IR spectroscopy

Question 1

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

Answer 1

True

Question 2

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

Answer 2

True

Question 3

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

Answer 3

y - % transmittance

x - wavenumber

Question 4

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

Answer 4

8

Question 5

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

Answer 5

50

Question 6

What are the two types of vibrations?

Answer 6

Stretching and bending

Question 7

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

Answer 7

True

Question 8

What are the two types of in-plane bending?

Answer 8

Scissoring

Rocking

Question 9

What are the two types of out of plane bending?

Answer 9

Wagging

Twisting

Question 10

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

Answer 10

True

Question 11

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

Answer 11

True

Question 12

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

Answer 12

True

Question 13

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

Answer 13

dipole moment

Question 14

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

Answer 14

True

Question 15

A molecule has dipole moment if?

Answer 15

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

Question 16

Dipole moment = separation x charge. True or false?

Answer 16

True

Question 17

How does dipole moment affect intensity of absorption?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

Because heavier atoms make it harder to stretch the bond

Question 20

Stretching requires less energy than bending. True or false?

Answer 20

False

Question 21

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

Answer 21

True

Question 22

What are the uses of IR spectroscopy?

Answer 22

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

Question 23

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

Answer 23

False

Question 24

A primary amine gives a _____ peak with _____ sharp spikes

Answer 24

broad

two

Question 25

A secondary amine gives a ______ peak with _____ sharp spike

Answer 25

broad

one

Question 26

Alcohol OH bond is a _____ peak

Answer 26

rounded

Question 27

What are the two types of instrumentation for IR spec?

Answer 27

Dispersive instrument

Fourier Transform instrument

Question 28

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

Answer 28

True

Question 29

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

Answer 29

KBr, NaCl, CaF2

Question 30

For aqueous samples, what cell types are used?

Answer 30

non-hygroscopic material - diamond, AgCl

Question 31

What are the applications of near IR (NIR)?

Answer 31

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