6.3.2 Spectroscopy

Question 1

What has a chemical shift value of 0 ppm

Answer 1

TMS (tetramethylsilane)

Question 2

How to run an NMR spectrometer

Answer 2

Sample dissolved in solvent and placed in narrow NMR sample tube, with TMS

Question 3

What can you find out from C13 NMR spectra

Answer 3

Number of carbon environments
Types of carbon environments present

Question 4

What can you find out from H1 NMR spectra

Answer 4

Number of proton environments
Types of proton environments
Relative numbers of each type of proton
Number of protons adjacent to a given proton

Question 5

How to test for -OH and -NH2 groups in proton NMR

Answer 5

Proton exchange is used:
Proton NMR run as normal
Small volume of D2O added, mixture is shaken and second spectrum is run
OH and NH2 protons will be replaced by D
Peaks will disappear which helps you identify them

Question 6

Why is proton exchange used

Answer 6

OH and NH2 could be involved in hydrogen bonding
NMR peaks for these groups are often broad and have variable chemical shift

Question 7

What is the solvent used in NMR

Answer 7

CDCl3