Espectroscopía generalidades II-2012(1)
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Espectroscopía QUIMICA ORGANICA II. BORRADOR. II-2012
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Transcript of Espectroscopía generalidades II-2012(1)
Espectroscopía
QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
ESPECTRO ELECTROMAGNÉTICO
QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
excites vibrational energy levels
QUIMIC
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A II. B
ORRADOR. II-20
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An absorption band due to a particular functional group always appears in the same general region.
wavenumber = v
APARIENCIA DEL ESPECTRO IR
QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
Generalizations
1
2c M
k
k = force constant of bond (proportional to bond strength)
M = reduced mass of atoms (proportional to mass of atoms)
1. stronger bonds absorb at higher wavenumber (larger k)
2. stretches absorb at higher wavenumber than bends (larger k)
3. bonds to H absorb at higher wavenumber (smaller mass)
4. polar bonds have more intense absorptions (smaller %T)
QUIMIC
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A II. B
ORRADOR. II-20
12
Enlaces sencillos a Hidrógeno
O-H
3550-3200 cm-1 intense (polar) very broad (H bonding)
O H O
H
decreasing bond strength
> N-H
3400-3200 less intense less broad NH2 has 2 NH has 1
> CspH
3300
> Csp2H
3100 -3000
> Csp3H 3000 -2850
CH
O
> 2830 -2700 two bands
3000 cm-1 divides sp2 and sp3
QUIMIC
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ORRADOR. II-20
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Triples enlaces
C N C C
2260-2200 more intense
2150-2100 less intense less polar
For symmetrical alkynes, this band can be very weak.
CH3CH2 C C CH2CH3
QUIMIC
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ORRADOR. II-20
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Double Bond Region
C
O
C
N
C
C
~1700 cm-1 very intense (polar) very useful
lower wavenumber (uncommon)
1660-1640 less intense (nonpolar)
four bands near 1600, 1580, 1500, and 1450 variable position and intensity (use caution)
QUIMIC
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A II. B
ORRADOR. II-20
12
Csp3-H (<3000)
QUIMIC
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ORRADOR. II-20
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3000 divides Csp2-H and Csp3-H
QUIMIC
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ORRADOR. II-20
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Csp-H
QUIMIC
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Csp2-H Csp3-H
QUIMIC
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ORRADOR. II-20
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2. 13C Magnetic Resonance Spectroscopy
Apariencia
QUIMIC
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A II. B
ORRADOR. II-20
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QUIMIC
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ORRADOR. II-20
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Cuántas señales debe dar? Simule el espectro
QUIMIC
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ORRADOR. II-20
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CH3
CH3
CH3
CH3
CH3
CH3
A cuál xileno corresponde?
QUIMIC
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ORRADOR. II-20
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Chemical shift position on x-axis info about C to which the H is bonded
multiplicity number of peaks in group info about nearby H’s
Integral area under a peak is proportional to the number of H’s
RMN 1H QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
Inductive Effects
X C HElectronegative X pulls electrons away from H; H is deshielded; appears more downfield
C is slightly more electronegative than H
QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
Table 14.1
QUIMIC
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ORRADOR. II-20
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Simule el espectro del siguiente compuestos
QUIMIC
A ORGANIC
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ORRADOR. II-20
12
DU = 1
Qué compuesto es? Cómo se calcula el IDH?
QUIMIC
A ORGANIC
A II. B
ORRADOR. II-20
12
