PHYSICAL METHODS IN ORGANIC CHEMISTRY

The purpose of the course is to give the students theoretical and practical grounds to record and interpret IR, NMR and MS spectra of organic compounds.

Infrared Spectroscopy (IR). Basic theoretical concepts. Energy levels and vibrational frequency in diatomic and polyatomic molecules. Stretching and bending vibrations. Classifications of absorptions bands. Model for the bond vibrational excitation. Instrumentation for dispersive infrared spectroscopy. Instrumentation for Fourier transform infrared (FT-IR) spectroscopy. Sample preparation and IR spectra acquisition. IR spectra interpretation of alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, phenols, ethers, aldehydes, ketons, carboxylic acids and their salts, anhydrides, esters, amides, amines, nitriles, isocyanates, imines, nitro compounds, sulfur compounds, alkyl and aryl halides.

Nuclear Magnetic Resonance (NMR). Magnetic properties of atomic nuclei. Nuclear spin transitions and their energy. Nuclear precession and nuclear magnetic resonance. Population densities of nuclear spin states. CW NMR spectrometer. Stationary frame of reference and rotating frame of reference. Relaxation times. Pulsed Fourier transform (FT) spectrometer. Chemical shift. Diamagnetic shielding and shielding constant. Factors influencing chemical shift (variation). Diamagnetic anisotropy. Spin-spin splitting rule. Origin of spin-spin splitting. Geminal and vicinal coupling. “Long range” coupling: meta and para coupling in

aromatic compounds, allylic and homoallylic coupling, virtual coupling, W coupling in saturated compounds. Factors influencing the coupling constant. Chemical shift and coupling of protons bonded to oxygen, nitrogen and sulfur. Chemical and magnetic equivalence. Homotopic, enantiotopic and diastereotopic protons. First and second order spectra. AX, AB, AMX, AA’XX’ and AA’BB’ spin systems. Homonuclear decoupling. Empirical correlations to calculate chemical shifts: Shoolery rule for alkanes and Pascual-Meier-Simon rule for alkenes. ¹³C magnetic resonance. Totally coupled, totally decoupled and “off resonance” spectra. Nuclear Overhauser effect. Incremental shift parameters for linear and branched aliphatic hydrocarbons, for alkenes and aromatic compounds. APT, DEPT, NOE difference spectra. 2D NMR spectroscopy: COSY, HETCOR.

Mass Spectrometry (MS). Fundamental theoretical concepts. Single-focusing mass spectrometer. Electron Impact ion source. Methods for introduction of solid, liquid and gaseous samples. Magnetic mass analyzer and its fundamental equation. Resolving power. Double-focusing mass spectrometer. Quadrupole, ion trap and time of flight mass analyzers. Ion detectors and data recording. Molecular peak, isotopic peaks, base peak, metastable peaks. Nitrogen rule. Determination of molecular ion elemental composition. Main fragmentation mechanisms: homolitic and heterolitic scission, scissions with rearrangment. Factors determining general patterns of fragmentation. Typical fragmentation of alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, aromatic hydrocarbons, alcohols, phenols, ethers, thiols, thiophenols, thioethers, aldehydes, ketons, esters, acids, anhydrides, amides, amines, nitriles, isocyanates, nitro compounds, halogenated compounds. Chemical Ionization. Fast Atom Bombardment. Gaschromatography and HPLC coupled to mass spectrometry. Electrospray. MALDI-TOF.

R. M. Silverstein, F. x. Webster, D. J. Kiemle- Identificazione Spettrometrica di Composti Organici-II Edizione -Casa Editrice Ambrosiana.

G. M. LAMPMAN, D. L. PAVIA, , G. S. KRIZ, and J. R. VYVYAN - Introduction to Spectroscopy: a Guide for Students of Organic Chemistry - BROOKS/COLE – CENGAGE Learning. (amazon.uk).

B. GIOIA, R. STRADI, E. ROSSI - Guida al Corso di Metodi Fisici in Chimica Organica - Vol. I: Infrarosso - Vol. II: Massa - Vol. III: NMR – Edizioni CUSL- (Cooperativa Universitaria Studio e Lavoro - P.zza L. da Vinci 32 Milano).

M. Hesse, H. Meier, B. Zeeh - Metodi Spettroscopici nella Chimica Organica – Edizione II- EdiSES- Via Nuova San Rocco 62/A Napoli.

G. F. PEDULLI - Metodi Fisici in Chimica Organica - Piccin - Padova.