haloalkanes

Question 1

what is a haloalkane ?

Answer 1

• an haloalkane is an alkane with at least 1 halogen atom in place of a hydrogen atom

Question 2

what are examples of haloalkanes ?

Answer 2

• tricholoromethane
• 2-iodo-propane
• 2-bromo-2-chloro-1,1,1,-trifluoroethane

Question 3

complete the for - 2-bromo-2-chloro-1,1,1,-trifluoroethane
skeletal formulae
molecular fomulae
structural formulae

Answer 3

find your answer yourself

Question 4

how do carbon and halogen bond ?

Answer 4

• halogens are generally more electronegative than carbon
  –> so halogen bond is polar

Question 5

draw carbon-halogen bond and label ?

Answer 5

• c = positive carbon centre
• halogen = electronegtaive halogen

Question 6

what is carbon in terms of electron whise ?

Answer 6

electron deficient meaning that it can be attacked by a nucleophiles

Question 7

what is a nucleophile ?

Answer 7

• an electron pair donor

Question 8

what can a nucleophile be ?

Answer 8

• a negative ion or an atom with a lone pair of electrons

Question 9

what can a nucleophile do ?

Answer 9

it donates an electron pair to somewhere without enough electrons

Question 10

what are examples of nucleophile’s ?

Answer 10

OH- , CN- and NH3

Question 11

what do nucleophiles react with ?

Answer 11

halogens

Question 12

what is another example of nucleophile ?

Answer 12

• water but it reacts slowly

Question 13

what can haloalkanes make ?

Answer 13

can be hydrolysed to make alcohols

Question 14

what conditions is needed for halogens to be hydrolsed to an alcohol ?

Answer 14

warm aqeous alkali
e.g. sodium hydroxide or potassium hydroxide

Question 15

what type is reaction is halogen –> alcohol

Answer 15

nucleophillic substitution reaction

Question 16

what is the general equation for haloalkanes to be hydrolysed to alcohols ?

Answer 16

OH-/H20
R-X + OH- ———–> R-OH + X-
reflux

Question 17

show the mechanism of bromoethane being hydrolysed into alcohols

Answer 17

find in textbook in answer :)

Question 18

describe the mechanism for bromoethane into an alcohol

Answer 18

1. OH- nucleophile which provides a pair of electrons for Cdelta plus
2. C-Br bond breaks heterolytically –> both electrons from the bond are taken by Br-
3. Br- falls off as OH- bonds to the carbon

Question 19

what type nucleophile is water ?

Answer 19

a weak one

Question 20

how will water react with a halogen ?

Answer 20

• it will eventually substitute for the halogen
  –> it’s just a much slower reaction than the others

Question 21

what would be the general equation for halogen reacting with water ?

Answer 21

R-X + H2O –> R-OH + H+ + X-

Question 22

what would happen if bromoethane reacted with water (write a balanced equation)

Answer 22

CH3CH2Br + H2O –> C2H5OH + H+ + Br-

Question 23

what causes the haloalkanes to be hydrolysed quickly ?

Answer 23

• depend on the bond enthalpy

Question 24

the faster hydrolysis….

Answer 24

as bond enthalpy decreases –> the bonds are getting weaker

Question 25

what happens with weaker carbon-halogen bonds ?

Answer 25

- break more easily so they react faster

Question 26

which haloalkanes have the weakest bonds ?

Answer 26

iodoalkanes have the weakest bonds --> so they hydrolyse the fastest

Question 27

which haloalkanes have the strongest bonds ?

Answer 27

fluoroalkanes have the strongest bonds --> so they're the slowest at hydrolysing

Question 28

how can one compare reactivity of haloalkanes ?

Answer 28

- by doing an experiment

Question 29

how can one conduct the experiment of a haloalkane ?

Answer 29

1. mix a haloalkne with water , it reacts to form an alcohol 2. put Ag nitrate solution in the mixture too --> the Ag ions react with halide ions as they form --> giving a silver halide precipitate 3. to compare the reactivities , set up 3 test tuves ach containing dfferent halolakane, ethanol and silver nirate solution (this contains the water)

Question 30

what is the symbol equation of the form an AgH ?

Answer 30

Ag (aq) + X- (aq) -->AgX (s)

Question 31

how does all the haloalkanes react ?

Answer 31

2-iodopropane --> a pale yellow preciptate quickly forms bromoalkanes --> reacts slower than I so forms a cream precipitate chloroalkanes --> forms a white preciptate the slowest of all