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Orgo. I > Quiz #3 > Flashcards

Quiz #3 Flashcards

1
Q

Which alkene is more stable, trans or cis?

A

Trans, strain is reduced

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2
Q

How do you assign priority under the E, Z system?

A

Same as under the R, S system

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3
Q

Which alkene has less strain, E or Z?

A

E

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4
Q

Which alkene has more strain, E or Z?

A

Z

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5
Q

Which carbocation is the most stable?

A

Tertiary

Bonded to 3 other non H groups

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6
Q

Which carbocation is the least stable?

A

Methyl carbocation

Bonded to 3 H’s, no C/R

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7
Q

Hyperconjugation

A

When electrons from adjacent C-H bonds overlap with the unhybridized p-orbital of the carbocation for stability

This is the phenomenon that stabilizes carbocatioins

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8
Q

Why will a reaction’s major product always be the one with the more stable carbocation intermediate?

A

Regioselectivity

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9
Q

Regioselectivity

A

The preference of chemical bonding/breaking in one direction over all other possible directions.

Follows Markovnikov’s rule

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10
Q

Markovnikov’s rule

A

Predicts the regiochemistry of an HX addition to unsymmetrically substituted alkenes.

X bonds to the most substituted carbon. H bonds to the carbon with the most hydrogens.

This gives the best carbocation stability, and is the reason why regioselectivity is a thing

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11
Q

1,2 Shift

A

When an atom or group, including its bonding electrons, moves to an adjacent electron deficient atom.

When doing this, move the smallest atom or group possible

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12
Q

Stereoselective reactions

A

Reactions in which one stereoisomer is formed in preference to all others

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13
Q

Catalyst

A

A reagent that gets consumed and remade throughout a reaction. It increases the rate of the reaction

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14
Q

Concerted mechanism

A

Multiple bonds are being broken and/or made within the same reaction step, happens all at the same time

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15
Q

Nucleophiles

A

Regions of electron density, capable of donating a pair of electrons

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16
Q

What things can act as nucleophiles?

A

Lone pairs and pi bonds

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17
Q

Electrophiles

A

Electron poor regions, capable of accepting a pair of electrons when attacked by a nucleophile

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18
Q

What things can act as electrophiles?

A

Cations (positively charged atoms), cations that are formed only as part of a resonance structure, and the atom directly bonded to an electronegative atom (so in O-C-C, the middle C is an electrophile)

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19
Q

What does nucleophilicity measure?

A

How quickly a nucleophile will attack an electrophile. It’s a kinetic phenomenon

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20
Q

What are the 4 types of arrow pushing patterns for ionic rxn mechanisms?

A

Nucleophilic attack

Proton transfer

Loss of a leaving group

Carbocation rearrangement

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21
Q

Nucleophilic attack

A

Electron dense nucleophile attacks the electron poor electrophile, forming a new bond and attaching the nucleophile to the electrophile

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22
Q

Proton transfer

A

An electron dense base steals an acidic proton

Results in the base gaining an H and the acid losing an H, two ions are generated

23
Q

Loss of a leaving group

A

Something detaches from a larger molecule. A single (sigma) bond is broken

24
Q

Carbocation rearrangement

A

The placement of a molecule’s electron deficient center (positive charge) changes. Atoms/substituent groups can be rearranged when doing so

25
When drawing an energy diagram, what do the humps correspond to?
Each hump is a step in the mechanism process, a transition state The highest hump requires the most activation energy. This is the process's rate determing step
26
Do factors that speed up the rate of the non rate determining steps affect the reaction's overall speed?
No Only factors affecting the rate determining step can affect the reaction's overall speed
27
When drawing an energy diagram, what do the valleys correspond to?
Intermediate molecules
28
Can carbocations be part of a reaction's starting materials?
No They are intermediates of reactions, and are very short lived
29
Can carbocations be a reaction's ending material?
No They cannot be products because they are too short lived. They are reaction intermediates only
30
Methyl carbocation
Least stable Carbocation is bonded to 3 H's, no C/Rs
31
Primary carbocation
Third most stable Carbocation is bonded to 2 H's and 1 R
32
Secondary carbocation
Second most stable Carbocation is bonded to 1 H and 2 R
33
Tertiary carbocation
Most stable Carbocation is bonded to 3 R's, no H
34
Quaternary carbocation
Doesn't exist!
35
What kinds of things stabilize carbocations?
Hyperconjugation Resonance (creates delocalization) Carbocations are also super stable when they are at a benzylic position (on a carbon atom directly connected to, but not a part of, an aromatic ring)
36
When will a carbocation rearrange?
If doing so will generate a more stable carbocation
37
How do carbocations rearrange?
Two main mechanisms, methyl shift and hydride shift Methyl shift is moving a methyl (H3C-) substituent, hydride shift is moving an H-
38
Why do we propose reaction mechanisms?
To explain our experimental observations A good mechanism explains both the stereochemical outcomes and regiochemical outcomes
39
Stereochemical outcomes
Deals with issues of stereochemistry, ex... What happened to the chiral center's configuration? Did a new chiral center form, and if so which configuration is predominating, or is it racemic? If multiple diastereomeric products were possible, which ones did we actually obtain?
40
Which types of reactions must you deal with issues of stereochemistry?
Substitution rxns, elimination rxns, sometimes addition rxns
41
Regiochemical outcomes
Term for the issues that arise when more than one region of a molecule can react Important when a reaction generates constitutional isomers, rather than stereoisomers Only relevant to addition reaction when adding two different groups Refers to the positioning of the different groups in addition reactions, where each group is installed, and when in the reaction the installation takes place Use to answer questions like... Which product predominates? Which is the major product and which is the minor?
42
Additon reactions - basic definition
Addition of two groups across a double bond (pi bond breaks to add a group to each end)
43
When is regiochemistry relevant to an addition reaction?
When two DIFFERENT groups are being added to an ASYMMETRICAL alkene If two methyl groups are added, then regiochemistry is not applicable! If the alkene is symmetrical, then regiochemistry is not applicable!
44
When is regiochemistry NOT relevant to an addition reaction?
When two of the SAME groups are being added AND When two different groups are being added to a symmetrical alkene
45
Markovnikov addition
Large atom/group ends up on more substituted carbon H ends up on less substituted carbon (term for regiochemistry)
46
Anti-Markovnikov addition
Large atom/group ends up on the carbon with the most H's H ends up on more substituted carbon (term for regiochemistry)
47
Large atom/group ends up on more substituted carbon H ends up on less substituted carbon
Markovnikov addition
48
Large atom/group ends up on less substituted carbon H ends up on more substituted carbon
Anti-Markovnikov addition
49
Syn addition
Both groups are being added on the same side of the plane Two possible products arise (pair of enantiomers) (term for stereochemistry)
50
Anti addition
The two groups are being added on opposite sides of the plane Two possible products arise (pair of enantiomers) (term for stereochemistry)
51
Both groups are being added on the same side of the plane
Syn addition (stereochemical term)
52
The two groups are being added on opposite sides of the plane
Anti addition (stereochemical term)
53
What kinds of reactions display rearrangements?
Ones that proceed through a carbocation intermediate

Orgo. I (14 decks)

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