chemical shift
DESCRIPTION
Chemical Shift. Carbon-13 Spectra. How many C-13 signals? Which signals are further upfield ? Can the compounds be differentiated?. Correlation Chart. Same number of signals Occur in different areas of spectrum Predictable shifts. Chemical Shift Tables. Complex vs simple Basics: - PowerPoint PPT PresentationTRANSCRIPT
Chemical Shift
Carbon-13 Spectra
• How many C-13 signals?
• Which signals are further upfield?
• Can the compounds be differentiated?
OH
O
Correlation Chart
• Same number of signals
• Occur in different areas of spectrum
• Predictable shifts
020406080100120140160180200220PPM
O
020406080100120140160180200220PPM
OH
Chemical Shift Tables• Complex vs simple• Basics:– Alkane: 5-45ppm– C-Q: 40-70ppm– sp: 70-100ppm– sp2: 100-160 ppm– Carbonyl: 160-220
ppm
Predict C-13 Chemical Shifts
• If carbon fits two categories, choose higher shift
Cl O
O
OH
OH
O
O
More subtle points
• Inductive effects• Additive effects• More substituted
sp3 carbon is further downfield
7.9
35.9
210.8
43.5
31.0
33.8
29.4
20.4
11.6
O
7.9
32.1
207.3
79.2 57.2
O
O
More subtle points• Carbonyls– Above 200ppm,
ketone and aldehyde
– Below 200ppm, O=C-Q
– Explain by shielding and resonance
O O
OH
O
OH
O
OH
O
More subtle points
• Alkene vs Alkyne
Which Structure(s) Fit?
CDCl3TMSabsent
Which Structure Fits?
C3H8O
Proton NMR Shifts
Basic Correlation Chart
• How many 1H signals?• Shift? Proton NMR Chemical Shift (ppm)
alkane CH3 0.9alkane CH2 1.3alkane CH 1.7X=C-C-H(Ph-C-H orO=C-C-H)
2-3
O-C-HX-C-H
3-4
(sp2) C=C-H 5-6Ph-H 7-8O=C-H 9-10O=C-O-H 10-12O-H, N-H 1-5
O
O
OH
NH
O
Common “exceptions”
• Phenyl protons give one “signal” even if nonequivalent
O
Common “exceptions”• Exchangeable protons are broad and small• Washed away with D2O
012345PPM
OH