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chem > topic 6d: halogenoalkanes > Flashcards

topic 6d: halogenoalkanes Flashcards

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1
Q

primary halogenoalkane

A

one carbona ttached to the carbon atom bonded to the halogen

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2
Q

secondary ha

A

2 carbons attached to the carbon atom bonded to the halogen

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3
Q

tertiary ha

A

3 carbons attached to the carbon atom bonded the halogen

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4
Q

waht reactions can HA undergo

A

elimination
substitution

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5
Q

nucleophile

A
  • electron pair donator
  • has a lone pair
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6
Q

type of substitution

A

nucelophilic substitution

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7
Q

what happbesin substiution

A

swapping a halogen atom for another atom/group of atoms

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8
Q

rate of nucleophilic substitution depends on…

A

strength of C-X BOND
- the weaker the bond, the easier it is to break, the faster the reaction

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9
Q

halogenoalkane + KOH (aqueous)

A
  • aquous (water+ethanol COSOLVENT)
  • KOH (or NaOH)
  • heat under reflux
  • produce alcohols
  • :OH- nucleophile
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10
Q

stregnth of oh- nueclophile v water

A

OH- stronger Nu than water as has a full negative charge so more strongly attracted to delta + c

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11
Q

halogenoalkane + silver nitrate

A
  • aqueous silver nitrate
  • in WATER AND ETHANOL (cosolvents)
  • warm water nucleophile
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12
Q

ha + potassium cyanide

A
  • nitriles
  • cyanide ion is nucleophile
  • INCREASES LENGTH OF CARBON CHASIN
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13
Q

ha + ammonia

A

PRIMARY AMINS
- amonia dissolved in ethanaol
- HEAT IN A SEALED VESSEL (under pressure)
- ammonia nucleophile
- meth/eth/prop YL AMINE
- prevent over sub using excess ammonia

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14
Q

ha + KOH (ehtanolic)

A
  • alkenes
    -only ethanol
  • heat under reflux
  • OH- acts as a base
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15
Q

hydrolysis

A

splitting of a molecule by reaction with water

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16
Q

water as a nucleophile

A

POOR
- reacts slowly with HA in nucleophilic substition reaction

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17
Q

how to compare rate of hydrolysis

A
  • add ethanol
  • add silver nitrate
  • compare rate of formation of precipitate
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18
Q

AgI colour + speed

A
  • yellow ppt
  • fastest speed
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19
Q

AgBr colour and speed

A
  • cream ppt
  • mid speed
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20
Q

AgCl colour and speed

A
  • white ppt
  • slowest
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21
Q

primary HA nu sub mechanism

A

SN2

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22
Q

tertiary HA nu sub mechanism

A

SN1

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23
Q

why tertiary do SN1

A
  • tertairy CARBOCATION more stable
  • more alkyl groups causing positive inductive effect
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24
Q

why primary dont do sn1

A
  • primary carbocation unstable
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25
Q

why primary do SN1 but tertiary dont

A
  • nuclephle must attack at opposite side to leaving group
  • too much steric hindrance w tertiary
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26
Q

ha + KOH diff types of reaction

A
  • AQUOUS = substiuttion to form alochol
  • ETHANOLIC = elimination to form alkene
  • usually both happen
  • primary tend to wards sub, tertiary towards elimination
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27
Q

all C-X bonds…

A

are polar
C-F most polar

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28
Q

solublility of HA

A
  • insoluble in water
    HA have large R groups non polar
    SOLUBLE IN HYDROCARBON
29
Q

BOILING POINT

A
  • increases down group
  • eg R-I has highest
  • size of atom (LFs) outweighs polarity
30
Q

reactivty of ha depends on

A

strength of C-X bond

31
Q

how does the hydrolysis work

A
  • C-X breaks
  • X- ion released in solution
  • reacts w Ag+ to form AgX solid
32
Q

CH3Cl + OH (aqeuous)

A

CH3OH + Cl-

33
Q

CH3Cl+ CN-

A

CH3CN + Cl-

34
Q

CH3Cl + 2NH3

A

CH3NH2 + NH4Cl

35
Q

describe SN1

A
  • C-X bond spontaneously breaks (SLOW AS RDS)
  • forms the carbocation intermediate. draw nucleophile attacking a C-H bond
  • final step with full product + halide ion
36
Q

SN1 exo or endo

A
  • exothermic
  • energy profile = reactants low, intermediate high, products very low
37
Q

chiral defintion

A
  • 4 different groups attached to carbon
  • non superimposable on its mirror image
38
Q

