Chapter 7 Day 22

Question 1

When can an alkyl halide undergo a substitution reaction?

Answer 1

When reacted with a nucleophilic reagent

Question 2

When can an alkyl halide undergo an elimination reaction?

Answer 2

When reacted with a basic reagent

Question 3

When can an alkyl halide undergo both a substitution reaction and an elimination reaction?

Answer 3

When the reagent can act as both a nucleophilic reagent and a basic reagent. The two pathways will compete with each other

Question 4

What makes a good leaving group?

Answer 4

A good leaving group is a conjugate base of a strong acid. This means that it is a weak base (strong acid-weak base)

Question 5

What are the steps to naming a molecule?

Answer 5

1. Identify the name and the parent chain
2. Identify the name of the substituents
3. Assign a number to each substituent
4. Assemble the name alphabetically
   (5. ) If there is a stereo-center, you must give a letter (R or S)

Question 6

What is an alpha carbon?

Answer 6

The carbon directly connected to the halide

Question 7

What types of alkyl halides are there, in regards to the branching at the alpha carbon?

Answer 7

• Primary (1 alkyl group)
• Secondary (2 alkyl groups)
• Tertiary (3 alkyl groups)

Question 8

What is required when a molecule undergoes a substitution reaction?

Answer 8

• Loss of leaving group

- Nucleophilic attack

Question 9

What are the two possible mechanisms of a substitution reaction?

Answer 9

• A concerted reaction (SN2 mechanism)

- A stepwise reaction (SN1 mechanism)

Question 10

What are the main ideas of an SN2 mechanism?

Answer 10

• Includes one group being substituted for another group
• Occurs when the alkyl halide is being treated with a (strong) nucleophile (usually charged)
• Backside attack
• The bond of a leaving group is broken at the same time the bond of the nucleophile is being made (concerted process)
• Rate of reaction depends on the concentration of both molecules (substrate and nucleophile, bimolecular dependent)
• The halogen is expelled as an anion
• Has 2 curved arrows
• If this occurs at a chiral center (4 different substituted C), the configuration gets inverted (inversion of stereochemistry- R would turn into S, S would turn into R)
• Methyl groups & Primary group are more reactive (less statically hindered)
• Alpha substituents have a significant effect on rate, while beta substituents have a slight effect on rate (branching hinders the backside attack of nucleophile, causing a slower rate of reaction)

Question 11

What are the main ideas of an SN1 mechanism?

Answer 11

• Includes one group being substituted for another group
• Occurs when the alkyl halide is being treated with a nucleophile
• The leaving groups leave first
• A carbocation intermediate is formed
• Nucleophilic attack occurs
• Rate of reaction only depends on the concentration of one molecule (substrate)
• Loss of leaving group is the limiting step

Question 12

What are common strong nucleophiles?

Answer 12

I-, Br-, Cl-, HS-, RS-, HO-, RO-, NC- (usually anions & polarizable atoms)

Question 13

What are common weak nucleophiles?

Answer 13

H2O, ROH (usually not charged such as water and alcohols)