1 YSU YSU YSU YSU 2 E = h i.e. Energy of the radiation is - PDF document

YSU 400 MHz Nuclear Magnetic Resonance Spectrometer(s) YSU YSU NMR spectroscopy: Based on the response of magnetic nuclei to an external magnetic field and an energy source (Radio frequency) IR spectroscopy: Response of bonds within organic molecules to externally applied Infra Red light UV/Vis spectroscopy: Response of electrons within bonds to externally applied UV or Visible light Mass spectrometry: Response of molecules to being bombarded with high energy particles such as electrons YSU YSU 1

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E = h  i.e. Energy of the radiation is directly proportional to its frequency (n = Planck’s constant)  = c/  i.e. Frequency of the radiation is inversely proportional to its wavelength (c = speed of light) E = hc/  i.e. Energy of the radiation is inversely proportional to its wavelength Take home : Longer wavelength, lower energy Higher frequency, higher energy YSU YSU YSU YSU Nuclear spins of protons ( 1 H nucleus) ‐ Figure 13.3 3

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YSU YSU Position of signal is the chemical shift downfield upfield downfield upfield YSU YSU 5

Chemical shift (  ) = position of signal – position of TMS peak x 10 6 spectrometer frequency Enables us to use same scale for different size spectrometers (60 MHz, 400 MHz, 850 MHz, etc.) throughout the world TMS = (CH 3 ) 4 Si, signal appears at 0 Hz on spectrum, therefore used as reference Chemical shifts are reported as ppm (parts per million) relative to TMS and usually occur in the 0 ‐ 12 ppm range for 1 H spectra YSU YSU CH 3 F CH 3 OCH 3 (CH 3 ) 3 N CH 3 CH 3 4.3 3.2 2.2 0.9 i.e. electronegativity of other atoms plays a role in shift CH 3 CH 3 CH CH ~0.9 ppm 2 1 0 YSU YSU PPM 6

~2.2 ppm 2 1 0 YSU YSU PPM H 3 C O CH 3 ~3.2 ppm 3 2 1 0 PPM YSU YSU 7

CH 3 F ~4.3 ppm YSU YSU H H H H H CH 3 CH 3 H H H H H Fig 13.8 7.3 7 3 5 3 5.3 0.9 0 9 Pi electrons reinforce external field and signals show downfield YSU YSU 8

~0.9 ppm “R 3 C ‐ H – alkyl” 2 1 0 PPM ~5.3 ppm “C=C ‐ H alkene” pp 5 4 3 2 1 0 PPM ~7.3 ppm “Ar ‐ H benzene” YSU YSU 7 6 5 4 3 2 1 0 PPM CH 3 H 3 C CH 3 H 3 C CH 3 N CH 3 O 7 6 5 4 3 2 1 0 PPM Spectra typically have multiple signals the number depending on the number of unique types of protons YSU YSU 9

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YSU YSU 2 1 0 PPM Simple alkane protons – R 2 CH 2 From spectroscopy sheet – chemical shift ~ 0.9 ‐ 1.8 ppm YSU YSU 11

H 3 C O CH 3 3 2 1 0 PPM Ether protons ‐ O ‐ C ‐ H From spectroscopy sheet – chemical shift ~ 3.3 ‐ 3.7 ppm YSU YSU CH 3 OCH 2 OCH 3 5 4 3 2 1 0 PPM Two types of ether protons ‐ O ‐ C ‐ H From spectroscopy sheet – chemical shift ~ 3.3 ‐ 3.7 ppm CH 2 further downfield (two neighbouring O atoms) YSU YSU 12

O H 10 8 6 4 2 0 PPM Aldehyde proton ‐ CHO From spectroscopy sheet – chemical shift ~ 9 ‐ 10 ppm 3 types of Ar ‐ H proton – chemical shift ~ 6.5 ‐ 8.5 ppm YSU YSU 10 8 6 4 2 0 PPM Carboxylic acid proton ‐ CO 2 H From spectroscopy sheet – chemical shift ~ 10 ‐ 13 ppm 3 types of Ar ‐ H proton – chemical shift ~ 6.5 ‐ 8.5 ppm YSU YSU 13

5 1 10 8 6 4 2 0 PPM Lines on spectra are curves Areas underneath each curve give a reliable ratio of the different numbers of each type of proton YSU YSU CH 3 CH 2 OCH 3 3 3 2 3 2 1 0 PPM Areas are given as a ratio , not an absolute number YSU YSU 14

