IR

Question 1

What do molecules do with IR energy

Answer 1

Vibrate

Question 2

Modes of vibration

Answer 2

Symmetric and asymmetric stretch
Bending
Rocking
Twisting
Scissoring

Question 3

What does the intensity of a band governed by

Answer 3

The size of the dipole moment of the bond.
Ie bugger the difference in en the bugger the band

Question 4

What type of bands are ir silent

Answer 4

A band which involves no change in dipole moment eg oxygen molecule

Question 5

Nh2 bond

Answer 5

3400cm-1

Question 6

Oh bond

Answer 6

3500 cm-1

Question 7

C-h bind

Answer 7

3000cm-1

Question 8

C=o bind

Answer 8

1700cm-1

Question 9

Why should water be mimimised in IR. Sample peropwrtion

Answer 9

Water is IR active

Question 10

prep method

Answer 10

2mg is ground with about 300mg KBR and pressed to a thin disc under pressure . This is because kbr is inert and 2mg is v small .

If the sample isn’t a solid you can produce a liquid film , by taking a small drop of the lowuid compound and sandwiching it between two NACl /KCL ‘windows ‘.

If you don’t have a good solid or kbr you can use a nujol mull.
Solid or semi solid sample is made lowuid enough to be spread like lowuid film.
Nujol contributes its own peak .