Chapter 7 Part 1: Understanding Sn1 and Sn2 Flashcards

1
Q

What is an alkyl halide? vinyl halide? aryl halide?

A

alkyl - halide bonded to sp3 carbon
vinyl - halide bonded to c=c
aryl - halide bonded to benzene ring

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2
Q

What degree halide is RCH2-X? R2CH-X? R3C-X?

A

One R group - 1st degree
Two R groups - 2nd degree
Three R groups - 3rd degree

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3
Q

How does the size of the R group/ size of the halide effect boiling and melting points?

A

as the size of the R group increases, surface area increases and BP&MP increase.
as the size of X increases it becomes more polarizable, BP&MP increase.

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4
Q

What kind of reactions do alkyl halides undergo with nucleophiles?

A

Substitution. The X in C-X is replaced by the nucleophile.

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5
Q

What kind of reactions do alkyl halides undergo with bronstead lowery bases?

A

Elimination. The X from C-X and a Hydrogen from a beta carbon are removed and a pi bond is formed.

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6
Q

How many steps are in the Sn2 Mechanism

A

1

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7
Q

In the Sn2 mechanism is the alkyl halide in the rate eqation? is the nucleophile? How do their concentrations affect the rate?

A

Sn2 = One Step = All reactants in rate equation:

rate=k[alkyl halide][:Nu-]

Changing the concentration of either reactant has a mirroring effect on the rate.

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8
Q

What is meant by backside attack? how does this affect the stereochemistry of the product? Which mechanism does this apply to?

A

:Nu approaches from the side opposite of the halide. This results in an inversion of the product. Applies to all Sn2 reactions

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9
Q

What degree halides can undergo Sn2 reactions? Rank from slowest to fastest reaction.

A

Methyl Halides (CH3-X), 1st and 2nd degree alkyl halides.
Slow——>Fast
2nd 1st CH3-X
—————————————————————–>
^Both occur very fast^

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10
Q

What is steric hindrance?

A

A decrease in reaction speed because of bulky groups around the reaction site.

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11
Q

How does steric hindrance of the alkyl halide affect the Sn2 mechanism?

A

Bulky R groups make the backside attack by the :Nu more difficult. This decreases the speed of the reaction

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12
Q

Does the Sn2 mechanism use 1st or 2nd order kinetics?

A

2nd order kinetics

rate=k[RX][:Nu-]

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13
Q

Does the Sn1 mechanism use 1st or 2nd order kinetics?

A

1st order kinetics.

rate=k[RX]

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14
Q

What is the first step of the Sn1 mechanism? What does this produce?

A

Heterolysis (breaking) of the bond between C and X. Produces a carbocation.

    C---/---X creates C(+) & X:(-)
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15
Q

What is a racemic mixture?

A

An equal mixture of two enantiomers produced by the Sn1 mechanism.

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16
Q

Which side of the stereogenic carbon does the nucleophile attack in the Sn1 mechanism.

A

Attacks the front or backside resulting in a racemic mixture

17
Q

Which alkyl halides react via the Sn1 mechanism?

Rank from slowest to fastest

A

2nd and 3rd degree halides.

Slower Fast
————————————————————–>
2ºR-X 3ºR-X

18
Q

Carbons with 3 R groups produce a ______ stable carbocation than Carbons with 1 R group. Why?

A

R3C-X produces a more stable carbocation than RCH2-X.

R groups are more polarizable than H atoms, so the (+) charge of the carbocation can be better dispersed.

19
Q

As the stability of the carbocation increases, the rate of the Sn1 reaction________

A

increases