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CHM 110 > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

Which is stronger, CH or CX bonds?

A

CH

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2
Q

Where does the dipole point in CX

A

towards the halogen (negative sigma charge)

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3
Q

Chlorofluorocarbons (CFC’s)

A
  • Widely used as nontoxic heat transfer agents (coolants in AC)
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4
Q

What type of reaction is halogenating an alkane

A

substitution reaction

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5
Q

Polarizability

A

measure of distortion of e- density about the atom

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6
Q

As polarizability increases

A

So does BP (MW is also higher)

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7
Q

Nucleophilic substitution definition

A

the replacement of a group by an incoming nucleophile

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8
Q

What is the leaving group known as

A

electrophile

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9
Q

Nucleophile loves:

A

nucleus (positive charge)

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10
Q

electrophile loves

A

e- (Negative charge)

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11
Q

Common nucleophiles

A

salts of nucleophilic anion

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12
Q

common electrophiles

A

SP3 hybridized alkyl halides

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13
Q

Nucleophile properties

A
  • Negatively charged are best
  • any atom with a lone pair could be a nucleophile
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14
Q

Least to most reactive leaving groups

A

the weaker the bond, the more reactive the leaving group

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15
Q

Walden inversion

A

the inversion of the configuration of a chiral center in a molecule

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16
Q

which reactions do Walden inversions occur?

A

SN2

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17
Q

SN2 reactivity trend

A

Tertiary carbons are the least reactive while Primary carbons are the most reactive (less hindered)

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18
Q

Are anions always needed as nucleophiles

A

No, but they are the best nucleophiles

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19
Q

Nucleophilicity

A

is a particular nucleophile strength at attacking an electrophile

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20
Q

SN1 reaction rate dependent on

A

electrophile concentration only

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21
Q

SN2 reaction rate dependent on

A

Electrophiles and nucleophile equally important

22
Q

Carbocation stability of SN1

A

tertiary are most stable, methyl are least stable (rate increases with stability)

23
Q

stereochemistry of SN1

A

Racemates (mixtures) are formed from reactions

24
Q

Why do racemates form In SN1

A

carbocation intermediate is planar and can be “attacked” from the top or bottom face

25
Q

What happens if SN1 or E1 reactions involve carbocations

A

They will rearrange to form a more stable cation if possible

26
Q

Best type of Solvent for SN2

A

polar aprotic solvents

27
Q

Aprotic solvents

A

lack an OH or NH2 group and therefore do not stabilize cations/ anions

28
Q

Nonpolar solvents (SN2)

A

are not good at solubilizing substrates

29
Q

Tosylates are

A

great leaving groups

30
Q

Kinetics of SN1

A

1st order rxn in alkyl halide
1st order rxn in nucleophile
Rate dependent on haloalkane and it’s rate of disappearance

31
Q

3 requirements for nucleophile substitution to occur

A
  • SP3 central atom
  • a nucleophile
  • 1g bonded to central atom ???????
32
Q

What makes a group a good nucleophile

A

its looking for a base with lone pair and is not sterically restricted

33
Q

what makes a good leaving group

A

weak base with conj acid having a low PKA

34
Q

SN1 prefers which solvent

A

polar protic (uses as nucleophile)

35
Q

SN2 prefers which solvent

A

polar aprotic solvent

36
Q

relationship between SN1 and SN2

A

They are competing reactions

37
Q

degrees of saturation prefered by SN1

A

the more the better (secondary and tertiary

38
Q

Degrees of substitution perferred by SN2

A

primary/ secondary groups

39
Q

Nucleophicity of SN1

A

poor

40
Q

Nucleophicity of SN2

A

Good

41
Q

Nucleophilicity trend

A

The less tightly held the shell is the higher the nucleophilicity is

42
Q

relationship between base strength and nucleophilicity

A

the more basic (lower PKA), the better the nucleophile

43
Q

structure of haloalkane SN1

A

electronic factors

44
Q

structure of haloalkane SN2

A

steric factors (sensitive to hindrance)

45
Q

What happens if nucleophile is solvated well with a protic solvent

A

The rxn will slow

46
Q

What happens if nucleophile is solvated well with aprotic solvents

A

rxn will be as fast as the nucleophile allows

47
Q

solvent effect on SN1

A

separation of opposite charged

48
Q

SN1 polar solvents

A

solvate both anions and cations

49
Q

How many steps does SN1 have?

A

2, a carbocation intermediate is formed

50
Q

how many steps in SN2

A

1

CHM 110 (9 decks)

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