16 Halogen Derivatives

Question 1

Halogenoalkanes/Alkyl Halides

Answer 1

R-X

Question 2

Primary, Secondary and Tertiary Halogenoalkanes

Answer 2

Number of R groups attached to the C atom bonded to the X atom
Primary: 1 R group
Secondary: 2 R groups
Tertiary: 3 R groups

Question 3

Halogenoarenes

Answer 3

Ar-X
X group is attached directly to an aromatic ring

Question 4

Trend of boiling points of R-X

Answer 4

As size of X atom increases (down Group 17), boiling point increases

Question 5

Factors affecting boiling point of R-X

Answer 5

1. id-id interactions between R-X molecules (increases down Group 17)
2. Polarity of R-X bond (decreases down Group 17)
   Effect 1»_space;> Effect 2

Question 6

Solubility of R-X

Answer 6

Insoluble. Energy released from forming new interactions between R-X and H2O is less than energy required to overcome initial interactions between R-X and H2O

Question 7

Forming R-X

Answer 7

1. FRS (from Alkanes)
2. Electrophilic Addition (from Alkenes)
3. Nucleophilic Substitution (from Alcohol) *

Question 8

Alcohols, R-OH -> Alkyl Halides, R-X

Answer 8

1. HX (g), heat
2. conc. HCl, ZnCl2 catalyst, HUR
3. PX3, rtp
4. PCl5 (s), rtp
5. SOCl2

Question 9

Order of reactivity of R-X

Answer 9

R-I > R-Br > R-Cl > R-F
Due to strength of C-X bond

Question 10

Reasons for low reactivity of Aryl Halides (Ar-X)

Answer 10

1. Partial double bond character in C-X bond (resonance)
2. Decreased polarity of C-X bond (electron drift from X atom to electron deficient C atom)
3. Presence of electron-rich ring (hinders nucleophilic attack)

Question 11

Alkyl Halides, R-X -> Alcohols, R-OH

Answer 11

NaOH (aq) or KOH(aq), HUR
Nucleophilic addition
(Alc medium results in elimination)

Question 12

Alkyl Halides, R-X -> Nitrile, R-CN

Answer 12

ethanolic NaCN/KCN, HUR
Nucleophilic addition

Question 13

Alkyl Halides, R-X -> Amines, R-NH2

Answer 13

Excess ethanolic NH3, heat in sealed tube
(Not using excess results in further nucleophilic substitution, resulting in secondary, tertiary amines and quaternary ammonium salt)
Nucleophilic addition

Question 14

Alkyl Halides, R-X -> Alkenes, R=R

Answer 14

ethanolic NaOH/KOH, HUR
Nucleophilic elimination

Question 15

SN2 nucleophilic substitution

Answer 15

Bimolecular (second order) reaction
Back-side attack -> Transition state complex -> Inverted configuration
Favored by primary R-X

Question 16

SN1 nucleophilic substitution

Answer 16

Unimolecular (first order) reaction
Heterolytic cleavage of C-X bond -> Nucleophilic attack from either side
Favored by tertiary R-X