experimental determination of structure

Question 1

What is Elemental microanalysis used for

Answer 1

Elemental microanalysis is used to determine the masses of C, H, O, S and N in a sample of an organic compound in order to determine its empirical formula.

Question 2

what can Elemental microanalysis can be determined from

Answer 2

Elemental microanalysis can be determined from:
 combustion product masses
 percentage product by mass

Question 3

what does an empirical formula show

Answer 3

An empirical formula shows the simplest ratio of the elements in a molecule.

Question 4

what can mass spectrometry can be used to determine

Answer 4

Mass spectrometry can be used to determine the accurate gram formula mass (GFM) and structural features of an organic compound

Question 5

what can the mass-to-charge ratio of the parent ion can be used to determine

Answer 5

The mass-to-charge ratio of the parent ion can be used to determine the GFM of the molecular ion, and so a molecular formula can be
determined using the empirical formula.

Question 6

how does mass spectrometry work

Answer 6

In mass spectrometry, a small sample of an organic compound is bombarded by high-energy electrons. This removes electrons from
the organic molecule generating positively charged molecular ions known as parent ions. These molecular ions then break into smaller
positively charged ion fragments. A mass spectrum is obtained showing a plot of the relative abundance of the ions detected against the mass-to-charge (m/z) ratio.

Question 7

what can the fragmentation data can be interpreted to gain

Answer 7

The fragmentation data can be interpreted to gain structural information.

Question 8

what is Infrared spectroscopy is used to identify

Answer 8

Infrared spectroscopy is used to identify certain functional groups in an organic compound.

Question 9

When infrared radiation is absorbed by organic compounds what happens

Answer 9

When infrared radiation is absorbed by organic compounds, bonds
within the molecule vibrate (stretch and bend).

Question 10

what do the wavelengths of
infrared radiation that are absorbed depend on

Answer 10

The wavelengths of
infrared radiation that are absorbed depend on the type of atoms that make up the bond and the strength of the bond.

Question 11

In infrared spectroscopy, what is passed through a sample of the organic compound

Answer 11

In infrared spectroscopy, infrared radiation is passed through a sample of the organic compound and then into a detector that measures the intensity of the transmitted radiation at different wavelengths.

Question 12

what is The absorbance of infrared radiation is measured in

Answer 12

The absorbance of infrared radiation is measured in
wavenumbers, the reciprocal of wavelength, in units of cm-1.

Question 13

what can Proton nuclear magnetic resonance spectroscopy (proton NMR or 1 H NMR) give information about

Answer 13

Proton nuclear magnetic resonance spectroscopy (proton NMR or 1 H NMR) can give information about the different chemical environments of hydrogen atoms (protons or 1 H) in an organic molecule, and about how many hydrogen atoms there are in each of these environments

Question 14

how do h nuclei behave

Answer 14

H nuclei behave like tiny magnets and in a strong magnetic field some align with the field (lower energy), whilst the rest align against it (higher energy).

Question 15

what does absorption of radiation in the radio frequency region of the electromagnetic spectrum cause

Answer 15

Absorption of radiation in the radio frequency region of the electromagnetic spectrum causes the 1
H nuclei to ‘flip’ from
the lower to the higher energy alignment. As they fall back from the higher to the lower energy alignment the emitted radiation is detected and plotted on a spectrum.

Question 16

In a 1 H NMR spectrum what is the chemical shift related to

Answer 16

In a 1 H NMR spectrum the chemical shift, δ , (peak position) is related to the environment of the 1 H atom and is measured in parts per million (ppm).

Question 17

h graph

Answer 17

The height of an integration curve is proportional to the number of 1 H atoms in that environment, and so a ratio of 1 H atoms in each environment can be determined.

Question 18

what is the standard reference substance used in 1 H NMR spectroscopy

Answer 18

The standard reference substance used in 1 H NMR spectroscopy is tetramethylsilane (TMS), which is assigned a chemical shift value equal to zero.

Question 19

how can H NMR spectra be obtained

Answer 19

H NMR spectra can be obtained using low-resolution or high-resolution NMR.

Question 20

what is the difference between high resolution and low resolution 1 h NMR

Answer 20

High-resolution 1 H NMR uses higher radio frequencies than those used in low-resolution 1 H NMR and provides more detailed spectra.

Question 21

Low- and high-resolution 1 H NMR spectra can be analysed, and low resolution 1 H NMR spectra can be …?

Answer 21

Low- and high-resolution 1 H NMR spectra can be analysed, and low resolution 1 H NMR spectra can be sketched for any given compound.