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IB Chemistry > o chem– halogenoalkanes and alcohols > Flashcards

o chem– halogenoalkanes and alcohols Flashcards

ADD NITROBENZENE RXN MECH

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
what affects the rate of Sn2 reaction?
steric hindrance
26
the Sn1 mechanism is a ___ step reaction
2
27
when is Sn1 mechanism favoured?
when a stable carbocation intermediate can form
28
when a stable carbocation can form, is the Sn1 or Sn2 mechanism favoured?
Sn1
29
what is the order of the Sn1 reaction?
first
30
are the products of Sn1 or Sn2 optically active?
typically Sn2
31
why is the product of Sn1 reactions usually optically inactive?
a racemic mixture is formed (if the final product has a chiral carbon)
32
draw out the Sn1 mechanism in the reaction of 2-bromo-2-methylpropane with NaOH
-
33
draw the energy profile diagram for Sn1 mechanism
-
34
why would a racemic mixture form from Sn1 mechanism?
- 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
what is a leaving grp?
the halogen in the Sn reaction
36
how does the identity of X in the halogenoalkane affect the rate of the Sn reaction?
stronger C-X bond -> lesser rate
37
why does the C-X bond affect the rate of nucleophilic substituition?
in both Sn1 + Sn2, RDS involves breaking of the C-X bond
38
the leaving grp/halogens are _________
nucleophilic
39
why does the nucleophilicity of the leaving group affect the rate of Sn?
a weaker nucleophile will have less of the reverse rxn occuring
40
how does the strength of the nucleophile used affect the rate of reaction?
nuc strength incr, ROR incrs
41
what does protic mean?
presence of N-H and/or O-H bond that can participate in H-bonding
42
which reaction mechanism is favoured in a polar, protic solvent?
Sn1
43
which reaction mechanism is favoured in non polar, aprotic solvents
Sn2
44
why is Sn1 favoured in polar, protic solvents?
- the polar, protic solvents can solvate the intermediates - thus stabilising them -> allowing Sn1 to proceed
45
Sn1 and Sn2 produce...
alcohols
46
halogenoalkanes can undergo a reaction with OH- (aq) under ______ to form an alcohol
reflux
47
what are the three reactions lead to the formation of alcohol?
- electrophilic addition of alkenes - nucleophilic substitution of halogenoalkanes - reduction of ketones, aldehydes, carboxylic acids
48
reduction of aldehydes form _______ alcohols
primary
49
what substance, when reduced, forms a secondary alcohol?
ketones
50
what substance(s), when reduced forms a primary alcohol?
aldehydes, carboxylic acids
51
what are two reducing agents for the reduction of aldehydes, ketones and carb acids to form alcohols
LiAlH4 or NaBH4
52
why would LiAlH4 be used to reduce carboxylic acids?
the reduction of carb acids requires a stronger reducing agent
53
what are the 3 different methods and the conditions and reagents for the reduction of aldehydes and ketones
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
reducing agents for reduction of aldehydes and ketones - weakest: - strongest:
H2 LiAlH4
55
what are the conditions and reagents for the reduction of carboxylic acids to alcohols?
LiAlH4 in dry ether followed by addition of dilute acid
56
alcohols can be ________ to form CO2 and H2O
combusted
57
which alcohols do not undergo oxidation?
tertiary
58
alcohols are oxidised to aldehydes under _________ and further oxidised to __________________
controlled conditions, carb acids
59
alcohols are oxidised by _________ (method) to aldehydes
distillation
60
what is the procedure involved in the synthesis of carb acid from alcohol?
reflux
61
name 2 common oxidising agents and the observation when they are used
- K2Cr2O7– orange -> green - KMnO4 – purple -> colourless
62
what is produced when benzene is nitrated
nitrobenzene
63
what is the mechanism for nitration of benzene?
-
64
how is a phenylamine is produced?
from the reduction of nitrobenzene
65
what reactants do you need for the nitration of benzene?
conc HNO3/conc H2SO4
66
how is the electrophile NO2+ generated?
reacting HNO3 and H2SO4
67
what is the equation for the generation of electrophile NO2+ in the nitration of benzene?
-
68
what reactants and conditions are needed for the reduction of nitrobenzene?
- Sn in conc HCl - heat under reflux - NaOH (aq)
69
how many stereoisomers does a molecule w n chiral centres have?
2^n

IB Chemistry (12 decks)

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