3. halogenoalkanes

Question 1

h alkanes can undergo what 2 mechanisms

Answer 1

nucleophilic substitution (w :OH-, :CN-, :NH3)

elimination reaction with :OH-

Question 2

nucleophile

Answer 2

lone pair donor

Question 3

what drives nucleophilic substitution

Answer 3

nucleophile attracted to C-X bond because of it’s polarity. the C is delta +ve so nucleophile is attracted to the +ve charge

Question 4

process of nucleophilic substitution

Answer 4

e- pair on nucleophile -> C

e- pair in C-X cov bond -> X

forms halide ion and product

Question 5

conditions and products of ns with oh ion

Answer 5

warm aqueous

produces alcohol

Question 6

conditions +why, and products of ns with cn ion

Answer 6

dissolved in ethanol (ethanolic)
- if aqueous then OH- ions of water will act as nucleophile

use solid kcn normally
- bc gaseous hcn is difficult to maintain, and cn is toxic

Question 7

conditions +why, and products of ns with nh3 ion

Answer 7

for the process after the ammonia is added the N has whole +ve charge

then another ammonia acts as a base by accepting a h+

the e- pair in cov n-h bond is donated to N

hot conced ammonia in excess. bc product is a nucleophile too so to minimise further substitution
—-
—-
formed ammonium ion and an amine

Question 8

process of elimination reaction w :OH-

Answer 8

OH- ions acts as a base (proton acceptor)

takes away H on the C next to the C in the CX bond. e- pair in that cov bond goes to C-C cov bond. CX cov bond goes to halogen

Question 9

requirements for elimination

Answer 9

needs to be a H on the C next to the C in the CX bond

Question 10

conditions and products of elimination

Answer 10

hot ethanolic (in these conditions OH- of NaOH acts as a base)

forms alkenes, water, halide ion

Question 11

how can we investigate the reactivity of h alkanes ?

Answer 11

adding NaOH so a ns reaction will occur, the halogen will be displaced and halide ions will form

then adding acidified AgNO3 which tests for the halide ion by forming precipitates

Question 12

how does this reaction tell us about the reactivity of h alkanes

Answer 12

reactivity ultimately depends on the bond strength and the polarity. increased polarity increases reactivity because ns is driven by that delta +ve charge. weaker bond strength increases reactivity because easier to break the bonds

investigation showed the i.alkanes are more reactive than bromo than chloro than fluoro

fluro has the most polarity but has lowest reactivity. showing that bond strength is the most significant factor in h alkanes reactivity - i alkanes have weak bonds and that’s what makes them most reactivity