Spectroscopy. Empirical Formula: Chemical Formula: Index of Hydrogen Deficiency (IHD)

Transcription

1 Spectroscopy Empirical Formula: Chemical Formula: Index of Hydrogen Deficiency (IHD) A)From a structure: B)From a molecular formula, C c H h N n O o X x, Formula for saturated hydrocarbons: Subtract the number of hydrogens the compound has: Subtract the number of halogens the compound has: The Oxygen is ignored: For Nitrogen add one H: Multiply by 0.5: What is the IHD of the following molecular formulas? C 6 H 10 C 6 H 6 C 4 H 8 O C 4 H 9 N C 2 Cl 2 55

2 Electromagnetic Radiation (EMR): Wave-like properties: Particle-like properties: Energy States: Quantization of Energy: 56

3 Infra red (IR) spectroscopy Vibrations of covalent bonds within a molecule Vibrations: IR region spectrum Two regions: cm -1 known as the functional group region, and < 1000 cm -1 known as the fingerprint region functional group region: fingerprint region: 57

4 Hookes' Law 1. stronger bond (larger k value), υ increases. increasing bond strength compare: C-C C=C C C C-C-H C=C-H C C-H 2. heavier atoms attached (larger m value), υ decreases. increasing reduced mass: C-H C-C C-Cl C-Br C-I 58

5 Bond Base Value Strength / Shape 1 C=O 1715 s, "finger" 2 O-H 3600 s, brd 3 N-H 3500 m 4 C-O 1100 s 5 C=C 1650 w alkene aroma tic m-s 6 C C 2150 w, sharp 7 C-H 3000 s 8 C N 2250 m, sharp Comments 59

6 Sample IR Spectra: toluene Acetone (2-propanone) 60

7 2-propanol: Butanoic acid 61

8 Methyl acetate or methyl ethanoate: 62

9 Nuclear Magnetic Resonance (NMR): 1 H NMR or proton NMR or PMR or just NMR 13 C NMR or CMR Only certain molecules can show absorbance in NMR What is happening: 63

10 64

11 Chemical Shift NMR spectrum: Resonance: Chemical shift: 65

12 Calculate the chemical shift of a peak that occurs Hz downfield of TMS on a spectrum recorded using a 90 MHz spectrometer? Calculate the frequency of the chemical shift of chloroform (CHCl 3, δ=7.28 ppm) relative to TMS on a spectrum recorded on a 300 MHz spectrometer? Shielding in 1 H-NMR 66

13 Factors which affect chemical shift: Electronegativity: Compound, CH 3 X X Electronegativity of X CH 3 F F CH 3 OH O CH 3 Cl Cl CH 3 Br Br CH 3 I I CH 4 H (CH 3 ) 4 Si Si Cumulative effect CH 2 Cl CHCl Distance effect CH 2 - CH 2 - CH 2 Br Chemical shift δ / ppm

14 Magnetic Anisotropy 68

15 Hydrogen Bonding D 2 O (deuterium oxide) exchange experiment. 1 H-NMR Chemical shifts 69

16 I 70

17 Coupling in 1 H-NMR Cl CH 3 with CH next door Cl H Cl H Cl H H H H Ho H H 71

18 CH with CH 3 next door 72

19 1,1-dichloroethane: δ = 5.9 ppm δ = 2.1 ppm Coupling Constant, J Pascal's Triangle 73

20 Predicting Spectra Predict the spectrum for propane including multiplicity and the relative intensities in propane (CH 3 CH 2 CH 3 ). How many different types of hydrogen? What is the chemical shift? What is the integration? What is the multiplicity? What are the intensities? 74

21 Complex Coupling Patterns 75

22 76

23 Interpreting 1 H-NMR Spectra How many types of H? how many groups of signals in the spectra What types of H? chemical shift of each group How many H of each type are there? integration (relative area) for each group. What is the connectivity? coupling patterns. Integration Coupling 77

24 Peak Chemical Shift (δ) ppm A Integration Equivalent Hydrogens Multiplicity Neighboring Hydrogens Possible Group circle the H B C D E 78