Module 3 thingz

Question 1

What is a covalent bond?

Answer 1

The bond formed when one electron on each atom is shared with the other

Question 2

How do you find the formal charge?

Answer 2

Formal charge: Valence electrons - (bonds + dots)

Question 3

How are sigma bonds made?

Answer 3

e.g. In h2 when two ls electrons end up in an orbital made from the overlap of the two 1s orbitals –> This is a sigma oribtal

Question 4

What is a thiol functional group?

Answer 4

R-SH

Question 5

What are constitutional isomers?

Answer 5

Isomers with a different order of attachment of their atoms

Question 6

What are stereoisomers?

Answer 6

Isomers with the same order of attachment of atoms, but a different orientation of their atoms in space

Question 7

What are enantiomers?

Answer 7

Steroisomers that are non superimposable mirror images of each other

Question 8

What are diastereomers?

Answer 8

Stereoisomers that are not mirror images

Question 9

What is the Z stereoisomer?

Answer 9

Bonds at a double bond are at the same side

Question 10

What is the E stereosiomer?

Answer 10

Bonds at a double bond are on different sides

Question 11

What are the E and Z stereoisomers rules?

Answer 11

• Priories assigned based on atomic number
• Where two atoms are the same, consider what is attached
• One of higher takes priorities over may of lower
• Double bonds treated at two single bonds

Question 12

What is a chiral molecule?

Answer 12

Not superimposable on its mirror image is described as
being chiral. They contain 4 different groups attached.
–> Enantiomers

Question 13

How do we distinguish between enantiomers?

Answer 13

Their interactions with plane polarised light.

–> They rotate plane polarised light in opposite directions

Question 14

What is a racemic mixture?

Answer 14

A 1:1 mixture of two enantiomers
(+-)
–> Has no specific rotation, as they cancel out, so are not optically active

Question 15

What are the rules for naming enantiomers?

Answer 15

1. Identify the asymmetric C atom
2. Assign priorites to the four molecules
3. Draw the structure of the molecule viewed down the bin from C to to the lowest priority
4. IF the arrangement of the remaining bonds from 1 to 3 appear clockwise assign R, if they appear anticlockwise assign S

Question 16

What are diatereoisomers?

Answer 16

Occur in compounds with more than one asymmetric carbon (have a maximum of 2^n stereoisomers)
–> They do not have similar physical properties

Question 17

What are organic molecules?

Answer 17

They are carbon based

Question 18

What is homolytic bond cleavage?

Answer 18

One electron is transferred to each of the two atoms. The species generation are radicals (X. and Y.)

Question 19

What is heterolytic bond cleavage?

Answer 19

Two electrons are transferred from the bond to one atom

Obtain charged intermediates

Question 20

What is a Sn2 Nucleophilic sub reaction?

Answer 20

X leaves and Nu:- attaches
rate = k [C-X] [Nu:-]
–> Strong Nu can make up for a poor leaving group
–> Good Nu is essential

Question 21

What are some features of the Sn2 transition state?

Answer 21

• Effective collision has taken place
• Corresponds to maximum free energy
• Nu and the X both loosely bound to C (partial bond)
• If its activation energy is high, reaction will be slow

Question 22

What is a Sn1 reaction?

Answer 22

X leaves and then Nu:- attaches
rate = k[C-X]
–> Slow first step
–> Carbocation formed as the reaction intermediate, will react with any Nu
–> Major product from this reaction with most abundant Nu
–> Transition states with one extended bond
–> Strong leaving group is essential, strong Nu is not essential

Question 23

What do Sn2 reactions produce and why?

Answer 23

One product which has inversion of stereochemistry, as Nu approaches from the back of the molecule, pushing the other atoms forward

Question 24

What does the Sn1 reaction produce and why?

Answer 24

Two products with retention and inversion of stereochemistry
–> Nucleophile can approach and attach to planar intermediate (carbocation) from either side

Question 25

What determined weather a reaction goes via Sn1 or Sn2?

Answer 25

Sn2

• -> methyl or primary (Easy if C groups are small)
• -> Fast if nucleophile is not sterically hindered

Sn1

• -> Rate of reaction increases with methyl < 1 < 2 < 3
• -> Alkyl groups are e donating (stabilise intermediate)
• -> Diminishes charge on C

Question 26

Why is sn1 fast in polar solvents?

Answer 26

As the transition state can be stabilised by polar effect at C (positive) and H-bonding to leaving group (negative)

Question 27

Why is Sn2 not fast in polar solvents?

Answer 27

The solvent will make the Nu more sterically hindered by bonging to it through H bonding and then it cannot attack in a Sn2 reaction

Question 28

What are elimination reactions mechanisms determined by?

Answer 28

Base strength
strong base = E2
weak base = E1

Question 29

What is a E1 reaction?

Answer 29

rate = k[C-Cl]
Two step process
--> Strong base is not required
--> H-bonding solvents promote reaction
--> E1 most common when leaving group is tertiary

Question 30

What is a E2 reaction?

Answer 30

rate = k[CH3][OH-]

• -> Halide and base involved in single, rate determining step
• -> Must have a strong base e.g. OH
• -> Possible for primary, secondary or tertiary compounds

Question 31

What are the differences between Sn2 and E2?

Answer 31

Sn2

• • Requires backside attack
• • Difficult if reaction centre crowded
• -> rate order 1 > 2 > 3

E2

• • Easily accessible H+ is removed
• • Little difference in ease of H+ removal for 1, 2 and 3

Question 32

What are the steps of an addition reaction?

Answer 32

1. HBr dissociates into H+ and Br-
2. Slow addition of an H+ electrophile to the electron rich double bond (rate determining)
3. Fast attack by a Nu at the carbocation intermediate
   rate = k[H+][CH2=CH2]

Question 33

What can a Br2 addition produce?

Answer 33

A bromonium carbocation intermediate

Question 34

Are 1 prime or 2 prime carbocations more stable?

Answer 34

2 prime as they have more alkyl groups to stablise the intermediate