Term
| _________ is the elimination of a hydrogen and a halogen from an alkyl halide to form an alkene. |
|
Definition
|
|
Term
| _________ dehydrohalogenations take place in one step, in which a strong _________ abstracts a proton from one carbon atom as the _________ _________ leaves the adjacent carbon. |
|
Definition
1) E2
2) Base
3) Leaving group |
|
|
Term
*Dehydrohalogenation by the E2 Mechanism*
_________ elimination takes place by a _________ one-step reaction.
A strong _________ abstracts a proton on a carbon next to the one bearing a _________.
The _________ _________ leaves simultaneously. |
|
Definition
1) E2
2) Concerted
3) Base
4) Hydrogen
5) Leaving group |
|
|
Term
The E2 dehydrohalogenation gives excellent yields with bulky _________ and _________ alkyl halides, such as tert-butyl bromide.
A strong _________ forces second-order elimination (E2) by abstracting a _________.
The molecule's bulkiness hinders _________, and a relatively pure elimination product results.
_________ halides are the best E2 substrates as they are prone to elimination and cannot undergo _________ substitution. |
|
Definition
1) Secondary
2) Tertiary
3) Base
4) Proton
5) SN2
6) Tertiary
7) SN2 |
|
|
Term
Use of a Bulky Base:
If a substrate is prone to _________, a bulky base can minimize this approach.
Large alkyl groups on a bulky base hinder its approach to attack a carbon atom (_________), yet it can easily abstract a proton (_________).
Some of the bulky groups bases commonly used for elimination are _________-_________ _________, _________, _________ and _________. |
|
Definition
1) Substitution
2) Substitution
3) Elimination
4) tert-butoxide ion
5) Diisopropylamine
6) Triethylamine
7) 2,6-dimethylpyridine |
|
|
Term
Formation of the Hofmann Product:
Bulky bases can also accomplish dehydrohalogenations that do not follow the _________ _________.
_________ _________ often prevents a bulky base from abstracting a proton that leads to the (least/most) highly substituted alkene.
In this case, it abstracts a less hindered proton, often the one that leads to formation of the (least/most) highly substituted product, known as the _________ product. |
|
Definition
1) Zaitsev rule
2) Steric hinderance
3) Most
4) Least
5) Hofmann |
|
|
Term
| The _________ product is the least highly substituted product while the _________ product is the most highly substituted product. |
|
Definition
|
|
Term
| A reaction with an ethoxide ion is likely to give the _________ product, while a reaction with tert-butoxide ion is likely to give the _________ product. |
|
Definition
|
|
Term
| Like the SN2 reaction, the E2 reaction is _________: different stereoisomers of the reactant give different stereoisomers of the product. |
|
Definition
|
|
Term
The _________ reaction is stereospecific because it normally goes through an _________ and _________ transition state.
The products are _________, and different _________ of starting materials commonly give different _________ of alkenes. |
|
Definition
1) E2
2) Anti
3) Coplanar
4) Alkenes
5) Diastereomers
6) Diastereomers |
|
|
Term
*Stereochemistry of the E2 Reaction*
Most E2 reactions go through an _________-_________ transition state. |
|
Definition
|
|
Term
Nearly all cyclohexanes are most stable in _________ conformations.
In the _________, all the carbon-carbon bonds are _________, and any two adjacent carbon atoms have _________ bonds in an anti-coplanar conformation, ideally oriented for the _________ reaction. |
|
Definition
1) Chair
2) Chair
3) Staggered
4) Axial
5) E2 |
|
|
Term
| A _________-_________ relationship is one in which the axial bonds on two adjacent carbon atoms are trans to one another. |
|
Definition
|
|
Term
| An _________ elimination can occur on a cyclohexane only if the _________ and _________ _________ can get into a _________-_________ arrangement. |
|
Definition
1) Proton
2) Leaving group
3) Trans-diaxial |
|
|
Term
| In a chair conformation of a cyclohexane ring, a trans-diaxial arrangement places the two groups _________ and _________. |
|
Definition
|
|
Term
| Vicinal dibromides (two bromines on adjacent carbon atoms) are converted to alkene by reduction with _________ ion in _________. |
|
Definition
|
|
Term
| A _________ is a reaction in which a vicinal dibromide is converted to an alkene through reduction (iodide ion in acetone). |
|
Definition
|
|
Term
_________ is formally a reduction because a molecule of Br2 is removed.
The reaction with iodide takes place by the _________ mechanism, with the same geometric constraints as the E2 _________.
Elimination usually takes place through an _________-_________ arrangement. |
|
Definition
1) Debromination
2) E2
3) Dehydrohalogenation
4) Anti-coplanar |
|
|
Term
*E2 Debromination of a Vicinal Dibromide*
E2 debromination takes place by a _________, stereospecific mechanism.
_________ ion removes one _________ atom, and the other leaves as _________ ion. |
|
Definition
1) Concerted
2) Iodide
3) Bromine
4) Bromide |
|
|
Term
First-order dehyrohalogenation usually takes place in a good ionizing solvent (such as an _________ or _________), without a strong _________ or _________ to force second-order kinetics.
The substrate is usually a _________ or _________ alkyl halide. |
|
Definition
1) Alcohol
2) Water
3) Nucleophile
4) Base |
|
|
Term
| First-order elimination requires ionization to form a _________, which loses a proton to a weak _________ (usually the solvent). |
|
Definition
|
|
Term
| E1 dehydrohalogenation is generally accompanied by _________ substitution, because the nucleophilic solvent can also attack the _________ directly to form the substitution product. |
|
Definition
|
|
