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IB Chemistry > o chem– halogenoalkanes and alcohols > Flashcards

o chem– halogenoalkanes and alcohols Flashcards

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1
Q

primary halogenoalkanes have ____ alkyl group bonded to the halogenated carbon atom

A

one

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2
Q

why do halogenoalkanes have higher boiling points than similar alkanes?

A
  • halogenoalkanes have net dipole moment -> pd-pd
  • thus more energy req to overcome -> higher b.p.
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3
Q

what is the trend of b.p down the homologous series

A

increases

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4
Q

why does the b.p. of halogenoalkanes increase down the homologous series?

A
  • electron cloud size ↑
    • more polarisable
  • strength of LDF ↑ -> energy required ↑
  • ↑ b.p.
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5
Q

the b.p. of halogenalkanes down the halogen grp _________ (changes how?)

A

increases

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6
Q

why does the b.p. of halogenoalkanes increase down the halogen grp?

A
  • electron cloud size ↑
    • more polarisable
  • LDF ↑ -> energy required ↑
  • ↑ b.p.
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7
Q

why are halogenoalkanes/arenes generally insoluble in water

A

the energy released from dp-dp interactions btw halogenoalkanes/arenes + water is insufficient to overcome H bonding in water

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8
Q

why are halogenoalkanes/arenes generally soluble in non polar organic solvents?

A

the energy released from LDF in halogenoalkanes/arenes + non polar solvent is sufficient to overcome dp-dp btw halogenoalkanes + LDF btw solvent

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9
Q

what are nucleophiles? (short defin.)

A

electron-rich species that possesses at least one lone pair of e- which can react w e- deficient centres

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10
Q

nucleophile can either be _______ or __________ charged

A

neutral, negatively

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11
Q

nucleophilic substitution of halogenoalkanes produce…

A

alcohols

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12
Q

what are the conditions for nucleophilic substitution of halogenoalkanes?

A

heat under reflux

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13
Q

_______ halogenoalkanes undergo Sn2

A

primary

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14
Q

secondary halogenoalkanes undergo _______

A

Sn1 and Sn2

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15
Q

________ halogenoalkanes undergo Sn1

A

tertiary

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16
Q

what order of reaction is Sn2?

A

second order

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17
Q

why is Sn2 second order? (understand)

A

the ROR of the RDS depends on concentrations of the nucleophile and the halogenoalkane

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18
Q

why is Sn1 first order? (understand)

A

the ROR of the RDS depends on the concentration of the halogenoalkane only

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19
Q

when is the Sn2 mechanism favoured?

A

when the halogenoalkanes have low steric hindrance

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20
Q

if the final product contains a chiral carbon, there will be an _______ of the stereochemistry

A

inversion

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21
Q

why does the Sn2 mechanism result in an inversion of the reactant?

A
  • nucleophile attacks halogenoalkane from the back side
  • product undergoes inversion of configuration
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22
Q

which mechanism for the reaction of halogenoalkanes is one step?

A

Sn2

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23
Q

draw out the Sn2 mechanism for the reaction of NaOH with bromoethane

A

-

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24
Q

draw the energy profile diagram for Sn2 mechanism

A

-

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25
Q

what affects the rate of Sn2 reaction?

A

steric hindrance

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26
Q

the Sn1 mechanism is a ___ step reaction

A

2

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27
Q

when is Sn1 mechanism favoured?

A

when a stable carbocation intermediate can form

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28
Q

when a stable carbocation can form, is the Sn1 or Sn2 mechanism favoured?

A

Sn1

29
Q

what is the order of the Sn1 reaction?

A

first

30
Q

are the products of Sn1 or Sn2 optically active?

A

typically Sn2

31
Q

why is the product of Sn1 reactions usually optically inactive?

A

a racemic mixture is formed (if the final product has a chiral carbon)

32
Q

draw out the Sn1 mechanism in the reaction of 2-bromo-2-methylpropane with NaOH

A

-

33
Q

draw the energy profile diagram for Sn1 mechanism

A

-

34
Q

why would a racemic mixture form from Sn1 mechanism?

