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
Electromagnetic Radiation (EMR): Wave-like properties: Particle-like properties: Energy States: Quantization of Energy: 56
Infra red (IR) spectroscopy Vibrations of covalent bonds within a molecule Vibrations: IR region spectrum Two regions: 4000-1000 cm -1 known as the functional group region, and < 1000 cm -1 known as the fingerprint region functional group region: fingerprint region: 57
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
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
Sample IR Spectra: toluene Acetone (2-propanone) 60
2-propanol: Butanoic acid 61
Methyl acetate or methyl ethanoate: 62
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
64
Chemical Shift NMR spectrum: Resonance: Chemical shift: 65
Calculate the chemical shift of a peak that occurs 655.2 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
Factors which affect chemical shift: Electronegativity: Compound, CH 3 X X Electronegativity of X CH 3 F F 4.0 4.26 CH 3 OH O 3.5 3.4 CH 3 Cl Cl 3.1 3.05 CH 3 Br Br 2.8 2.68 CH 3 I I 2.5 2.16 CH 4 H 2.1 0.23 (CH 3 ) 4 Si Si 1.8 0 Cumulative effect CH 2 Cl 2 5.30 CHCl 3 7.27 Distance effect CH 2 - CH 2 - CH 2 Br Chemical shift δ / ppm 1.25 1.69 3.30 67
Magnetic Anisotropy 68
Hydrogen Bonding D 2 O (deuterium oxide) exchange experiment. 1 H-NMR Chemical shifts 69
I 70
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
CH with CH 3 next door 72
1,1-dichloroethane: δ = 5.9 ppm δ = 2.1 ppm Coupling Constant, J Pascal's Triangle 73
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
Complex Coupling Patterns 75
76
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
Peak Chemical Shift (δ) ppm A Integration Equivalent Hydrogens Multiplicity Neighboring Hydrogens Possible Group circle the H B C D E 78