Review Chap 5-7

Question 1

What would NaNH2 (or a similar molecule) be used for in a reaction?

Answer 1

To strip a triple bondC-H -> Triple bondC: (E2 reaction)

Question 2

What would CH3Br (or any CH3(halogen)) be used for in a reaction?

Answer 2

To donate a methyl group to a negatively charged C

Question 3

What would CH3CH2Br (or any CH3CH2(halogen)) be used for in a reaction?

Answer 3

To donate an ethyl group to a negatively charged C

Question 4

What would Li/NH3 (or Na/NH3) be used for in a reaction?

Answer 4

Weak hydrogenation, triple bond -> TRANS double bond

Question 5

What would H2/Pd(or any other metal)/CaCO3 (or Ni2B) be used for in a reaction?

Answer 5

Weak hydrogenation, triple bond -> CIS double bond

Question 6

What would H2/Pd(or any other metal) be used for in a reaction?

Answer 6

Without the presence of CaCO3, Strong hydrogenation, triple bond -> single bond

Question 7

What would H2SO4 (or any other strong acid) be used for in a reaction?

Answer 7

Used in E1 reactions to protonate the OH group

Question 8

What would a strong base (HO-, RO-, H-, NH2-, C-) be used for in a reaction?

Answer 8

Used in an E2 reaction to pull a hydrogen and form a double bond

Question 9

What would a weak base be used for in a reaction?

Answer 9

If also a weak nucleophile, an S1 reaction

Question 10

What would a weak nucleophile be used for in a reaction?

Answer 10

S1 reaction(must allow the carbocation to form)

Question 11

What is indicated by the use of KOC(CH3)3?

Answer 11

Bulky base. Normally in E2 reaction you form the most substituted product. In this case you would form the least substituted product

Question 12

Which reactions could have carbocation intermediates?

Answer 12

SN1 and E1

Question 13

What is a Vicinal Dihalide?

Answer 13

Halogens on adjacent carbons

Question 14

What is a meso compound?

Answer 14

Has two or more chiral centers, achiral (due to the plane of symmetry), and optically inactive

Question 15

What is the equation for the max # possible stereoisomers?

Answer 15

2^(#chiral centers)

Question 16

What is a 1,2 - Hydride shift (or 1,2-Methyl shift and when would it occur?

Answer 16

Moves hydride (or methyl) to an adjacent carbocation. Only happens if the molecule gains stability through resonance or through an increase in substituents

Question 17

How do you determine if a molecule is chiral?

Answer 17

Chiral molecules have enatiomers (non-superimposable mirror images), no place of symmetry. You can test this via a 2 group switch

Question 18

What are the rules for the removal of a hydrogen in a alkene/yne synthesis reaction (E2)?

Answer 18

Must be adjacent, opposite side

Question 19

What is the relationship in physical properties between two enantiomers(mirror image non-superimposable)?

Answer 19

Enantiomers have the same physical properties, they rotate the plane of light with the same rotation but opposite sign

Question 20

What is the mechanism for a SN1 reaction?

Answer 20

Three step reaction: 1)Leaving group leaves, formation of the carbocation 2)Nucleophilic attack of the carbocation (attachment) 3)Deprotonation by a base. May also be accompanied by a carbocation rearrangement between step 1,2 if increases the stability, may also be accompanied by the formation of a better leaving group (addition of hydrogen to OH to form water, a good leaving group)

Question 21

What is the mechanism for an SN2 reaction?

Answer 21

One step reaction: The nucleophile attacks at the leaving group’s carbon at the same time the leaving group leaves. There is a transition state with both the leaving group and the nucleophile partially bonded to the carbon. The nucleophile attacks from the opposite side if there is one

Question 22

What is the mechanism for an E1 reaction?

Answer 22

Two step reaction: 1)Loss of a leaving group to form a carbocation intermediate 2)Nucleophilic removal of a hydrogen to form a double bond. May also be accompanied by a carbocation rearrangement. If an alcohol reaction, it involves the addition of a hydrogen to the OH group to form water, a better leaving group. The strong acid used is a catalyst because you get it back

Question 23

What is the mechanism for an E2 reaction?

Answer 23

One step reaction: The nucleophile removes a hydrogen adjacent and to the opposite side as the carbocation, which was formed by the removal of a leaving group (Same as an S2 reaction but forms a double bond (nucleophilic removal of a hydrogen instead of a nucleophilic attachment to a carbocation))

Question 24

What is the relationship in physical properties between two diastereomers(non-superimposable not mirror images)?

Answer 24

Diastereomers have different physical properties

Question 25

How do you tell if a molecule is optically active?

Answer 25

It is chiral

Question 26

How do you tell the speed of a reaction/ whether it favors SN1 or SN2?

(type of substrate, reactant, solvent)

Answer 26

3prime favors SN1, 1prime, methyl favors SN2
Weak Nucleophile favors SN1, strong nucleophile favors SN2
Aprotic favors basicity (F->I-), Protic favors nucleophilicity (I->F-)
A good leaving group is EN-, preferably large atom

Question 27

The favored mechanism (major product in a mechanism) will be

Answer 27

More stable. (Prime, resonance, more substitutions(alkene) (if not a bulky base)

Question 28

What are the E, Z nomenclature rules?

Answer 28

Same rules as R and S for priority. E is trans, Z is cis

Question 29

Describe the relationship between heat of hydrogenation/combustion and stability

Answer 29

The more stable the less heat of hydrogenation/combustion

Question 30

Describe the synthesis of alkynes from vicinal dihalides

Answer 30

a compound that has two halogens on adjacent carbons goes through a double dehydrohalogenation (2 e2 reactions)

Question 31

Describe the synthesis of alkynes from geminal dihalides

Answer 31

a compound that has two halogens on the same carbon goes through a double dehydrohalogenation (2 e2 reactions)

Question 32

How is nucleophilicity determined in polar protic solvents?

Answer 32

Follows level of solvation, smaller molecules are solvated more

Question 33

How is nucleophilicity determined in polar aprotic solvents?

Answer 33

Since only cations are solvated, it follows basicity