RPA - Analysis

Question 1

what is the stationary and mobile phase in TLC?

Answer 1

Stationary - silica plate

Mobile - solvent appropriate for compound

Question 2

What is the stationary and mobile phase in GC?

Answer 2

stationary - solid on solid support (tube)

Mobile - carrier gas

Question 3

What is the stationary and mobile phase in gas-liquid chromatography?

Answer 3

Stationary - liquid on solid support

mobile - carrier gas

Question 4

What can we infer from the peak height of H1 NMR?

Answer 4

The relative intensity shows how many hydrogens are in each environment

Question 5

Which groups do not exhibit splitting?

Answer 5

-OH,-NH, COOH groups

Question 6

What technique can we use to identify -OH/-NH groups?

Answer 6

Run a second NMR with D2O, which exchanges protons with the OH/NH groups using labile protons, so does not show up on the second run.

Question 7

What solvent is commonly used in both C13 and H1 NMR? Why

Answer 7

CDCl3. It is unreactive, volatile, and does not show up on H1 NMR, and shows one peak on C13, which is normally removed.

Question 8

What is the standard used in NMR, why do we use it, and what makes it good at its job?

Answer 8

TMS (Tetramethylsilane) is the standard, because it produces a high peak of relative intensity 12, which is a single peak, due to the hydrogens in equivalent environment. THis is normally added to calibrate the machine, as TMS should have a ppm value of 0. It is unreactive, and volatile so can be removed easily from the sample to make the analysis non-destructive.

Question 9

What is the group next to a hydrogen environment showing splitting of 4 (quartet)

Answer 9

CH3, using the n+1 rule,.

Question 10

What happens if a triplet and quartet are spotted in H1 NMR?

Answer 10

They are likely to be CH2-CH3 next to each other, as they give each other the splitting pattern. This is common in ester groups containing O-CH2-CH3.

Question 11

How should you lay out answers to NMR analysis questions?

Answer 11

In a table - ppm-environment-splitting-inference from splitting-integration.

Question 12

How are components separated in TLC?

Answer 12

Adsorbtion

Question 13

How are components separated in a liquid stationary phase e.g. GLC?

Answer 13

relative solubility

Question 14

Which groups do not split?

Answer 14

NH, OH, COOH

Question 15

When identifying splitting patterns, how do you describe the adjacent group e.g. for quartet?

Answer 15

splitting of 4, hence three adjacent hydrogens using n+1 rule, hence CH3 group.

Question 16

If there are two different groups attached to aromatic ring, and 4 carbon-13 peaks, which positions are the groups in?

Answer 16

1,4

Question 17

Give seven marks worth of things you can find from high resolution H1 NMR

Answer 17

Shift - environment
#peaks - total # environments
splitting - adjacent hydrogens
integration - relative # protons in environment
D2O - removes peaks due to OH/NH
n+1 rule - refers to splitting where n=number of adjacent hydrogens and n+1 = #peaks observed.