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33 Cards in this Set
- Front
- Back
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Beta elimination |
A reaction in which a proton from the beta position is removed together with the leaving group, forming a double bond. Also called a 1,2 elimination |
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Dehydrohalogenation |
A beta elimination reaction in which the leaving group is specifically a halide |
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Deydration |
A beta elimination reaction in which the leaving group is water |
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Degree of Substitution |
A way of designating the number of alkyl groups connected to the double bond |
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How many carbons do you need before a cycloalkene is capable of accomodating a trans pi bond? |
Seven |
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Bredt's Rule |
Bredt's rule states that it is not possible for a bridgehead carbon of a bicyclic system to posses a C=C double bond if it involves a trans pi bond being incorporated in a small ring |
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Rule of thumb for stability of cis- and trans- alkenes |
Cis alkenes will be less stable than its stereoisomeric trans alkene |
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E2 reactions |
An elimination reaction in which the proton transfer and the loss of the leaving group happen at the same time. |
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Why can E2 reactions work with tertiary substrates? |
Because the nucleophile is acting as a base and is more than happy to take a proton off of the edge of the molecule, making steric hindrances non-existant |
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Degree of substrates versus rate of reactivity in E2 reactions |
Slowest is primary Second fastest is secondary Fastest is tertiary |
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Regiochemistry |
This occurs when an E2 reaction can produce more than 1 possible product. |
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Zaitsev product |
The more substituted alkene is regiochemistry |
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Hofmann product |
The less substituted alkene is regiochemistry |
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E1 Mechanism |
The elimination reaction that is a stepwise mechanism in which the loss of a leaving group and proton transfer happen in different steps |
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Degree of substrate versus reactivity for E1 reactions |
Primary is the least reactive Secondary is the second most reactive Tertiary is the most reactive |
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Are there any differences in regioselectivity for E1 reactions compared to E2 reactions? |
Yes, the regiochemical outcome of an E1 process cannot be controlled by choosing a different base |
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Stereoselective |
A reaction in which the substrate produces 2 stereoisomers in unequal amounts |
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Anti-coplanar |
When the substituents off of the carbon that are in the same plane as the new pi bond are across from each other |
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Syn-coplanar |
When the substituents off of the carbon that are in the same plane as the new pi bond are on the same side as each other |
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Which coplanar conformation will elimination occur in cyclical compounds |
The anti-coplanar conformation, resulting in only one specific stereoisomeric product |
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Periplanar |
A situation in which the proton and the leaving group are nearly coplanar (for example, a dihedral angle of 178° or 179°) |
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What conformation do the proton and the leaving group have to be in repect to each other? |
Anti-periplanar |
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For cyclohexane, what is the conformation needed for elimination? |
Anti-periplanar |
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3 steps of figuring out whether or not something is an elimination of substitution reaction |
1. Determine the function of the reagent 2. Analyze the substrate and determine the expected mechanism 3. Consider any relevant regiochemical and stereochemical requirements |
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2 factors that influence nucleophilicity |
1. Charge (negative charge means stronger nucleophile) 2. Polarizability (the ability of an atom to distribute its electron density unevenly, larger atoms are better at this) |
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2 groups that act only as nucleophiles |
1. Halides 2. Sulfur nucleophiles |
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What mechanism is used if the reagent functions only as a base |
E2 |
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What mechanism is used if the reagent is both a strong nucleophile and strong base, and the carbocation is 1° |
SN2 major product and E2 minor product |
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What mechanism is used if the reagent is both a strong nucleophile and strong base, and the carbocation is 2° |
E2 major product and SN2 minor product |
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What mechanism is used if the reagent is both a strong nucleophile and strong base, and the carbocation is 3° |
E2 product only |
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What mechanism is used if the reagent is both a weak nucleophile and weak base, and the carbocation is 1° |
An impractical SN2 and E2 product |
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What mechanism is used if the reagent is both a weak nucleophile and weak base, and the carbocation is 2° |
An impractical SN1, SN2, E1, and E2 product |
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What mechanism is used if the reagent is both a weak nucleophile and weak base, and the carbocation is 3° |
SN1 and E1 product |