A
  • the carbocation is trigonal planar
  • nucleophile has equal chance of attacking from either side of the plane
  • thus equal amts of enantiomers are formed
35
Q

what is a leaving grp?

A

the halogen in the Sn reaction

36
Q

how does the identity of X in the halogenoalkane affect the rate of the Sn reaction?

A

stronger C-X bond -> lesser rate

37
Q

why does the C-X bond affect the rate of nucleophilic substituition?

A

in both Sn1 + Sn2, RDS involves breaking of the C-X bond

38
Q

the leaving grp/halogens are _________

A

nucleophilic

39
Q

why does the nucleophilicity of the leaving group affect the rate of Sn?

A

a weaker nucleophile will have less of the reverse rxn occuring

40
Q

how does the strength of the nucleophile used affect the rate of reaction?

A

nuc strength incr, ROR incrs

41
Q

what does protic mean?

A

presence of N-H and/or O-H bond that can participate in H-bonding

42
Q

which reaction mechanism is favoured in a polar, protic solvent?

A

Sn1

43
Q

which reaction mechanism is favoured in non polar, aprotic solvents

A

Sn2

44
Q

why is Sn1 favoured in polar, protic solvents?

A
  • the polar, protic solvents can solvate the intermediates
  • thus stabilising them -> allowing Sn1 to proceed
45
Q

Sn1 and Sn2 produce…

A

alcohols

46
Q

halogenoalkanes can undergo a reaction with OH- (aq) under ______ to form an alcohol

A

reflux

47
Q

what are the three reactions lead to the formation of alcohol?

A
  • electrophilic addition of alkenes
  • nucleophilic substitution of halogenoalkanes
  • reduction of ketones, aldehydes, carboxylic acids
48
Q

reduction of aldehydes form _______
alcohols

A

primary

49
Q

what substance, when reduced, forms a secondary alcohol?

A

ketones

50
Q

what substance(s), when reduced forms a primary alcohol?

A

aldehydes, carboxylic acids

51
Q

what are two reducing agents for the reduction of aldehydes, ketones and carb acids to form alcohols

A

LiAlH4 or NaBH4

52
Q

why would LiAlH4 be used to reduce carboxylic acids?

A

the reduction of carb acids requires a stronger reducing agent

53
Q

what are the 3 different methods and the conditions and reagents for the reduction of aldehydes and ketones

A
  1. LiAlH4 in dry ether + addition of dilute acid
  2. NaBH4 in dry ethanol + addition of dilute acid
  3. heat w H2, Ni catalyst
54
Q

reducing agents for reduction of aldehydes and ketones
- weakest:
- strongest:

A

H2
LiAlH4

55
Q

what are the conditions and reagents for the reduction of carboxylic acids to alcohols?

A

LiAlH4 in dry ether followed by addition of dilute acid

56
Q

alcohols can be ________ to form CO2 and H2O

A

combusted

57
Q

which alcohols do not undergo oxidation?

A

tertiary

58
Q

alcohols are oxidised to aldehydes under _________ and further oxidised to __________________

A

controlled conditions, carb acids

59
Q

alcohols are oxidised by _________ (method) to aldehydes

A

distillation

60
Q

what is the procedure involved in the synthesis of carb acid from alcohol?

A

reflux

61
Q

name 2 common oxidising agents and the observation when they are used

A
  • K2Cr2O7– orange -> green
  • KMnO4 – purple -> colourless
62
Q

what is produced when benzene is nitrated

A

nitrobenzene

63
Q

what is the mechanism for nitration of benzene?

A

-

64
Q

how is a phenylamine is produced?

A

from the reduction of nitrobenzene

65
Q

what reactants do you need for the nitration of benzene?

A

conc HNO3/conc H2SO4

66
Q

how is the electrophile NO2+ generated?

A

reacting HNO3 and H2SO4

67
Q

what is the equation for the generation of electrophile NO2+ in the nitration of benzene?

A

-

68
Q

what reactants and conditions are needed for the reduction of nitrobenzene?

A
  • Sn in conc HCl
  • heat under reflux
  • NaOH (aq)
69
Q

how many stereoisomers does a molecule w n chiral centres have?

A

2^n

IB Chemistry (12 decks)

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