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Flashcards in IR spectroscopy Deck (31):
1

IR energy is too low to cause electronic transitions. True or false?

True

2

Molecules remain in ground state even after absorbing IR. True or false?

True

3

What is on the x and y axis of IR spectrums?

y - % transmittance
x - wavenumber

4

At the higher energy end of the spectrum, there is a vibration every ____ femto seconds

8

5

At the lower energy end of the spectrum there is a vibration every ____ femto seconds

50

6

What are the two types of vibrations?

Stretching and bending

7

An asymmetrical stretch takes more energy than a symmetrical stretch. True or false?

True

8

What are the two types of in-plane bending?

Scissoring
Rocking

9

What are the two types of out of plane bending?

Wagging
Twisting

10

Only vibrations that result in net change in polarity of a bond, give rise to IR bands, True or false?

True

11

Symmetrical bonds with no dipole moments (e.g. N2, O2) give no IR peaks. True or false?

True

12

Symmetrical stretches give no rise to peaks but asymmetrical do. True or false?

True

13

In order for IR to be active, a vibration must cause a change in _____ ______ of the molecule

dipole moment

14

Molecular asymmetry by stretching and/or bending is a requirement for excitation by IR. True or false?

True

15

A molecule has dipole moment if?

The centre of positive charge is different to the centre of negative charge

16

Dipole moment = separation x charge. True or false?

True

17

How does dipole moment affect intensity of absorption?

The bigger the electronegativity difference, the greater the dipole moment and the higher the intensity

18

The absorption of IR for a given bond depends on what 3 things?

the mass of the atom connected to the bond
strength of the bond
dipole moment

19

Why does the mass of an atom connected to the bond have an effect on absorption of IR?

Because heavier atoms make it harder to stretch the bond

20

Stretching requires less energy than bending. True or false?

False

21

Stronger bonds require more energy to vibrate and so are at a higher frequency. True or false?

True

22

What are the uses of IR spectroscopy?

Identification of bonds
Obtain structural information about functional groups of drug molecule
Detecting polymorphs of drugs

23

Complete structure of drug can be assigned from IR. True or false?

False

24

A primary amine gives a _____ peak with _____ sharp spikes

broad
two

25

A secondary amine gives a ______ peak with _____ sharp spike

broad
one

26

Alcohol OH bond is a _____ peak

rounded

27

What are the two types of instrumentation for IR spec?

Dispersive instrument
Fourier Transform instrument

28

The cells in the dispersive instrument have to be made of a certain material which are inactive in the region. True or false?

True

29

For non-aqueous samples, what cell types are used?

KBr, NaCl, CaF2

30

For aqueous samples, what cell types are used?

non-hygroscopic material - diamond, AgCl

31

What are the applications of near IR (NIR)?

Quality control, particle size i.e. physical properties of formulation