Molecular Shape & Reactivity

Question 1

What is drug structure controlled by?

Answer 1

Structure + orientation of functional groups

Question 2

What is functional group structure controlled by?

Answer 2

Electronic arrangement
= individual atoms
= valency
= hybridisation

Question 3

Describe ethane

Answer 3

C2H6
2 carbons = both tetrahedral 
C-H  formed by overlap sp3 C + H s orbital
C-C formed by overlap of 2 C sp3 
109.5 degrees

Question 4

How can ring structures be simply made?

Answer 4

By having 2 sp3-sp3 C-C bonds

Question 5

Describe bonds in ethene

C2H4

Answer 5

Each C has 4 bonds
Hybridisation of s with 2x 2p = 1 p orbital left non-hybridised
120 degrees

Question 6

What is e- repulsion minimised by in ethene?

Answer 6

3x sp2 orbitals

point corners of equilateral triangle

Question 7

Where is the unhybridised p orbital?

Answer 7

Perpendicular to plane

Question 8

How is the double bond formed in ethene?

Answer 8

1st = overlap of sp2 from each C = sigma bond
2nd = side to side overlap of unhybridised p orbital = pi bond

Question 9

Describe the bonds in ethyne

C2H2

Answer 9

Triple bond

Hybridisation of only 2 orbitals (sp) = 2 p orbitals left (2p)

Question 10

Describe sp orbitals in ethyne

C2H2

Answer 10

2 side to side overlap = 2 pi bonds

C form 1 sigma bond

Question 11

Describe bonding in methyl cation

Answer 11

C positively charged
Bonded to 3x H
sp2 hybridisation
Non-hybridised p remains empty + perpendicular to plane

Question 12

Describe bonding in methyl radical

Answer 12

C bonded to 3x H

sp2 hybridised

Question 13

What is the difference between methyl cation and methyl radical?

Answer 13

Radical has one more e- that resides in non-hybridised p orbital

Question 14

Describe bonding in methyl anion

Answer 14

C bonded to 3x H
3 bonding pairs + 1 L.P
Negatively charged C = sp3
L.P resides in sp3

Question 15

How are the 3 bonds formed in methyl anion?

Answer 15

sp3-s overlap

Question 16

What does nitrogen hybridise to form?

Answer 16

4x sp3 orbitals

1 = occupied by 2x non-bonding e-

Question 17

How are N-H formed?

Answer 17

sp3-s overlap

Question 18

Describe bonding in amines

Answer 18

N has same geometry as in NH3

C-N bonds formed by sp3-sp3 overlap

Question 19

What can Hs be replaced by in amines?

Answer 19

1 alkyl or aryl group = primary amine
2 alkyl or aryl group = secondary amine
3 alkyl or aryl group = tertiary amine

Question 20

Why can H2O + NH3 act as bases (nucleophiles)?

Answer 20

Use L.P to bond H+

Formal charge of +1

Question 21

What is the bond angle of N-H?

Answer 21

109.5 degrees

Question 22

How are O-H bonds formed?

Answer 22

sp3-s orbital overlap

Question 23

How are C-O bonds formed?

Answer 23

sp3-sp3 orbital overlap

Question 24

How are S-H bonds formed?

Answer 24

sp3-s orbital overlap

Question 25

How are S-C bonds formed?

Answer 25

sp3-sp3 orbital overlap

Question 26

What can O + N form?

Answer 26

Double bonds

Question 27

What can N form?

Answer 27

Triple bonds

Question 28

What does phosphorus use for bonding?

Answer 28

3rd shell e-

Question 29

Why does phosphorus use 3rd shell e- for bonding?

Answer 29

Smaller energy gap between the occupied 3p orbitals + vacant 3d orbitals

Question 30

Where is the bond formed in HF?

Answer 30

Between H 1s orbital + F 2sp3 orbital

Question 31

Where is the bond formed in HCl?

Answer 31

Between H 1s + Cl 3sp3

Question 32

What happens to e- density in region of s-sp3 overlap as size of hydrogen halide increases?

Answer 32

Decreases | = H-X bond becomes weaker

Question 33

What happens to hydrogen halide bond strength down the group?

Answer 33

Decreases

Question 34

How is the C-X bond formed in alkyl halides?

Answer 34

sp3-sp3 orbital overlap

Question 35

What happens as size of halogen increased in alkyl halides?

Answer 35

sp3 orbital from higher shell used in bond decreased in e- density = longer + weaker

Question 36

What is electronegativity?

Answer 36

Tendency of an atom to pull bonding e- towards itself

Question 37

What is a polar covalent bond?

Answer 37

Covalent bond in which e- distribution between atom is unsymmetrical

Question 38

Describe inductive effect

Answer 38

Atom's ability to polarise a bond | e- -attracting or e- -withdrawing effect transmitted through S bonds

Question 39

What do electronegative elements have?

Answer 39

e- -withdrawing inductive effect

Question 40

What is dipole moment a measure of?

Answer 40

Net polarity of a molecule

Question 41

What are covalent compounds composed of?

