Chapter 6D - Halogenoalkanes

Question 1

What’s the difference between primary , secondary and tertiary halogenoalkanes ?
(3)

Answer 1

• primary - X attaches to C with just one alkyl group
• 2• = 2 Alkyl groups
• 3• = 3 alkyl groups

Question 2

What’s a nucleophile ?

1

Answer 2

-electron pair donor

Question 3

-halogenoalkanes + potassium hydroxide ? 
Condition 
Temperature 
Forms ? 
(5)

Answer 3

• nucleophilic substitution
• form Alcohol
• Warm
• REFLUX
• OH- is the nucleophile

Question 4

Hydrolysis of halogenoalkanes ?

3

Answer 4

• forms ALCOHOL
• hydrolysis is when water breaks bonds
• nucleophilic substitution with water

Question 5

Which halogenolalkanes are the most reactive ?

1

Answer 5

• tertiary ( with bromoalkanes)

Question 6

Silver nitrate + aqueous halide solution
???
(1)

Answer 6

• Ag+ + X- —> AgX

Question 7

Which halogenoalkane reacts the quickest ?
(4)
Explainnnnn

Answer 7

• the larger the Halogen - the LONGER the C-X bond
• Iodoalkane =largest =weakest bond
• hydrolysis the fastest
• the fluoroalkanes = strongest bond = slowest to hydrolyse

Question 8

potassium cyanide + Halogenoalkane
-mechanism?
-produces? C chain?
-Conditions ?
(5)

Answer 8

• in ethanol & reflux
• CN- nucleophile
• nucleophilic substitution
• forms A NITRILE
• CARBON CHAIN LENGTH INCREASES BY ONE

Question 9

Halogenoalkanes + warm ethanolic ammonia ?

3

Answer 9

• nucleophilic substitution
• NH3= NUCLEOPHILE
• produces primary amine

Question 10

how does the nuclephilic substitution of a halogenoalkane with ethanolic ammonia work ?
(6)

Answer 10

• step 1 : NH3- LONE PAIR IS ATTRACTED TO DELTA POSITIVE CARBON .(C-X BOND IS POLAR AND HALOGEN ARE GENENERALY MORE ELECTRONEGATIVE)
  -STEP 2 : the NH3 attaches to Carbon and Halogen ion is released .
  -step 3: one of the H from NH3 is lost because it replaced by a H in the carbon chain (see page 208 in txt bk)
  -step 4: the removed H is attacked by another NH3 to form NH4+ ion and a primary amine - functional group
  NH2 .
• There is a lone pair on both amine and NH4+ SO this can lead to further chain reaction and further products
  so LIMIT THIS BY USING EXCESS AMMONIA

Question 11

Reaction with HOT ethanolic potassium hydroxide 
(4)
-mechanism 
-what it produces 
-how and whats the base

Answer 11

• ELIMINATION
• produces alkenes
• OH- = BASE
• reflux!

Question 12

REACTION with warm AQUEOUS potassium hydroxide
-mechanism
-what does it make ?
(2)

Answer 12

• NUCLEOPHILIC SUBSTITUTION

- produces ALCOHOL

Question 13

outline the hydrolysis of halogenoalkanes which makes it possible to distinguish between Cl/Br/I
(5)

Answer 13

-NaOH + drop of halogenoalkane
-heat
-acidify with HNO3
-add few drops of AgNO3 :
AgCl–>white
AgBr–>cream
AgI –>Yellow

Question 14

What happens to bond enthalpy as you go down group 7 halogenoalkanes ? (3)

Answer 14

• bond gets longer / hence weaker
• bond enthalpy DECREASES
• FASTER HYDROLYSIS