Halogeno Alkanes Flashcards
what are halogeno alkanes
are saturated organic compounds consisting of carbon, hydrogen and the halogen atoms (F, Cl, I, Br)
what are alkyl halides
• A simpler group of halogeno alkanes
In this group there is only 1 halogen atom
general formula of alkyl halides
Cn H2n+1 X
characteristics of alkyl halides
Most of the alkyl halides are colourless liquids
For a series of corresponding (same number of C atoms) alkyl halides, the boiling point increases from the fluoro compound (Fl) - the iodo compound (I) due to stronger intermolecular forces as the halogen atom becomes bigger
3 types of alkyl halides
- primary
- secondary
- tertiary
what are primary alkyl halides
• one in which the carbon atom which has the halogen atom is bonded to two hydrogen atoms
R CH2 X
what are secondary alkyl halides
the carbon atom which is bonded to the halogen must have:
- only 1 H atom
- 2 alkyl groups (may be identical or different)
general formula for secondary alkyl halides
R3 CHX R’
what are tertiary alkyl halides
• the carbon atom bonded to the halogen has no hydrogen bonded to it
• this carbon atom is bonded to 3 alkyl groups
what is the general formula for tertiary alkyl halides
R3 C X
what is nucleophilic substitution
the negatively charged nucleophiles (halogen atom) is attracted to the C atom bonded to the halogen since it has a partial positive charge
the alkyl halides are saturated componds so the nucleophiles will substitute the halogen compound
two types of mechanisms of nucleophilic substitution
Sn1 mechanism for tertiary alkyl halides
Sn2 mechanism for primary alkyl halides
Sn2 Mechanism
In the slow step, the nucleophile approaches the partially positive C atom, the C-X bond becomes longer and weaker
then an unstable intermediate is formed in which the nucleophile and halogen are partially bonded to the same C atom
in the fast step, the unstable intermediate quickly breaks down into the substituted product
the C-X bond is broken and C-OH bond is completely formed
Sn1 Mechanism for Tertiary Alkyl Halides
in the slow step, the C-X bond is broken and a positively charged intermediate (carbocation) is formed
in the fast step, the carbocation quickly bonds to the nucleophile to complete the reaction
what happens when nucleophilic substitution occurs
the C-Halogen bond must be broken
since the bond becomes weaker from C-F to C-I, the iodo compounds will be the most reactive since it is easiest to break
reaction of NaOH hydrolysis
when an alkyl halide is heated under reflux with NaOH, the OH- substitutes the halogen and an alcohol is formed
what method is used when the substance being produced is volatile
the impure mixture is heated in a reaction vessel which is attached to a condenser
steps in conversion to a nitrile
when bromoethane is heated under reflux with aqueous KCN or NaCN, the CN nucleophile substitutes the Br atom and a nitrile will be formed
in the reaction, an extra carbon atom is introduced into the organic compound
conversation of an alkyl halide to an amine
when iodoethane is reacted with ammonia, the amide nucleophile substitutes the halogen to produce an amine
the reaction is done by mixing the alkyl halide with excess ammonia in a sealed tube and heating to 100 deg C
preparation of alkyl halides
The alkyl halides are prepared by passing the halogen hydride through the alcohol, boiling under reflux in the presence of ZnCl catalyst
preparation of alkyl chlorides
they can be prepared by heating an alcohol under reflux with PCl5 or SOCl2
the Cl substitutes the OH and HCl fumes are evolved
