halogenoalkanes

Question 1

how do steric factors affect which mechanism (SN1 or SN2) halogenoalkenes undergo?

Answer 1

1° RX: SN2
minimal steric hindrance

unfavourable for 3° RX to undergo SN2 as the bulky alkyl groups will block the backside attack of the nucleophile

Question 2

how do electronic factors affect which mechanism the halogenoalkanes undergo?

Answer 2

alkyl groups: e- donating
more alkyl groups, less e- deficient the C is, less susceptible to nucleophilic attack

thus reactivity is CH3X>1° RX>2° RX>3° RX

Question 3

how does the stability of the carbocation affect which mechanism the halogenoalkane undergoes?

Answer 3

the greater the number of e- donating alkyl groups, the more dispersed the +ve charge on the carbocation, the more stable the carbocation

since SN1 involves the formation of a carbocation, SN1 is favoured for 3° RX

Question 4

conditions for R-OH to R-X?

Answer 4

PX3, heat/PCl5/SOCl2(preferred)/HX, heat

Question 5

condition for R-X to R-OH?

Answer 5

NaOH/KOH (aq), heat

Question 6

condition for R-X to R-CN?

Answer 6

ethanolic NaCN/KCN, heat

Question 7

condition for R-CN to R-COOH?

Answer 7

hydrolysis: H2SO4/NaOH (aq), heat

Question 8

condition for R-CN to R-CH2NH2?

Answer 8

LiAlH4 in dry ether or H2, Ni catalyst, heat

Question 9

condition for R-X to R-NH2?

Answer 9

excess conc NH3, heat

Question 10

distinguishing test between alkyl halide and aryl halide?

Answer 10

1. NaOH (aq), warm
2. Cool and acidify with HNO3 (aq)
3. AgNO3 (aq)

chloride: white ppt
bromide: cream ppt
iodide: yellow ppt