2 types of STEREO isomerism

A
  1. geometric (z,e)
  2. optical (chirality)
39
Q

C-X bond fission

A

heterolytically
forms ions

40
Q

bond formed in substitution

A

DATIVE bond between nucleophile and carbon
halide is leaving group

41
Q

sn2 named beacuse

A

-2nd order overall
- 2 species in RDS

42
Q

sn1 named becuase

A

-1st order overall
- 1 species in RDS

43
Q

SN2 describe mechanism (draw)

A
  • 3d arrangement
  • c-x bond breaks to the x. simultaneoulsy lone pair from nucleophile goes to central c
    -STEP2: TRANSITION STATE: partial bonds form , one w nucleophile and one with halogen. overall charge if nucleophile was charged
  • final product 3d structure + halide
44
Q

sN2 energy profile

A
  • exo
  • rectants higher than products
45
Q

need for ethanol + water cosolvent

A
  • used with KOH and silver nitrate
  • water dissolves the other thing, ethanol dissolves halogenoalkane
46
Q

cyanide ion dot and cross

A

c triple bond n
new elecrton on c
- LP ON C IS MORE REACTIVE THAN THAT ON N

47
Q

ha + cyanide product

A

alkane nitrile
eg butane nitrile

48
Q

sn2 is the one with the …

A

HALF BONDS

49
Q

why is the NH3 heat in a sealed vessel under pressure not heat under reflux

A
  • NH3 boiling temp is below that of water
  • so wont condense in a water cooled condenser
50
Q

describe SN2 with the ammonia

A

-c-x bond breaks, lone pair on nh3 goes to delta + c
- second step with half bonds
- 3rd step; full 3d without halide. n-h breaks so n+, lone pair on another nh3 forms bond with h
- final has nh2 + nh4x

51
Q

why do u get oversubtituition with ammonia

A
  • lone pair of electrons on the nitrogen in the organic product
52
Q

what happens with xs halogenoalkane in the ha + ammonia

A

larger proprotion of oversubstitution so more quaternary ammonium salt

53
Q

describe the oh ethanol + ha mechanism elimination

A

TAKE ADJACENT CARBON TO C-X
- nucleophile arrow to H
- SAME h-c arrow to c-c
-c-x to x
- forms the alkene AND X- AND H2O

54
Q

nh3 CONDITIONS

A
  • concentrated nh3
  • ethanolic
  • head in sealed vessel under high pressure
55
Q

waht to remember about product of sn1

A

reverse the wedge and dashed line

56
Q

hoew to test for halogenoalkane

A
  • mix w ethanol
  • add agno3 and warm in water bath
57
Q

alterntive testing for halogeolakne

A
  • add KOH
  • nitric acid (prevents formation of silver oxide)
  • silver nitrate
58
Q

why do primary go by sn2

A

IF SN1:
- forms a v unstable primary carbocation
ADVANTAGE SN2
- low activation energy barrier as little steric hindrance around delta + carbon, so neuclophiles can easily attack

59
Q

SN2 products polarimeter

A
  • if reactant was a single enantiomer, product is the other enantiomer.
    -in polarineter, rotation of light (optical activity) reversed
60
Q

SN1 assessing products

A
  • equal propbability of nucleophile attacking above or below plane
  • equal conc of each enantiomer made so no overall efefct on rotation of light
61
Q

why if both are chiral does one NOT rotate lifht

A
  • the first is a single enantiomer
  • second is a RACEMIC MIXTURE: equal amounts of both enantiomers
62
Q

SN2 POLARIMETER

A
  • optical activity, rotated in opposite direction
  • ONE ENANTIOMER FORMED
    -Nuclophile attacks from the opposite side to the leaving group -> only on ONE SIDE
63
Q

2 ENANTIOMERS HOW TO DISTINGUISH

A
  • rotate the plane of plane polarised light
  • equally but in opposite directions
64
Q

SN1 POLARIMETER

A
  • no effect
  • racemic mixture
  • CARBOCATION TRIGONAL PLANAR INTERMEDIATE
  • equal prob of attack of nucleophile above and below the pla e
65
Q

stereoisomers

A
  • same structural formula
  • different spatial arangement
66
Q

role of water in nucleohpilic substitution (2)

A
  • nucleophile
  • bonds to carbocation
67
Q

role of ater in elimination

A
  • acts as a base
  • removes a proton
68
Q

how are ions formed in the halogenoalkane even though theres only covalent bonds (2)

A
  • water hydrolyses haloalkane
  • heterolytic bond fission of c-hal to form ions
69
Q
A

chem (16 decks)

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