Experimental Determination of Structure

Question 1

What is elemental analysis also known as?

Answer 1

combustion analysis

Question 2

What is the empirical formula?

Answer 2

the simplest ratio

Question 3

What can combustion analysis not give?

Answer 3

the percentage of oxygen

Question 4

What is a mass spectrometer?

Answer 4

an instrument which can be used to determine the accurate formula mass of organic compounds

Question 5

What does the height of the lines in a mass spectrum represent?

Answer 5

the abundance of ions of a particular mass/charge ratio

Question 6

What does the peak with the highest m/z ratio provide?

Answer 6

the molecular mass

Question 7

What is the case with molecular ions formed by the collision of a molecule?

Answer 7

the molecules formed can either be stable enough to remain intact during their progress through the mass spectrometer or will have sufficient energy imparted by the collision to break specific bonds and produce a pattern of fragment ions at the detector

Question 8

What does a mass spectrometer do?

Answer 8

it automatically compares the mass spectrum of a compound against a database of compounds to allow identification

Question 9

Why is infrared spectroscopy used?

Answer 9

to identify functional groups and structural features in an organic compound

Question 10

What does infrared spectroscopy cause?

Answer 10

the bonds to stretch and vibrate

Question 11

What can be said about the frequency of the vibration produced by infrared spectroscopy?

Answer 11

it is dependent on the mass of the atoms and the strength of bond

Question 12

What happens as the mass increases?

Answer 12

the vibration decreases

Question 13

Summary of radiation and molecules

Answer 13

The wavelength of light absorbed that results in the different vibrations will depend on the type of chemical bond and the group of atoms at the end of these bonds

Question 14

When is infrared spectroscopy used?

Answer 14

in forensics, polymers chemistry and quality control

Question 15

What does NMR stand for?

Answer 15

Nuclear magnetic resonance

Question 16

What can NMR be used to tell us?

Answer 16

• the different chemical environments of protons (hydrogen) atoms in a molecule
• how many different protons (hydrogens) are in each of these environments

Question 17

What is the chemical shift?

Answer 17

The signal from any given proton is measured in ppm from TMS and is called the chemical shift of the proton and is given the symbol delta

Question 18

What are high-resolution NMR run using?

Answer 18

higher frequencies and more powerful magnets

Question 19

How can the number of lines within a multiplet be determined?

Answer 19

by looking at the number of H-atoms on the neighbouring carbon

Question 20

What is the number of peaks in a multiplet given by?

Answer 20

the n+1 rule

Question 21

What causes the separation of ions in a mass spectrometer?

Answer 21

A magnetic field

Question 22

In which technique would a test sample be destroyed?

Answer 22

X-ray crystallography

Question 23

What can be said about electron spins when there is no magnetic field?

Answer 23

The spins are random

Question 24

What happens in an nmr spectroscopy when there is a magnetic field?

Answer 24

The nuclei position themselves in alignment with the magnetic field

Question 25

What is the difference when the electrons are alinged with the magnetic field or against the magnetic field?

Answer 25

There is an energy difference

Question 26

What is the energy difference equal to?

Answer 26

The energy of the radiowaves

Question 27

What is the energy dependant on?

Answer 27

The environment of the protons

Question 28

What can be said about solvents used for NMR?

Answer 28

They must not contain any hydrogen