Nuclear Magnetic Resonance Spectroscopy

Question 1

NMR Spectroscopy

Answer 1

Compound analysed for 1H atoms - compared with a standard Tetramethylsilane - TMS (Si(Ch3)4)

Question 2

Why is TMS used

Answer 2

Hydrogen atoms less deshielded than any H atoms in any organic compound

Si less electronegative than carbon

12 H atoms of TMS are chemically equivalent - strong signal for comparison

Question 3

Features NMR spectrum

Answer 3

•Horizontal axis - chemical shift delta/ppm (parts per million) fight to left

•Vertical Axis - may or not be present - if labelled its Signal Intensity

•No. peaks identifies no. diff chemical env of H atoms

Question 4

What is the Area under each Peak equivalent to

Answer 4

Ratio of H atoms in each chemical environment

Integration trace can be given to indicate the ratio of

Question 5

Spin-Spin Splitting Pattern

Answer 5

Caused by H atoms bonded to adjacent carbon atoms

Depends on n+1 rule- if 2 H bonded to adjacent carbon atoms, peak split into 3

If no H atoms bonded to adjacent carbon - peak is not split (one peak)

Question 6

Singlet

Answer 6

Not split at all

Question 7

Doublet

Answer 7

A signal that appears as a pair of lines of equal intensity

Question 8

Triplet

Answer 8

Signal that appears as three lines in the approximate intensity ratio (1:2:1)

Question 9

Quartet

Answer 9

Signal that appears as four lines in the approximate intensity ratio (1:3:3:1)

Question 10

Low-Resolution NMR

Answer 10

Spectrum does not show the spin-spin splitting pattern

Question 11

High-Resolution NMR

Answer 11

Spectrum does show the spin-spin splitting pattern

Question 12

H atoms Bonded to EN atoms or C attached to EN atoms

Answer 12

Deshielded
Appear more downfield
Higher Chemical Shift Value

Question 13

H atoms in alkyl groups - no EN atoms

Answer 13

Less deshielded
Appear more upfield
Lower Chemical Shift Value

Question 14

What is the peak at delta=0

Answer 14

Chemically equivalent H atoms in TMS