Today:
• Brief Review of Mass Spectroscopy
• Discussion/Review of H-NMR, CMR
Next time (our last lab lecture):
Your questions
Final Exam at 2:10 pm in your Lab!
•Exam covers the material of the second half of the
semester(only): “Unknowns”.
•Study/ review lab lectures, your labs, practice questions,
sample final (in eres file).
•Same rules as for Midterm. No calculator needed.
•Spectral correlation charts will be provided.
Mass Spectrometry
Summary
(Examine your Unknown #3 Mass spectrum!)
Molecular weight:
•
Molecular ion peak M+ ?
•
odd-numbered (N ...) ?
•
isotope peaks (Cl, Br)?
•
Alcohols …
Recognize typical fragments:
H2O, alkyl, acyl, tropylium ion …
Weights of common fragments or neutral losses
O
15 = CH3 18 = H2O 29 = C2H5 43 = C3H7 or
O
31 = CH3O
O
57 = C4H9 or
71 = C5H11 or
45 = CH3CH2O
O
79Br 81Br
85 = C6H13 or 35Cl
77 =
O
C
CH2
91 =
105 =
37Cl
phenetole
3-methoxytoluene
Salicylaldehyde
Benzoic acid
M+ = 122
This is the mass spectrum
for which compound?
91
77
107
NMR
Basic Information from Proton NMR
(Examine your Unknown #3 H-NMR spectrum!)
Number of signals
Number of different types of protons
Chemical shifts
Type of environment for protons
Integration
Ratios of numbers of protons
Splitting of Signals
Information about neighboring protons
Solvent peaks …..
Proton NMR Chemical Shifts ()
For 1H NMR, the scale generally extends from 0-12 ppm
(TMS standard)
• Simple hydrocarbon protons absorb in the region 0.5-1.5
• Protons on a carbon adjacent to a carbonyl are shifted to 2
ppm (acetone!)
• Electronegative atoms (O, halogens) move protons to 3-4
• Alkene protons are shifted to 5-6
• Aromatic protons to 7-8 (Amide CONH is also found here)
• Aldehydic protons to 10
• Most highly shifted protons are generally those of carboxylic
acids, with values of 12
• Can also be far downfield: phenol OH, enol
Proton NMR Chemical Shifts for Common
Functional Groups
For 1H NMR, the scale generally extends from
0-12 ppm
Proton NMR Common Splitting Patterns
A
J’s (Hz)!
B
Practice Proton NMR
Practice Proton NMR
http://www.aist.go.jp/RIODB/SDBS/cgi-bin/cre_index.cgi
13C
NMR Chemical Shifts
for Common Functional Groups
Range 0-220 ppm (TMS standard)
Proton noise-decoupled
Integration not useful
(Examine your Unknown #3 CMR spectrum!)
•Simple methyl carbons tend to absorb in the region 15-30, simple
methylene carbons are shifted to 20-65
• Electronegative atoms (O, halogens) move attached carbons to 40-80
• Alkyne carbons are shifted to 70-90,
• alkene carbons to 100-150,
• aromatic carbons to 120-170
• Most highly shifted carbons are generally those of carbonyls, with
values of 180-220.
13C
NMR Chemical Shifts
for Common Functional Groups
13C
NMR Practice
How many types of C ? Indicated by how many signals there are in the
spectra (solvent peaks ….)
What types of C ? Indicated by the chemical shift of each signal
13C
Symmetry!
NMR Practice
13C
NMR Practice
How many signals would you expect in the 13C spectrum
of
• o-xylene
• m-xylene
• p-xylene?
Next time (our last class):
• Your questions
• Final Exam at 2:10 pm in your Lab
(Begin studying early!)
Exam covers the material of the second half of the semester:
“Unknowns”.
Study/ review lab lectures, your labs, practice questions, sample final.
Same rules as for Midterm. No calculator needed.
Spectral correlation charts will be provided.
How your C336 class grade is calculated ….