Halogenoalkane Reactions and Mechanisms Flashcards Preview

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

Flashcards in Halogenoalkane Reactions and Mechanisms Deck (36)
1

what are the four substitution reactions we need to know

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

2

what are the conditions for the four reaction

- reaction 1 = warm
- reaction 2 = heating under reflux
- reaction 3 = heating under reflux
- reaction 4 = heat in a sealed tube

3

what type of reaction is reaction 1

a hydrolysis reaction

4

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

an alcohol

5

what is the attacking nucleophile in the reaction

the OH- ion from KOH

6

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

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

7

what is the advantage of writing out the ionic equation

it clearly shows the nucleophile

8

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

nitriles

9

what is the attacking nucleophile

the CN- ion`

10

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

- CH3-CH2Br + KCN = CH3-CH2CN + KBr

11

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

- propanentrile
- because it now contains an extra carbon atom

12

how are primary amines made

- by heating a halogenoalkane with ammonia solution in a heated tube
- it is reaction 4

13

what is the attacking nucleophile

the NH3 molecule

14

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

- CH3-CH2-CH2l + NH3 = CH3-CH2-CH2NH2 + HI
- propylamine

15

what actually happens during reaction 4 before it is complete

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

16

what would a more accurate equation of the reaction then be

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

17

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

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

18

what is the ionic equation for this second step

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

19

therefore, what are the final products

propylamine and ammonium iodide

20

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

nucleophilic substitution

21

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

- 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

why is the carbon atom electron deficient in the first place

- 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

what bonds are formed and broken at the same time

- a C-O bond forms
- at the same time the C-X bond is broken

24

what is this kind of bond breaking called

heterolytic fission

25

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

- 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

what do both of those arrows indicate

- 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

how would the mechanism of reaction 4 start off

- 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

how would your curly arrows look like this first stage

- 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

what happens in the second step

- another ammonia molecule acts a base
- this removes a hydrogen atom from the ion formed in the first step

30

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

- 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

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

a base instead of a nucleophile

32

what does the OH- ion react with

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

33

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

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

34

what does this reaction with ethanol being the solvent therefore produce

an alkene with water and a salt

35

why is this reaction referred to as an elimination reaction

- because the H and X are removed from the halogenoalkane
- but are not replaced by other atoms

36

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

- nitriles contain the C-CN group
- primary amines contain the C-NH2 group