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Chemistry 6 - Organic Chemistry > Halogenoalkane Reactions and Mechanisms > Flashcards

Halogenoalkane Reactions and Mechanisms Flashcards

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1
Q

what are the four substitution reactions we need to know

A
  • reaction 1 - RX + H20 = ROH
  • reaction 2 - RX + KOH = ROH
  • reaction 3 - RX + KCN = RCN
  • reaction 4 - RX + NH3 = RNH2
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2
Q

what are the conditions for the four reaction

A
  • reaction 1 = warm
  • reaction 2 = heating under reflux
  • reaction 3 = heating under reflux
  • reaction 4 = heat in a sealed tube
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3
Q

what type of reaction is reaction 1

A

a hydrolysis reaction

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4
Q

what does the reaction between a halogenoalkane and aqueous potassium hydroxide make

A

an alcohol

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5
Q

what is the attacking nucleophile in the reaction

A

the OH- ion from KOH

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6
Q

what would the structural formula and ionic structural formula for the reaction between 1-chloropropane and potassium hydroxide making propan-1-ol be

A
  • CH3-CH2-CH2Cl + KOH = CH3-CH2-CH2OH + KCl

- CH3-CH2-CH2Cl + OH- = CH3-CH2-CH2OH + Cl-

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7
Q

what is the advantage of writing out the ionic equation

A

it clearly shows the nucleophile

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8
Q

for reaction 3, what does heating a halogenoalkane with potassium cyanide dissolved in ethanol, under a reflux, make

A

nitriles

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9
Q

what is the attacking nucleophile

A

the CN- ion`

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10
Q

what would the structural formula for the reaction between bromoethane and potassium cyanide be

A
  • CH3-CH2Br + KCN = CH3-CH2CN + KBr
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11
Q

what would the name of the produced organic product be and why

A
  • propanentrile

- because it now contains an extra carbon atom

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12
Q

how are primary amines made

A
  • by heating a halogenoalkane with ammonia solution in a heated tube
  • it is reaction 4
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13
Q

what is the attacking nucleophile

A

the NH3 molecule

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14
Q

what is the structural formula for the reaction between 1-iodopropane and ammonia as well as the products name

A
  • CH3-CH2-CH2l + NH3 = CH3-CH2-CH2NH2 + HI

- propylamine

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15
Q

what actually happens during reaction 4 before it is complete

A
  • the organic product is a base

- this means that it would react with the inorganic acid HI to from a salt

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16
Q

what would a more accurate equation of the reaction then be

A

CH3-CH2-CH2I + NH3 = CH3-CH2-CH2NH3+ + I-

17
Q

if a salt is produced as well rather than just the primary amine, how do you produce a high yield of amine

A
  • use ammonia in excess

- some of this excess reacts in a second step to produce the amine

18
Q

what is the ionic equation for this second step

A

CH3-CH2-CH2HN3+ I- + 2NH3 = CH3-CH2-CH2NH2 + NH4+ I-

19
Q

therefore, what are the final products

A

propylamine and ammonium iodide

20
Q

if the attacking species of a substitution reaction is nucleophile, what is the full name of the reaction

A

nucleophilic substitution

21
Q

what is the main mechanism of reaction 2 between a halogenoalkane and aqueous potassium hydroxide

A
  • the oxygen on the hydroxide ion donates a lone pair of electrons to the electron deficient carbon atom bonded to the halogen
  • the electronegativity of the halogen causes the C-X bond to break, resulting in the hydroxide ion bonding with the carbocation to make an alcohol
22
Q

why is the carbon atom electron deficient in the first place

A
  • because the halogen atom is electronegative
  • this means that the shared electron moves towards the halogen more, making the carbon atom partially positively charged
  • hence why the negative hydroxide ion is attracted to it
23
Q

what bonds are formed and broken at the same time

A
  • a C-O bond forms

- at the same time the C-X bond is broken

24
Q

what is this kind of bond breaking called

A

heterolytic fission

25
Q

where would your curly arrows be if you were drawing this mechanisms

A
  • one arrow would be going from the lone pair of electrons on the oxygen atom of the hydroxide ion to the electron deficient carbon atom
  • the other arrow would be going from the bond between the carbon atom and the halogen to the halogen itself
26
Q

what do both of those arrows indicate

A
  • the first arrow shows the oxygen bonding to the carbon atom
  • the second arrow shows the electrons in the C-X bond moving to the halogen
27
Q

how would the mechanism of reaction 4 start off

A
  • the nitrogen atom of the ammonia would donate a lone pair of electrons to the electron deficient carbon atom
  • leading to the formation of a C-N bond
  • at the same time the electrons in the C-X bond move to the X atom
  • leading to that bond breaking
28
Q

how would your curly arrows look like this first stage

A
  • the same as the ones for reaction 2

- but instead you have formed a positively charged nitrogen ion bonded to 3 hydrogens and a carbon

29
Q

what happens in the second step

A
  • another ammonia molecule acts a base

- this removes a hydrogen atom from the ion formed in the first step

30
Q

what ions do you have in the first and second step and how do they interact

A
  • the ion in the first step is the negatively charged halogen ion
  • the ion in the second step is the positively charged ammonia ion
  • they both react to form an ammonium halide
31
Q

what does the OH- ion act as if ethanol is the solvent that reaction 2 happens in

A

a base instead of a nucleophile

32
Q

what does the OH- ion react with

A

the hydrogen atom attached to the carbon atom next to the carbon with the C-X bond

33
Q

what would the equation be for the reaction between 2-bromopropane and ethanolic potassium hydroxide

A

CH3-CHBr-CH3 + KOH = CH2=CH-CH3 + H2O + KBr

34
Q

what does this reaction with ethanol being the solvent therefore produce

A

an alkene with water and a salt

35
Q

why is this reaction referred to as an elimination reaction

A
  • because the H and X are removed from the halogenoalkane

- but are not replaced by other atoms

36
Q

what is the difference between nitrile organic compounds and primary amine organic compounds

A
  • nitriles contain the C-CN group

- primary amines contain the C-NH2 group

Chemistry 6 - Organic Chemistry (20 decks)

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