Lab 5: Alkene Bromination/Dehydrohalogenation and the Elimination Reaction
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20 Terms
Which chemical shift corresponds to an alkene proton?
0.9 ppm
5.6 ppm
8.5 ppm
1.3 ppm
5.6 ppm
Which experiment outcome best supports E2?
Single alkene stereochemistry
Racemic mixture
Carbocation evidence
Rearranged products
Single alkene stereochemistry
Which NMR feature helps distinguish alkene substitution patterns?
Solvent peak
Integration and splitting patterns
Chemical shift alone
Baseline noise
Integration and splitting patterns
Which alkene shows lowest heat of hydrogenation?
Cis alkene
Most substituted alkene
Least substituted alkene
Terminal alkene
Most substituted alkene
Which type of reaction involves the concerted removal of a proton and leaving group?
SN2
SN1
E2
E1
E2
Which NMR feature confirms E2 stereospecificity?
Single alkene isomer signals
Broad singlet
Solvent peak
Integration
Single alkene isomer signals
Which alkene proton would appear farthest downfield?
Alkyl methylene
Allylic proton
Proton on disubstituted alkene
Methyl proton
Proton on disubstituted alkene
What functional group is formed after two dehydrohalogenation reactions of a vicinal dibromide?
A carbocation
An alkene
A bromonium ion
An alkyne
An alkyne
Which elimination requires a strong base?
Solvolysis
E2
E1
SN1
E2
A terminal alkene usually shows how many vinylic protons?
Two
Three
One
Four
Three
Anti-periplanar geometry is required for:
E2 elimination
E1 elimination
SN2
SN1
E2 elimination
Which solvent best stabilizes carbocations and favors E1?
Water
Toluene
Ether
Hexane
Water
Which peak disappears after elimination?
Methyl proton
Alkene proton
Alkyl halide proton
Solvent
Alkyl halide proton
Why are polar protic solvents avoided for E2?
They promote radicals
They deactivate bases
They stabilize nucleophiles poorly
They increase sterics
They deactivate bases
What is the rate law for an E1 reaction?
Rate = k[substrate][base]
Rate = k[substrate]
Rate = k[base]
Rate = k[carbocation]
Rate = k[substrate]
A vinyl proton next to CH₃ will most likely appear as:
Quartet or multiplet
Doublet
Triplet
Singlet
Quartet or multiplet
E1 reactions commonly compete with:
SN2
Addition
SN1
E2
SN1
How many proton signals in cis-2-butene?
4
3
2
1
2
Which condition favors E2 over SN2?
Low temperature
Polar protic solvent
Weak base
Bulky base
Bulky base
Which reaction benefits most from increased heat?
Elimination
SN2
Addition
Reduction
Elimination