Chapter 13. R.F.----µ-wave----I.R. (Heat)------Visible------U.V X-Ray------γ-Ray SPECTROSCOPY. Definition: Types to Be Covered:

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1 hamras Glendale ommunity ollege rganic hemistry 105 Exam 4 Materials hapter 13 SPETRSPY Definition: Types to Be overed: A) Infrared Spectroscopy (IR) B) Nuclear Magnetic Resonance Spectroscopy (NMR) ) Ultra-Violet Spectroscopy (UV) Electromagnetic Radiation Spectrum: R.F.----µ-wave----I.R. (eat)------visible------u.v x-ray------γ-ray 3 x 10 2 cm cm 1

2 Energy for Electromagnetic Radiation: E = h.ν E = ν.λ Proportionalities of: a) Energy & Frequency: b) Wavelength & Frequency: c) Energy & Wavelength: Inrfared Spectroscopy * First hand information is about the bond types present in the sample compound. * The information then could be used to conclude about the functional group(s) present in the sample compound. * Based on the vibrations of bonds as a result of absorbing the IR radiation. * Modes of Vibration: 1. Stretching: symmetric and asymmetric R R R R c c 2

3 2. Bending: Scissoring, rocking, wagging, and twisting R R R R R R R R c c c c * ow many vibrational modes does a molecule (with n atoms) have? EXAMPLE: * ow does IR spectroscopy work? 3

4 IR Beam Generator Sample IR beam ollector * The Axes on an IR spectrum: % Transmittance vs. wavenumber % Transmittance: Wavenumber: 4

5 * Typical Window of IR Wavenumbers: * hange of Energy across the spectral Wavenumber: * Two Main Regions on IR Spectrum: Fingerprint & Functional Group regions. The spectrum of wavenumbers (IR radiation range) sweeps the sample. Variations in Bond Strength & Modes of Vibration: 5

6 Important Stretching Frequencies Bond Type Wavenumber (cm 1 ) Intensity = N Medium = Medium to weak = Medium Aromatic = Strong = Strong Strong N Medium (alcohol) Strong (acid) Strong N Medium Aromatic Medium Aliphatic Medium SAMPLE INFRARED SPETRA: Ethylbenzene 6

7 yclohexene 1-exanol Pentanoic acid 7

8 1. Energy needed for stretching vs. bending Additional Points on IR Spectroscopy 2. Stretching wavenumber for different carbonyl double bonds: = stretch (cm 1): = stretch (cm 1): = stretch (cm 1): 1822* 1783 = stretch (cm 1):

9 9 1 NMR Spectroscopy Basic Physics Principles: For a molecule: To simplify: There is a net magnetic moment. Now let s consider this on a statistical scale: N S N S

10 A view at the magnetic moments reveals a random distribution of them: RANDM DISTRSIBUTIN The NMR Experiment 1. The NMR instrument is essentially composed of a large and strong magnet. Sample is placed in the instrument. 1. RANDM DISTRIBUTIN F MAGNETI MMENTS Bo NMR Instrument 2. ALIGNMENT WIT (AND AGAINST) TE MAGNETI FIELD. 10

11 2. Against E With B o 3. RESNANE Against E De-Excitation With Excitation R.F. 4. For every type of resonance a peak will appear on the NMR spectrum. Also, every electronically different type of proton (hydrogen) in the given sample, produces a peak at a different frequency. Electronically Different Types of Protons Label the electronically different types of protons in the structures below: l l l 2 N 11

12 Information Sources on the 1 -NMR Spectrum Information Source elps Learn About 1. ID (Index of ydrogen Deficiency) The degree of unsaturation in the sample molecule. 2. hemical Shift Type of proton. 3. Integration Relative number of protons giving rise to the peak. 4. Multiplicity The number of protons on the immediately neighboring atoms. 1. ID: If the molecular formula is given, the ID could be calculated via the following equation: ID = X + N 2 EXAMPLE: ID: l Rings: ID: p-bonds: ID: 12