Answer 41

Discrete molecules

Question 42

What are the 4 main type of interactions?

Answer 42

Van der Waals Dipole-dipole interactions Hydrogen bonding Ion-ion

Question 43

Describe Van Der Waals

Answer 43

Weak interactions caused by momentary change in e- density | Present in non-polar compounds

Question 44

What determines the strength of Van Der Waals?

Answer 44

SA of molecule

Question 45

What is polarizability?

Answer 45

Measure of how e- cloud around an atom responds to changes in its electronic environment

Question 46

What are dipole-dipole interactions?

Answer 46

Attractive forces between the permanent dipoles of 2 polar molecules

Question 47

Describe H bonding

Answer 47

Most important | Short range, directional, inter or intramolecular no-bonded interaction

Question 48

Describe how H bonding works

Answer 48

Non-bonded interaction between H atom bonded to electronegative atom + another electronegative atom

Question 49

What is the e- deficient H called?

Answer 49

Hydrogen bond donor

Question 50

What is the e- rich H called?

Answer 50

Hydrogen bond acceptor

Question 51

What is H bonding important for?

Answer 51

Drug molecule - receptor interactions

Question 52

What are the conformational strains for alkanes? | Ethane

Answer 52

Staggered | Eclipsed

Question 53

What is the torsional strain? | Alkanes

Answer 53

Repulsion felt by bonding e- as they pass close to bonding e- of an adjacent substituent

Question 54

What is conformational analysis? | Alkanes

Answer 54

Investigation of a compound's conformations + their relative stabilities

Question 55

Describe conformation of butane

Answer 55

Rotation can occur around all 3 bonds Staggered conformers of equal energy Eclipsed conformers of equal, BUT higher energy

Question 56

What does rotation around the C2-C3 bond of butane give?

Answer 56

``` 6 important conformations Staggered gauche Eclipsed Staggered anti Eclipsed Staggered gauche Eclipsed ```

Question 57

What is gauche conformation compared to anti?

Answer 57

Less stable due to repulsive Van Der Waals between 2 CH3

Question 58

Describe conformation of cycloalkanes

Answer 58

Molecules not static = rotation around each C-C continuous = many interconverting conformers can exist at any 1 time =separation of conformers not possible

Question 59

Why is separation of conformers not possible in cycloalkanes?

Answer 59

Due to paid speed of inter-conversion

Question 60

What is the relative no. of molecules in a particular conformation of cycloalkanes dependent on?

Answer 60

Conformer stability with majority in staggered conformations

Question 61

What is the difference with cycloalkane formation?

Answer 61

Ring rotation is limited = molecules twist + bend to minimise source of strain

Question 62

What are the different sources of strain?

Answer 62

Angle strain Torsional strain Steric strain

Question 63

What is angle strain?

Answer 63

Deviation from ideal tetrahedral bond angle

Question 64

What is torsional strain?

Answer 64

Repulsion of proximate bonding e-

Question 65

What is steric strain?

Answer 65

Where atoms/groups approach too closely

Question 66

Describe conformations of cyclopropane

Answer 66

Torsional strain = C-H bonds eclipsed | Angle strain = orbitals overlap at slight angle

Question 67

What does the conformations do to cyclopropane?

Answer 67

Weaker + more reactive than typical alkane bonds

Question 68

Describe conformations of cyclobutane

Answer 68

Torsional strain= 1 C lies 25 degrees above plane of other 3

Question 69

Is the angle strain of cyclobutane less or more than cyclopropane?

Answer 69

MORE | = larger number of ring H

Question 70

Describe conformations of cyclopentane

Answer 70

Twists to non-planar conformation = C-C 108 degrees = C5 out of plane

Question 71

Is the angle strain of cyclopentane less or more than cyclobutane + cyclopropane?

Answer 71

LESS

Question 72

What would the planar cyclopentane exhibit?

Answer 72

Minimal angle strain | Large torsional strain = H eclipsed

Question 73

Describe conformations of cyclohexane

Answer 73

No angular strain = C-C-C 111.5, close to 109.5 | No torsional strain = neighbouring C-H staggered

Question 74

What conformation does cyclohexane adopt?

Answer 74

Chair conformation/ boat conformation

Question 75

What can happen to chair conformations?

Answer 75

Interconvert = exchanging axial + equatorial positions

Question 76

Describe monosubstituted cyclohexane conformations

Answer 76

2 chair conformations not equal stability | Bulkier substituent = greater preference for equatorial substitution

Question 77

Why is there an energy difference between axial + equatorial conformations?

Answer 77

Steric strain caused by 1,3-diaxial interactions

Question 78

Describe disubstituted cyclohexane conformations

Answer 78

1,2-dimethylcyclohexane Trans-isomer 2 methyl groups on opposite faces Exist in diequatorial conformation

Question 79

What are all substituents in glucose?

Answer 79

Equatorial

Question 80

What are all substituents in mannose?

Answer 80

1 OH group axial | = mannose more strained