3 OCH 2 CH 3 3 2 2 2 2 O CH 3 7 6 5 4 3 2 1 0 PPM YSU YSU H H H C C Cl H Cl H Cl YSU YSU 15

H H H C C H H H Br Br YSU YSU H H H H C C C H H Br H H Br H YSU YSU 16

General rule for splitting patterns For simple cases, multiplicity for H = n + 1 Where n = number of neighbouring protons 1 1 neighbour, signal appears as a doublet i hb i l d bl t 2 neighbours, signal appears as a triplet 3 neighbours, signal appears as a quartet 4 neigbours, signal appears as a quintet, etc. Complex splitting patterns are referred to as multiplets YSU YSU H H Cl C C Br Cl Br H o For red H : neighbouring H (blue) has two possible alignments, either with, or against, the external field (Ho). This effects the local magnetic environment around the red H and thus there are two slightly different frequencies (and thus chemical shifts) at which the red H resonates. The same applies to the blue H. YSU YSU 17

Red H will be a triplet Blue H’s will be a doublet YSU YSU Red H will be split into a quartet, blue H’s will be split into a doublet YSU YSU 18

Gaps between lines (in Hz) will be the same for adjacent protons (here ~7.4 Hz). This is known as the coupling constant. YSU YSU CH 3 CH 2 but which one? CH 3 CH 2 O 7 6 5 4 3 2 1 0 PPM Find J and match signals YSU YSU 19

If nonequivalent neighbours have same J value then n+1 applies for signal CH 3 CH 2 CH 2 CH 2 Cl CH 3 CH 2 CH CH CH CH 3 CH 2 CH 2 3 2 1 0 YSU YSU PPM When nonequivalent neighbours have different J values then n+1 does not apply for signal Generally for alkene protons: J trans > J cis YSU YSU 20

YSU YSU Figure 13.21 Acidic protons exchange with any H 2 O in sample YSU YSU 21

N-H N-H YSU YSU H-2 H-4 H 4 H-3 H 2 H-5 H N-H O N H 5 O H 1 H 3 H1, H2, H3, and H4 hard to distinguish just from coupling constants (all t, J ~9 Hz) YSU YSU 22

Figure 13.23 YSU YSU • Carbon 13 isotope and not 12 C is observed in NMR spectroscopy • 13 C very low abundance (<1%), consequently integration not useful • Spectra usually “decoupled” and signals are observed as singlets • Number of distinct signals indicates distinct types of carbon N b f di i i l i di di i f b • Same ideas about shielding/deshielding apply in 13 C spectroscopy • Spectra often measured in CDCl 3 and referenced to either the C in TMS (0 ppm) or the C in CDCl 3 , which shows as a triplet at 77.0 ppm YSU YSU 23

O CH 3 O O O O 180 160 140 120 100 80 60 40 20 0 PPM 13 C NMR (ppm) 21, 52, 121, 122, 120, 126, 132, 134, 148, 168, 169 YSU YSU O H CH 3 H 3 C H CH 3 200 180 160 140 120 100 80 60 40 20 0 PPM 13 C NMR (ppm) 23, 28, 32, 128, 151, 197 YSU YSU 24

YSU YSU 6 5 4 3 2 1 0 PPM 200 180 160 140 120 100 80 60 40 20 0 PPM O 200 200 180 180 160 160 140 140 120 120 100 100 80 80 60 60 40 40 20 20 0 0 PPM YSU YSU 200 180 160 140 120 100 80 60 40 20 0 PPM 25

Not covering 13.17 ‐ 13.19 YSU YSU H 3 C CH 3 Information on the types of bonds within molecules O H YSU YSU 26

Figure 13.25 YSU YSU Don’t memorize, learn to use as you practice problems YSU YSU 27

CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Figure 13.31 YSU YSU H 2 C=CHCH 2 CH 2 CH 2 CH 3 Figure 13.32 YSU YSU 28

Figure 13.33 YSU YSU Figure 13.34 YSU YSU 29

Figure 13.35 YSU YSU Figure 13.37 Figure 13.38 Useful for identifying chromophores in molecules (benzene rings, conjugated YSU YSU alkene systems) ‐ More useful in Biochemistry 30

Gives information on molecular mass and structure YSU YSU Gives information on molecular mass and structure YSU YSU 31

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