More more revision

Question 1

What are isomers?

Answer 1

Molecules that have the same molecular formula but different structural formulae are
called isomers

Question 2

When do structural isomers occur?

Answer 2

Structural isomers occur when the atoms are bonded together in a different order in each
isomer.

Question 3

When do stereoisomers occur?

Answer 3

Stereoisomers occur when the order of the bonding in the atoms is the same but the
spatial arrangement of the atoms is different in each isomer

Question 4

What are the two types of stereoisomers?

Answer 4

, geometric and optical.

Question 5

What are geometric isomers?

Answer 5

• can occur when there is restricted rotation around a carbon-carbon double bond or a carbon-carbon single bond in a cyclic compound
• must have two different groups attached to each of the carbon atoms that make up the
  bond with restricted rotation
• can be labelled cis or trans according to whether the substituent groups are on the
  same side (cis) or on different sides (trans) of the bond with restricted rotation
• have differences in physical properties, such as melting point and boiling point
• can have differences in chemical properties

Question 6

What are optical isomers?

Answer 6

• occur in compounds in which four different groups are arranged tetrahedrally around a central carbon atom (chiral carbon or chiral centre)
• are asymmetric
• are non-superimposable mirror images of each other
• can be described as enantiomers
• have identical physical properties, except for their effect on plane-polarised light
• have identical chemical properties, except when in a chiral environment such as that
  found in biological systems (only one optical isomer is usually present)
• rotate plane-polarised light by the same amount but in opposite directions and so are
  optically active

Question 7

What is a racemic mixture?

Answer 7

when a pair of enantiomers are mixed in equal amounts. They are optically inactive because the rotational effect of the plane-polarised light cancels out

Question 8

What is elemental microanalysis?

Answer 8

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 9

How can elemental microanalysis be determined from?

Answer 9

• combustion product masses
• percentage product by mass

Question 10

What is mass spectrometry used to determine?

Answer 10

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

Question 11

What happens during mass spectronmetry?

Answer 11

• 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 12

What can a mass-to-change ratio of the parent ion be used to determine?

Answer 12

To determine the GFM of the
molecular ion, and so a molecular formula can be determined using the empirical formula.

Question 13

What does infrared spectroscopy do?

Answer 13

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

Question 14

What happens when infrared is absorbed by organic compounds?

Answer 14

• bonds within the molecule vibrate (stretch and bend).

Question 15

What happens during the process of infrared spectroscopy?

Answer 15

• infrared radiation is passed through a sample of the organic
  compound
• then into a detector that measures the intensity of the transmitted radiation
  at different wavelengths.
• The absorbance of infrared radiation is measured in
  wavenumbers, the reciprocal of wavelength, in units of cm^-1

Question 16

What is proton nuclear magnetic resonance spectroscopy?

Answer 16

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

Question 17

How does proton NMR work?

Answer 17

• 1H 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).
• Absorption of radiation in the radio frequency region of the electromagnetic spectrum causes the 1H 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 18

What is the chemical shift in 1H NMR spectrum related to?

Answer 18

related to the environment
of the 1H atom and is measured in parts per million (ppm)

Question 19

What is TMS?

Answer 19

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

Question 20

What is the area under the peak?

Answer 20

related to the number of 1H atoms in that environment and is
often given by an integration curve on a spectrum

Question 21

What is the height of the integration curve proportional to?

Answer 21

proportional to the number of 1H atoms in that environment, and so a ratio of 1H atoms in
each environment can be determined.

Question 22

What is high resolution 1H NMR?

Answer 22

• uses higher radio frequencies than those used in low-resolution
• provides more detailed spectra

Question 23

What happens in high resolution 1H NMR?

Answer 23

In a high-resolution 1H NMR an interaction with 1H atoms on neighbouring carbon atoms
can result in the splitting of peaks into multiplets. The number of 1H atoms on neighbouring
carbon atoms will determine the number of peaks within a multiplet and can be determined
using the n+1 rule, where n is the number of 1H atoms on the neighbouring carbon atom.

Question 24

What can 1H NMR low resolution do?

Answer 24

1H NMR spectra can be sketched for any given compound
- tells us how many different chemical environments the protons exist in
- How many protons are in each environment
- the type of proton environment

Question 25

What are drugs?

Answer 25

Drugs are substances that alter the biochemical processes in the body
Drugs that have beneficial effects are used in medicines.

Question 26

How do drugs work?

Answer 26

Drugs generally work by binding to specific protein molecules. These protein molecules
can be found on the surface of a cell (receptor) or can be specific enzyme molecules within
a cell.

Question 27

What do medicines contain?

Answer 27

• the drug
• ingredients such as fillers to add bulk or sweeteners to improve the taste

Question 28

What is a structural fragment of a drug?

Answer 28

The structural fragment of a drug molecule that allows it to form interactions with a receptor binding site or to an enzyme active site normally consists of different functional groups correctly orientated with respect to each other.

Question 29

What does the wavelengths of infrared absorbed depend on?

Answer 29

the type of atoms that make up the bond and the strength of the bond