Review Chap 5-7 Flashcards
What would NaNH2 (or a similar molecule) be used for in a reaction?
To strip a triple bondC-H -> Triple bondC: (E2 reaction)
What would CH3Br (or any CH3(halogen)) be used for in a reaction?
To donate a methyl group to a negatively charged C
What would CH3CH2Br (or any CH3CH2(halogen)) be used for in a reaction?
To donate an ethyl group to a negatively charged C
What would Li/NH3 (or Na/NH3) be used for in a reaction?
Weak hydrogenation, triple bond -> TRANS double bond
What would H2/Pd(or any other metal)/CaCO3 (or Ni2B) be used for in a reaction?
Weak hydrogenation, triple bond -> CIS double bond
What would H2/Pd(or any other metal) be used for in a reaction?
Without the presence of CaCO3, Strong hydrogenation, triple bond -> single bond
What would H2SO4 (or any other strong acid) be used for in a reaction?
Used in E1 reactions to protonate the OH group
What would a strong base (HO-, RO-, H-, NH2-, C-) be used for in a reaction?
Used in an E2 reaction to pull a hydrogen and form a double bond
What would a weak base be used for in a reaction?
If also a weak nucleophile, an S1 reaction
What would a weak nucleophile be used for in a reaction?
S1 reaction(must allow the carbocation to form)
What is indicated by the use of KOC(CH3)3?
Bulky base. Normally in E2 reaction you form the most substituted product. In this case you would form the least substituted product
Which reactions could have carbocation intermediates?
SN1 and E1
What is a Vicinal Dihalide?
Halogens on adjacent carbons
What is a meso compound?
Has two or more chiral centers, achiral (due to the plane of symmetry), and optically inactive
What is the equation for the max # possible stereoisomers?
2^(#chiral centers)
What is a 1,2 - Hydride shift (or 1,2-Methyl shift and when would it occur?
Moves hydride (or methyl) to an adjacent carbocation. Only happens if the molecule gains stability through resonance or through an increase in substituents
How do you determine if a molecule is chiral?
Chiral molecules have enatiomers (non-superimposable mirror images), no place of symmetry. You can test this via a 2 group switch
What are the rules for the removal of a hydrogen in a alkene/yne synthesis reaction (E2)?
Must be adjacent, opposite side
What is the relationship in physical properties between two enantiomers(mirror image non-superimposable)?
Enantiomers have the same physical properties, they rotate the plane of light with the same rotation but opposite sign
What is the mechanism for a SN1 reaction?
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)
What is the mechanism for an SN2 reaction?
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
What is the mechanism for an E1 reaction?
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
What is the mechanism for an E2 reaction?
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))
What is the relationship in physical properties between two diastereomers(non-superimposable not mirror images)?
Diastereomers have different physical properties
How do you tell if a molecule is optically active?
It is chiral
How do you tell the speed of a reaction/ whether it favors SN1 or SN2?
(type of substrate, reactant, solvent)
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
The favored mechanism (major product in a mechanism) will be
More stable. (Prime, resonance, more substitutions(alkene) (if not a bulky base)
What are the E, Z nomenclature rules?
Same rules as R and S for priority. E is trans, Z is cis
Describe the relationship between heat of hydrogenation/combustion and stability
The more stable the less heat of hydrogenation/combustion
Describe the synthesis of alkynes from vicinal dihalides
a compound that has two halogens on adjacent carbons goes through a double dehydrohalogenation (2 e2 reactions)
Describe the synthesis of alkynes from geminal dihalides
a compound that has two halogens on the same carbon goes through a double dehydrohalogenation (2 e2 reactions)
How is nucleophilicity determined in polar protic solvents?
Follows level of solvation, smaller molecules are solvated more
How is nucleophilicity determined in polar aprotic solvents?
Since only cations are solvated, it follows basicity
