LECTURE 21 OPTICAL SPECTROSCOPY I INFRARED

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LECTURE 21 OPTICAL SPECTROSCOPY I INFRARED
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IR SPECTROMETERS ARE UBIQUITOUS
BEGIN HERE
P 8
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USING IR DATA IN OSA
COMPOUND 25-1 C8H10O2 aD 126.9 IR ?
3151, 2962, 2901, 1654, 1562, 1471, 1361, 1246,
1216, 1094 UV blank
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USING IR DATA IN OSA
COMPOUND 25-1 C8H10O2 aD 126.9 IR ?
3151, 2962, 2901, 1654 (CC), 1562, 1471, 1361,
1246, 1216, 1094 UV blank
CC with three possibilities
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USING IR DATA IN OSA
COMPOUND 25-1 C8H10O2 aD 126.9 IR ?
3151, 2962, 2901, 1654 (CC), 1562, 1471, 1361,
1246, 1216, 1094 UV blank
13C (125 MHz, CDCl3) d26.2 (T), 68.4 (D), 97.0
(D), 143.2 (D)
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USING IR DATA IN OSA
COMPOUND 25-1 C8H10O2 aD 126.9 IR ?
3151, 2962, 2901, 1654 (CC), 1562, 1471, 1361,
1246, 1216, 1094 UV blank
13C (125 MHz, CDCl3) d26.2 (T), 68.4 (D), 97.0
(D), 143.2 (D)
1H (400 MHz, CDCl3) d2.18 dddd 1.3, 2.0,
4.8, 17.6 Hz 2H 2.37 tdd 2.0, 5.8, 17.6 Hz 2H
4.14-4.17 m, 2H 4.65
dddd J 1.3, 2.0, 4.8, 6.3 Hz 2H 6.39 td
2.0, 6.3 Hz, 2H
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USING IR DATA IN OSA
COMPOUND 25-1 C8H10O2 aD 126.9 IR ?
3151, 2962, 2901, 1654 (CC), 1562, 1471, 1361,
1246, 1216, 1094 UV blank
13C (125 MHz, CDCl3) d26.2 (T), 68.4 (D), 97.0
(D), 143.2 (D)
1H (400 MHz, CDCl3) d2.18 dddd 1.3, 2.0,
4.8, 17.6 Hz 2H 2.37 tdd 2.0, 5.8, 17.6 Hz 2H
4.14-4.17 m, 2H 4.65
dddd J 1.3, 2.0, 4.8, 6.3 Hz 2H 6.39 td
2.0, 6.3 Hz, 2H
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4.16
1H (400 MHz, CDCl3) d2.18 dddd 1.3, 2.0,
4.8, 17.6 Hz 2H 2.37 tdd 2.0, 5.8, 17.6 Hz 2H
4.14-4.17 m, 2H 4.65
dddd J 1.3, 2.0, 4.8, 6.3 Hz 2H 6.39 td
2.0, 6.3 Hz, 2H
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SCHEMATIC DIAGRAMIR SPECTROMETER
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P 5
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TYPES OF VIBRATIONS
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transmittance

• T I/IO A LOG10 (IO/I)
• I light transmitted through the sample
• I0 blank
• Absorbance (A)
• STRONG PEAK large absorbed light
• ENERGY ABSORBED 1 10 kcal/mol

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transmittance

• T I/IO A LOG10 IO/I
• STRONG PEAK large amt. of absorbed light
• Strong peak s Medium m
• Weak w Variable v

Notes A molecule absorbs max amount of energy B
/ B filter switching points C glitches D / E
medium intensity peak F shoulder
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FUNDAMENTALS N atoms 3n deg of
freedom 3-translation 3-rotational
motions ?3n-6 vib deg of freedom
LARGE NUMBER OF IR BANDS POSSIBLE
(see pg 321)
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FUNDAMENTALS BOND E C-C lt CC lt C?C vs.
1126lt1653lt2096
3 translation 3 rotational Hooks
Law m1, m2 atomic mass c speed of light
motions ?3n-6 vib deg of freedom
(stretch)
p323
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p325
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P325 CHART 8.1
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p329
IR LIMITATIONS note weak CC stretch1460cm-1
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FUNCTIONAL GROUP ID - NO OVERALL STRUCTURE
p330
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FUNCTIONAL GROUP ID - NO OVERALL STRUCTURE
P 331
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p324
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p318
p323
p324
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C10H12O calc .0966 U 5
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C10H12O calc .0966 U 5 IR 3400 -OH
3000 3100 CC or 2840 CH
stretch 1600-2000 aromatic ring
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p326
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C10H12O calc .0966 U 5 IR 3400 -OH
3000 3100 CC or 2840 CH
stretch 1600-2000 see p337
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IR 1600-2000
pg 337
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IR 1600-2000
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C10H12O U 5
U 4 1
No 1H NMR vinyl Hs
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COSY
COSY
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SUMMARY

• Infrared involves atom vibrations of 3 Kcal in
  strength.
• Three types of vibrations (a) stretch, (b) R/S,
  (c) T/W.
• Hookes Law Equation allows calculation of
  stretching freq. Between to atoms of mass m1
  m2.
• Hookes Law good agreement between calculated
  and observed peak positions.
• Use five steps of pg. 332 334 to ID functional
  groups.
• IR information is most valuable when used
  alongside NMR data.