proton decoupling experiments; 13C NMR: Generalities, Experiment BB and NOE effect, Off resonance; 1HNMR: Homotopic, enantiotopic, diasterotopic protons; 2D NMR: HSQC and HMBC Spectra; Prediction of NMR spectra of structural isomers; Effect of the chemical environment on chemical shifts; Characteristics of a UV spectrum, epsilon and band shift; Effect of double bond conjugation on a UV spectrum; IR spectra analysis: characteristic regions; IR theory; etc...