Halogenoalkanes
Primary Halogenoalkane: Halogenoalkane that has a maximum of one carbon directly
attached to the carbon which is bonded to the halogen
Physical Properties:
-Electronegativity decreases down the group
-Strong polarity of C-F and C-Cl gives rise to permanent dipole-dipole attractions
-If a molecule is symmetrical and has polar bonds = non-polar
-Halogenoalkanes have a sweet, sickly smell
-Immiscible with water
Trends in BP:
BPs of chloro and fluoroalkanes is greater than alkanes of similar RMM due to the presence
of permanent dipole-dipole attractions
As methane alkanes increase in RMM, BP increases as there are more electrons etc
1-chloropropane has a lower BP than 1-chlorobutane because of RMM
Preparation of a halogenoalkane from an alcohol
Alcohol + HX → Halogenoalkane + Water
The HBr is generated in situ :
CH3CH2CH2CH2OH + HBr → CH3CH2CH2CH2Br +
H2O NaBr + H2S04(conc) → NaHSO4 + HBr
Butan-1-ol 1-bromobutane
Halogenoalkane from an alkane
-UV light, free radical photochemical substitution
-CH4 + Cl2 → CH3Cl + HCl
From an alkene
-C2H4 + HBr → C2H5Br
-Electrophilic addition
Reactions
Reaction with alkali: OH-
-CH3CH2CH2Br + OH- → CH3CH2CH2OH + Br-
-Heat under reflux with NaOH aqueous w. some ethanol for an hour
-Nucleophilic substitution, hydrolysis
Primary Halogenoalkane: Halogenoalkane that has a maximum of one carbon directly
attached to the carbon which is bonded to the halogen
Physical Properties:
-Electronegativity decreases down the group
-Strong polarity of C-F and C-Cl gives rise to permanent dipole-dipole attractions
-If a molecule is symmetrical and has polar bonds = non-polar
-Halogenoalkanes have a sweet, sickly smell
-Immiscible with water
Trends in BP:
BPs of chloro and fluoroalkanes is greater than alkanes of similar RMM due to the presence
of permanent dipole-dipole attractions
As methane alkanes increase in RMM, BP increases as there are more electrons etc
1-chloropropane has a lower BP than 1-chlorobutane because of RMM
Preparation of a halogenoalkane from an alcohol
Alcohol + HX → Halogenoalkane + Water
The HBr is generated in situ :
CH3CH2CH2CH2OH + HBr → CH3CH2CH2CH2Br +
H2O NaBr + H2S04(conc) → NaHSO4 + HBr
Butan-1-ol 1-bromobutane
Halogenoalkane from an alkane
-UV light, free radical photochemical substitution
-CH4 + Cl2 → CH3Cl + HCl
From an alkene
-C2H4 + HBr → C2H5Br
-Electrophilic addition
Reactions
Reaction with alkali: OH-
-CH3CH2CH2Br + OH- → CH3CH2CH2OH + Br-
-Heat under reflux with NaOH aqueous w. some ethanol for an hour
-Nucleophilic substitution, hydrolysis
