Bio-molecules basics

Question 1

Give the evidence for quantization of energy

Answer 1

When heat/electrical energy is applied to elements in gaseous form emission of radiation at discrete wavelengths is observed

Question 2

What must the difference in electronegativity be for a bond to be considered covalent?

Answer 2

Less than 1.7

Question 3

What are the difference in electronegativity be for a bond to be considered ionic?

Answer 3

Greater than or equal to 1.7

Question 4

What must be true of electrons in a covalent bond?

Answer 4

For a covalent bond to be formed the number of electrons in a bonding orbital must be greater than the number of electrons in an anti-bonding orbital

Question 5

Is an anti-bonding orbital higher or lower energy?

Answer 5

Higher

Question 6

Is a bonding orbital higher or lower energy?

Answer 6

Lower

Question 7

When are sigma bonds formed?

Answer 7

When one pair of electrons are shared between 2 atoms

Question 8

What is a non-bonding orbital?

Answer 8

An orbital which contains a pair of electrons which is not undergoing bonding (e.g. a lone pair)

Question 9

How is dependence of dispersion forces calculated?

Answer 9

1/r⁶

Question 10

How can dispersion forces be maximised?

Answer 10

When opposing surfaces are complementary in shape

Question 11

Over what kind of distance do dispersion forces act?

Answer 11

Close distances

Question 12

How strong are dispersion forces?

Answer 12

Very weak

Question 13

When are dipole-dipole interactions strongest?

Answer 13

When the molecules have permanent dipoles

Question 14

How is dependence of dipole-dipole interactions calculated?

Answer 14

1/r⁶

Question 15

What does the value of dependence represent?

Answer 15

The distance over which a force is effective over

Question 16

Over what kind of distance is steric repulsion effective over?

Answer 16

very short distances

Question 17

What is the approximate dependence calculation for steric repulsion?

Answer 17

1/r¹²

Question 18

What is steric repulsion?

Answer 18

The repulsion atoms experience when brought very close together due to the negative charge electrons in the outer shell of atoms

Question 19

What forces do van der Waals forces take into account?

Answer 19

• Dispersion forces
• Dipole-dipole interactions
• Steric repulsion

Question 20

What is the stereochemistry of the products of an SN2 reaction?

Answer 20

Produces 100% of one enantiomer

Question 21

What is the stereochemistry of the products of SN1 reaction?

Answer 21

Produces 50% of 1 enantiomer and 50% of the other enantiomer

Question 22

What is generally the rate limiting step of SN1 reactions?

Answer 22

The formation of the intermediate

Question 23

What is the stereochemistry of the products of SN2 reactions?

Answer 23

Inverted

Question 24

Compare the types of nucleophiles required for SN1 and SN2 reactions

Answer 24

Weak nucleophiles are needed for SN1 reactions whilst strong nuclephiles are needed for SN2 reactions

Question 25

What is the oxidation state of oxygen in peroxides?

Answer 25

-1

Question 26

What is bond length determined by?

Answer 26

* atomic radii of atoms joined by the bond * type of covalent bond

Question 27

Why do double and triple bonds have shorter bond lengths?

Answer 27

Increased electron density affordsa greater attractive force on the nuclei of bonded atoms

Question 28

Do atomic orbitals exhibit the geometries predicted by VSEPR?

Answer 28

No

Question 29

How many electrons can an f orbital contain?

Answer 29

Up to 14

Question 30

Why is the arrangement of valence electrons as predicted by VSEPR?

Answer 30

Due to the hybridisation of atomic orbitals

Question 31

Which orbitals hybridise to form sp³

Answer 31

one s orbital and 3 p orbitals hydridise to form 4 sp³ orbitals

Question 32

What configuration do 4 sp³ orbitals produce?

Answer 32

Tetrahedral

Question 33

What are the 2 circumstances when there is restricted bond rotation of single bonds?

Answer 33

* steric hindrance * Delocalised systems

Question 34

Why can mutiple bonds not rotate?

Answer 34

Rotating effectively disrupts the p-orbital overlap 'breaking' the pi bond whicn is energetically unfavourable

Question 35

When does diastereomerism occur?

Answer 35

When 2 or more stereoiosmers of a compound have different configurations at one or more of the equivalent stereocentres

Question 36

What is conformational isomerism?

Answer 36

A form of stereoisomerism in which the isomers can be interconverted exculsively by rotations about formally single bonds

Question 37

What is a rotamer?

Answer 37

Any of a set of conformers that arise from restricted rotation around a single bond