unit 3 chemistry cover

Question 1

What does the combination of two atomic orbitals result in?

Answer 1

The formation of a bonding molecular orbital and an antibonding orbital. The bonding molecular orbital encompasses both nuclei.

Question 2

What is the basis of bonding between atoms?

Answer 2

The attraction of the positively charged nuclei and the negatively charged electrons in the bonding molecular orbital.

Question 3

What happens in a non polar covalent bond?

Answer 3

The bonding molecular orbital is symmetrical about the midpoint between two atoms.

Question 4

What do polar covalent bonds result from?

Answer 4

Bonding molecular orbitals that are asymmetric about the midpoint between two atoms.

Question 5

Where are sigma molecular orbitals?

Answer 5

Along the axis of the covalent bond.

Question 6

Where are pi molecular orbitals?

Answer 6

They lie perpendicular to the axis of the covalent bond.

Question 7

What are the electrons in the benzene system?

Answer 7

Delocalised.

Question 8

What is a chromophore?

Answer 8

A group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum.

Question 9

How can monohaloalkanes form alkenes?

Answer 9

By taking part in elimination reactions using a strong base, such as potassium or sodium hydroxide in ethanol.

Question 10

What mechanisms can monohaloalkanes take part in for nucleophilic substitution reactions?

Answer 10

SN1 and SN2

Question 11

What is SN1?

Answer 11

A nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate.

Question 12

What is SN2?

Answer 12

A nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state.

Question 13

What is elemental microanalysis used for?

Answer 13

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 14

What can elemental microanalysis be determined from?

Answer 14

♦ combustion product masses
♦ percentage product by mass

Question 15

What can mass spectrometry be used to determine?

Answer 15

The accurate gram formula mass (GFM) and structural features of an organic compound.

Question 16

What happens in mass spectrometry?

Answer 16

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.

Question 17

How is a mass spectrum obtained?

Answer 17

Showing a plot of the relative abundance of the ions detected against the mass-to-charge (m/z) ratio.

Question 18

What is infrared spectroscopy used for?

Answer 18

To identify certain functional groups in an organic compound.

Question 19

In infrared spectroscopy, what happens?

Answer 19

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 20

What can proton nuclear magnetic resonance spectroscopy (proton NMR or 1H NMR) give information about?

Answer 20

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 21

How do 1H nuclei behave?

Answer 21

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 22

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

Answer 22

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 23

In a 1H NMR spectrum, what is the chemical shift, δ , (peak position) related to?

Answer 23

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

Question 24

How can 1H NMR spectra be obtained?

Answer 24

Using low-resolution or high- resolution NMR.

Question 25

What are many drugs that act on enzymes classified as?

Answer 25

Enzyme inhibitors and act by binding to the active site of the enzyme and blocking the reaction normally catalysed there.