Unit 2-Haloalkanes

Question 1

What is a haloalkane (halogenoalkane or alkyl halide)?

Answer 1

Haloalkanes are substituted alkanes in which one or more of the hydrogen atoms are replaced with a halogen atom

Question 2

What is a monohaloalkane?

Answer 2

Substituted alkane containing only one halogen atom

Question 3

Explain the difference between a primary, secondary and tertiary monohaloalkane.

Answer 3

Classified according to the number of alkyl
groups attached to the carbon atom containing the halogen atom

Question 4

What types of reactions can monohaloalkanes undergo?

Answer 4

Elimination reactions to form alkenes

and

nucleophilic substitution reactions to form alcohols, ethers or nitriles.

Question 5

How can monohaloalkanes be converted into alkenes?

Answer 5

elimination reaction using a strong base, such as
potassium or sodium hydroxide in ethanol

Question 6

How would a monohaloalkane be converted into an alcohol?

Answer 6

nucleophilic substitution reaction with aqueous alkalis e.g. NaOH (aq)

Question 7

How would a monohaloalkane be converted into an ether?

Answer 7

nucleophilic substitution reaction with alcoholic alkoxides eg CH₃CH₂O^-

Question 8

How would a monohaloalkane be converted into an nitrile?

Answer 8

Take part in nucleophilic substitution reaction with ethanolic cyanide

eg CN^- (eth)

Question 9

How would a monohaloalkane be converted into an alkene?

Answer 9

Take part in elimination reactions using a strong base, such as
potassium or sodium hydroxide in ethanol.

(ethanol –> elimination)

Question 10

What are the two types of nucleophilic substitution?

Answer 10

S_N1 and S_N2

Question 11

What is the difference between S_N1 and S_N2 reactions?

Answer 11

S_N1 is a nucleophilic substitution, 1st order - one molecule in slowest step - tertiary haloalkanes

S_N2 is a nucleophilic substitution, 2nd order - 2 molecules in slowest step - primary haloalkanes

Question 12

What type of intermediate is formed in an SN1 reaction?

Answer 12

trigonal planar carbocation

Question 13

What type of intermediate is formed in an SN2 reaction?

Answer 13

a single five-centred, trigonal bipyramidal transition state

Question 14

Which type of haloalkane is most likely to react by an SN2 reaction?

Answer 14

Primary haloalkanes most likely and tertiary haloalkanes are least likely to proceed by a SN2 reaction mechanism

Question 15

Which type of haloalkane is most likely to react by an SN1 reaction?

Answer 15

Tertiary haloalkanes are the most likely and primary haloalkanes the least likely to proceed by a SN1 reaction mechanism.