13 2. hemical Shift: Where the peak appears on the X-axis of the NMR window (in units of ppm), could indicate what type of proton gives rise to the peak. A table of the most common 1 -NMR chemical shifts is shown below: The Effect of Neighboring atoms on hemical Shift: 13

14 EXAMPLE: 1.8 ppm 5.3 ppm I 1.7 ppm I I 1.6 ppm l 1.4 ppm 1.4 ppm 3.2 ppm 3.4 ppm 3. Integration: Relative number of protons giving rise to a peak. Definition of Integral: Three forms integration appears on NMR spectra: 1. As calculated areas under peaks: 3 PPM As lines over the peaks: 3 2 PPM

15 3. As relative -count over the peaks PPM 1 0 **A Few Examples of 1 -NMR Spectra: PPM l l 3.86 l 3 2 PPM

16 **ydrogens Bonded to eteroatoms: PPM

17 4. Multiplicity: Spin-Spin Splitting 50:50 B o No neighboring A SINGLET Splitting by each neighboring Resulting in a DUBLET A B Split 1 Split 2 By A DUBLET By B DUBLET of DUBLET WY A TRIPLET??? TRIPLET 17

18 Is there a case where a doublet of doublets is resulted? EXAMPLES: Br Br Br 18

19 Examples of 1 -NMR Spectra with Multiplicity: 4 3 PPM Solving the Spectrum: Given the spectrum and the structure, the peaks should be: a) assigned to different types of protons in the molecule b) the multiplicities of the peaks should be consistent with the corresponding assigned protons c) the relative number of protons elucidated from the NMR spectrum should be consistent with the ratios present in the molecule. Labeled Structure -Type Approx. hem. Shift (ppm) Multiplicity Integration 19

20 4 3 PPM Type Approx. hem. Shift (ppm) Multiplicity Integration 20

21 Molec. Formula: 5 9 l 2 ID: PPM Type Approx. hem. Shift (ppm) Multiplicity Integration 21

22 The Difference Between PREDITING and INTERPRETING 1 -NMR Spectra: Predict the 1 -NMR spectrum for benzoic acid: -Type Approx. hem. Shift (ppm) Multiplicity Integration Predicted Spectrum: (ppm)

23 Actual Spectrum: 10 More points for 1 -NMR: 8 6 PPM The protons bonded to heteroatoms (mostly and N) arte ALWAYS singlets in 1 -NMR spectra. (They NEVER couple). Also, they usually appear as bumps rather than typical peaks. 2. Solvent Peak: The most commonly used solvent for 1 -NMR spectroscopy is deuterated chloroform (Dl 3 ). It appears at 7.27 ppm, and always is a singlet. Usually its size is much smaller than the peaks of the sample. 3. Reference peak: The reference compound TMS (tetramethylsilane) ( 3 ) 4 Si apprears at 0.00 ppm (is set at that value) and always is a singlet. NMR Peak Resolution The larger the electronic difference between two protons, the larger the magnitude of the J value for their splitting. The smaller the electronic difference between two protons, the smaller the magnitude of the J value for their splitting. Br Trans-Vicinal (J = 17 z) Geminal (J = 2 z) is-vicinal (J = 11 z) 23

24 13 -NMR Spectroscopy -13 Vs. -12: omparison-ontrast with 1 -NMR: 1. Isotopic abundance: 2. Peak size: 3. Integration (area vs. height): 4. oupling: 5. Multiplicity: 6. Spectral window and chemical shift: 7. Dl 3 peak: 24

25 8. TMS peak: Sample 13 -NMR Spectra: Ethyl acetate 3-pentanone 25

26 1-phenyl-2-propyn-1-ol 26

27 UV-Vis (Ultraviolet-Visible) Spectroscopy Excites the p-bonds (weaker than s, therefore excitable with UV-Vis light. onjugation and the wavelength for the UV-Vis energy for excitation: Alkene UV-Vis Wavelength Ethylene ,3-butadiene ,4,6-octatriene lycopene