CHEM 344 Spring 2025 Spectroscopy & WebMO Exam (100 pts)
Name:
TA Name:
Exam Length = 120 min
Directions for drawing molecules, reactions, and electron-pushing mechanisms:
Draw all lone pairs, bonds, arrows, formal charges, and stereochemistry explicitly in all molecular
structures.
Take care when drawing molecules and labeling them with NMR assignments so that you do not change
the chemical formula. Examples for 2-methyl-2-butanol are shown below.
acceptable acceptable acceptable unacceptable unacceptable
Directions for all calculations:
Explicitly show all work on all calculations and include all important labels.
1
, 1) The solvent-free Wittig reaction of an ylide (carbethoxymethylene)triphenylphosphorane and 9-
anthraldehyde generates a mixture of up to two isomers. Analyze the spectra of 9-anthraldehyde and
the major product of the Wittig reaction (recrystallized from methanol) shown below. (42 pts total)
a) Benzaldehyde exists as a planar Cs structure, while 9-anthraldehyde exists as a twisted C1 structure.
Use the computational results provided for the optimized structure of 9-anthraldehyde to justify the
conformational change compared to benzaldehyde. (6 pts)
benzaldehyde, planar (Cs) 9-anthraldehyde, twisted (C1)
top view side view top view side view
1.89 Å
2.37 Å
0.0° 11.6°
(dihedral angle 11.6°)
b) State the stereochemical relationship between the two possible Wittig reaction products and state
whether you expect them to have the same or different 1H-NMR spectra. (2 pts)
The B3LYP NMR chemical shifts are provided below for 9-anthraldehyde.
11.60
10.21 8.78 180.6
7.63 122.5 116.7 115.7
7.77
124.9 126.2 130.1 122.4
119.8 124.2 124.2 118.7
7.50 7.46
123.0 132.1 124.9
7.81 9.62 7.91
2
Name:
TA Name:
Exam Length = 120 min
Directions for drawing molecules, reactions, and electron-pushing mechanisms:
Draw all lone pairs, bonds, arrows, formal charges, and stereochemistry explicitly in all molecular
structures.
Take care when drawing molecules and labeling them with NMR assignments so that you do not change
the chemical formula. Examples for 2-methyl-2-butanol are shown below.
acceptable acceptable acceptable unacceptable unacceptable
Directions for all calculations:
Explicitly show all work on all calculations and include all important labels.
1
, 1) The solvent-free Wittig reaction of an ylide (carbethoxymethylene)triphenylphosphorane and 9-
anthraldehyde generates a mixture of up to two isomers. Analyze the spectra of 9-anthraldehyde and
the major product of the Wittig reaction (recrystallized from methanol) shown below. (42 pts total)
a) Benzaldehyde exists as a planar Cs structure, while 9-anthraldehyde exists as a twisted C1 structure.
Use the computational results provided for the optimized structure of 9-anthraldehyde to justify the
conformational change compared to benzaldehyde. (6 pts)
benzaldehyde, planar (Cs) 9-anthraldehyde, twisted (C1)
top view side view top view side view
1.89 Å
2.37 Å
0.0° 11.6°
(dihedral angle 11.6°)
b) State the stereochemical relationship between the two possible Wittig reaction products and state
whether you expect them to have the same or different 1H-NMR spectra. (2 pts)
The B3LYP NMR chemical shifts are provided below for 9-anthraldehyde.
11.60
10.21 8.78 180.6
7.63 122.5 116.7 115.7
7.77
124.9 126.2 130.1 122.4
119.8 124.2 124.2 118.7
7.50 7.46
123.0 132.1 124.9
7.81 9.62 7.91
2
