Slide Number 1Slide Number 2Organic Structure DeterminationGeneral StrategySlide Number 5How it works?Nuclear Magnetic Resonance (NMR)Nuclear Magnetic Resonance (NMR)Example: 1,4-dimethylbenzeneTypical 1H NMRExampleSlide Number 12Slide Number 13Detecting the Signal: Fourier Transform NMR spectrometersSlide Number 15Chemical ShiftSlide Number 17Slide Number 18Slide Number 19Slide Number 20OverviewExampleSlide Number 23Integration of SignalsSlide Number 25Coupling (Signal Splitting)Slide Number 27Pascal’s TriangleHow to Interpret Proton NMR SpectraSlide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37ExamplesSlide Number 39Extension to 13C NMRSlide Number 41Slide Number 42Vinyl Bromide (CH2=CHBr)Slide Number 44Slide Number 45AnnouncementsSlide Number 47Slide Number 48Splitting Tree Diagrams & origin of Signal SplittingRecognizing Splitting PatternsSlide Number 51Slide Number 52Slide Number 53Proton NMR Spectra and Rate ProcessesExamplesSlide Number 56Slide Number 57Slide Number 58Structure EffectsSlide Number 60Slide Number 61Slide Number 62Slide Number 64Slide Number 65Slide Number 66Slide Number 68Slide Number 69Slide Number 70How it works?Introduction FragmentationSlide Number 74Fragmentation by Cleavage at a Single BondSlide Number 76Slide Number 77Slide Number 78Slide Number 79Slide Number 80Isotopes in Mass SpectraIsotopes in Mass SpectraSlide Number 83Slide Number 84Exact mass of NucleidesIsotopic Patterns for Cl and BrSlide Number 87Slide Number 88Slide Number 89Slide Number 90Slide Number 91Slide Number 92Slide Number 93Slide Number 94Slide Number 95Slide Number 96Slide Number 97Chapter 9 Nuclear Magnetic Resonance and Mass Spectroscopy: Tools for Structure Determination 1In this chapter : 1. Nuclear magnetic resonance (NMR), a form of spectroscopy that is one of the most powerful tools for the identification of functional groups and for the determination of connections between the atoms in molecules 2. Mass spectroscopy (MS), which allows the determination of exact molecular formulas of molecules both large and small Spectroscopy: the study of the interaction of energy with matter. Energy applied to matter can be absorbed, emitted, cause a chemical change, or be transmitted. Spectroscopy can be used to elucidate the structure of a molecule. 2Organic Structure Determination • Classic Methods – Boiling points – Refractive Index – Functional groups tests – Combustion Analysis – Degradation • Require large quantities of sample and are time consuming • Spectroscopic Methods – Mass Spectroscopy, MS (Molecular Mass & fragmentation patterns) – Infrared Spectroscopy, IR (Characteristic functional groups) – Ultraviolet Spectroscopy, UV (Characteristic chromophores) – Nuclear Magnetic Resonance (NMR) Combination of these spectroscopic techniques provides a rapid, accurate, and powerful tool for Identification and Structure Elucidation of organic compound 3General Strategy 6-NMR Full Structure Determination 5-Ultraviolet (UV) Useful for conjugated systems (e.g. dienes, enones, aromatics) 4- Infrared Red (FTIR) Identify Functional groups (C=O, O-H, NH2, COOH) 3- Degree of Unsaturation From Molecular Formula 2-Mass Spectroscopy (MS) Molecular Weigh, Molecular Formula & Fragmentation Pattern 1-Elemental Analysis Empirical Formula (e.g. C2H4O) 4The Electromagnetic Spectrum Electromagnetic radiation has the characteristics of both waves and particles. The wave nature of electromagnetic radiation is described by wavelength (λ) or frequency (ν). The relationship between wavelength (or frequency) and energy (E) is well defined. Wavelength and frequency are inversely proportional (ν= c/λ). The higher the frequency, the greater the energy of the wave. The shorter the wavelength, the greater the energy of the wave. NMR involves absorption of energy in the radiofrequency range. 5How it works? 6 http://www.youtube.com/watch?v=uNM801B9Y84Nuclear Magnetic Resonance (NMR) 1. Nuclei: Proton (1H), carbon-13 (13 C) and others behave as tiny magnets. When placed in a magnetic field and irradiated with radio frequency energy, these nuclei absorb energy at frequencies based on their chemical environments. NMR spectrometers are used to measure these absorptions. 7Nuclear Magnetic Resonance (NMR) 1. The number of signals in the spectrum tells us how many different sets of protons there are in the molecule 2. The position of the signals in the spectrum along the x-axis tells us about the magnetic environment of each set of protons arising largely from the electron density in their environment 3. The multiplicity (or splitting pattern) of each signal tells us about the number of protons on atoms adjacent to the one whose signal is being measured Chemical shits in ppm Signals Multiplicity (coupling constant) 8Example: 1,4-dimethylbenzene 1. Chemical Shift (δ) in ppm (parts per million) 2. Integration (areas of peaks ⇒ no. of H) 3. Multiplicity (spin-spin splitting) and coupling constant UPFIELD (shielded) DOWNFIELD (deshielded) TMS (tetramethylsilane) Unreactive, stable, volatile and high field, single signal 9Record as:1H NMR (300 MHz, CDCl3):4.35 (2H, t, J = 7.2 Hz, Hc)2.05 (2H, sextet, J = 7.2 Hz, Hb)1.02 (3H, t, J = 7.2 Hz, Ha)δchemicalshift (δ) in ppmno. of H(integration)multiplicitycouplingconstantin HzTypical 1H NMR • NMR Solvents – Should not contain hydrogen – Commonly: CDCl3 ; D-DMSO ; CD3OD ; C6D6 ; D2O 10Example • The 300-MHz 1H NMR spectrum of 1,4-dimethylbenzene 11The magnetic field associated with a spinning proton The spinning proton resembles a tiny bar magnet Nuclear Spin: The Origin of the Signal The nuclei of NMR-active nuclei behave like tiny bar magnets. In the absence of an external magnetic field these bar magnets are randomly orientated. In an external magnetic field they orient either with (α spin state) or against (β spin state) the magnetic field. 12 http://www.youtube.com/watch?v=7aRKAXD4dAg&list=PLB766F879698E2A1E http://www.youtube.com/watch?v=jUKdVBpCLHM&list=PLB766F879698E2A1E1H: I = ½ (two spin states: +½ or -½) ⇒ (similar for 13C, 19F, 31P) 12C, 16O, 32S: I = 0⇒ Do not give an NMR spectrum Nuclear Spin: The Origin of the Signal Nuclei aligned with the magnetic field are lower in energy than those aligned against the field. The nuclei aligned with the magnetic field can be flipped to align against it