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.

Knowledge and understanding: the course provides the tools necessary for the interpretation of spectra and the recognition of unknown organic structures.

Ability to apply knowledge and understanding: during the lessons and exercises the student acquires the skills necessary for the recognition of organic functions, the quantifications of the atoms present and the connectivity between them.

Learning skills: the student becomes able to apply spectroscopy to the recognition of organic compounds.

Making judgments: the student develops critical skills in spectroscopic analysis, throught the interpretation of IR, NMR and mass spectra.

Deepening of an exemplary case: the student understands and explains spectra of unknown structures and discusses the position of the signals.

Ability to solve a problem: the spectra of unknown structures, recorded with different techniques, are interpreted by the student who then deals with the various problems related to the evaluation of an unknown structure and the presence or absence of the different functional groups.

Lectures (6 CFU) and classroom exercises (2 CFU). The teacher will use Power Point projections.

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.

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

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