Spectroscopy

Question 1

Describe the IR absorption of O-H

Answer 1

Broad peak around 2900 cm-1 to 3300 cm-1.

Question 2

Describe the IR absorption of C=O

Answer 2

Sharp peak near 1700 cm-1

Question 3

What does a-state mean in NMR?

Answer 3

Lower energy nuclei that are aligned with the B field

Question 4

What does ß-state mean in NMR?

Answer 4

Higher energy nuclei that are aligned opposite the B field

Question 5

What’s the H-NMR ppm shift for alkanes?

Answer 5

1-3ppm

Question 6

What’s the H-NMR ppm shift for alkenes?

Answer 6

4-7ppm

Question 7

What’s the H-NMR ppm shift for aldehydes?

Answer 7

9-10ppm

Question 8

What’s the H-NMR ppm shift for carboxylic acids?

Answer 8

10-12ppm

Question 9

What’s the H-NMR ppm shift for aromatic ring?

Answer 9

6-8.5ppm

Question 10

When do you observe coupling between H’s in H-NMR?

Answer 10

When H’s are within 3 bonds of each other

Question 11

Explain UV spectroscopy

Answer 11

Wavelength of max absorbance tells us extent of conjugation within conjugated systems. More conjugated = lower E = greater wavelength.

Question 12

Explain the two important peaks in mass spectrometry

Answer 12

The base peak is the highest intensity peak, and the molecular ion (parent ion) peak is the peak with the highest m/z and corresponds to the normal molecule in a cationic form (just +1), the molecular mass = the m/z ration (since z=1)